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Increasing water scarcity and Asia’s rapid economic and social development, specifically the growing demand for animal products and biofuels, is forcing farmers to transform their traditional lowland double-rice cropping systems [R-R] to mixed lowland-upland systems where upland crops such as aerobic rice [R-A] or maize [R-M] are grown instead of paddy rice during the dry period. Such changes have implications on the C and N cycling in the soil-plant system, including major shifts in soil greenhouse gas (GHG) emissions from CH4 to N2O once paddies are used for upland cropping. Moreover, soil organic carbon stocks are decreasing, thereby jeopardizing soil fertility. In this study, we investigated if straw residue incorporation and/or catch crop cultivation impairs the greenhouse gas footprint of diversifying rice cropping systems and thus, presents an alternative to open-field straw burning and intensive mineral N fertilization. For this, we calculate annual global warming potentials (GWP) and yield-scaled GWPs of three different rice systems (R-R: rice-rice, R-A: rice- aerobic rice, R-M: rice maize) without (control) or with additions of straw (+6 Mg ha−1 [S]) or + straw + mungbean as catch crop ([M + S]) on the basis of high-temporal-resolution GHG emissions (CH4 and N2O), and measurements of yield parameters. The field trial was carried out at the International Rice Research Institute (IRRI), Philippines, covering two full years. Although dry season N2O emissions increased twice- to threefold in the diversified systems (R-A, R-M), the strong reduction of CH4 emissions during this period resulted in significantly lower annual yield-scaled GWP as compared to the traditional R-R system. The same pattern was observed after application and incorporation of organic material (straw and mungbean), but led to higher substrate availability for methanogens during the following season. Therefore, the GWP was 9–39% higher in treatments including straw incorporation as compared to a control treatment without organic substrate amendments. Additional incorporation of mungbeans further increased GWPs, whereby the increment was highest in R-R rotation (88%) and lowest in R-M rotation (55%), with annual GHG emissions of 11.8 and 5.6 Mg CO2-eq ha−1, respectively. Our study shows that the yield-scaled GWP, as well as irrigation water demand, is lowest for rice-maize (R-M) cropping systems, followed by R-A and R-R systems. This ranking persists even with the incorporation of crop residues, a requirement for farmers as the ban of open-field burning is increasingly enforced. Our work also calls for a refinement of IPCC emission factors for lowland-upland rotations and the inclusion of the land-preparation period within the GHG balance of rice cropping systems.

Catch crop (green manure) planting is considered an efficient strategy to improve soil fertility in agro-ecosystems. Methane (CH4) emissions from paddies subjected to continuous green manure amendment though is a topic that remains unexplored. To clarify the impact of continuous green manure amendment on rice yield and CH4 emissions, a long-term trial (established in 2003, Yixing, China) was designed with the field observations conducted between 2019 and 2020. Two green manure crops (milk vetch, ryegrass) were selected as the catch crop with fallow as the control, all trialed at two N application rates i) low N dosage deriving from the optimum effect between yield-N fertilizer (LN, 200 kg ha-1), and ii) a higher N dose as the empirical farmer's dose (HN, 270 kg ha-1). The results showed that continuous green manure amendment notably increased soil organic carbon (SOC) compared to that of the control, while HN significantly increased the dissolved organic nitrogen compared to LN. The rice yield among treatments remained similar, ranging from 8.6 t ha-1 to 9.4 t ha-1 (two years’ average). CH4 emissions were notably related to green manure, and remained unaffected by N application rate. Ryegrass amendment after 18 years remarkably stimulated the CH4 emissions compared to other treatments, while the difference between milk vetch-amended and fallow treatments was found insignificant. Ryegrass increased soil mcrA gene with the abundance becoming the highest under HN. Methanogens abundance and SOC content were the main factors affecting CH4 emissions under ryegrass addition. Moreover, the CH4 emission intensity was aligned with CH4 emissions mainly due to the similar rice yield. Overall, continuous milk vetch planting is a recommended catch crop strategy that increases soil fertility and maintains rice yield without increasing CH4 emissions.

Nitrate that originates from agriculture is linked to a series of deleterious environmental consequences that are closely related to human health. Therefore, it is vital to design cropping systems that can produce acceptable crop yields while minimizing the impact of surplus soil nitrate. To develop quantitative estimations, data from 2008 to 2016 were evaluated using multiple regression models. A split-plot field experiment was conducted, with the main treatments of growing Huai bean, soybean and mung bean in summer as leguminous green manure (LGM) while fallow as the control. Four synthetic N rates (0, 108, 135 and 162kgha-1) were applied as sub-treatments at wheat seeding. The N accumulation for LGMs ranged from 61 to 90kgha-1, and that of Huai bean was 46% higher than the average value of soybean and mung bean (P

This study is the first to estimate the effect of Agri-Environmental Schemes (AES) on nutrient runoff using abatement data and water samples on a large scale. This unique combination of data sources identifies all farms located upstream from a given water sampling site. By using watersheds that cover 91% of the Swedish land area and AES payments to 83% of Swedish farms, the study is almost a full population evaluation. A watershed fixed-effect model estimates whether within-watershed variation in AES payments affects nitrogen and phosphorus concentrations in water samples. For the period 1997–2013, the study finds that higher uptake of the AES Wetland, Catch crop/No autumn tillage, Environmental protection measures and Culturally significant landscape elements was associated with reduced nutrient runoff. However, uptake of Grassed buffer zones, Pastures and meadows and Organic production was associated with increased nutrient runoff.

Soil erosion caused by water has been monitored for 17 years on 465 ha cropland in Lower Saxony (Northern Germany). The 86 monitored fields are representative for three different typical agricultural landscapes with an intermediate to high water erosion risk in Northern Germany. The monitoring scheme included regularly conducted erosion damage mapping and cultivation surveys. The collected data encompasses 1275 field years and 1355 mapped erosion systems, giving evidence on the extent, frequency and rate of soil erosion by water. Mean mapped soil loss for all fields was relatively small at 0.85 t ha−1 a−1. The highest rate for a single field amounted to 7.02 t ha−1 a−1. Variability of soil loss in time and space was high: annual losses (mean of all fields) ranged between 0.04 and 2.81 t ha−1 a−1. The highest annual loss on a single field was 53.07 t ha−1. Every year, at least 24% of the monitored fields were not affected by erosion, only 1.3% of the monitored area eroded at least once a year. Spatial analysis of mapped erosion features shows that the highest soil loss is located in topographically-defined flow paths and in wheel tracks oriented in line of the steepest slope. Cultivated crops and tillage management have a high influence on loss rates ranging from 0.07 for catch crop to 2.78 t ha−1 a−1 for potato. Additionally, the results prove that farmers in the investigation areas were able to significantly reduce soil loss rates of the five most important crops from 0.6 to 0.37 t ha−1 a−1 by using conservation tillage measures. The annual variability in the collected data emphasises the importance of appropriate long-term monitoring programmes to create sound data on the extent, frequency and rate of soil erosion by water at a field to landscape scale.

Components of the field nitrogen (N) balance (input and surplus) are often used to predict nitrate leaching from agricultural lands. However, management factors, such as use of catch crops, greatly affect the actual loss and are a key to reduce N leaching. The present study is based on the 4th cycle of a long-term crop rotation experiment in Denmark, and it aims to quantify, from a crop rotation perspective, the influence on N leaching from N input and surplus or management factors. The experiment included three cropping systems (two organic and one conventional) with or without use of animal manure and catch crops. N leaching was calculated from measurements of nitrate in soil water sampled with ceramic suction cups installed at 1 m depth in all plots. At the rotation level, over a four years period, N leaching was positively related to N input and surplus. However, the overall effect of N input and surplus on N leaching was lower than the effect of use of catch crops. The response rates of N leaching to increasing N inputs and N surplus were about 0.08 and 0.19-0.25, respectively. Catch crops reduced N leaching by 23 kg N ha-1, irrespective of conventional and organic management system, with legume-based catch crops being as effective as non-legumes. Animal manure increased N leaching in one of the organic systems. The organic system with two years of green manure per rotation cycle was the one at highest risk of N leaching, especially from crops following green manure incorporation. Spring wheat and potatoes were the two crops with highest N leaching, and a stable low level of N leaching was only achieved above a crop-specific threshold in catch crop biomass.

The environmental and economic sustainability of future cropping systems depends on adaptation to climate change. Adaptation studies commonly rely on agricultural systems models to integrate multiple components of production systems such as crops, weather, soil and farmers' management decisions. Previous adaptation studies have mostly focused on isolated monocultures. However, in many agricultural regions worldwide, multi-crop rotations better represent local production systems. It is unclear how adaptation interventions influence crops grown in sequences. We develop a catchment-scale assessment to investigate the effects of tactical adaptations (choice of genotype and sowing date) on yield and underlying crop-soil factors of rotations. Based on locally surveyed data, a silage-maize followed by catch-crop-wheat rotation was simulated with the APSIM model for the RCP 8.5 emission scenario, two time periods (1985-2004 and 2080-2100) and six climate models across the Kaituna catchment in New Zealand. Results showed that direction and magnitude of climate change impacts, and the response to adaptation, varied spatially and were affected by rotation carryover effects due to agronomical (e.g. timing of sowing and harvesting) and soil (e.g. residual nitrogen, N) aspects. For example, by adapting maize to early-sowing dates under a warmer climate, there was an advance in catch crop establishment which enhanced residual soil N uptake. This dynamics, however, differed with local environment and choice of short- or long-cycle maize genotypes. Adaptation was insufficient to neutralize rotation yield losses in lowlands but consistently enhanced yield gains in highlands, where other constraints limited arable cropping. The positive responses to adaptation were mainly due to increases in solar radiation interception across the entire growth season. These results provide deeper insights on the dynamics of climate change impacts for crop rotation systems. Such knowledge can be used to develop improved regional impact assessments for situations where multi-crop rotations better represent predominant agricultural systems.

International audience; During the fallow period, crucifers grown as catch crops are known to effectively reduce nitrate leaching, while legumes act mainly as green manure by releasing large amounts of mineral nitrogen (N) for the subsequent cash crop once incorporated into the soil. Crucifer-legume cover crop mixtures could be an effective solution for obtaining these two ecosystem services because they combine advantages of both species. However, crucifers might be a poor companion crop due to their high competition for abiotic resources and a potential allelopathic effect on legumes when grown with them. The aim of our study was to assess performances of a wide range of bispecific crucifer-legume mixtures to provide both catch crop and green manure services. A two-year experiment was conducted at two sites (near Toulouse and Orleans, France) where cultivars from eight crucifer species (rape, white mustard, Indian mustard, Ethiopian mustard, turnip, turnip rape, radish and rocket) and nine legume species (Egyptian clover, crimson clover, common vetch, purple vetch, hairy vetch, pea, soya bean, faba bean, and white lupin) were tested in sole-crop and bispecific mixtures (substitutive design of 50%-50% sole crops). We measured cover crop biomass and N acquisition to assess the soil nitrate catch crop service and N green manure service for the subsequent cash crop. In all experiments, compared to bare soil, crucifer-legume mixtures and crucifer sole cover crops provided the same level of nitrate catch crop service by reducing soil mineral N by an average of 59%, while legume sole cover crops reduced it by at least 35%, which is significant. In addition, within 6 months after termination, crucifer-legume mixtures mineralised more N (mean of 22 kg N ha(-1)) and thus had a larger N green manure effect for the subsequent cash crop than crucifer sole cover crops (mean of 8 kg N ha(-1)). This was due to greater N acquisition and a lower C:N ratio of crucifer-legume mixtures; even though crucifers always had advantage in acquiring N, legumes acquired enough N to provide an effective green manure service. These results were consistent in all of our experiments, which represent a wide range of crucifer-legume cover crops, demonstrating their generality. They also demonstrate the compatibility and complementarity of these species when grown together. In conclusion, combining crucifers and legumes as cover crops is an effective solution for obtaining multi-ecosystem services related to N recycling by providing both nitrate catch crop and N green manure services.

Soil phosphorus (P) leaching is one of the major causes of diffuse P losses towards the environment in north-west Europe. In order to cut back these P losses over the long term, soil P stocks need to be drastically reduced. Greenhouse experiments have shown that a rapid reduction of the plant available P pool is attained by reducing the P fertilizer input to zero while cropping, but field trials confirming these findings are rare. Moreover, important additional questions arise in any P mining strategy: (i) to what extent will crop performance be affected in high P soils under 0 P fertilization, (ii) which crops reduce soil P stocks most efficiently and (iii) how can soil organic carbon (SOC) levels be maintained when organic fertilizers are no longer applied. In order to address these questions we set up two 0 P fertilization field trials at sites with a very high initial soil P status (i.e. a P saturation degree > 30%). On each site, we compared the effect of 0 P fertilization on crop yield, soil P status and SOC level to a business as usual scenario, for two crop rotations. At the first site, a comparison was made between a mixed crop rotation with or without the inclusion of a catch crop. At the second site, a comparison was made between an arable/grass and a vegetable crop rotation. Four consecutive years of 0 P fertilization had no effect on neither the crop yield nor the crop P uptake. Further, English ryegrass, silage maize, celeriac and Chinese cabbage made the largest contribution to P removal. Although 0 P fertilization reduced the P balance at field level with 102–121 kg P ha-1 over four years, this had no significant (measurable) effect yet on the soil P stocks. Continuation of these experiments over a longer time will thus be needed to allow to see any such effects. Simulations of the evolution of the SOC levels over a thirty-year period showed that the use of grass as green manure or as main crop only allows to partially maintain the SOC levels in the absence of any organic fertilizers. These results indicate that P mining is a challenging task, that will take a long time to reduce the soil P stocks and that will come at a cost for the farmer.

The European legislative guidelines on the Common Agricultural Policy (CAP) lead to an obligation of area-wide information about cross-compliant Greening measures in EU countries. But by on-site controlling, agricultural authorities can monitor only a small portion of all registered parcels. With the Copernicus Programme, the freely available Sentinel-1 and Sentinel-2 imagery increasingly supports remote sensing-based agricultural monitoring on a large-scale. However, most prototypes lack the topic of winter catch cropping. Therefore, we developed a new machine learning method for catch crop monitoring and detection at the parcel-level. To gain training and test data for supervised machine learning, we collected winter catch crop parcel data from different years (2016–2019) and four federal states in Germany. Normalized Difference Vegetation Index (NDVI) time series were calculated for each parcel from Sentinel-2 data within the typical winter catch crop cultivation season (July-April). We revealed distinctive temporal patterns of catch cropping and developed nineteen descriptive features for automatized prediction. Then, we trained fifteen Random Forest classifiers comprising different regions and years and conducted a multi-level validation to identify the model with the highest robustness on new data. The Random Forest classifier trained with the input data from all federal states and years outperformed the other models. It reached a mean prediction accuracy of 84% for both classes (catch crop and non-catch crop) across eleven different spatio-temporal domains. Under optimal annual weather conditions it reached accuracies close to 90%. Anomalies caused by heat waves and early frost events were found to have a high influence on the phenology of catch crops and thus lead to reduced prediction accuracies. From the set of predictors, those features with the highest importance measured the correlation between the observed time series and a simulated NDVI phenological profile. We concluded that catch cropping parcels are automatically separable from parcels with other winter cultivations (e.g., winter cereals, grasslands, fallow) with Sentinel-2 NDVI time series data. Different catch crop subgroups (i.e., seed mixes) could not be differentiated by our approach due to very similar phenological profiles. Nonetheless, the used approach allows for large-scale winter catch crop monitoring and supports authorities in the selection of parcels with high demand for on-site controlling. By merging the training datasets from different federal states and years, we could overcome the typical spatial and temporal overfitting problem in machine learning. Therefore, the study’s final classifier can be reliably transferred to new datasets in Germany and other regions with similar bio-geographical conditions.

The experiments comprised three vegetation periods of five sorghum varieties. Novel data on the development of biomass yield, maturity level and biogas production were gained. Dry matter (DM) biomass yield ranged between 15.7 and 20.67 t ha −1 when sorghum was grown as main crop. The variety SOR 4 achieved a methane yield of 6500 m 3 ha −1 . The suitability of different sorghum varieties as summer catch crops was measured and assessed by combining growing degree days (GDD; temperatures > 10 °C) and maturity stage. This paper introduces a correlation of yields in course of the vegetation period with GDD values which enables to transfer yield and economic efficiency predictions from present results to other sites. Sorghum is able to provide high-yields when used as catch crop, whereby an adapted varietal selection is indispensable. The sorghum variety SOR 2 (year2) of 1100 growing degree days (GDD) proofed to be fast ripening and is especially suitable as a summer catch crop. This variety achieved mean DM yields of 12.4 t ha −1 when used as summer catch crop. Within this study crop maturities between 20 and 45% DM were investigated. Within this range, no decrease in specific methane yield with the increase in maturity and DM yield was observed. The three year experimental data also included one year with low precipitation. The statistical analysis did not reveal a significant influence of the precipitation on the biomass yield which confirms the drought resistance of sorghum. This result is especially important in view of adaptation to climate change.

The expansion of biogas feedstock cultivation may affect a number of ecosystem processes and ecosystem services, and temporal and spatial dimensions of its environmental impact are subject to a critical debate. However, there are hardly any comprehensive studies available on the impact of biogas feedstock production on the different components of nitrogen (N) balance. The objectives of the current study were (i) to investigate the short-term effects of crop substrate cultivation on the N flows in terms of a N balance and its components (N fertilization, N deposition, N leaching, NH3 emission, N2O emission, N recovery in harvested product) for different cropping systems, N fertilizer types and a wide range of N rate, and (ii) to quantify the N footprint of feedstock production in terms of potential N loss per unit of methane produced. In 2007/08 and 2008/09, two field experiments were conducted at two sites in Northern Germany differing in soil quality, where continuous maize (R1), maize–whole crop wheat followed by Italian ryegrass as a double crop (R2), and maize–grain wheat followed by mustard as a catch crop (R3) were grown on Site 1 (sandy loam), and R1 and a perennial ryegrass ley (R4) at Site 2 (sandy soil rich in organic matter). Crops were supplied with varying amounts of N (0–360 kg N ha−1, ryegrass: 0–480 kg N ha−1) supplied as biogas digestate, cattle slurry, pig slurry or calcium-ammonium nitrate (CAN). Mineral-N fertilization of maize-based rotations resulted in negative N balances at N input for maximum yield (Nopt), with R2 having slightly less negative balances than R1 and R3. In contrast, N balances were close to zero for cattle slurry or digestate treatments. Thus, trade-offs between substrate feedstock production and changes of soil organic matter stocks have to be taken into consideration when evaluating biogas production systems. Nitrogen losses were generally dominated by N leaching, whereas for the organically fertilized perennial ryegrass ley the ammonia emission accounted for the largest proportion. Nitrogen balance of the ryegrass ley at Nopt was close to zero (CAN) or highly positive (cattle slurry, digestate). Nitrogen footprint (NFP) was applied as an eco-efficiency measure of N-loss potential (difference of N input and N recovery) related to the unit methane produced. NFP ranged between −11 and +6 kg N per 1000 m3 methane at Nopt for maize-based rotations, without a significant impact of cropping system or N fertilizer type. However, for perennial ryegrass ley, NFP increased up to 65 kg N per 1000 m3. The loose relation between NFP and observed N losses suggests only limited suitability for NFP.

Biochar has been frequently suggested as an amendment to improve soil quality and mitigate climate change. To investigate the optimal management of nitrogen (N) fertilization, we examined the combined effect of biochar and N fertilizer on plant N uptake and N2O emissions in a cereal rotation system in a randomized two-factorial field experiment on a sandy loam soil in Brandenburg, Germany. The biochar treatment received 10Mgha−1 wood-derived biochar in September 2012. Four levels of N fertilizer, corresponding to 0, 50%, 100%, 130% of the recommended fertilizer level, were applied in winter wheat (Triticum aestivum L.)) and winter rye (Secale cereal L.) in 2013 and 2014 followed by the catch crop oil radish (Raphanus sativus L. var. oleiformis). Biomass and N uptake of winter wheat and winter rye were significantly affected by the level of N fertilizer but not by biochar. For N uptake of oil radish an interaction effect was observed for biochar and N fertilizer. Without applied fertilizer, 39% higher N uptake was found in the presence of biochar, accompanied by higher soil NH4+ content and elevated cumulative CO2 emissions. At 130% of the recommended fertilizer level, 16% lower N uptake and lower cumulative N2O emissions were found in the biochar-mediated treatment. No significant change in abundance of microbial groups and nosZ gene were observed. Our results highlight that biochar can have a greenhouse gas mitigation effect at high levels of N supply and may stimulate nutrient uptake when no N is supplied.

This study was focused on modeling soil water, carbon (C), and nitrogen (N) dynamics in soil and crop emphasizing uncertainties in model parameterization and the evaluation of potential water stress for silage maize cultivations on a drained field. The CoupModel was applied on different management systems for silage maize ( Zea mays ) in monoculture and undersown with grass ( Lolium perenne L.) on a sandy-humic soil. Four different fertilization levels with 0, 150 kg of mineral-N, 40 m 3 of cattle slurry (72–148 kg N ha −1 year −1 ), and combined slurry/mineral-N (222–298 kg N ha −1 year −1 ) were simulated over five years. Results were based on most plausible parameter combinations regarding simulated biomass obtained from 10,000 runs by the Generalized Likelihood Uncertainty Estimation (GLUE) approach. The uncertainty in model parameterization was reduced significantly by limiting the number of simulations for each treatment sequentially resulting in quartile coefficients of variation ( CV *) CV * values of evapotranspiration and total runoff ranged between 0 and 26% and 8–21%, respectively, on half-yearly basis. Significant differences between the cropping systems were found, even though the soil water balance was positive for all systems, and the potential water stress was only minor in bi-cropping systems.

In Central Europe, various plant species including large-grain legumes and their mixtures are grown as catch crops, particularly between grains harvested early and subsequent summer crops. This article investigates the question of how soil structure in the topsoil is influenced when catch cropping with large-grain legumes (experimental factor A: without catch crop, with catch crop) under different ploughless tillage conditions during catch crop seeding (experimental factor B: deep tillage/25–30 cm, shallow tillage/8–10 cm). Five one-year trials were performed using standard machinery at various sites in Germany. Soil core samples extracted from the topsoil in the spring after catch crop cultivation served to identify air capacity, saturated hydraulic conductivity and precompression stress. The above-ground and below-ground biomass yields of the catch crops were also determined at most of the sites. In addition, the soil compaction risk for the working steps in the experiments was calculated using the REPRO model. The dry matter yield of the catch crops varied considerably between the individual trial sites and years. In particular, high levels of dry matter were able to form in the case of early seeding and a sufficient supply of precipitation. The soil structure was only rarely affected positively by catch crop cultivation, and catch crops did not contribute in the short term to loosening already compacted topsoils. In contrast, mechanical soil stresses caused by driving over the ground and additional working steps used in cultivating catch crops often led to lower air capacity in these treatments. This is consistent with the soil compaction risks calculated using the REPRO model, which were higher in the treatments with catch cropping. Catch crop cultivation also only resulted in improved mechanical stability at one location. The positive effect of deep ploughless tillage on air capacity and saturated hydraulic conductivity, however, became more clearly evident regardless of catch crop cultivation. In order for catch crop cultivation with large-grain legumes to be able to have a favourable impact on soil structure, it is therefore important that cultivating them does not result in any new soil compaction. In the conditions evaluated, deep tillage was more effective at loosening compacted topsoil than growing catch crops.

Cauliflower (Brassica oleracea L. var. botrytis) has high nitrogen (N) demand during growing, but due to its low N use efficiency and N-rich residues, it may cause N losses by leaching after harvest. A field experiment was conducted to investigate the effect of overwintering grass-clover as an intercrop and moderately reduced N fertilization on organic cauliflower yield and risk of nitrate leaching. The experiment tested sole-cropped (S) and intercropped (I) systems using a substitution design and two N fertilizer rates (180 and 230 kg N ha−1). To investigate the competition between cauliflower and grass-clover, cauliflower grown alone with empty grass-clover rows (Semp) and grass-clover grown alone with empty cauliflower rows (GCemp) were included. The results showed that marketable yield was maintained in the I system compared to in the S system when calculated per meter crop row, and when N fertilization was moderately reduced. The Relative Competition Index (RCI) values in the I system were lower than 0, indicating that cauliflower growth was not interfered in the I system. The ability for aboveground N accumulation in the S and I systems was similar, but the N content of cauliflower residues in the S system was 33 and 23 kg ha−1 higher than in the I system in 2012 and 2013, respectively. The S system had 168 kg Ninorg ha−1 in the soil layer of 0–1.5 m at the start of leaching in 2013, which was 40 kg N ha−1 higher than the I system. Reduced N fertilizer level led to 22 kg ha−1 lower soil Ninorg at the end of leaching. However, the effect of system and N level on soil residual Ninorg per unit marketable yield was not significantly different. Intercropping cauliflower with overwintering grass-clover and moderately reduced N fertilization was feasible in organic cauliflower production, with regard to maintaining marketable yield and reducing the risk of nitrate leaching in the agroecosystem.

The export of winter wheat straw for bioenergy may reduce soil C stocks and affect N losses. Establishing fast-growing catch crops between successive wheat crops could potentially offset some of the C and N losses. Another option is to sow wheat earlier, increasing biomass production during the autumn. The effects of straw export, oil radish catch crop and early sowing of wheat on soil C storage, N leaching losses and N 2 O emissions were simulated by applying the Daisy model to winter wheat grown continuously for a period of 100 years on a sandy loam soil in a Danish climate. The simulations included five levels of initial soil C content (1–3% C), three levels of straw incorporation (0, 50 and 100%), +/− catch crop (oil radish) and two sowing dates (1 and 22 September). Exporting the entire straw production reduced soil C stocks by 1.2 to 14% after 100 years, depending on the initial C content. Inclusion of the oil radish catch crop could offset this loss by 2–3 percentage points. Earlier sowing of wheat increased straw production by 18% and reduced loss of soil C by 3–5 percentage points compared to normal sowing time with full straw export. Catch crops and early sowing also reduced N-leaching losses compared to a scenario with full straw export. Early sowing of wheat performed better than the oil radish catch crop in reducing N leaching and N 2 O emissions. Sensitivity analyses showed that a wetter climate had little effect on soil C storage, but increased N leaching losses by up to 48%. Loss of soil C and leaching of N increased when early-sown wheat was subject to winter-kill and when sandy loam soil was replaced by a sand soil. When wheat is grown continuously, losses of C are mainly defined by the initial soil C content (reflecting the management and land-use history of the soil) and by the level of straw export. The use of oil radish catch crops and early sowing of wheat may offset some of the adverse effects of straw export.

The CropSyst model was parameterized and verified for garlic with data from six field experiments carried out in southern Spain from 2008 to 2011. The model simulated well crop dry matter production, N uptake, and yield from field plots with different N fertilization treatments. A garlic–wheat rotation was then simulated for a 30-year period to evaluate the role of wheat after garlic as a catch crop that utilizes and reduces the loss of residual soil N left at the time of garlic harvest. The scenarios studied were the combination of seven rates of mineral N fertilization in garlic (0, 50, 100, 150, 200, 250 and 300 kgN/ha) and three rates in wheat (30, 70 and 110 kgN/ha). Fertilization rates of 150 kgN/ha in garlic and 70 kgN/ha in wheat were found to provide the best tradeoff between N loss reductions (N leaching and N gas emissions) while attaining near-maximum yields. Increasing fertilization to 200 and 110 kgN/ha for garlic and wheat, respectively, rates not atypical in the region, had a minimum effect on yields but increased average N losses over the rotation by 19 kgN/ha/2-year (29%). Further reductions of N losses by decreasing N fertilization below the best tradeoff point are possible at the expense of crop yield.

Accurate estimation of animal manure nitrogen (N) availability is required to maximize crop N use efficiency and reduce environmental N losses. Many field and laboratory experiments have shown that first-year net mineralization of manure organic N is often negligible, which often causes crop available N to approximate the ammonium N content of the manure. Anaerobic digestion increases the ammonium share and reduces the C to organic N ratio of animal manures, potentially increasing their N fertilizer value. In 2011, we undertook a three-year field experiment in Northern Italy to estimate the N fertilizer value of four manures: undigested cattle slurry, digested cattle slurry-maize mix, and liquid and solid fractions of the digested slurry-maize mix. The experiment also allowed us to test if ammonium recovery was similar among manures, and between manures and ammonium sulphate. Fertilizers were applied annually to plots before silage maize cultivation that was followed by an unfertilized Italian ryegrass crop. Results showed that the recovery of ammonium from manure in maize did not differ significantly compared to ammonium sulphate among all the fertilizers in 2013; however, in 2011 and 2012 it was significantly lower for all manures except digested slurry-maize mix and its liquid fraction in 2011. The increased recovery of applied N in 2012 and 2013 for solid fraction and undigested manure were likely due to the residual effect of previously applied organic N.

When grass-clover leys have been ploughed nitrate leaching may increase. However, management of leys before or after ploughing may affect the leaching risk. We examined the effect of cultivating a six year ley, which the last two years had been treated differently (grazing only; spring cut followed by grazing, and spring and autumn cuts with grazing during the summer season only) on nitrate leaching in maize with/without a catch crop (per. ryegrass) and with/without slurry application (135 kg total-N ha −1 ). An unfertilized barley harvested for silage with a catch crop of Italian ryegrass was used as reference. Shortening the grazing season in the grass-clover ley phase did not affect leaching after ploughing. In the following maize, the use of a perennial ryegrass catch crop in a high-yielding maize crop was not able to reduce nitrate leaching significantly, although leaching and maize yield tended to be lower with the catch crop. In unfertilized treatments both maize yields and nitrate leaching were significantly lower compared with treatments with slurry application. The unfertilized barley undersown with Italian ryegrass reduced leaching much more than unfertilized maize with perennial ryegrass as an undersown catch crop, despite yields of barley and ryegrass being less than half of the dry matter yields of unfertilized maize. The experiment illustrates that growing maize after ploughing of grass-clover leys without environmental consequences is difficult.

Catch crops may strongly reduce nitrate leaching during autumn and winter in temperate climates. Authorities therefore aim to stimulate farmers to place catch crops in their rotations by allowing them to apply more nitrogen (N) to their fields. Furthermore, some regulations make it possible to fertilize catch crops after harvest of specific crops such as winter cereals, even if catch crops are sown during late summer. Some farmers claim that this practice is essential for a good development of the catch crop. However, it is not sure whether this summer fertilization to catch crops could result in any additional nitrate leaching, compared to nitrate leaching under non-fertilized catch crops. We therefore designed field experiments including four different catch crop species, each of them sown after harvest of winter cereals at two different dates, and each of them receiving two different doses of pig slurry or receiving no fertilizer at all. Experiments were installed on sites with different soil textures in northern Belgium. Based on the results of soil mineral N and N uptake, we assessed the risk of additional nitrate leaching caused by fertilization of catch crops. We found that the apparent uptake of N released from pig slurry was rather limited but sufficient to avoid additional nitrate leaching on sandy soils, mainly due to supplementary immobilization of the applied N occurring during mineralization of the cereal crop residues. It is critical to mention the limiting conditions that we found to be adequate from our results: catch crops were to be sown in good circumstances before September and could only receive the smallest dose of pig slurry, which was approximately 60 kg N ha−1. On silty soils, however, we found even under these conditions a few indications of small amounts of additional nitrate leaching. As fertilization did not seem mandatory to develop an effectively functioning catch crop and as there was no indication of reduced nitrate losses due to this practice, we would rather discourage fertilization of catch crops to exclude any environmental risk. However, fertilization significantly increased the catch crop yield, so the decision to fertilize or not may also be seen as a trade-off between minor amounts of additional nitrate leaching and enhanced biomass-related effects, such as the additional input of organic carbon into the soil.

Greenhouse vegetable cultivation is often associated with the rapid accumulation of nitrate in soils. Therefore, N management strategies are needed for greenhouse vegetable production systems. The objective of the present study was to evaluate the effects of a summer catch crop on vegetable crop yields. Maize, as an N catch crop, was planted in leafy vegetable (garland chrysanthemum) and fruit vegetable (green soybean) greenhouse cropping systems during the summer of two consecutive years. Maize removed 4.9–11.8 g N m−2 from the greenhouse soil and also improved soil penetration resistance. The first year cultivation of maize increased the yield of garland chrysanthemum leaves but not the yield of green soybean. In first year, the yield of garland chrysanthemum showed negative correlation with SPAD value and nitrate content in leaves, while the yield of green soybean was positively correlated with shoot fresh weight and dry weights of roots and nodules. During the second year, cultivation of the catch crop clearly increased the yield of both garland chrysanthemum and green soybean. Positive correlations were observed between yield and SPAD value in garland chrysanthemum, and between yield and nodule dry weight in green soybean, respectively. These results indicate that using maize as a catch crop in soil with excessive N accumulation can improve soil conditions and promote subsequent crop growth. However, the effect of catch crop cultivation on yield was dependent on the type of subsequent crop.

High-yielding perennial grass can, when compared to classical grain crop production, considerably increase biomass yields per unit area in Northern European agriculture, which is important to meet the demand for biomass in a growing bioeconomy. Potential benefits for the carbon footprint will, however, depend on greenhouse gas (GHG) emissions during the entire biomass production cycle, which includes grassland renovation at regular intervals to maintain high biomass yields. The renovation phase may accelerate nitrous oxide (N2O) emissions associated with residue decomposition. This study examined the effect of renovating a six-year old festulolium (x Festulolium braunii L.) crop on N2O emissions. As a secondary objective, the study evaluated the potential for mitigating N2O emissions in spring by spraying the sward with a nitrification inhibitor containing 3,4-dimethylpyrazole phosphate (DMPP) prior to cultivation. A replicated split-plot design was used, where one half of each main plot was rotovated and seeded with spring barley (Hordeum vulgare L.) as a catch crop during spring, followed by ploughing and reseeding of festulolium in the autumn. In the other half of each main plot, festulolium was left without cultivation as reference. Four subplots were defined within both cultivated plots and reference plots with (“+DMPP”) or without (“−DMPP”) DMPP spraying of festulolium before cultivation, and with (“F”) or without (“NF”) fertilisation with 119, 425 and 50 kg N ha−1 in spring barley, festulolium and re-established festulolium, respectively. All four combinations of DMPP treatment and fertilisation were represented, i.e., F+DMPP, F-DMPP, NF+DMPP and NF-DMPP. Monitoring of N2O emissions occurred in two periods, April–June (“spring”) and August-October (“autumn”). In the autumn, where festulolium was reestablished, N2O emissions were only monitored in the plots without DMPP treatment in spring, since potential legacy effects of DMPP were not part of this study. Cultivation increased N2O emissions 2.5-fold in spring, and 2-fold in autumn, compared to uncultivated plots. The N2O emissions induced by fertilisation were similar from cultivated and reference plots, and emission factors for spring barley (Apr–Jun), re-sown festulolium (Aug–Oct) and uncultivated festulolium (reference, Apr-Oct) during the monitoring periods were, respectively, 0.40, 0.42 and 0.12%. Spraying festulolium with DMPP delayed the transformation of ammonium to nitrate during spring. DMPP did not reduce N2O emissions significantly in this study. In contrast, there was an apparent interaction between decomposing residues and mineral fertiliser with respect to emissions of N2O, which is a potential GHG mitigation target.

Planting a cover crop between the main cropping seasons is an agricultural management measure with multiple potential benefits for sustainable food production. In the maize production system of the Netherlands, an effective establishment of a winter cover crop is important for reducing nitrogen leaching to groundwater. Cover crop establishment after maize cultivation is obliged by law for sandy soils and consequently implemented on nearly all maize fields, but the winter-time vegetative ground cover varies significantly between fields. The objectives of this study are to assess the variability in winter vegetative cover and evaluate to what extent this variability can be explained by the timing of cover crop establishment and weather conditions in two growing seasons (2017–2018). We used Sentinel-2 satellite imagery to construct NDVI time series for fields known to be cultivated with maize within the province of Overijssel. We fitted piecewise logistic functions to the time series in order to estimate cover crop sowing date and retrieve the fitted NDVI value for 1 December (NDVIDec). We used NDVIDec to represent the quality of cover crop establishment at the start of the winter season. The Sentinel-2 estimated sowing dates compared reasonably with ground reference data for eight fields (RMSE = 6.6 days). The two analysed years differed considerably, with 2018 being much drier and warmer during summer. This drought resulted in an earlier estimated cover crop sowing date (on average 19 days) and an NDVIDec value that was 0.2 higher than in 2017. Combining both years and all fields, we found that Sentinel-2 retrieved sowing dates could explain 55% of the NDVIDec variability. This corresponded to a positive relationship (R2 = 0.50) between NDVIDec and the cumulative growing degree days (GDD) between sowing date and 1 December until reaching 400 GDD. Based on cumulative GDD derived from two weather stations within Overijssel, we found that on average for the past three decades a sowing date of 19 September (± 7 days) allowed to attain these 400 GDD; this provides support for the current legislation that states that from 2019 onwards a cover crop should be sown before 1 October. To meet this deadline, while simultaneously ascertaining a harvest-ready main crop, in practice implies that undersowing of the cover crop during spring will gain importance. Our results show that Sentinel-2 NDVI time series can assess the effectiveness and timing of cover crop growth for small agricultural fields, and as such has potential to inform regulatory frameworks as well as farmers with actionable information that may help to reduce nitrogen leaching.

Cover crops (CC) may play an essential role in the recycling of nutrients in organic farming systems with cereals. Harvest time of cereals and management of straw in the field can affect the growth of CC and subsequent nitrogen (N) fertiliser replacement value (NFRV) in the following crop. This study investigates 1) the effect of harvest time, 2) cutting height of straw and 3) straw removal from the main crop on CC growth, composition, uptake and NFRV in the following crop and 4) the effect of CC harvest in autumn on the NFRV in the succeeding crop. A CC mixture of mainly red clover, with chicory and ryegrass was sown under a spring barley crop in 2017, and replicated in 2018. Four strategies of barley harvest were conducted: 1) early harvest as whole crop or 2) early harvest of the upper parts only, 3) at maturity with straw removed or 4) at maturity with straw left on the field surface. Subsequently, CC and high stubbles of left straw were harvested and removed in autumn in half of the field replicates. The residual effect was measured in spring barley in the succeeding year. The CC aboveground biomass dominated by the clover had an N uptake for both years of 40−77 kg N ha−1. Variability was significant between years but not caused by the harvest time or by straw management. In the succeeding year, residues from barley and CC could replace 61−85 kg N ha−1 of mineral N fertiliser, which were mostly derived from CC roots and stubble. High straw stubble left (40 cm length) significantly reduced the NFRV of CC shoots by 20%. Root residues (including barley and CC roots) contributed a substantial N supply to the following crop irrespective of aboveground CC biomass. The availability of N derived from CC shoot mineralisation differed significantly in the two years and was also influenced by straw left from the previous crop.

The use of alternative biocidal compounds to replace chemical pesticides after the Directive 2009/128/EC has raised renewed interest in the biofumigation technique. In particular, the defatted seed meals (DSM) derived from Brassicaceae plant tissues with high glucosinolate content represent an efficient practice to control soil-born plant pathogens and pests that can be applied in synergy to catch crop green manures. For a wider and safer application of this technique, the impacts on non-target soil microorganisms and free-living nematodes have to be investigated in more depth. In this pot-scale experiment a naturally nematode-infected soil was amended with a glucosinolate-containing DSM from Brassica carinata, a non-glucosinolate-containing DSM from sunflower and the metam-sodium fumigant. Tomato plants were transplanted and checked for the presence of pests and/or pathogens and plant vigour. The response of soil microbial communities was assessed by PCR-DGGE analysis of bacterial 16S rRNA and fungal 18S rRNA genes, whereas nematode indices were applied to assess their community structure 0, 10, 32 and 62 days after the treatments. Significant shifts were observed among both bacterial and fungal communities, whereas various changes of nematode communities occurred depending on the nematode family. Similar changes initially occurred in both bacterial and fungal community structure in response to DSM and VAP amendments, but after 62 days fungal communities were more strongly shaped by VAP fumigation than bacteria. The non-biofumigant SUN treatment added organic matter into the soil inducing significant changes in microbial communities, but it was not effective against Meloidogyne incognita root infestation. Although the free-living nematode structure was negatively influenced by all treatments, B. carinata DMS proved the best compromise between efficiency to control M. incognita and environmental impact. These results confirmed the interesting potential of biofumigant DSM amendments as alternatives to chemical fumigants for a more environment-friendly control of some soil-borne diseases.

The nitrate (N) present in soil at the end of autumn is prone to leach during winter and spring in temperate climates if not taken up by plants. In Denmark catch crops are used as a regulatory tool to reduce N leaching and therefore a shift from winter cereals to spring cereals with catch crops has occurred. Quantitative data is missing on N leaching of a catch crop compared to a winter cereal in a conventional cereal-based cropping system. The aim of the study was to investigate whether fodder radish ( Raphanus sativus L.) (FR) would be more efficient than winter wheat ( Triticum aestivum L.) (WW) at depleting the soil of mineral nitrogen (N min ) before winter. A secondary aim was to study the agreement between three different root measuring methods: root wash (RW), core break (CB) and minirhizotron (MR). The third aim of the was to correlate the N uptake of FR and WW with RLD. An experiment was made to see if and how root growth was affected by the minirhizotron tube. The experiments were conducted on a Danish sandy loam soil. From September to November the amount of soil N min decreased from 49 kg N ha −1 to 14 kg N ha −1 under FR and increased from 28 kg N ha −1 to 44 kg N ha −1 under WW. A test of correlations between root measuring methods showed that there was only a significant positive correlation for FR between CB and RW ( R 2 = 0.77) and for WW between CB and MR ( R 2 = 0.26). We conclude that FR is more efficient than WW at tightening the N cycle in the autumn by a greater depletion of soil N min . From the comparison of root methods, we conclude that root growth in the subsoil was overestimated for FR by the MR method. This was due to preferential root growth along the MR tubes. The root densities/intensities measured with the three root measuring methods were not directly comparable.

Catch crops that are cultivated for green manure play an important role in improving soil properties. A 3-year field experiment was conducted to investigate the effect of catch crop (pea, Pisum sativum L.) management, i.e., incorporation of catch crop in October/November (autumn) and March (spring), and without catch crop (control), on soil organic carbon (SOC), microbial biomass carbon (MBC) and the activities of carbon (C)-cycle enzymes, including cellulase (Cel), β -glucosidase (Glu) and invertase (Inv). Additionally, soil total nitrogen (TN) and pH KCl were investigated. The catch crop was cultivated from August to October each year during 2008–2010. Soil samples were collected from the field of spring barley ( Hordeum vulgare L.) that had been grown after the catch crop. Soil samples for microbial activity determination were taken in March, May, June and August in 2009, 2010 and 2011, while SOC and TN contents as well as pH KCl were determined in March and August. The chemical properties studied did not show significant changes as influenced by the experimental factors. The use of catch crop significantly increased the MBC content and the activities of C-cycle enzymes compared to the control. When the catch crop was incorporated in spring, a significantly higher MBC content was noted in March and May compared to autumn incorporation. Moreover, the spring incorporation of the catch crop significantly increased the Glu activity (except March), while the activities of Cel and Inv as well as the rate of soil basal respiration were usually unaffected by the time of catch crop incorporation. Greater microbial biomass and higher enzyme activities in the catch crop-treated soil, compared to the control, indicated that the application of the catch crop as a green manure could be recommended as a promising technique to increase the biological activity of the soil. Since there was no significant effect or no consistent results were obtained related to the time of catch crop incorporation, both spring and autumn applications can be recommended as a management tool to improve the status of soil properties during the growth of a subsequent crop.

Overuse of fertilizers and the resultant pollution and eutrophication of surface and groundwater is a growing issue in China. Consequently, improved management strategies are needed to optimize crop production with reduced nutrient inputs. Conventional fertilization (CF), reduced fertilization (RF), and reduced fertilization with maize (Zea mays L.) as a summer catch crop (RF+C) treatments were evaluated in 2008 and 2009 by quantifying tomato (Lycopersicon esculentum) fruit yield and soil nutrient balance in a greenhouse tomato double-cropping system. Fertilizer nitrogen (N) application was reduced by 37% in the RF and RF+C treatments compared to the CF treatment with no significant reduction in fruit yield. Mean soil mineral N (Nmin) content to a depth of 180 cm following tomato and maize harvest was lower in the RF and RF+C treatments than in the CF treatment. Residual soil Nmin content was reduced by 21% and 55% in the RF and RF+C treatments, respectively, compared to the CF treatment. Surplus phosphorus (P) and potassium (K) contents in the RF+C treatment were significantly lower than those in the RF treatment, mainly due to additional P and K uptake by the catch crop. We concluded that for intensive greenhouse production systems, the RF and RF+C treatments could maintain tomato fruit yield, reduce the potential for nitrate (NO−3-N) leaching, and with a catch crop, provide additional benefits through increased biomass production.

Late season catch crops could be an effective tool to conserve highly available N after grazing of green manures. An experiment was established to investigate the productivity and N capturing abilities of barley (Hordeum vulgare cv. Cowboy) and oilseed radish (Raphanus sativus L.) crops seeded after a grazed green manure. Green manure was a mix of forage pea (Pisum sativum cv. 40–10), soybean (Gylcine max cv. Prudence) and oat (Avena sativa cv. Legget). The experiment was repeated twice in Carman, Manitoba in 2010 and 2011. Catch crops were seeded in late summer either no-till or after soil cultivation of the grazed plots. Wheat (Triticum aestivum cv. Waskada) was seeded in the second year as a test crop for both experiments. Catch crop productivity and N uptake was influenced by season (greater in the wetter year) and catch crop type (barley and radish produced 1990 and 1490 kg ha−1, respectively) but not tillage system. The catch crops had their greatest overall effect on soil NO3-N content in 2010 under conditions of high autumn precipitation when N leaching was more severe. Here, the catch crops significantly reduced NO3-N at all depths. Under drier conditions in 2011, catch crops only reduced NO3-N in the top 30 cm. There was average 57 and 12 kg ha−1 more soil NO3-N in plots with no catch crops than plots where catch crops were grown in 2010 and 2011, respectively. Wheat N uptake at maturity was reduced around 25% when grown after catch crops. Similarly, wheat grain yield was 12–31% less after catch crops than no catch crops. This study showed that catch crops can be used to capture excess nutrients after grazing, but N release from the selected catch crops in the following year was not in synchrony with the wheat N demand.

Intensive arable crop production has major impacts on the environment and solutions for their reduction are needed. Diversification of crop rotations together with improved nitrogen management is an option for more eco-efficient cropping systems. The potentials for reducing the environmental impacts cropping systems were investigated by means of life cycle assessment (LCA) in three regions in France (Beauce, Burgundy and Moselle). The crop management data were compiled by the Chambers of Agriculture in the three regions based on field survey data (2002–2009 in Burgundy and Moselle and 2004–2008 in Beauce) and completed by experts. The LCA calculations were carried out by the SALCA-crop tool, using the ecoinvent and SALCA inventory databases and SALCA emission models. The LCAs were calculated for crop combinations, which were an efficient way to analyse a large number of crop rotations. A crop combination is defined as the inventory of a given crop, with a defined preceding crop and eventually including a catch crop. Nitrogen management revealed to be a key driver for the environmental impacts. It dominated the non-renewable energy demand, the global warming potential, the ozone formation potential, the acidification potential, and the eutrophication potential. Strong correlations between N fertilisation and these environmental impacts were found. The introduction of pea allowed to reduce the total eutrophication over the whole crop rotation. The mitigation of environmental impacts was not only possible per hectare, but also per € gross margin II. The eco-efficiency can thus be improved by reducing the level of N fertilisation. A reduction of N fertilisation could be achieved also by a reduction of the fertiliser doses to the non-legume crops, in addition to the introduction of legumes. Both ways proved to be effective and the combination of both was the most promising. However, trade-off between environmental and economic goals was identified. Diversification of cereal intensive crop rotations proved to be generally favourable from an environmental point of view. Catch crops had favourable effects on nutrient leaching a slightly favourable effects on biodiversity and soil quality. The ecotoxicity potentials were dominated by a few active ingredients only; the diversification did not lead to generally reduced ecotoxicity potentials. Diverse crop rotations with reduced N input are a promising way to reduce the environmental impacts of intensive arable crop rotations.

Winter turnip rape [Brassica rapa L. ssp. oleifera (DC.) Metzg.] is an oilseed crucifer mainly grown in Nordic and Baltic countries. It can be undersown in a spring cereal as an alternative to sowing of pure stand in late July. Establishment by undersowing helps to utilize the short growing season at high latitudes. However, as undersown crops tend to affect the growth and yield of their companion crops, the effect of undersown winter turnip rape on cereal yield and quality needs to be assessed. Additionally, an evaluation of the suitability of different cereals as companion crops to winter turnip rape is required before practical recommendations can be made. The suitability of four spring cereals as companion crops to winter turnip rape was studied in three field experiments. Two-row barley, six-row barley, wheat and oat were sown at two different densities, with and without undersown winter turnip rape, sowing density depending on the density of the cereal. Undersowing winter turnip rape in a cereal did not markedly affect cereal yield. In some years six-row barley and oat with undersown winter turnip rape produced more yield than corresponding pure stands, indicating a possible facilitative effect of the undersown crucifer on the two cereal species. The results suggest that the most compatible cereals as companion crops with undersown winter turnip rape are six-row barley and oat. Mixed stand cultivation could be improved trough the identification of the optimal cereal–winter turnip rape combinations.

Catch crops are a potential option to reduce phosphorus (P) losses, but little is known about their establishment success and capacity to retain P on clayey soils in regions with short autumns, e.g. Sweden. This study screened biomass production and P retention by eight catch crop species: the perennials chicory (Cichorium intybus L), cocksfoot (Dactylis glomerata L), perennial ryegrass (Lolium perenne L.) and red clover (Trifolium pratense L) and the annuals phacelia (Phacelia tanacetifolia L), white mustard (Sinapis alba L), oilseed radish (Raphanus sativus L oleiformis) and white radish (R. longipinnatus). The catch crops were grown at six field sites, where the perennial species were under-sown with barley and the annual species were after-sown following barley harvest. Biomass production, P content in above-ground and below-ground plant parts and content of available P in the soil were determined in autumn and survival rate of the catch crops in the following spring. Biomass production and P retention in autumn both differed significantly between species (p < 0.0001), and were greatly affected by site-specific conditions and time of sowing, which differed between experiments. Growth of catch crops can also be suppressed by low precipitation. Content of P in roots varied substantially between species, a factor which must be considered in species comparisons. The under-sown species produced more or equivalent amounts of biomass, retained more or equivalent amounts of P in autumn and survived better over winter than the after-sown species. Thus under-sown catch crops generally seem more suitable as catch crops for P.

Pharmaceutical companies have a growing demand for herb raw material, including German chamomile ( Chamomilla recutita (L.) Rauschert), produced according to the rules of Good Agricultural Practices (GAP) for medicinal plants. These rules, among others, require limitation of the application of mineral fertilizers and pesticides. Catch crops can improve soil fertility and reduce weed infestation for subsequent crops. The aim of this study was to evaluate the effect of stubble catch crops and different nitrogen doses on anthodia and herb yield, and content and yield of essential oil from a diploid and tetraploid cultivar of German chamomile. In the 3-year experiment, two chamomile cultivars were grown – Mastar (2n) and Dukat (4n). They were sown after ploughing legume mixture or buckwheat ( Fagopyrum esculentum Moench) stubble catch crops; nitrogen fertilization rates were 0, 30, 60, and 90 kg N ha −1 . It was found that fertilization with 60 and 90 kg N ha −1 reduced chamomile weed infestation to a greater extent than the use of catch crops. The highest yield of anthodia was obtained after the application of the highest nitrogen rate. The herb and oil yield from herb were highest after the application of 60 kg N ha −1 . Cultivation of Dukat after a legume catch crop allowed for a reduction in nitrogen fertilizer rate from 90 to 60 kg N ha −1 without a decrease in anthodium yield. Buckwheat catch crop inhibited the growth of chamomile. A higher yield of anthodia was collected from the cultivar Dukat, but the essential oil content was higher in anthodia of Mastar. The content of chamazulen in essential oil from anthodia was 17.7 and 17.2%, α-bisabolol 23.0 and 21.1%, respectively, from Mastar and Dukat. The essential oil from herb contained mainly farnesene and en-in-dicycloether. The requirements of Good Agricultural Practices in chamomile cultivation can be met by the application of legume stubble catch crops, choice of suitable cultivar, and by adopting the nitrogen rate appropriate for the aim of cultivation.

Dent corn, as a catch crop used for salt removal, was cultivated at different densities, i.e ., 7.3 (low density), 59.7 (normal density), and 119.5 plants m −2 (high density), during a 50 d fallow period after cultivation of a commercial crop in a greenhouse, to analyze the characteristics of nutrient salt (N, K, Mg, and Ca) uptake by roots and to study the effect of plant density on the characteristics associated with crop water use. Leaf area index for the high and normal density treatments reached extremely high values of 24.3 and 14.9, respectively. These values induced higher transpiration rates that were estimated using the Penman-Monteith model with the incorporation of specific parameters for crop and greenhouse conditions. The total N, K, Mg, and Ca contents in the crop canopy at harvest were 26.8, 13.0, 1.0, and 1.7 g m −2 , respectively, under the high density treatment. The dynamics of salt uptake rates for high, normal, and low density treatments were evaluated by assessing weekly changes in salt content, and were subsequently compared against the transpiration rate. A positive linear relationship was obtained between these 2 parameters for all 3 density treatments and all tested salts. Hence, higher transpiration rates caused higher salt uptake rates through water absorption. On the other hand, salt uptake efficiency per unit water use by cultivation was lower in the low density treatment. Therefore, management procedures with dense planting that induce higher transpiration rates and lower evaporation rate are extremely important for the effective cultivation of corn catch crops.

The advantages and disadvantages of varying mixture proportion of crimson clover (Trifolium incarnatum L.) and Italian ryegrass (Lolium multiflorum Lam.), used as winter cover crops, and cover crop biomass management before maize sowing (Zea mays L.) were studied in a series of field experiments in Eastern Slovenia. Pure stands and mixtures of cover crops on the main plots were split into different cover crop biomass management subplots: whole cover crop biomass ploughed down before maize sowing, aboveground cover crop biomass removed before ploughing and sowing, or aboveground cover crop biomass removed before sowing directly into chemically killed residues. Cover crop and cover crop biomass management affected the N content of the whole aboveground and of grain maize yields, and the differences between actual and critical N concentrations in the whole aboveground maize yield. The whole aboveground and grain maize dry matter yields, and the apparent remaining N in the soil after maize harvesting, showed significant interaction responses to cover crop × management, indicating positive and negative effects. Crimson clover in pure stand provided high, and pure Italian ryegrass provided low maize dry matter yields and N content in the yields in all the observed methods of biomass management. However, within individual management, mixtures containing high proportions of crimson clover sustained maize yields and N contents similar to those produced by pure crimson clover. Considering the expected ecological advantages of the mixtures, the results thereby support their use.

The fluctuation of rainfall is the primary limiting factor for sustainability of rain-fed vegetable cropping systems in mid-Yunnan plateau. Our objectives were to evaluate effects of an alternative plastic mulching practice (narrow vs. wide plastic mulch) and an additional catch crop (broccoli–zucchini–winter wheat vs. broccoli–zucchini–fallow) on the soil moisture status, crop yield and water use efficiency (WUE) in the rain-fed vegetable cropping systems. Rainfall was much low and erratic during the entire experiment period compared with the long-term average (1971–2000). The 0–60 cm soil water storage (113 mm) of growing season was significantly higher under wide plastic mulch plots than narrow plastic mulch plots (99 mm). Fruit yield and water use efficiency of broccoli and zucchini were enhanced with wide plastic mulch during growing season in the three years experiment. Compared with the broccoli–zucchini–fallow plots, the broccoli–zucchini–winter wheat rotation treatment did not significantly decrease available soil water at broccoli transplanting stage. This implicated that the addition of winter wheat in the vegetable cropping system would not pose serious consequences for water storage. The results obtained in this study have practical implications for sustainability of the rain-fed vegetable culture.

Energy crop production for fermentation in biogas plants significantly increased in the last years. At present maize is the most common energy crop for biogas production due to high dry matter and methane yields together with advanced breeding activities. In Germany nearly 80% of all energy crop biogas production is based on maize for silage. This dominance frequently causes environmental risks like soil erosion, nutrient losses and increased use of pesticides. Furthermore it puts societies’ acceptance towards biogas production increasingly at risk. Thus, the development of innovative cropping systems is essential for a sustainable energy crop production. This paper reviews results from 3 years field trials at seven locations with 12 different double-cropping systems (turnip rape, rye and mixture of rye–winterpea as first crops and maize, sorghum, sunflower and mixture of maize–sunflower as succeeding second crops) in comparison with three sole crops systems as references: maize and sunflower after mustard as catch crop and energy rye, harvested at dough ripeness as whole-crop silage. Double-cropping systems with rye or rye–pea as first crop and maize as second crop achieved highest DM yields of 23 t DM ha−1 on average, followed by sole cropped maize and double-cropping system of turnip rape and maize. Sole-cropped sunflowers had the lowest yield with nearly 15 t DM ha−1, followed by winter rye harvested at dough ripeness. Yields of other double-cropping systems had an intermediate position between those treatments. Methane yield per hectare was positively correlated with DM yield. Double cropping systems mostly achieved lower DM contents than sole cropping systems due to later sowing and altered photoperiodic influences. Further research on cultivars suitable for late sowing dates is necessary. Methane yield of crops was very similar with 282–298 Nl kg−1 oDM, except for sorghum with 255 Nl kg−1 oDM on average. Hence, differences in chemical components did not result in large changes regarding to methane yield, again except for sorghum, probably due to higher lignin contents. Double-cropping systems had mostly higher yield stability than sole cropping systems. The cultivation of two crops within 1 year may also spread the risk of weather extremes among two crops (or more if mixtures are grown) resulting in higher yield stability. This property is getting increasingly important with regard to climate change. Hence, double-cropping systems may contribute to a more sustainable energy crop production.

The promotion of electricity generation from renewable energy sources has led to a substantial expansion of biogas production in Germany, with most biogas plants co-digesting slurry and crops, and maize being by far the most dominant substrate. At present only limited information is available on the agronomic and environmental performance of biogas cropping systems, and on the fertilizer value of biogas residues. In a two-year field experiment at two sites in northern Germany differing in soil quality, we analyzed the dry matter (DM) yield, N yield, methane yield, and the N balance of different cropping systems: (i) maize monoculture (R1), (ii) maize–whole crop wheat followed by Italian ryegrass as a double crop (R2), (iii) maize–grain wheat followed by mustard as a catch crop (R3), and (iv) perennial ryegrass ley (R4). Rotations R1, R2 and R3 were grown at Site 1 (sandy loam), whereas R1 and R4 were tested at Site 2 (humus sand). Crops were supplied with varying amounts (0–360 kg N ha −1 , ryegrass: 0–480 kg N ha −1 ) of biogas residue, cattle slurry, pig slurry, or mineral N fertilizer, which allowed quantifying their N use efficiency in terms of apparent N recovery (ANR) and relative N fertilizer value (RNFV). No significant interactions of crop rotation and fertilizer type on DM and methane yield, plant N recovery, as well as N balance, were detected at Site 1, where R1 (19.3 t DM ha −1 ; 6750 m 3 N CH 4 ha −1 ; N: norm conditions, i.e. 273 K, 1024 hPa) clearly out-yielded R2 (16.8 t DM ha −1 ; 5351 m 3 N CH 4 ha −1 ) and R3 (12.8 t DM ha −1 ), while R2 had a higher plant N recovery. At Site 2, the perennial ryegrass ley achieved substantially lower maximum DM and methane yield (13.9 t DM ha −1 ; 4251 m 3 N CH 4 ha −1 ) than maize monoculture (17.3 t DM ha −1 ; 6038 m 3 N CH 4 ha −1 ). Fertilizer type affected grass performance: application of biogas residue resulted in lower yield and N recovery, but higher N balance than mineral fertilizer and cattle slurry. The N use efficiency of biogas residue application depended on the crop rotation. Biogas residue resulted in higher ANR and RNFV compared to pig slurry in R1, whilst in R2 the reverse occurred, and effects were similar to cattle slurry in R4. The results revealed that, except for grassland, substrate cropping based on biogas residues can exploit the yield potential without causing high N surplus.

Energy balances are increasingly used to assess the energy efficiency and productivity of agricultural production. In this study, energy balances for sugar beet cultivation in commercial farms in Germany were calculated. 109 farmers with 285 fields were interviewed about the sugar beet cultivation 2004. The energy input and the energy output were calculated with standardised balance-sheet approaches and energy equivalents. Calculated energy balance parameters were the energy gain (energy output less input), the output–input ratio (energy output versus input) and the energy intensity (energy input versus natural yield measured in Grain Equivalents). A factor analysis was performed to explain the variation of the energy balance parameters between the fields by crucial factors for energetic efficiency and productivity. Fields with similarly valued factors were grouped into common clusters by a cluster analysis and a discriminant analysis. The influence of specific growing conditions and cultivation methods on the energy balances were examined for the clusters. Total energy input (median: 17.3 GJ ha−1), energy output (261.7 GJ ha−1), energy gain (244.6 GJ ha−1), output–input ratio (15.4) and energy intensity (87.4 MJ GE−1) revealed a significant variation. The total energy input was significantly lower and the energy yield was significantly higher than in previous studies. Thus, the energy gain and the output–input ratio have clearly risen compared to earlier studies. Today, sugar beet cultivation is energetically more productive and efficient than the cultivation of many other arable crops in Middle Europe. The intensity of the cultivation measures irrigation, catch crop cultivation, tillage and N fertilisation as well as the management of all cultivation measures and the site were determined as crucial factors for energy efficiency and productivity. The intensity of the different cultivation measures influenced the total energy input significantly, but no influence on the energy output was determined. In contrast, the cultivation management (quality and adaptation of cultivation measures) was mainly responsible for the energy output. Whereas the cultivation management mostly explained the energy gain, the factor cultivation management and the factors representing cultivation intensity together were responsible for the output–input ratio. Cluster and discriminant analysis resulted in the formation of 13 clusters. For clusters with an above-average energy gain and output–input ratio, the intensity and in particular the management of cultivation measures were essential for optimising the energy balance.

Use of catch crops as a green manure may increase soil fertility due to improved soil organic matter content as well as soil biological activities. We conducted a 3-year field experiment to evaluate the impact of catch crops [oilseed radish (OR) ( Raphanus sativus L.) and field pea (FP) ( Pisum sativum L.)] and inorganic N fertilization at 0, 40, 80, 120, 160 kg N ha − 1 year − 1 on the activities of soil enzymes (β-glucosidase — GLU, nitrate reductase — NR, urease — UR, arginine deaminase — ADA, acid and alkaline phosphatase — P AC and P AL ) and chemical properties of typical Alfisol . Each year, catch crops were sown at the beginning of August and ploughed three months later in 2005, 2006 and 2007. Then the main crop – spring wheat ( Triticum aestivum L.) – was grown in 2006, 2007 and 2008. Soil samples were taken twice a year, in spring before spring wheat sowing (March or April) and in summer, immediately after the harvest. In March (April 2006) organic carbon (C ORG ) and available potassium (K AVAIL ) did not show significant changes as influenced by catch crops. Total nitrogen (N TOT ) content was significantly lower in control soil than in catch crop treatments, while the concentration of available P (P AVAIL ) behaved in the opposite way. N fertilization rates did not significantly affect the chemical properties of soil without catch crops (C) (with the exception of Mg AVAIL concentration). In contrast, the chemical properties did not show clear tendencies depending on N fertilization in soil with field pea or oilseed radish. Significantly higher soil enzymatic activities were observed in the catch crops treatment than in the control (C). The studied enzymes also showed a significantly higher activity in the FP than in the OR when both catch crops were compared (with the exception of ADA and P AL activities in August and GLU activity in March (April 2006)). Both P AC and P AL as well as GLU, ADA and NR activities were always higher in August than in March (April 2006), while UR (with the exception of 2007) behaved in a reverse manner. The enzyme activities were 10–26% lower at a rate of 160 kg N ha − 1 year − 1 compared to the highest activity noted in the case of a rate of 40 and/or 80 kg N ha − 1 year − 1 with the exception of UR activity, which was unaffected by N fertilization rates. Cultivation of catch crops for so-called green manure can be useful management practice for enhancing soil biological activity as evaluated by enzymatic activity. Enzyme activities were more sensitive to the presence of catch crop green biomass and N fertilization rates than chemical properties. Therefore, they might be useful as an early indicator in the evaluation of the alteration of soils caused by different agricultural activities.

Power based on biomass, in particular biogas, is increasing, with a concomitant increase in the need for energy crop production. The objective of this study was to determine the profitability of biogas substrate production on a marginal site in southwestern Germany. The effects of crop rotation and nitrogen fertilization level were evaluated in a three-year filed experiment. Production costs for supply of biogas substrates and sales of produced electricity were assessed using five crop rotations (CR1: annual monoculture maize; CR2: perennial monoculture perennial ryegrass; CR3: perennial monoculture Jerusalem artichoke; CR4: three-course crop rotation of sorghum – winter triticale – clover grass; CR5: four-course crop rotation of catch crop – maize – winter wheat – winter triticale) and three nitrogen fertilization levels (zero, middle and high levels of nitrogen). The variables were production costs, dry matter yield, substrate costs, energy output, biomass energy supply price, biomass energy sales price and sale/supply ratio. Production costs increased in the order CR4 (1252 € ha−1 a−1)

A field experiment was carried out in an arable organic cropping system and included a sequence with sole cropped fababean (Vicia faba L.), lupin (Lupinus angustifolius L.), pea (Pisum sativum L.), oat (Avena sativa L.) and pea–oat intercropping with or without an undersown perennial ryegrass (Lolium perenne L.) – white clover (Trifolium repens L.) catch crop followed by a first crop of spring wheat (Triticum aestivum L.) and second crop of winter triticale (Triticale hexaploide L.). The rotation sequence was repeated twice. Natural 15N abundance techniques were used to determine grain legume N2 fixation and 15N labeling technique to determine the fate of pea and oat residue N recovery in the subsequent crop. The subsequent spring wheat and winter triticale crop yields were not significantly affected by the previous main crop, but a significant effect of catch crop undersowing was observed. A higher soil mineral N content in the soil profile without undersown grass-clover increased the spring wheat yield. This effect was circumvented in the subsequent winter triticale, where yields in the treatments with catch crops undersown were significantly greater. The grass-clover catch crop after grain legumes had a higher grass proportion before incorporation as compared to grass-clover after oat, which had the greatest clover proportion. The dynamic response of interspecific interactions in the catch crop to the soil mineral N levels is moderating the preceding effect of main crops in the subsequent cereal – and sometimes to a higher degree than the main crop effect. For research involving rotation principles it is recommended to evaluate cumulative effects over several years and not only single seasons.

The main purpose of this study was to examine the influence of three sowing dates (mid of September, beginning of October, mid of October) on the winter hardiness and productivity of six different genotypes of winter peas (Pisum sativum L.). The two field trials were conducted with winter peas in either pure stands as winter catch crop for biomass yield (three seasons) or mixed stands with rye as a seed legume (two seasons; seeding rate 20 and 225 germinable seeds m−2, respectively) on the experimental farm of the University of Kassel, Germany. The main findings suggest that only those genotypes can be recommended for cultivation that have adequate winter hardiness. Results support the conclusion that winter peas have sufficient winter hardiness for cultivation in transitional climatic conditions when they display a rosette growth with small leaves and short internodes at the onset of winter and possess quantitative photoperiodic sensitivity. For these genotypes, no impact of the sowing date on the extent of winter hardiness could be determined. In the experiment winter pea pure stands, the highest biomass yield (assessed at the onset of flowering) was determined for the earliest sowings. In the experiment with winter pea/rye mixture, the influence of sowing date on seed yield of the frost-resistant peas was negligible.

A 3-year field study (2007–2009) was conducted in separately tile-drained plots on a sandy soil in south-west Sweden to determine nitrogen (N) and phosphorus (P) leaching losses from potatoes to the drainage system. Different types of potatoes were grown and harvested at different times followed by different crops in order to identify the potato type/following crop system with the lowest risk of N and P leaching losses. Accumulated annual amounts of N and P lost to drainage between May (potato planting) and the following April varied between 13 and 72 kg N ha −1 and 0.04 and 0.24 kg P ha −1 depending on treatment and year. P leaching losses from this particular soil were low and differences between potato types not distinct, but there were significant differences between years. Abnormally high precipitation in summer 2007 led to significantly higher P leaching losses than in other years. N leaching losses were also higher in 2007, but differences between potato types were found in all years. Despite the high mineral soil nitrogen content (N min ) after harvest in June, early potatoes (EP) with oilseed radish (oil) as catch crop showed the lowest N leaching losses of all potatoes. Potatoes harvested in August (table potato; TP) and September/October (late potato; LP) followed by triticale (tri) sown in October showed the highest leaching losses. Thus under current climate conditions in Sweden, oilseed radish after EP is a suitable catch crop for N, while triticale sown in October is ineffective in preventing N leaching after potatoes. The late harvest of starch potatoes (SP) did not allow establishment of a following crop. However, SP showed lower N leaching losses than TP + tri and LP + tri due to lower residual N min in deeper soil layers, low temperatures after harvest decreasing soil N mineralisation and higher C:N ratio of the potato haulm leading to lower N mineralisation potential. As a mean of all years, N leaching losses during and after EP + oil and SP were similar to those from the reference crop spring barley (SB), whereas TP + tri and LP + tri require countermeasures against N leaching.

In 1988–2009, efforts involving manure regulations, subsidies and advisory work were made to reduce losses of nitrogen (N) and phosphorus (P) from arable land to water in Sweden, especially southern Sweden. To evaluate ensuing long-term trends, nutrients in total and dissolved form were monitored in drainage water from 13 fields under ordinary cultivation. The Mann-Kendall test, adjusted for biweekly sampling, revealed significant decreasing trends (magnitude 3% per year) in nitrate–nitrogen (NO 3 –N) concentrations in two fields. One of these had received no manure and had been subjected to delayed tillage after fallow since 1993, while the other had been frequently cropped with a catch crop combined with spring tillage since 1999. An additional decreasing trend in dissolved reactive P (DRP) was observed over the years from this and another field, both with unfertilised fallow grown as an interior buffer on an area at the field outlet, one in 1999–2010 and the other since 2001. By contrast, there was an increasing trend in DRP in a field with accelerating P loads that included almost yearly manure additions to crops following potatoes and sugar beet. However, the general DRP level in the drainage water was low (4–13 μg L −1 ), probably as a result of high P sorption capacity of the topsoil and subsoil. No significant trends in total P or particulate P were found for any of the fields. The importance of long-term monitoring of nutrients in water leaving agricultural fields in order to estimate trends in nutrient losses is discussed.

Autumn tillage strategies designed to reduce leaching losses of nitrogen (N) from arable fields were examined on a medium clay soil (approx. 40% clay) in terms of their effects on accumulation of soil mineral N (SMN) during autumn and winter, crop N uptake, grain yield (spring-sown cereals) and soil structure over the long term (1997–2004). Tillage strategies included mouldboard ploughing (20–25 cm depth) and stubble cultivation (10–12 cm depth) in different combinations and timing, together with different options for straw management and catch crops. Postponing mouldboard ploughing from early September to early November significantly decreased SMN content during autumn and winter, although levels were generally low in all treatments. On average, the soil profile down to 90 cm depth contained 30 kg N ha−1 in November and 27 kg N ha−1 in December with early mouldboard ploughing, while the corresponding figures for late mouldboard ploughing were 16 and 21 kg N ha−1. Stubble cultivation stimulated N mineralisation but the increase in SMN from tillage in September to November was only 3 kg ha−1 after stubble cultivation, compared with 8 kg ha−1 after mouldboard ploughing. Stubble cultivation before late mouldboard ploughing resulted in 6 kg ha−1 higher SMN during autumn than late ploughing without preceding cultivation. Postponement of mouldboard ploughing significantly decreased grain yield by on average 11% and this negative effect accumulated over time. A catch crop compared with no catch crop reduced SMN during autumn and winter by 3–5 kg ha−1 and had no significant yield effect. Effects of straw incorporation were small and could not be significantly proven either for SMN or yield. Transport of SMN to deeper layers was generally limited and SMN did not decrease during winter, indicating a minor impact of tillage time on N leaching risk. No significant changes in soil physical parameters were detected, but the results indicated poorer soil structure after tillage in late autumn compared with early autumn in terms of higher soil bulk density, lower aggregate stability in water, and lower infiltration rate. Overall, considering the short-term and long-term negative effects on yield and possibly soil structure, the benefit of delaying tillage seems small on this clay soil.

Catch crop root growth and nitrogen (N) uptake from both shallow and deeper soil layers are important for N management in arable farming systems, particularly in climates where excess winter precipitation induces N leaching. We simulated the root growth and biomass yield of three common catch crops [chicory (Cichorium intybus L.), fodder radish (Raphanus sativus L.) and perennial ryegrass (Lolium perenne L.)] and their effect on soil mineral N (NO3− and NH4+) in different soil layers by using the FASSET model. The simulated results of catch crop biomass and root growth and mineral N in the soil profile were validated against two years (2006 and 2007) of observations taken in Foulum and Flakkebjerg, Denmark. Once the model was validated, the effect of these three catch crops on N leaching and grain yield of spring barley monoculture was simulated for 30 years. Both measurements and model simulations showed that fodder radish developed the deepest root system and depleted N from deeper soil layers than chicory and ryegrass. Thirty years of simulations showed that the system with ryegrass catch crop had a smaller amount of N leaching from 1 m depth than the system with other catch crops and without catch crops. However, estimated total N leached at 2 m soil depth was smallest in the system with fodder radish followed by the system with chicory, indicating that these catch crops are capable of taking soil N also from below 1 m depth. On average, the system with fodder radish was estimated to decrease N leaching from 2 m depth by 79% compared with the system without catch crops, resulting in an average spring barley grain yield increase of 2%. Chicory and ryegrass correspondingly contributed to reducing N leaching from 2 m soil depths by 71 and 67% when compared with the system without catch crop. The system planted to chicory and ryegrass catch crops decreased spring barley yield by 3 and 5%, respectively, probably because of competition between the cereal crop and the catch crop for N, water and light. Discontinuation of catch crop use increased slightly not only the spring barley yield but also N leaching by about 17%. Inclusion of catch crop in the system increased soil total N and C content by 16–46 kg N ha−1 year−1 and 170–498 kg C ha−1 year−1, respectively, as compared to the system without catch crop. The increase was largest with the use of ryegrass catch crop. -------------------------------------------------------------------------------- Catch crop root growth and nitrogen (N) uptake from both shallow and deeper soil layers are important for N management in arable farming systems, particularly in climates where excess winter precipitation induces N leaching. We simulated the root growth and biomass yield of three common catch crops [chicory (Cichorium intybus L.), fodder radish (Raphanus sativus L.) and perennial ryegrass (Lolium perenne L.)] and their effect on soil mineral N (NO3− and NH4+) in different soil layers by using the FASSET model. The simulated results of catch crop biomass and root growth and mineral N in the soil profile were validated against two years (2006 and 2007) of observations taken in Foulum and Flakkebjerg, Denmark. Once the model was validated, the effect of these three catch crops on N leaching and grain yield of spring barley monoculture was simulated for 30 years. Both measurements and model simulations showed that fodder radish developed the deepest root system and depleted N from deeper soil layers than chicory and ryegrass. Thirty years of simulations showed that the system with ryegrass catch crop had a smaller amount of N leaching from 1 m depth than the system with other catch crops and without catch crops. However, estimated total N leached at 2 m soil depth was smallest in the system with fodder radish followed by the system with chicory, indicating that these catch crops are capable of taking soil N also from below 1 m depth. On average, the system with fodder radish was estimated to decrease N leaching from 2 m depth by 79% compared with the system without catch crops, resulting in an average spring barley grain yield increase of 2%. Chicory and ryegrass correspondingly contributed to reducing N leaching from 2 m soil depths by 71 and 67% when compared with the system without catch crop. The system planted to chicory and ryegrass catch crops decreased spring barley yield by 3 and 5%, respectively, probably because of competition between the cereal crop and the catch crop for N, water and light. Discontinuation of catch crop use increased slightly not only the spring barley yield but also N leaching by about 17%. Inclusion of catch crop in the system increased soil total N and C content by 16–46 kg N ha−1 year−1 and 170–498 kg C ha−1 year−1, respectively, as compared to the system without catch crop. The increase was largest with the use of ryegrass catch crop.

Two main challenges facing organic arable farming are the supply of nitrogen (N) to the crop and the control of perennial weeds. Nitrate leaching from different organic arable crop rotations was investigated over three consecutive four-year crop rotations in a field experiment at three locations in Denmark (12 years in total). The experimental treatments were: (i) crop rotation, (ii) catch crop and (iii) animal manure. Nitrate leaching was estimated from measured soil nitrate concentration in ceramic suction cells and modelled drainage. There were significant effects on annual N leaching of location (coarse sand > loamy sand > sandy loam) and catch crops (without > with). Including a grass-clover green manure on 25% of the area did not increase N leaching compared with crop rotations without green manure. Also the application of animal manure did not influence N leaching, probably because even in the manured treatments the application rate was lower than crop demand. The results identify management of crop and soil during autumn as the main determinant of N leaching. Nitrate leaching was lowest for a catch crop soil cover during autumn and winter (avg. 20 kg N ha−1), a soil cover of weeds/volunteers had on avg. 30 kg N ha−1, and the largest N leaching losses were found after stubble cultivation (avg. 55 kg N ha−1). The N leaching losses increased with increasing number of autumn soil cultivations

Organic and conventional farming practices differ in the use of several management strategies, including use of catch crops, green manure, and fertilization, which may influence soil properties, greenhouse gas emissions and productivity of agroecosystems. An 11-yr-old field experiment on a sandy loam soil in Denmark was used to compare several crop rotations with respect to a range of physical, chemical and biological characteristics related to carbon (C) and nitrogen (N) flows. Four organic rotations and an inorganic fertilizer-based system were selected to evaluate effects of fertilizer type, catch crops, of grass-clover used as green manure, and of animal manure application. Soil was sampled from winter wheat and spring barley plots on 19 September 2007, 14 April 2008 and 22 September 2008, i.e. before, during, and after the growth season. The soils were analyzed for multiple attributes: total soil organic carbon (SOC), total N, microbial biomass N (MBN), potentially mineralizable N (PMN), and levels of potential ammonium oxidation (PAO) and denitrifying enzyme activity (DEA). In situ measurements of soil heterotrophic carbon dioxide (CO2) respiration and nitrous oxide emissions were conducted in plots with winter wheat. In April 2008, prior to field operations, intact soil cores were collected at two depths (0–5 and 5–10 cm) in plots under winter wheat. Water retention characteristics of each core were determined and used to calculate relative gas diffusivity (DP/Do). Finally, crop growth was monitored and grain yields measured at harvest maturity. The different management strategies between 1997 and 2007 led to soil carbon inputs that were on average 18–68% and 32–91% higher in the organic than inorganic fertilizer-based rotations for the sampled winter wheat and spring barley crops, respectively. Nevertheless, SOC levels in 2008 were similar across systems. The cumulative soil respiration for the period February to August 2008 ranged between 2 and 3 t CO2–C ha−1 and was correlated (r = 0.95) with average C inputs. In the organic cropping systems, pig slurry application and inclusion of catch crops generally increased soil respiration, PMN and PAO. At field capacity, relative gas diffusivity at 0–5 cm depth was >50% higher in the organic than the inorganic fertilizer-based system (P < 0.05). Crop yields in 2008 were generally lower in the low-input organic rotations than in the high-input inorganic fertilizer-based system; only spring barley in rotations with pig slurry application and incorporation of a catch crop prior to sowing obtained grain yields similar to levels achieved in the system where inorganic fertilizer was applied. These results suggest that within organic cropping systems, both microbial activity and crop yields could be enhanced through inclusion of catch crops. However, the timing of catch crop incorporation is critical.