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Weeds represent a significant threat to crop yields and global food security. We analysed data on weed competition from the world's longest running agricultural experiment to ask whether potential yield losses from weeds have increased in response to management and environmental change since the advent of the Green Revolution in the 1960s. On plots where inorganic nitrogen fertiliser has been applied, potential yield losses from weeds have consistently increased since 1969. This was explained by a warming climate, measured as air temperature averaged over the growing season for the weeds, and a shift towards shorter crop cultivars. Weeds also reduced yield proportionally more on plots with higher rates of nitrogen which had higher yields when weeds were controlled; the relative benefit of herbicides was, therefore, proportional to potential crop yield. Reducing yield losses from weed competition is increasingly challenging because of the evolution of herbicide resistance. Our results demonstrate that weeds now represent a greater inherent threat to crop production than before the advent of herbicides and integrated, sustainable solutions to weed management are urgently needed to protect the high yield potential of modern crop genotypes., The world's longest running agricultural field experiment has plots that have never received herbicides. When yields from these plots were compared to those from equivalent plots where weeds are controlled with herbicides, we observed increasing yield losses between 1969 and 2014. This was explained by rising temperatures and the shift towards shorter crop cultivars.

The development of resilient cropping systems with high yield stability is becoming increasingly important due to future climatic and agronomic challenges. Consequently, it is essential to compare the effects of different agronomic management practices, such as cropping sequences and nutrient supply, on the stability of crop yields. Long-term experiments are a valuable resource for investigating these effects, as they provide enough time to accurately estimate stability parameters. The objective of the current study was to compare the effects of different cropping sequencing (#1: continuous v. rotational), fertilization (#2: mineral v. organic) and straw management techniques (in the case of continuous wheat; #3: removal v. incorporation) on the yield stability of winter wheat; yield risk (the probability of yield falling below a threshold yield level) and inter-annual yield variability were used as stability indicators of the effects. Long-term yield data from the Broadbalk Wheat Experiment (Rothamsted, UK) were analysed using a mixed model. Overall, the results showed that rotational cropping combined with sufficient mineral N fertilizer, with or without organic manure, ensured stable wheat yields while reducing yield risk. In contrast, higher yield risks and inter-annual yield variabilities were found in continuous wheat sections with less mineral N fertilizer or with organic manure only.

Global plant sulphur (S) deficiency is increasing because of a reduction in sulphate-based fertiliser application combined with continuous S withdrawal during harvest. Here, we applied (13)C, (15)N, (14)C, and (35)S quad labelling of the S-containing amino acids cysteine (Cys) and methionine (Met) to understand S cycling and microbial S transformations in the soil. The soil microorganisms absorbed the applied Cys and Met within minutes and released SO(4)(2−) within hours. The SO(4)(2−) was reutilised by the MB within days. The initial microbial utilisation and SO(4)(2−) release were determined by amino acid structure. Met released 2.5-fold less SO(4)(2−) than Cys. The microbial biomass retained comparatively more C and S from Met than Cys. The microorganisms decomposed Cys to pyruvate and H(2)S whereas they converted Met to α-ketobutyrate and S-CH(3). The microbial stoichiometries of C, N, and S derived from Cys and Met were balanced after 4 d by Cys-derived SO(4)(2−) uptake and Met-derived CO(2) release. The microbial C:N:S ratio dynamics showed rapid C utilisation and loss, stable N levels, and S accumulation. Thus, short-term organic S utilisation by soil microorganisms is determined by amino acid structure whilst long-term organic S utilisation by soil microorganisms is determined by microbially controlled stoichiometry.

Soil organic carbon (SOC) sequestration across agroecosystems worldwide can contribute to mitigate the effects of climate change by reducing levels of atmospheric CO2. Stabilisation of organic carbon (OC) in the fine soil fraction (< 20 µm) is considered an important long-term store of SOC, and the saturation deficit (difference between measured OC and estimated maximum OC in the fine fraction) is frequently used to assess SOC sequestration potential following the linear regression equation developed by Hassink (1997). However, this approach is often taken without any assessment of the fit of the equation to the soils being studied. The statistical limitations of linear regression have previously been noted, giving rise to the proposed use of boundary line (BL) analysis and quantile regression (QR) to provide more robust estimates of maximum SOC stabilisation. The objectives of this work were to assess the suitability of the Hassink (1997) equation to estimate maximum fine-fraction OC in UK grassland soils of varying sward ages and to evaluate the linear regression, boundary line and quantile regression methods to estimate maximum fine-fraction OC. A chronosequence of 10 grasslands was sampled, in order to assess the relationship between sward age (time since the last reseeding event) and the measured and predicted maximum fine-fraction OC. Significantly different regression equations show that the Hassink (1997) equation does not accurately reflect maximum fine-fraction OC in UK grasslands when determined using the proportion of the fine soil fraction (< 20 µm, %) and measured fine-fraction OC (g C per kg soil). The QR estimate of maximum SOC stabilisation was almost double that of the linear regression and BL analysis (0.89 ± 0.074, 0.43 ± 0.017 and 0.57 ± 0.052 g C per kg soil, respectively). Sward age had an inconsistent effect on the measured variables and potential maximum fine-fraction OC. Fine-fraction OC across the grasslands made up 4.5 % to 55.9 % of total SOC, implying that there may be either high potential for additional C sequestration in the fine fraction of these soils or that protection in aggregates is predominant in these grassland soils. This work highlights the need to ensure that methods used to predict maximum fine-fraction OC reflect the soil in situ, resulting in more accurate assessments of carbon sequestration potential.

The current study focuses on yield and nutritional quality changes of wheat grain over the last 166 years. It is based on wheat grain quality analyses carried out on samples collected between 1850 and 2016. Samples were obtained from the Broadbalk Continuous Wheat Experiment (UK) and from herbaria from 16 different countries around the world. Our study showed that, together with an increase in carbohydrate content, an impoverishment of mineral composition and protein content occurred. The imbalance in carbohydrate/protein content was specially marked after the 1960’s, coinciding with strong increases in ambient [CO2] and temperature and the introduction of progressively shorter straw varieties. The implications of altered crop physiology are discussed., This work was supported by the Spanish Innovation and Universities Ministry (AGL2016-79868-R; PCIN-2017-007), BBSRC Institute Strategic Programme grants, Designing Future Wheat (BB/P016855/1) and Soil to Nutrition (S2N, BBS/E/C/00I0310), the Long-term Experiments National Capability grant (BBS/E/C/000J0300), the Lawes Agricultural Trust and the Basque Country Government consolidated group programme (IT‐932‐16).

Soil organic carbon (SOC) sequestration across agroecosystems worldwide can contribute to mitigate the effects of climate change by reducing levels of atmospheric CO2. Mineral associated organic carbon (MAOC) is considered an important long-term store of SOC and the saturation deficit (difference between measured MAOC and estimated maximum MAOC) is frequently used to assess SOC sequestration potential following the linear regression equation developed by Hassink (1997). However, this approach is often taken without any assessment of the fit of the equation to the soils being studied. The statistical limitations of linear regression have previously been noted, giving rise to the proposed use of boundary line (BL) analysis and quantile regression (QR) to provide more robust estimates of maximum SOC stabilisation. The objectives of this work were to assess the suitability of the Hassink (1997) equation to estimate maximum MAOC in UK grassland soils of varying sward ages and to evaluate the linear regression, BL and QR methods to estimate maximum MAOC. A chronosequence of 10 grasslands was sampled, in order to assess the relationship between sward age (time since last reseeding event) and current and predicted maximum MAOC. Significantly different regression equations show that the Hassink (1997) equation does not accurately reflect maximum MAOC in UK grasslands when determined using the proportion of fine soil fraction and current MAOC. The QR estimate of maximum SOC stabilisation was almost double that of linear regression and BL analysis (0.89 ± 0.074, 0.43 ± 0.017 and 0.57 ± 0.052 g C kg−1 soil, respectively). Sward age had an inconsistent effect on the measured variables and potential maximum MAOC. MAOC across the grasslands made up 4.5 to 55.9 % of total SOC, implying that there may be either high potential for additional C sequestration in the mineral fraction of these soils, or stabilisation in aggregates is predominant in these grassland soils. This work highlights the need to ensure that methods used to predict maximum MAOC reflect the soil in situ, resulting in more accurate assessments of carbon sequestration potential.

The organic carbon reservoir of soils is a key component of climate change, calling for an accurate knowledge of the residence time of soil organic carbon (SOC). Existing proxies of the labile SOC pool such as particulate organic carbon or basal respiration tests are time consuming and unable to consistently predict SOC mineralization over years to decades. Similarly, models of SOC dynamics often yield unrealistic values of the size of SOC kinetic pools. Rock-Eval® 6 (RE6) thermal analysis of bulk soil samples has recently been shown to provide useful and cost-effective information regarding the long-term in-situ decomposition of SOC. The objective of this study was to design a method based on RE6 indicators to assess for a given soil, the proportion of SOC that will be mineralized in the coming 20 years.To do so, we needed samples ready to be analyzed using RE6 with a known proportion of SOC mineralized in 20 years. We used archived soil samples from 4 long-term bare fallows and 8 C3/C4 chronosequences. For each sample, the value of bi-decadal SOC mineralization was obtained from the observed SOC dynamics of its long-term bare fallow plot or the calculated C3-derived SOC decline following the conversion to C4 plants. Those values ranged from 0.3 to 14.3 gC·kg−1 (concentration data), representing 8.6 to 52.6% of total SOC (proportion data). All samples were analyzed using RE6 and simple linear regression models were used to predict bi-decadal SOC loss (concentration and proportion data) from 4 RE6 parameters: 1) HI (the amount of hydrogen-rich effluents formed during the pyrolysis phase of RE6; mgCH.g-1 SOC), 2) OIRE6 (the O recovered as CO and CO2 during the pyrolysis phase of RE6; mgO2.g-1 SOC), 3) PC/SOC (the amount of organic C evolved during the pyrolysis phase of RE6; % of total SOC) and 4) T50 CO2 oxidation (the temperature at which 50% of the residual organic C was oxidized to CO2 during the RE6 oxidation phase; °C).The RE6 HI parameter yielded the best predictions of bi-decadal SOC mineralization, for both concentration and proportion data. PC/SOC and T50 CO2 oxidation parameters also yielded significant regression models. The OIRE6 parameter was not a good predictor of bi-decadal SOC loss, with non-significant regression models. The results showed that SOC chemical composition (HI is a proxy for SOC H/C ratio), and to a lesser degree SOC thermal stability, are related to bi-decadal SOC dynamics. The RE6 thermal analysis method can therefore provide a quantitative and accurate estimate of SOC biogeochemical stability.

Over the last half century, society’s dependence on insect-assisted pollination of crops has risen by over 300% globally, while recent findings have estimated a 76% decline in flying insect biomass over the last 27 years. These losses in invertebrate numbers are thought to be due to a possible combination of various factors including parasites and diseases, agricultural intensification, climate change and possible chemical exposure including pesticides such as neonicotinoids.Neonicotinoids are one of the most widely used insecticides on the global market. Their systemic mechanisms allow for ease of application and relatively successful outcomes in controlling biting and sucking invertebrates, however neonicotinoids have been strongly associated with recent declines in non-target organisms. Many neonicotinoids come directly in contact with the soil, either through application as a seed coating or soil drench, or through spray drift and drip from foliar applications. Relatively little research has focussed on the movement, fate and interactions of these chemicals in UK soils under general field management strategies, although evidence suggests that the addition of soil bio-amendments, such as fertilisers, can influence the mechanisms behind pesticide mobility.My study aims to quantify the effects of Acetamiprid-based pesticide mixtures on below-ground soil functions, through the analysis of their movement and behaviour in soils of contrasting organic matter contents. A secondary aim is to assess the impact of neonicotinoids on select non-target organisms.We used 14C labelled Acetamiprid to track the behaviour of the mixtures compared to the pure active ingredient. Previous research has only used the pure active ingredient, however this isn’t representative of true field scenarios. These spiked pesticides were added to soils of contrasting organic matter content collected from a long-term experiment at Woburn Experimental Farm, Rothamsted Research. We assessed the behaviour of these mixtures across a range of leaching, sorption and mineralisation experiments.The mineralisation of all mixtures was found to be comparatively slow, with 80% of each chemical was recovered from the soil during the experiment. This, combined with low sorption and mineralisation rates, suggests that neonicotinoids are highly persistent within the environment.Ongoing work is being conducted to investigate the knock-on impacts and biological implications of acetamiprid use under true field conditions.

The link between carbon turnover model pools and measurable carbon fractions is of key interest for initial parameterisation and subsequent validation of dynamic soil carbon models. In this study we performed the established particle-size fractionation of soils from 54 intensively monitored sites in Germany and from archived samples from 5 other long-term experiments in Germany and the United Kingdom. The Rothamsted carbon (RothC) model was then used to compare the measured soil C fractionation from the 54 intensively monitored sites against modelled pools using spin-up equilibrium runs whilst dynamic (non-equilibrium) model runs were performed when comparing data from the long-term experiments. We detected good agreement between measured soil C fractions and modelled pools, indicated by correlation coefficients of 0.73 and 0.81 for the resistant plant material pool (RPM) and 0.91 and 0.94 for the humus pool (HUM) for the intensively monitored and the long-term sites, respectively. Slightly larger errors were detected for the intensively monitored sites together with a bias in the relationship between the RPM pool and particulate organic matter fraction. This bias detected for the intensively monitored sites indicated that the equilibrium assumption for arable agricultural sites, even though under crop cover for at least 50 years, might not be entirely valid. From the relative mean absolute error of 11% for the HUM pool and 26% for the RPM pool of the combined data set we conform that the measured fractions can be used to estimate the RothC model pools in arable soils. Given the magnitude of these errors, however, we rather suggest to apply the fractionation approach instead of using an equilibrium assumption for the RothC initialisation of arable sites.

The long-term increasing trend of annual mean temperature is only one aspect of recent climate change. Other changes in climate, seen in within-year weather patterns relevant to crop production, have also occurred since the late-19th Century. Multivariate analysis combining Prinipal Components Analysis and K-means clustering applied to temporal meteorological datasets (monthly summaries of rainfall, temperature and sunlight duration at Rothamsted Research, UK, between 1892 and 2016) identified ten distinct clusters of years, each with different annual weather patterns. The frequency of occurrence of the years within each cluster altered considerably during this period, with the late 20th and early 21st Century distinctly different to earlier in the 20th Century, providing clear evidence of climate change with regard to the whole weather profile rather than just warming alone. The most-frequently represented cluster of the 21st Century to date had warmer temperatures with more intense rainfall but a dry June, compared to all other clusters. Half of the clusters identified were not represented in the most-recent 25-year period. Analysis of the total biomass yield of winter wheat (Triticum aestivum L.), spring barley (Hordeum vulgare L.), and grassland amongst the different weather clusters showed that years in clusters typical of the 20th Century climate provided greater off-take than those from the early-21st Century, but this impact was less for the pasture than for the two cereal crops implying herbage production was the more resilient to the changing climate at this site.

The sequestration in soil of organic carbon (SOC) derived from atmospheric carbon dioxide (CO2) by replacing arable crops with leys, has been measured over 70 years on a sandy loam soil. The experiment was designed initially to test the effect of leys on the yields of arable crops. A 3-year grazed grass with clover (grass + clover) ley in a 5-year rotation with arable crops increased percentage organic carbon (%OC) in the top 25 cm of the soil from 0.98 to 1.23 in 28 years, but with little further increase during the next 40 years with all-grass leys given fertilizer nitrogen (N). In this second period, OC inputs were balanced by losses, suggesting that about 1.3% OC might be near the equilibrium content for this rotation. Including 3-year lucerne (Medicago sativa) leys had little effect on %OC over 28 years, but after changing to grass + clover leys, %OC increased to 1.24 during the next 40 years. Eight-year leys (all grass with N or grass + clover) in 10-year rotations with arable crops were started in the 1970s, and after three rotations %OC had increased to ca. 1.40 in 2000–2009. Over 70 years, %OC declined from 0.98 to 0.94 in an all-arable rotation with mainly cereals and to 0.82 with more root crops. Applications of 38 t ha−1 farmyard manure (FYM) every fifth year increased %OC by 0.13% by the mid-1960s when applications ceased. Soil treated with FYM still contained 0.10% more OC in 2000–2009. Changes in the amount of OC have been modelled with RothC-26.3 and estimated inputs of C for selected rotations. Little of the OC input during the 70 years has been retained; most was retained in the grazed ley rotation, but 9 t ha−1 only of a total input of 189 t ha−1. In other rotations more than 98% of the total OC input was lost. Despite large losses of C, annual increases in OC of 4‰ are possible on this soil type with the inclusion of grass or grass + clover leys or the application of FYM, but only for a limited period. Such increases in SOC might help to limit increases in atmospheric CO2. Highlights Can leys sequester significant amounts of atmospheric CO2 in SOM and contribute to the 4‰ initiative? Changes in the percentage and amount of OC were measured and modelled over 70 years and OC losses estimated. Three-year grass or grass + clover leys increased %OC, but only to an equilibrium level that was then maintained. Despite large losses, sequestering CO2-C at 4‰ year−1 by growing grass or grass + clover leys is possible.

Field data about the effect of soil pH on phosphorus (P) cycling is limited. A promising tool to study P cycling under field conditions is the 18O:16O ratio of phosphate (δ18OP). In this study we investigate whether the δ18OP can be used to elucidate the effect of soil pH on P cycling in grasslands. Soils and plants were sampled from different fertilisation and lime treatments of the Park Grass long term experiment at Rothamsted Research, UK. The soils were sequentially extracted to isolate different soil P pools, including available P and corresponding δ18OP values were determined. We did not observe changes in plant δ18OP value, but soil P δ18OP values changed, and lower δ18OP values were associated with higher soil pH values. At sites where P was not limiting, available P δ18OP increased by up to 3‰ when lime was applied. We show that the δ18OP method is a useful tool to investigate the effect of pH on soil P cycling under field conditions as it highlights that different soil processes must govern P availability as pH shifts. The next challenge is now to identify these underlying processes, enabling better management of soil P at different pH.

In the mid-19th century, John Bennet Lawes and Joseph Henry Gilbert established a series of field experiments at Rothamsted (Hertfordshire, in south-east UK) to examine the benefits of mineral fertilizers and organic manures on the production of several important agricultural crops. Seven of these “Classical” field experiments continue today. The Broadbalk Wheat, Hoosfield Spring Barley, and Park Grass Continuous Hay experiments are perhaps the most widely known of these long-term experiments. When the Classicals began, Lawes and Gilbert could not have envisaged the wide-ranging impact they would have on agricultural and other related sciences. They would probably also be surprised that the experiments have been maintained and that they have continued to be important platforms for research for such a long period. The experiments quickly demonstrated the importance of fertilizers and manures as a source of mineral nutrients, especially nitrogen (N) and phosphorus (P), for plant growth and development. Subsequent findings highlighted the need for good weed and disease control, the value of crop rotation, liming, and the use of modern short-strawed cereal varieties. Yield trends for wheat and barley on Broadbalk and Hoosfield, respectively, have followed the national averages, clearly demonstrating the capacity for arable soils in temperate Northwestern Europe to sustain good levels of crop production for well over a century provided exported nutrients are replaced, soil pH is kept around neutral, soil structure is maintained, and pests, weeds, and diseases are adequately controlled. In addition, the experiments generate information of value to agroecologists, farmers, and other land users on the management of seminatural systems to maintain and enhance biodiversity. They are an invaluable resource for monitoring the impact of agricultural management and environmental change, especially climate change, on the crop–soil system and other seminatural habitats. Provided the experiments, sample archive, and associated data are well-managed and used together with new analytical techniques and ideas, they will continue to provide a resource for agricultural research as relevant today as when the experiments started 175 years ago.

Highlights • Variation in yield-nitrogen responses explored using long-term experiments (LTEs). • Yield-nitrogen relationship modelled using linear-plus-exponential function. • Inter-annual variation in parameters explained using monthly weather summaries. • Modelling allows separation of effects of environmental and agronomic factors. • Selected monthly weather variables associated with key crop development processes., The effect of weather on inter-annual variation in the crop yield response to nitrogen (N) fertilizer for winter wheat (Triticum aestivvum L.) and spring barley (Hordeum vulgare L.) was investigated using yield data from the Broadbalk Wheat and Hoosfield Spring Barley long-term experiments at Rothamsted Research. Grain yields of crops from 1968 to 2016 were modelled as a function of N rates using a linear-plus-exponential (LEXP) function. The extent to which inter-annual variation in the parameters of these responses was explained by variations in weather (monthly summarized temperatures and rainfall), and by changes in the cultivar grown, was assessed. The inter-annual variability in rainfall and underlying temperature influenced the crop N response and hence grain yields in both crops. Asymptotic yields in wheat were particularly sensitive to mean temperature in November, April and May, and to total rainfall in October, February and June. In spring barley asymptotic yields were sensitive to mean temperature in February and June, and to total rainfall in April to July inclusive and September. The method presented here explores the separation of agronomic and environmental (weather) influences on crop yield over time. Fitting N response curves across multiple treatments can support an informative analysis of the influence of weather variation on the yield variability. Whilst there are issues of the confounding and collinearity of explanatory variables within such models, and that other factors also influence yields over time, our study confirms the considerable impact of weather variables at certain times of the year. This emphasizes the importance of including weather temporal variation when evaluating the impacts of climate change on crops.

Maintaining an adequate phosphorus (P) supply for plants and microorganisms is central to agricultural production; however, the long-term effects of organic manure and inorganic fertilizer application on soil P cycling remain unclear. Organic P cycling in a sandy loam soil receiving medium and high rates of farmyard manure (FYM) with and without mineral fertilisers was studied in a long-term field experiment with 14C/33P isotope labelling and metagenomic shotgun sequencing. FYM application alone negatively affected soil total P and organic P (Po) accumulation by enhancing crop offtake, enhancing Po mineralisation and stimulating P loss from the topsoil by reducing its P sorption potential. The P mineralisation/immobilisation rates detected by the 33P pool dilution method were significantly correlated with the abundance of microbial P cycling genes. Soil available C and N concentrations were related to gross P mineralisation/immobilisation rates and the abundance of P uptake/scavenging genes. Microbial genes related to P uptake and metabolism were more abundant than P scavenging genes, while P scavenging genes may work efficiently as both of them can sustain similar P mineralisation and immobilisation rates. The addition of FYM also promoted phosphatase activity reflecting the increased supply of Po in these soils. Our study demonstrates that long-term FYM application alters soil Po stocks and cycling, and that microbial functional gene abundance was coupled with P cycling rates.

Land application of farmyard manure (FYM) is a widespread agronomic practice used to enhance soil fertility, but its long-term effects on soil microbial carbon (C) and nitrogen (N) cycling have not been investigated in detail. Topsoils (0–23 cm) and subsoils (23–38 cm) were collected from a field trial on a sandy-textured soil where FYM had been applied at high (50–25 t ha−1 yr−1, 28 yr) and low rates (10 t ha−1 yr−1, 16 yr), and compared to soil treated only with synthetic NPK fertilisers. The turnover rate of key components of soil organic matter (SOM; proteins, peptides, amino acids, cellulose, and glucose) were evaluated by 14C labelling and measuring cellobiohydrolase, β-glucosidase, β-1,4-N-acetylglucosaminidase, L-leucine aminopeptidase, protease, and deaminase activities, whereas gross NH4+ and NO3− production and consumption were determined by 15N-isotope pool dilution. Microbial communities were determined using phospholipid fatty acid (PLFA) profiling. Our results indicate that long-term FYM addition significantly enhanced the accumulation of soil C and N, soil organic N (SON) turnover, exoenzyme activity, and gross NO3− production and assimilation. Rates of protein, peptide, and amino acid processing rate were 169–248, 87–147, and 85–305 mg N kgDWsoil−1 d−1, respectively, gross NH4+ and NO3− production and consumption were 1.8–5.8 mg N kgDWsoil−1 d−1, and the highest rates were shown under the high FYM treatment in topsoil and subsoil. The half-life of cellulose and glucose decomposition under the high FYM treatment were 16.4% and 31.0% lower than them in the synthetic NPK fertiliser treatment, respectively, indicating higher rates of C cycling under high manure application as also evidenced by the higher rate of CO2 production. This was ascribed to an increase in microbial biomass rather than a change in microbial community structure. Based on the high pool sizes and high turnover rate, this suggests that peptides may represent one of the dominant forms of N taken up by soil microorganisms. We conclude that long-term FYM application builds SOM reserves and induces faster rates of nutrient cycling by boosting microbial biomass rather than by changing its community composition.

Traditional methods to assess the soil organic carbon (SOC) content based on soil sampling and analysis are timeconsuming and expensive, and the results are influenced by the sampling design. The aim of this study was toinvestigate the potential of UAS (Unmanned Aerial Systems) multi-spectral imagery (480–1000 nm) for estimatingthe SOC content in bare cultivated soils at a high spatial resolution (12 cm).We performed UAS analysis onthe Hoosfield Spring Barley experiment at Rothamsted (UK) where adjacent plots with distinctly different SOCcontents, due to different long-term management practices, provide a valuable resource to evaluate thisapproach. We acquired images (wavelength: 480–550–670–780–880–1000 nm) at an altitude of 120 m overan area of 2 ha using a multi-spectral camera mounted on an UAS. The high-resolution images captured smallscalevariations at the soil surface (e.g. shadows, tillage andwheels marks). After a projection in newdimensionsby a PCA, we calibrated a support vector machine regression using observations fromconventional soil samplingand SOC measurements. The performance of the calibration had a R2 of 0.98 and a RMSE of 0.17%C. A crossvalidationshowed that the model was robust, with an average R2 of 0.95 and a RMSE of 0.21%. An externalvalidation dataset was used to evaluate the predicted spatial patterns of SOC content and a good fit with anRMSE 0.26%C was obtained. Although this study shows that the methodology has a clear potential for use inprecision agriculture or monitoring important soil properties following changes in management,we also identifyand discuss its limitations and current shortcomings.

Plant sulphur (S) deficiency is a worldwide concern. However, the mechanisms controlling the immobilization and mineralization of low-molecular weight organic S by soil microorganisms remain unclear. Therefore, we investigated the assimilation of carbon (C) and S by soil microorganisms using uniformly 14C- or 35S-labelled cysteine and methionine. The decomposition of cysteine and methionine in the soil occurred in three steps. First, the microbial biomass (MB) rapidly immobilised the added cysteine-S (55%–63%) and methionine-S (81%–84%) in less than 30 min. Subsequently, S in the MB was released as 35S-sulphate (release of S into the soil peaked at 1 h [21.4%] and 24 h [17.3%] after adding cysteine and methionine, respectively). Lastly, the released 35SO42− was reutilised by microorganisms. The amount of 14CO2 and 35SO42− released from methionine was much lower than that from cysteine. The addition of excess glucose-C or inorganic nitrogen and S had little effect on cysteine and methionine uptake rate, but had a major effect on microbial C use efficiency (CUE) and internal S partitioning and the subsequent release of SO42−. We conclude that the microbial community cycles S-containing amino acids at a high rate, irrespective of soil S and N status with a large proportion of the C used in catabolic processes.

In the face of climate change, the potential impacts of adverse weather conditions on the productivity and vulnerability of cropping systems (CS) worldwide constitute a key agronomic issue upon which global food security depends. To date, little information regarding how the diversity of CS or agricultural practices affect the long-term yield responses of winter barley is available. The aim of this study was to investigate the impact of CS diversity in terms of cropping sequences, organic matter supplies, and nitrogen (N) fertilization on the yield vulnerability of winter barley. Yields were evaluated in terms of their stability, environmental adaptability, and production risk (probability of yield loss). Data from a 27-year experiment were statistically analyzed using three mixed models giving residual maximum likelihood estimates including the Shukla stability variance index, the Finlay-Wilkinson environmental regression, and the Eskridge risk assessment approach. The results showed that winter barley grown in cropping sequences dominated by cereals had lower yield stability and environmental adaptability and greater production risks compared with winter barley grown in CS with higher crop diversity and additional organic matter inputs. When barley yields were compared at three doses of mineral N, the highest yield stability was achieved with the medium N dose (70 kg N ha−1), followed by the higher level of N (140 kg N ha−1). The most unstable yields with the highest production risks were observed when barley was grown without any mineral N fertilization. Overall, a higher level of crop diversity with organic matter inputs and intermediate N fertilization resulted in lower yield vulnerability in winter barley.

Our study tests the emerging paradigm that biochemical recalcitrance does not affect substantially long-term (50 years) SOC persistence. We analyzed the molecular composition of SOC in archived soils originating from four European long-term bare fallow experiments (Askov, Rothamsted, Versailles and Ultuna). The soils had been collected after various periods (up to 53 years) under bare fallow. With increasing duration of bare fallow without new organic inputs, the relative abundance of cutin- and suberin-derived compounds declined substantially, and the abundance of lignin-derived compounds was close to zero. Conversely, the relative abundance of plant-derived long-chain alkanes remained almost constant or increased during the bare fallow period. The relative abundance of N-containing compounds, considered to be abundant in SOC derived from microbial activity, increased consistently illustrating that microbial turnover of SOC continues even when plant inputs are stopped. The persistence of the different families of plant-derived compounds differed markedly over the scale of half a century, which may be ascribed to their contrasting chemical characteristics and recalcitrance, or to differences in their interactions with the soil mineral matrix, and likely some combination since chemical composition drives the degree of mineral association. Using soil from this unique set of long-term bare fallow experiments, we provide direct evidence that multi-decadal scale persistent SOC is enriched in microbe-derived compounds but also includes a substantial fraction of plant-derived compounds.

The electronic Rothamsted Archive, e-RA (www.era.rothamsted.ac.uk) provides a permanent managed database to both securely store and disseminate data from Rothamsted Research’s long-term field experiments (since 1843) and meteorological stations (since 1853). Both historical and contemporary data are made available via this online database which provides the scientific community with access to a unique continuous record of agricultural experiments and weather measured since the mid-19th century. Qualitative information, such as treatment and management practices, plans and soil information, accompanies the data and are made available on the e-RA website. e-RA was released externally to the wider scientific community in 2013 and this paper describes its development, content, curation and the access process for data users. Case studies illustrate the diverse applications of the data, including its original intended purposes and recent unforeseen applications. Usage monitoring demonstrates the data are of increasing interest. Future developments, including adopting FAIR data principles, are proposed as the resource is increasingly recognised as a unique archive of data relevant to sustainable agriculture, agroecology and the environment.

Once phosphorus (P) applications stop, it is important to know how long it will take for plant-available P in soil to decline to a particular level for soils with a history of intensive management. The rate of decline in the absence of applied P can be expressed as a half-life, that is the time in years for it to halve relative to the lowest level measured in the soil. This knowledge is essential when planning long-term policies for managing the P status of soils. It is important to farmers who wish to optimize applications of P fertilizers and make better use of accumulated P residues to ensure that plant-available P does not fall below the critical level for the soil and crop because of the risk of losing yield and the inefficient use of other inputs, especially N fertilizer. Lower levels of plant-available P are also desirable for environmental and ecological reasons. Allowing plant-available P to decline to the critical level from unnecessarily high concentrations will reduce the risk from P on eroded soil causing adverse effects of eutrophication in surface water. Low levels of plant-available P are usually considered necessary for establishing species-rich grassland. A method for determining the longer term decline in plant-available soil P from short-term measured values is presented.

The negative effect of increasing atmospheric nitrogen (N) pollution on grassland biodiversity is now incontrovertible. However, the recent introduction of cleaner technologies in the UK has led to reductions in the emissions of nitrogen oxides, with concomitant decreases in N deposition4. The degree to which grassland biodiversity can be expected to ‘bounce back’ in response to these improvements in air quality is uncertain, with a suggestion that long-term chronic N addition may lead to an alternative low biodiversity state5. Here we present evidence from the 160-year-old Park Grass Experiment at Rothamsted Research, UK6, that shows a positive response of biodiversity to reducing N addition from either atmospheric pollution or fertilizers. The proportion of legumes, species richness and diversity increased across the experiment between 1991 and 2012 as both wet and dry N deposition declined. Plots that stopped receiving inorganic N fertilizer in 1989 recovered much of the diversity that had been lost, especially if limed. There was no evidence that chronic N addition has resulted in an alternative low biodiversity state on the Park Grass plots, except where there has been extreme acidification, although it is likely that the recovery of plant communities has been facilitated by the twice-yearly mowing and removal of biomass. This may also explain why a comparable response of plant communities to reduced N inputs has yet to be observed in the wider landscape.

Changes in global soil carbon stocks have considerable potential to influence the course of future climate change. However, a portion of soil organic carbon (SOC) has a very long residence time (> 100 years) and may not contribute significantly to terrestrial greenhouse gas emissions during the next century. The size of this persistent SOC reservoir is presumed to be large. Consequently, it is a key parameter required for the initialization of SOC dynamics in ecosystem and Earth system models, but there is considerable uncertainty in the methods used to quantify it. Thermal analysis methods provide cost-effective information on SOC thermal stability that has been shown to be qualitatively related to SOC biogeochemical stability. The objective of this work was to build the first quantitative model of the size of the centennially persistent SOC pool based on thermal analysis. We used a unique set of 118 archived soil samples from four agronomic experiments in northwestern Europe with long-term bare fallow and non-bare fallow treatments (e.g., manure amendment, cropland and grassland) as a sample set for which estimating the size of the centennially persistent SOC pool is relatively straightforward. At each experimental site, we estimated the average concentration of centennially persistent SOC and its uncertainty by applying a Bayesian curve-fitting method to the observed declining SOC concentration over the duration of the long-term bare fallow treatment. Overall, the estimated concentrations of centennially persistent SOC ranged from 5 to 11 g C kg−1 of soil (lowest and highest boundaries of four 95 % confidence intervals). Then, by dividing the site-specific concentrations of persistent SOC by the total SOC concentration, we could estimate the proportion of centennially persistent SOC in the 118 archived soil samples and the associated uncertainty. The proportion of centennially persistent SOC ranged from 0.14 (standard deviation of 0.01) to 1 (standard deviation of 0.15). Samples were subjected to thermal analysis by Rock-Eval 6 that generated a series of 30 parameters reflecting their SOC thermal stability and bulk chemistry. We trained a nonparametric machine-learning algorithm (random forests multivariate regression model) to predict the proportion of centennially persistent SOC in new soils using Rock-Eval 6 thermal parameters as predictors. We evaluated the model predictive performance with two different strategies. We first used a calibration set (n = 88) and a validation set (n = 30) with soils from all sites. Second, to test the sensitivity of the model to pedoclimate, we built a calibration set with soil samples from three out of the four sites (n = 84). The multivariate regression model accurately predicted the proportion of centennially persistent SOC in the validation set composed of soils from all sites (R2 = 0.92, RMSEP = 0.07, n = 30). The uncertainty of the model predictions was quantified by a Monte Carlo approach that produced conservative 95 % prediction intervals across the validation set. The predictive performance of the model decreased when predicting the proportion of centennially persistent SOC in soils from one fully independent site with a different pedoclimate, yet the mean error of prediction only slightly increased (R2 = 0.53, RMSEP = 0.10, n = 34). This model based on Rock-Eval 6 thermal analysis can thus be used to predict the proportion of centennially persistent SOC with known uncertainty in new soil samples from different pedoclimates, at least for sites that have similar Rock-Eval 6 thermal characteristics to those included in the calibration set. Our study reinforces the evidence that there is a link between the thermal and biogeochemical stability of soil organic matter and demonstrates that Rock-Eval 6 thermal analysis can be used to quantify the size of the centennially persistent organic carbon pool in temperate soils.

We evaluated the “4 per 1000” initiative for increasing soil organic carbon (SOC) by analysing rates of SOC increase in treatments in 16 long‐term experiments in southeast United Kingdom. The initiative sets a goal for SOC stock to increase by 4‰ per year in the 0–40 cm soil depth, continued over 20 years. Our experiments, on three soil types, provided 114 treatment comparisons over 7–157 years. Treatments included organic additions (incorporated by inversion ploughing), N fertilizers, introducing pasture leys into continuous arable systems, and converting arable land to woodland. In 65% of cases, SOC increases occurred at >7‰ per year in the 0–23 cm depth, approximately equivalent to 4‰ per year in the 0–40 cm depth. In the two longest running experiments (>150 years), annual farmyard manure (FYM) applications at 35 t fresh material per hectare (equivalent to approx. 3.2 t organic C/ha/year) gave SOC increases of 18‰ and 43‰ per year in the 23 cm depth during the first 20 years. Increases exceeding 7‰ per year continued for 40–60 years. In other experiments, with FYM applied at lower rates or not every year, there were increases of 3‰–8‰ per year over several decades. Other treatments gave increases between zero and 19‰ per year over various periods. We conclude that there are severe limitations to achieving the “4 per 1000” goal in practical agriculture over large areas. The reasons include (1) farmers not having the necessary resources (e.g. insufficient manure); (2) some, though not all, practices favouring SOC already widely adopted; (3) practices uneconomic for farmers—potentially overcome by changes in regulations or subsidies; (4) practices undesirable for global food security. We suggest it is more realistic to promote practices for increasing SOC based on improving soil quality and functioning as small increases can have disproportionately large beneficial impacts, though not necessarily translating into increased crop yield.

Archived samples from the Park Grass Experiment, established in 1856, were analysed to determine the impacts of long-term phosphate fertiliser applications on arsenic concentrations in soil and herbage. In plots receiving 35 kg P ha −1 annually (+P), topsoil As concentrations almost doubled from an initial value of ∼10 mg kg −1 during 1888–1947 and remained stable thereafter. The phosphate fertilisers used before 1948 contained 401–1575 mg As kg −1 , compared to 1.6–20.3 mg As kg −1 in the later samples. Herbage samples from the +P plots collected during 1888–1947 contained significantly more As than those from the −P plots, but later samples did not differ significantly. Mass-balance calculations show that the increase in soil As can be explained by the As input from P fertiliser applications before 1948. The results demonstrate that the P fertilisers used on the Park Grass Experiment before 1948 caused substantial As contamination of the soil.

Under the increase in atmospheric CO2 during the last century, variable increases in the intrinsic water-use efficiency (Wi), i.e., the ratio between carbon assimilation rate (A) and stomatal conductance (gs), of C3 vegetation have been observed. Here, we ask if long-term nutrient status and especially nitrogen supply have an effect on the CO2 response of Wi in a temperate seminatural C3 grassland. This analysis draws on the long-term trends (1915-2009) in Wi, derived from carbon isotope analysis, of archived hay and herbage from the Park Grass Experiment at Rothamsted (South-East England). Plant samples came from five fertilizer treatments, each with different annual nitrogen (N; 0, 48 or 96 similar to kg similar to ha-1), phosphorus (P; 0 or 35 similar to kg similar to ha-1) and potassium (K; 0 or 225 similar to kg similar to ha-1) applications, with lime as required to maintain soil pH near 7. Carbon isotope discrimination (13?) increased significantly (P < 0.001) on the Control (0.9 parts per thousand per 100 similar to ppm CO2 increase). This trend differed significantly (P < 0.01) from those observed on the fertilized treatments (PK only: 0.4 parts per thousand per 100 similar to ppm CO2 increase, P < 0.001; Low N only, Low N+PK, High N+PK: no significant increase). The 13? trends on fertilized treatments did not differ significantly from each other. However, N status, assessed as N fertilizer supply plus an estimate of biologically fixed N, was negatively related (r2 similar to=similar to 0.88; P < 0.02) to the trend for 13? against CO2. Other indices of N status exhibited similar relationships. Accordingly, the increase in Wi at High N+PK was twice that of the Control (+28% resp. +13% relative to 1915). In addition, the CO2 responsiveness of 13? was related to the grass content of the plant community. This may have been due to the greater CO2 responsiveness of gs in grasses relative to forbs. Thus, the greater CO2 response of grass-rich fertilized swards may be related to effects of nutrient supply on botanical composition.

Results from the UK were reviewed to quantify the impact on climate change mitigation of soil organic carbon (SOC) stocks as a result of (1) a change from conventional to less intensive tillage and (2) addition of organic materials including farm manures, digested biosolids, cereal straw, green manure and paper crumble. The average annual increase in SOC deriving from reduced tillage was 310 kg C ± 180 kg C ha−1 yr−1. Even this accumulation of C is unlikely to be achieved in the UK and northwest Europe because farmers practice rotational tillage. N2O emissions may increase under reduced tillage, counteracting increases in SOC. Addition of biosolids increased SOC (in kg C ha−1 yr−1 t−1 dry solids added) by on average 60 ± 20 (farm manures), 180 ± 24 (digested biosolids), 50 ± 15 (cereal straw), 60 ± 10 (green compost) and an estimated 60 (paper crumble). SOC accumulation declines in long-term experiments (>50 yr) with farm manure applications as a new equilibrium is approached. Biosolids are typically already applied to soil, so increases in SOC cannot be regarded as mitigation. Large increases in SOC were deduced for paper crumble (>6 t C ha−1 yr−1) but outweighed by N2O emissions deriving from additional fertiliser. Compost offers genuine potential for mitigation because application replaces disposal to landfill; it also decreases N2O emission.&nbsp

Accurate characterization of dissolved organic matter (DOM) in soil is vital for understanding its functional signifi cance. In this study, we used ultrafi ltration to determine the molecular weight (MW) distribution of dissolved organic C (DOC), N (DON), and phenolics in two contrasting agricultural grassland soils. This MW fractionation (>100, 10–100, 1–10,and 1 kDa) in both soils. This high-MW fraction contained a signifi cant amount of organic N, however, and was no more enriched in phenolic-containing substances than the low-MW fraction. Our results are consistent with the view that soil solutions contain a diverse size range of organic compounds but that the high-MW fraction does not contain a disproportionate amount of phenolics or N.

Take-all, caused by the fungus Gaeumannomyces graminis var. tritici, is the most damaging root disease of wheat. A severe attack often leads to premature ripening and death of the plant resulting in a reduction in grain yield and effects on grain quality (Gutteridge et al. in Pest Manag Sci 59:215–224, 2003). Premature death of the plant could also lead to inefficient use of applied nitrogen (Macdonald et al. in J Agric Sci 129(2):125–154, 1997). The aim of this study was to determine crop N uptake and the amount of residual mineral N in the soil after harvest where different severities of take-all had occurred. Plant and soil samples were taken at anthesis and final harvest from areas showing good and poor growth (later confirmed to be caused by take-all disease) in three winter wheat crops grown on the same soil type on Rothamsted Farm in SE England in 1995, 2007 and 2008 (harvest sampling only). All crops received fertiliser N in spring at recomended rates (190–200 kg N ha−1). On each ocassion crops were assessed for severity of take-all infection (TAR) and crop N uptakes and soil nitrate plus ammonium (SMN) was determined. Grain yields were also measured. Grain yields (at 85% dry matter) of crops with moderate infection (good crops) ranged from 4.3 to 13.0 t ha−1, compared with only 0.9–4.5 t ha−1 for those with severe infection (poor crops). There were significant (P

The application of calcium- and magnesium-rich materials to soil, known as liming, has long been a foundation of many agro-ecosystems worldwide because of its role in counteracting soil acidity. Although liming contributes to increased rates of respiration from soil thereby potentially reducing soils ability to act as a CO2 sink, the long-term effects of liming on soil organic carbon (Corg) sequestration are largely unknown. Here, using data spanning 129 years of the Park Grass Experiment at Rothamsted (UK), we show net Corg sequestration measured in the 0–23cm layer at different time intervals since 1876 was 2–20 times greater in limed than in unlimed soils. The main cause of this large Corg accrual was greater biological activity in limed soils, which despite increasing soil respiration rates, led to plant C inputs being processed and incorporated into resistant soil organo-mineral pools. Limed organo-mineral soils showed: (1) greater Corg content for similar plant productivity levels (i.e. hay yields); (2) higher 14C incorporation after 1950s atomic bomb testing and (3) lower C:N ratios than unlimed organo-mineral soils, which also indicate higher microbial processing of plant C. Our results show that greater Corg sequestration in limed soils strongly reduced the global warming potential of long-term liming to permanent grassland suggesting the net contribution of agricultural liming to global warming could be lower than previously estimated. Our study demonstrates that liming might prove to be an effective mitigation strategy, especially because liming applications can be associated with a reduced use of nitrogen fertilizer which is a key cause for increased greenhouse gas emissions from agro-ecosystems.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; AbstractA large fraction of soil organic matter (OM) resists decomposition over decades to centuries as indicated by long radiocarbon residence times, but the mechanisms responsible for the long-term (multi-decadal) persistence are debated. The current lack of mechanistic understanding limits our ability to accurately predict soil OM stock evolution under climate and land-use changes. Using a unique set of historic soil samples from five long-term (27–79 years) bare fallow experiments, we demonstrate that despite wide pedo-climatic diversity, persistent OM shows specific energetic signatures, but no uniform chemical composition. From an energetic point of view, thermal analyses revealed that combustion of persistent OM occurred at higher temperature and provided less energy than combustion of more labile OM. In terms of chemical composition, persistent OM was H-depleted compared to OM present at the start of bare fallow, but spectroscopic analyses of OM functional groups did not reflect a consistent chemical composition of OM across sites, nor substantial modifications with bare fallow duration. The low energy content of persistent OM may be attributed to a combination of reduced content of energetic C–H bonds or stronger interactions between OM and the mineral matrix. Soil microorganisms thus appear to preferentially mineralize high-energy OM, leaving behind material with low energy content. This study provides the first direct link between long-term persistence of OM in soil and the energetic barriers experienced by the decomposer community.

The oxidative ratio (the ratio of moles of O-2 produced per mole CO2 sequestered - OR) of the organic matter in the terrestrial biosphere governs the ability of the terrestrial biosphere to uptake CO2. The value of OR is known to vary between environments, but it would also be expected to vary with management. This study measured the OR of plant and soil samples from the long-term grassland plots on the Park Grass experiment at Rothamsted (SE England). The selected plots included those with different fertilizer inputs, including farmyard manure or inorganic fertilizers and an unfertilized control, each with and without lime. The measurements show that: (i) Use of inorganic fertilizer caused the OR of soil organic matter to increase. (ii) Farmyard manure (FYM) caused OR of the soil to increase but that of the vegetation decreased. (iii) Liming had the effect of decreasing OR and counteracting effects of fertilizer. (iv) The OR of the ecosystem increased with FYM application but decreased with inorganic fertilizer application. The global pattern in the use of organic amendments and inorganic fertilizers suggests that the likely impact of the predicted increase in global inorganic fertilizer use will result in a net decrease in the OR of the organic matter of the terrestrial biosphere, and an increase in its ability to act as a carbon sink. Corresponding increases in global FYM use and its impact upon global OR are unlikely to be large enough to counteract this effect.

Last-century climate change has led to variable increases of the intrinsic water-use efficiency (W i; the ratio of net CO2 assimilation to stomatal conductance for water vapor) of trees and C3 grassland ecosystems, but the causes of the variability are not well understood. Here, we address putative drivers underlying variable W i responses in a wide range of grassland communities. W i was estimated from carbon isotope discrimination in archived herbage samples from 16 contrasting fertilizer treatments in the Park Grass Experiment, Rothamsted, England, for the 1915 to 1929 and 1995 to 2009 periods. Changes in W i were analyzed in relation to nitrogen input, soil pH, species richness, and functional group composition. Treatments included liming as well as phosphorus and potassium additions with or without ammonium or nitrate fertilizer applications at three levels. W i increased between 11% and 25% (P < 0.001) in the different treatments between the two periods. None of the fertilizers had a direct effect on the change of W i (ƊW i). However, soil pH (P < 0.05), species richness (P < 0.01), and percentage grass content (P < 0.01) were significantly related to ƊW i. Grass-dominated, species-poor plots on acidic soils showed the largest ƊW i (+14.7 μmol mol−1). The ƊW i response of these acidic plots was probably related to drought effects resulting from aluminum toxicity on root growth. Our results from the Park Grass Experiment show that W i in grassland communities consistently increased over a wide range of nutrient inputs, soil pH, and plant community compositions during the last century.

The Rothamsted Estate in Hertfordshire, United Kingdom, is home to the longest running ecological and agricultural experiments in the world that have generated unique data sets on the assembly and functioning of ecosystems that stretch back more than 170 years. In addition, the Rothamsted Sample Archive contains over 300,000 samples of dried soil, herbage, straw and grain dating back to the start of the first experiments. Additional long-term experiments were set up in the mid-1900s and the systematic sampling of invertebrates at Rothamsted started in 1964, which continues to this day in the form of the Rothamsted Insect Survey. Here, we introduce the resources available at Rothamsted for research on ecological processes that can only be understood using data over long time periods. Rather than cataloguing all the work that has been done using the data, we focus on new advances made in the last decade in areas of environmental monitoring, community ecology, evolutionary biology, ecosystem stability and resilience and microbial ecology. The combination of long-term data sets with archived plant and soil samples together with new analytical techniques mean that the Rothamsted long-term experiments and insect collections continue to be as relevant and valuable to scientists today as when they were originally set up.

Summary Angiosperm genome sizes (GS) range c. 2400‐fold, and as nucleic acids are amongst the most phosphorus‐ (P) and nitrogen (N)‐demanding cellular biomolecules, we test the hypothesis that a key influence on plant biomass and species composition is the interaction between N and P availability and plant GS.We analysed the impact of different nutrient regimes on above‐ground biomass of angiosperm species with different GS, ploidy level and Grime's C‐S‐R (competitive, stress‐tolerant, ruderal) plant strategies growing at the Park Grass Experiment (Rothamsted, UK), established in 1856.The biomass‐weighted mean GS of species growing on plots with the addition of both N and P fertilizer were significantly higher than that of plants growing on control plots and plots with either N or P. The plants on these N + P plots are dominated by polyploids with large GS and a competitive plant strategy.The results are consistent with our hypothesis that large genomes are costly to build and maintain under N and P limitation. Hence GS and ploidy are significant traits affecting biomass growth under different nutrient regimes, influencing plant community composition and ecosystem dynamics. We propose that GS is a critical factor needed in models that bridge the knowledge gap between biodiversity and ecosystem functioning.

Although it has been hypothesized that soluble organic nitrogen (SON) plays a central role in regulating productivity in some terrestrial ecosystems, the factors controlling the size of the SON pool in soil remain poorly understood. Therefore our principal aim in this work was to assess the impact of seven different land use systems (rough and managed grassland, deciduous and coniferous woodland, heathland, wetland and tilled land) on the size of the SON and inorganic N (NO−3, NH+4) pools in the surface soil layer (0–15 cm). After extraction with deionised water, we found that in most cases the size of the water extractable organic N (WEON) pool was similar in size to the inorganic N pool. In contrast, the KCl extractable organic N (KClEON) pool constituted the dominant form of soluble N in soils under all land uses, perhaps indicating that significant amounts were held on the soil exchange phase. In contrast to inorganic N, which varied significantly with land use, the size of the KClEON and WEON pool was similar for all land uses with the exception of KClEON in tilled land, where significantly lower amounts were observed. We conclude that SON constitutes an important soil N pool in a broad range of land uses, and that its role in microbial N assimilation, plant nutrition and ecosystem responses to atmospheric N deposition warrants further attention.

Dynamic simulation models are increasingly used in environmental and agricultural science. Here we present a method that allows models to be used to determine optimum timing of sampling for field trials. The model is used to decide when to concentrate sampling effort before the field trial begins. The model chosen to design sampling strategy should include an appropriately sensitive description of all processes that influence measurements significantly. The simulation is run, using predicted weather data, to generate the full time series before the trial begins. Every point in the simulation is considered initially to be a potential sampling point. The potential error due to not including a measurement at each point is calculated using the ‘dot-to-dot’ method of b10Smith et al. (2002) by omitting simulated values consecutively. The calculated potential error provides a measure of the priority that should be given to sampling at each point. Where the error introduced by omitting the simulated value exceeds an acceptable error, the value at the last discernible time step should be measured so that all statistically significant changes in the system can be observed. The output from the calculation is a plan of sampling times needed to capture all statistically significant events that are likely to occur over the course of the trial.

Dynamic simulation models are important tools for rationalizing complex changes in soil organic matter. Most such models for organic matter can be described as having either a pool structure or a continuous one. A pool structure can offer advantages in ease of use and transferability. Some pools are easily measured, whereas others cannot be measured directly. New methods of fractionation are being developed in an attempt to base models on measurable fractions. A requirement for such models is a demonstration that the measured fraction and model pool are equivalent. A measured fraction is equivalent to a model pool only if, within acceptable limits, it is unique as well as non-composite. If the measured fraction is not unique, describing it as a separate pool adds no extra information, while the added complexity can increase propagation of errors. If it is composite then the characteristics of the fraction will change with changing environment as a result of changing proportions of subpools. This will produce a model that cannot be applied without deriving parameters afresh: such a model is of greatly reduced value. Here we develop methods to examine if a fraction is both unique and non-composite. The tests for unique and composite pools were applied to the SUNDIAL (simulation of nitrogen dynamics in arable land) model of organic matter and nitrogen turnover in soil. Results suggest that the debris, biomass and humus pools are unique, but biomass and humus are composed of two or more subpools. This worked example illustrates how, given suitable data, any pool-based model can be tested by these methods.

An earlier paper (Macdonald et al., 1997; J. Agric. Sci. (Cambridge) 129, 125) presented data from a series of field experiments in which 15N-labelled fertilizers were applied in spring to winter wheat, winter oilseed rape, potatoes, sugar beet and spring beans grown on four different soils in SE England. Part of this N was retained in the soil and some remained in crop residues on the soil surface when the crop was harvested. In all cases the majority of this labelled N remained in organic form. In the present paper we describe experiments designed to follow the fate of this `residual' 15N over the next 2 years (termed the first and second residual years) and measure its value to subsequent cereal crops. Averaging over all of the initial crops and soils, 6.3% of this `residual' 15N was taken up during the first residual year when the following crop was winter wheat and significantly less (5.5%) if it was spring barley. In the second year after the original application, a further 2.1% was recovered, this time by winter barley. Labelled N remaining after potatoes and sugar beet was more available to the first residual crop than that remaining after oilseed rape or winter wheat. By the second residual year, this difference had almost disappeared. The availability to subsequent crops of the labelled N remaining in or on the soil at harvest of the application year decreased in the order: silty clay loam>sandy loam>chalky loam>heavy clay. In most cases, only a small proportion of the residual fertilizer N available for plant uptake was recovered by the subsequent crop, indicating poor synchrony between the mineralization of 15N-labelled organic residues and crop N uptake. Averaging over all soils and crops, 22% of the labelled N applied as fertilizer was lost (i.e., unaccounted for in harvested crop and soil to a depth of 100 cm) by harvest in the year of application, rising to 34% at harvest of the first residual year and to 35% in the second residual year. In the first residual year, losses of labelled N were much greater after spring beans than after any of the other crops.

In an earlier paper we presented data from an experiment in which nitrogen-15-labelled fertilizer was applied in spring to barley on the Rothamsted long-term Spring Barley Experiment, at rates of 48, 96 or 144 kg N ha−1. A substantial proportion (between 28 and 39%) of this 15N remained in the soil (0–70 cm) and stubble at harvest, mostly in organic form. The present paper follows the fate of this `residual' 15N over the following 2 years. Small amounts of `residual' 15N were recovered in the following two spring barley crops; 8% in the first and 3% in the second. The overall loss of `residual' 15N (i.e. `residual' 15N not recovered in crops and soil to a depth of 70 cm) over the 2 years was 23%. This is equivalent to just 8% of the total 15N originally applied. There was surprisingly little difference in the behaviour of the `residual' 15N in soils containing very different quantities of soil organic matter.

The existence of soluble organic forms of N in rain and drainage waters has been known for many years, but these have not been generally regarded as significant pools of N in agricultural soils. We review the size and function of both soluble organic N extracted from soils (SON) and dissolved organic N present in soil solution and drainage waters (DON) in arable agricultural soils. SON is of the same order of magnitude as mineral N and of equal size in many cases; 20–30 kg SON-N ha–1 is present in a wide range of arable agricultural soils from England. Its dynamics are affected by mineralisation, immobilisation, leaching and plant uptake in the same way as those of mineral N, but its pool size is more constant than that of mineral N. DON can be sampled from soil solution using suction cups and collected in drainage waters. Significant amounts of DON are leached, but this comprises only about one-tenth of the SON extracted from the same soil. Leached DON may take with it nutrients, chelated or complexed metals and pesticides. SON/DON is clearly an important pool in N transformations and plant uptake, but there are still many gaps in our understanding.

Long-term experiments are one vital tool for studying the impacts of agricultural management practices on soil properties and crop production; however, they have several limitations that must be recognized. Such experiments are resources for research – not museum exhibits that can never be altered. For example, in the Broadbalk Wheat Experiment (started 1843), the original large plots have been split so that additional cropping systems can be studied, in particular wheat grown in a crop rotation in addition to the original monoculture.

Soil organic C (SOC) contents in arable landscapes change as a function of management, climate and topography (Johnston et al, 2009). Traditional methods to measure soil C stocks are labour intensive, time consuming and expensive. Consequently, there is a need for developing low-cost methods for monitoring SOC contents in agricultural soils. Remote sensing methods based on multi-spectral images may help map SOC variation in surface soils. Recently, the costs of both Unmanned Aerial Vehicles (UAVs) and multi-spectral cameras have dropped dramatically, opening up the possibility for more widespread use of these tools for SOC mapping. Long-term field experiments with distinct SOC contents in adjacent plots, provide a very useful resource for systematically testing remote sensing approaches for measuring SOC. This study focusses on the Broadbalk Wheat Experiment at Rothamsted (UK). The Broadbalk experiment started in 1843. It is widely acknowledged to be the oldest continuing agronomic field experiment in the world. The initial aim of the experiment was to test the effects of different organic manures and inorganic fertilizers on the yield of winter wheat. The experiment initially contained 18 strips, each about 320m long and 6m wide, separated by paths of 1.5-2.5m wide. The strips were subsequently divided into ten sections (>180 plots) to test the effects of other factors (crop rotation, herbicides, pesticides etc.). The different amounts and combinations of mineral fertilisers (N,P,K,Na & Mg) and Farmyard Manure (FYM) applied to these plots for over 160 years has resulted in very different SOC contents in adjacent plots, ranging between 0.8% and 3.5%. In addition to large inter-plot variability in SOC there is evidence of within-plot trends related to the use of discard areas between plots and movement of soil as a result of ploughing. The objectives of this study are (i) to test whether low-altitude multi-band imagery can be used to accurately predict spatial patterns of SOC at a very high spatial resolution (< 10cm) (ii) to quantify the uncertainties on the predictions and potential of the method for monitoring SOC changes in experimental plots. This study used multi-band images with wavelengths between 450-1000nm taken at low altitude and at the landscape scale with a Tetracam Mini-MCA6. Images were taken of plots on section 9 on Broadbalk (continuous wheat) in November 2013 using a UAV-platform (Octocopter) at an altitude of 120m. The different images obtained were corrected for vignetting, noise and geometric deformation then stitched and georeferenced; the radiance was converted for reflectance with white calibration panels. Also, the vegetation effect (a cover mean of 10%) was removed by linear spectral unmixing. Finally, the spectra was calibrated and validated with SOC (0-5cm) measurements from 57 soil samples (37 calibration samples and 20 for the validation) taken along transect. The resulting map of SOC contents has a resolution of 10cm and an associated error of about the same magnitude as that for routine laboratory analyses (i.e. 0.2%). The map shows clear differences between plots relating to the different long-term fertilizer and organic manure inputs.

The purpose of this paper is to determine the effect of soil type and organic matter on the deformation characteristics of soil. We used triaxial testing to measure both the consolidation and shear deformation of soil. The novel application of this method was applied to soils from two experiments: on a clay loam and a sandy loam. The clay loam soil was from the long-term Broadbalk Experiment at Rothamsted Research, UK, where contrasting treatments had been applied since 1843. The sandy loam soil was from a straw incorporation experiment started in 1986. The clay loam soil from selected treatments from the Broadbalk Experiment had large difference in soil organic C (SOC) content due to additions of farmyard manure (FYM) or inorganic fertilizers for over 170 yr. There were no detectable differences in SOC or microbial biomass C in the sandy loam soil where straw had been incorporated. In addition to triaxial testing, we assessed soil physical condition with measurements of aggregate stability and aggregate tensile strength. From triaxial tests of the repacked soil, we found that soil type and SOC affected the compression characteristics. We also observed that deformation characteristics are more sensitive to small changes in soil management practices designed to increase the SOC content, than measurements of aggregate tensile strength, friability, or stability. We suggest that measurement of deformation characteristics is a potentially powerful approach for detecting or predicting changes in soil physical conditions as impacted by small changes in SOC content resulting from management practices.

Soils store and filter water, prevent flooding, support the production of fuel and fibre, provide habitat, help to create landscape and are a major carbon (C) store. They are, thus, an essential component of supporting, provisioning, regulating and cultural ecosystem services and determinants and constituents of well-being, providing security, the basic material for a good life, health and good social relations. However, calculations based on inherent land quality classes show that fertile soil (that is, soil free of constraints for agricultural production) irregularly covers no more than 12 % of the terrestrial land surface. More generally, soil fertility/quality is determined by the interactions between land management interventions by humans and the inherent physical, chemical and biological properties of a soil. Land and soil management based on the understanding of these interactions is one part of delivering food security. Even small changes in C content can have disproportionately large impacts on key soil properties. Practices to encourage maintenance of soil organic carbon (SOC) are important for ensuring sustainability of most if not all soil functions. This chapter considers the relationship between SOC and soil fertility and structure, ways of increasing SOC, some disadvantages of increasing SOC and two proposed ways of increasing SOC, fertility and sequestering C: the soil application of biochar and the cultivation of deeper rooting crops.

Current research on macronutrient cycling in UK agricultural systems aims to optimise soil and nutrient management for improved agricultural production and minimise effects on the environment and provision of ecosystem services. Nutrient use inefficiencies can cause environmental pollution through the release of greenhouse gases into the atmosphere and of soluble and particulate forms of N, P and carbon (C) in leachate and run-off into watercourses. Improving nutrient use efficiencies in agriculture calls for the development of sustainable nutrient management strategies: more efficient use of mineral fertilisers, increased recovery and recycling of waste nutrients, and, better exploitation of the substantial inorganic and organic reserves of nutrients in the soil. Long-term field experimentation in the UK has provided key knowledge of the main nutrient transformations in agricultural soils. Emerging analytical technologies, especially stable isotope labelling, that better characterise macronutrient forms and bioavailability and improve the quantification of the complex relationships between the macronutrients in soils at the molecular scale, are augmenting this knowledge by revealing the underlying processes. The challenge for the future is to determine the relationships between the dynamics of N, P and C across scales, which will require both new modelling approaches and integrated approaches to macronutrient cycling.