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Aims: A better understanding of how plant growth, N nutrition and symbiotic nitrogen fixation (SNF) are influenced by soil inorganic N availability, for a wide range of legume species, is crucial to optimise legume productivity, N2 fixation, while limiting environmental risks such as N leaching.Methods: A comparative analysis was performed for ten legume crops, grown in a field experiment and supplied with four N fertiliser rates. Dry matter, N concentration and SNF were measured. In parallel, root elongation rates were studied in a greenhouse experiment.Results: For most species, N fertilisation had little effect on plant growth and N accumulation. SNF was reduced by soil inorganic N available at sowing but with large differences in the magnitude of the response among species. The response varied according to plant N requirements for growth and plant ability to retrieve inorganic N. Accordingly, root lateral expansion rate measured in RhizoTubes was highly correlated with plant ability to retrieve inorganic N measured in the field experiment.Conclusion: Combining SNF response to soil inorganic N, shoot N and plant ability to retrieve inorganic N, allowed a robust evaluation of differential response to soil inorganic N among a wide range of legume species. [ABSTRACT FROM AUTHOR]

Background and Aims: Legume use in forage production may replace mineral fertiliser N input by biological nitrogen fixation in grass-legume mixtures. However, these systems may also have high phosphorus requirements. The aim of the study was to determine the amount and composition of C, N and P forms in grassland soil under two different graminaceous species grown in monoculture or in mixture with a legume. Methods: Cocksfoot and tall grass fescue were grown for four years as N-fertilised (165 kg ha) monocultures or in mixture with N-fixing Lucerne. We analysed for forage yields, soil organic matter (SOM) storage, and soils' content of soluble as well as insoluble mineral and organic N and P forms. Results: Our data showed higher forage yields on plots with Lucerne compared to plots with N fertilized graminaceous species. Lucerne proportion in mixtures changed from 40 % to more than 80 % after 4 years. Despite similar SOM contents, we observed changes of soluble and insoluble N and P forms. Inorganic P consumption by Lucerne seemed to be reduced in mixtures and storage of organic P enhanced in some cases. Conclusion: Different plant species and mixtures may have specific effects on soil parameters related to organic matter most probably due to plant specific rhizosphere effects. Negative effects of legumes on soil P may be attenuated when grown in mixture with grass. Ultimately, the effect of N-fertilizer replacement by legumes on SOM and nutrient forms may depend on the graminaceous species used for the mixture. [ABSTRACT FROM AUTHOR]

Croplands mainly act as net sources of the greenhouse gases carbon dioxide (CO) and nitrous oxide (NO), as well as nitrogen oxide (NO), a precursor of troposheric ozone. We determined the carbon (C) and nitrogen (N) balance of a four-year crop rotation, including maize, wheat, barley and mustard, to provide a base for exploring mitigation options of net emissions. The crop rotation had a positive net ecosystem production (NEP) of 4.4 ± 0.7 Mg C ha y but represented a net source of carbon with a net biome production (NBP) of -1.3 ± 1.1 Mg C ha y. The nitrogen balance of the rotation was correlated with the carbon balance and resulted in net loss (−24 ± 28 kg N ha y). The main nitrogen losses were nitrate leaching (−11.7 ±1.0 kg N ha y) and ammonia volatilization (−9 kg N ha y). Dry and wet depositions were 6.7 ± 3.0 and 5.9 ±0.1 kg N ha y, respectively. Fluxes of nitrous (NO) and nitric (NO) oxides did not contribute significantly to the N budget (NO: -1.8 ± 0.04; NO: -0.7 ± 0.04 kg N ha y) but NO fluxes equaled 16% of the total greenhouse gas balance. The link between the carbon and nitrogen balances are discussed. Longer term experiments would be necessary to capture the trends in the carbon and nitrogen budgets within the variability of agricultural ecosystems. [ABSTRACT FROM AUTHOR]

Catch crops can effectively decrease nitrate leaching in arable cropping systems but their long-term impacts on nitrogen mineralization are not well known. This study quantified the effects of continuous catch crops on net N mineralization, crop N uptake, crop N use efficiency and N leaching in three long-term (13-17 years) field experiments in northern France. Mustard was grown every year at Boigneville, radish every year at Thibie and ryegrass every 2 years at Kerlavic. The mean N content of catch crop residues at these sites was 33, 36 and 35 kg ha yr and their mean C:N ratio was 13, 17 and 28, respectively. Net mineralization was calculated with a mass balance of soil mineral N using measured inputs and outputs. Catch crop establishment enhanced annual mineralization by on average 26, 18 and 9 kg N ha yr respectively during the 13-17 year period. The difference in mineralization rate between catch crop and control treatments (extra mineralization) was positive from the first year at Boigneville, whereas it was negative or nil during the first 3-5 years at Thibie and Kerlavic. At the latter sites, the extra mineralization rate increased significantly over time at a rate of 2.0 and 2.6 kg N ha yr. At the end of the experiment, cumulative extra mineralization represented 72%, 60% and 23% of the total N added by catch crop residues at Boigneville, Thibie and Kerlavic, respectively. Repeated catch crops significantly increased N uptake and N use efficiency by main crops at Kerlavic and Thibie, but not at Boigneville. The efficiency of catch crops in reducing N leaching persisted over the years at all sites. A model simulating C and N dynamics during catch crop decomposition was able to reproduce the pattern of extra N mineralization kinetics with the various catch crop species, but underestimated the range of variation between sites. Better predictions were obtained when C or N inputs due to catch crops were increased by 10-57%, suggesting that the actual inputs could be markedly greater than those measured in catch crop residues. According to the model, the C:N ratio of catch crop residues largely explained differences in mineralization due to different catch crop species. [ABSTRACT FROM AUTHOR]

Modelling of the carbon dynamics in arable soils is complex and the accuracy of the predictions is unknown before the model is applied to each specific site. Objectives were (i) to test the accuracy of predictions of the carbon dynamics using the Rothamsted Carbon (RothC) Model in a field trial in Quzhou, North China Plain, using different methods for initialization and estimation of carbon input into the soil and (ii) to test the applicability of the RothC model for plots with either conventional tillage (CT) or no-tillage (NT) systems. A field trial was conducted with applications of differing amounts of N (0, 112 or 187 kg N ha−1 year−1), P (0, 75 or 150 kg P2O5 ha−1 year−1) and wheat straw (0, 2.25 or 4.5 t DM ha−1 year−1) in differing combinations with either CT or NT for 18 years. CT and NT affected stocks of soil organic carbon (SOC) similarly. Carbon inputs from crops were either estimated from published regression functions that relate C inputs to crop yield including rhizodeposition (models 1 and 2) or published root:aboveground biomass ratios (model 3). Model 1, which was not calibrated to the site conditions, was successful in predicting the carbon dynamics in seven out of nine treatments (model efficiencies EF ranged from 0.28 to 0.87), whereas for two treatments, EF (−0.35 and−2.3) indicated an unsuccessful prediction. The prediction of the C dynamics in NT experiments using model 1 was generally successful, but this may have been due to the fact that NT did not have a specific effect on SOC stocks for this trial. Model 2, which was the same as model 1 except for an optimization of the stock of inert organic matter using one treatment, predicted SOC stocks in the remaining eight treatments overall better than model 1. Model 3 was less successful than models 1 and 2 in all treatments (−19 ≤ EF ≤ 0.56). The results indicate that the RothC model may successfully predict C dynamics—for the site studied even without prior calibration as in model 1—, but care should be taken in choosing an appropriate approach for estimating C inputs into the soil. [ABSTRACT FROM AUTHOR]

Studies dynamics of biomass and nitrogen (N) accumulation of alfalfa under three N fertilization rates. Effect of N fertilization on the dynamics of biomass; Determination of N requirements per unit of shoot biomass; Maximum shoot growth reached with N fertilization.

Studies early sowing of winter rapeseed in reduction of winter nitrate leaching. Temperature which is required for freezing the leaves for the study; Percentage of nitrogen derived form labelled leaves; Increase in nitrogen recovery due to active absorption by rape in spring season.

The frequency of shoot removal in lucerne (Medicago sativa L.) has long been recognized as a key factor in its management and productivity. The present study was undertaken to determine the impact of cutting interval during spring (30 or 45 days) on the subsequent summer regrowth, in contrasting lucerne cultivars (cv. Europe and Lodi). In particular, the dynamics of shoot regrowth (leaf area index, radiation use efficiency, N accumulation in harvestable biomass) and its relationship with taproot organic reserves (starch and N contents) were studied. Results showed that increasing the duration of the spring regrowth had a positive effect on subsequent summer regrowth, but there were also effects of cultivars. During the first 14 days of summer regrowth, the 'Lodi' cultivar showed higher leaf area index (LAI) and greater photosynthetic active radiation interception than the 'Europe' cultivar. The organic reserve level was also affected by the length of the previous spring cutting treatment (45 days treatment > 30 days treatment) and cultivar (Lodi > Europe). Lodi accumulated a larger amount of starch and N reserves which were subsequently mobilized to a greater extent in the first three weeks of regrowth and this contributed to its faster initial shoot growth rate. Our results confirm the important role played by N and C taproot reserves in shoot growth rate in the first days following shoot removal. Results are discussed in relation to recent studies on the role of storage N compounds in regrowth, and the concepts of radiation use efficiency (RUE); nitrogen nutrition index (NNI), and the decline in N content seen during the accumulation of biomass in lucerne canopies. [ABSTRACT FROM AUTHOR]