Organic Arable Farming Research Articles

Survey of farm-gate N and P balances on arable and dairy organic and conventional farms in Sweden—basis for improved management

About half of all N and P loads to Swedish waters originate from agriculture and must decrease to reach environmental goals. Studying nutrient management at farm level can provide an understanding of nutrient recycling and the risk of losses. In a survey of organic and conventional dairy and arable farms in three southern counties of Sweden, farm-gate N and P balances and N use efficiency (NUE) were analysed. Crop distribution differed significantly between organic and conventional farms, with organic dairy farms having higher proportions of ley and pulse crops and organic arable farms having a much higher proportion of N-fixing crops than corresponding conventional farms. Conventional dairy and arable farms had on average 70% and 40% higher N surplus than corresponding organic farms. Farm-gate P surplus was larger on conventional dairy farms and much larger on organic arable farms, mainly due to purchase of P-rich organic fertilisers. Organic dairy farms had higher NUE than corresponding conventional farms, but the opposite was true for arable farms. However, in the southernmost county Skåne, where soil fertility and yield potential are high, NUE was similar on all arable farms. Total inputs of N and P were positively correlated with N and P surpluses, especially on dairy farms. Improved manure and crop residue management, reduced use of purchased mineral N fertilisers coupled to more uniform within-farm distribution of manure, use of catch crops, intercropping and organic fertilisers with appropriate N:P ratio are measures that can reduce farm nutrient surpluses and improve nutrient management on both organic and conventional farms.

Experiences from Conservation Agriculture Approaches on Conventional and Organic Arable Farms

Experiences from Conservation Agriculture Approaches on Conventional and Organic Arable Farms

Productivity, light interception and radiation use efficiency of organic and conventional arable cropping systems

How the productivity of crops in organic arable farming may be sustainably increased remains a key issue. We combined measurements of crop yield, total aboveground biomass (AGB) and light interception over a 4-year crop rotation cycle from 2015 to 2018 in a long-term experiment in Denmark with arable organic and conventional cropping systems. These cropping systems comprise one conventional (CGL) and two organic (OGL and OGC) crop rotations, where CGL and OGL had three spring cereal and one grain legume crop (faba bean) in the rotation, and the faba bean was in OGC replaced with grass-clover. All crop rotations were grown with and without the use of cover crops, and the organic systems were grown with and without the manure application. The light interception was calculated from measurements of spectral reflectance, and this allowed the AGB to be decomposed into accumulated intercepted PAR (AIPAR) and radiation use efficiency (RUE).The conventional cropping system (CGL) had significantly greater AGB, AIPAR and RUE compared with the corresponding organic, grain legume-based system (OGL). AIPAR of the organic grass-clover-based cropping system (OGC) was greater than CGL, although the contrary conclusion was found in AGB and RUE. Across crops, RUE was greatest for cereals and smallest for faba bean and grass-clover. AIPAR was consistently greatest for grass-clover, and both grass-clover and faba bean had smaller variability in AIPAR between years and treatments than the cereal crops. Cover crops significantly increased AGB and AIPAR in the organic cropping systems but not in CGL. RUE was not significantly affected by the inclusion of cover crops. The use of manure in the organic systems increased AGB, AIPAR and RUE. The results show that AIPAR can be higher in organic cropping systems compared with conventional cropping systems, but this is not translated into a greater yield of cereal crops. There is, therefore, a need for novel approaches to management and the use of biomass in organic cropping systems for increasing yields for feed and food, and which sustains soil fertility.

Weed Species Trait Selection as Shaped by Region and Crop Diversity in Organically Managed Spring Cereals

Weeds remain a challenge in organic arable farming, as well as supply ecosystem services. The aim is to control weed densities while hosting a diverse and manageable weed community, preventing domination of few deleterious species. Therefore, we want to understand how specific species are stimulated, and which traits are selected for. This study focuses on crop diversity hypothesizing that (1) regions and (2) crop diversity function as filters for specific weed species traits. We conducted a weed monitoring in spring cereals over 2 years on organic farms in five northern European regions. Management and weed trait variables collected for the occurring species allowed an RLQ fourth-corner analysis. The weed communities were regionally specific, but trait selection was not observed, except in Latvia. Hence, the regional species pool provided different species with similar traits. Crop diversity within the management of spring cereals, such as undersowing and cereal frequency in the rotation, affected weed traits. The number of years under organic production selected no traits, although species numbers are known to increase. Hence, general weed species diversity increased, irrespective of traits. We conclude that organic management may support the agility within the weed community against selection of species and act as a buffer rather than as filter.

Nitrogen-use efficiency of organic and conventional arable and dairy farming systems in Germany

Optimising nitrogen (N) management improves soil fertility and reduces negative environmental impacts. Mineral N fertilizers are of key importance in intensive conventional farming (CF). In contrast, organic farming (OF) is highly dependent on closed nutrient cycles, biological N fixation and crop rotations. However, both systems need to minimise N balances and maximise nitrogen-use efficiency (NUE). NUE of organic and conventional crop production systems was evaluated in three regions in Germany by analysing N input, N output and N balance of 30 pairs of one OF and one CF farm each from the network of pilot farms for the period 2009–2011; indicators were calculated using the farm management system REPRO. CF had higher N input in all farm pairs. In 90% of the comparisons, N output of CF was higher than OF, in 7% it was the same and in 3% lower. NUE was higher in 60% of the OF, the same in 37% and lower in only 3%. The NUE of crop production in OF was 91% (arable farms: 83%; mixed/dairy farms: 95%) and the NUE in CF was 79% (arable farms: 77%; dairy farms: 80%). N balance was lower in 90% of the OF. The yearly average N balance was four times higher in CF (59 kg N ha−1 a−1) than in OF (15 kg N ha−1 a−1). The results show a huge individual variability within OF and CF. Organic mixed/dairy farms had the lowest N balances and the highest NUE. A further expansion of OF area can help to reduce high N balances and increase the NUE of crop production.

Crop diversification affects weed communities and densities in organic spring cereal fields in northern Europe

Within organic crop production, weed interference remains one of the main constraints on productivity, yet diverse weed vegetation supports the ecosystem services of arable fields. The use of crop diversification could alter weed communities and increase diversity, preventing the dominance of single detrimental weed species. This study investigated the type of crop diversification implemented in organic cropping systems in northern Europe and whether this affects the arable weed vegetation. A weed survey was conducted in 207 organic spring-sown cereal fields in five northern European regions (Denmark, Finland, Germany, Latvia and Sweden). Weed density data were combined with management and crop diversification data collected on the farms. The data set was analysed using linear mixed models and multivariate ordinations. The 197 weed species recorded were representative for the type of organic arable farming conducted in the regions. The management and crop diversification variables studied differed considerably among the regions. Management, such as the type of spring-sown cereal and crop mixture during monitoring, the preceding crop and weed harrowing, primarily influenced weed densities, while weed diversity increased with the duration of organic management and use of winter cover crops. The weed species communities were altered by the crop diversification applied. This study reflects the impact of regionally varied crop diversity and reinforces the importance of regionally adapted crop and weed management.

Is organic agriculture in line with the EU-Nitrate directive? On-farm nitrate leaching from organic and conventional arable crop rotations

Sustainable intensive agriculture requires enhanced nitrogen use efficiency and reductions in nitrogen (N) leaching losses. To investigate if organic farming systems have potential to achieve this, a comparison between conventional and organic arable farming was carried out over a two-year period. Two differently managed specialized organic arable crop rotations (low N-intensive (Ol), semi-N-intensive (Os)), and a typical N-intensive conventional crop rotation (Ch) were studied. The study was done under commercial farm scale conditions covering close to 400 ha in total (5−23 ha field sizes) in a highly productive arable region on fertile soils in northern Germany. Nitrogen leaching losses were measured using ceramic suction cups. Two functional units were used as indicators for eco-efficiency: N losses per area and per unit of grain equivalent (GE) produced. Results revealed that organic arable crop rotations reduced the nitrate (NO3-N) leaching loads per area significantly, with losses (kg NO3−-N ha-1 a-1) of 22.0 in Ol, 24.4 in Os and 35.1 in Ch. In contrast, when using the functional unit ‘nitrate leaching per grain equivalent’ as an indicator for eco-efficiency the conventional system resulted in 50 % lower N leaching loads per GE. This was due to the much higher land use efficiency of the conventional system (115 GE ha-1 vs 36 GE ha-1 for Ol and 38 GE ha-1 for Os), which resulted in N leaching losses (kg NO3-N GE-1) of Ch 0.32 for Ch, 0.64 for Ol, and 0.66 for Os. Regarding EU-Nitrate directive threshold for drinking water of 11.3 mg NO3-N l-1, all crop rotations exceeded the critical load. For the various main crop/preceeding crop sequences, the soil mineral N content at the end of the vegetation period and the autumn N uptake were the best predictors for N leaching, whereas for the aggregated effect across the various crop rotations within a farm system the N balance was the best descriptor. Considering N leaching loads our results show that both, specialized arable conventional and organic farming systems fail to meet the requirements of given environmental standards for water protection in the EU. This suggests that integrated approaches beyond such specialised systems are necessary, which are based on a balanced combination of forages (with two year leys), catch crops and cash crops.

Nitrous Oxide Emissions and Methane Uptake from Organic and Conventionally Managed Arable Crop Rotations on Farms in Northwest Germany

Land-use extensification by shifting from conventional to organic arable farming is often discussed as a measure for reducing greenhouse gas (GHG) emissions from agricultural land. Doubts about the benefits arise when emissions are calculated per product unit, particularly where high yields are possible under conventional management. Among the non-CO2 GHG emissions, nitrous oxide (N2O) is the main contributor from arable land and is controlled by soil type, environmental conditions and management. In order to investigate how land-use change from conventional to organic farming would perform under highly productive site conditions in northwest Germany, and how this would affect the important greenhouse gases N2O and methane (CH4), an on-farm field research was conducted over two experimental years. Two site-specific organic crop rotations, (i) with 25% legumes (grass + clover - winter wheat – winter rye – oats) and (ii) with 40% legumes (grass + clover – winter wheat – winter rye – spring field peas – winter rye), were compared with (iii) a conventional arable rotation (winter oilseed rape – winter wheat – winter wheat – sugar beet – winter wheat) and two reference systems, (iv) extensive grassland and (v) a beech forest), which were chosen as the baseline. The results showed that organic farming had lower N2O emissions of 0.7 N2O–N ha−1 year−1 than the conventional rotation, with 2.1 kg N2O–N ha−1 year−1 (p < 0.05), but higher emissions than the extensive grassland (0.3 kg N2O ha−1 year−1) and beech forest (0.4 kg N2O ha−1 year−1). CH4 emissions were a negligible part of total GHG emissions (as CO2 equivalents) in the two arable systems, and considerable uptake of CH4 from the forest soils showed this was a GHG sink in the first experimental year. Organic systems produced up to 40% lower crop yields, but the emissions per product unit in rotation (iii) was not superior to (ii) during the two experimental years. Thus, arable organic farming showed the ability to produce agricultural commodities with low N2O emissions per unit area, and no differences in product-related emissions compared with conventional farming. Conventional and organic systems both showed potential for further mitigation of N2O emissions by controlling the field level nitrogen surplus to a minimum, and by the optimized timing of the removal of the grass–clover ley phase.

Impact of mineral fertilizers, growth stimulators, pH regulators, vitamins and pigment supplements on the vitality of entomopathogenic nematodes of Steinernematidae and Heterorhabditidae families

Parasites of agricultural crops cause significant losses of quality and decrease in the profitability of agricultural production. Complex measures against pests are aimed both at termination of parasites and prevention of repeated infection of plants. One of the most progressive ways of protecting plants against harmful insects is the use of entomopathogenic nematodes. This method is most expedient in the conditions of organic arable farming. The results of our study reveal the impact of the fertilizers in various concentrations on the vitality of nematode larvae (L3) of four species (Steinernema feltiae, S. kraussei, S. carpocapsae and Heterorhabditis bacteriophora) and the possibility of their combined application for the treatment of plants. Mineral fertilizers and stimulators of growth of plants in 1% concentration insignificantly reduced the vitality of larvae, allowing them to be applied at the same time. We determined the tolerance of invasive larvae to pH for S. carpocapsae equaling рН = 0.9–13.4; optimum values of рН without reliable increase in the mortality during 24 h – рН = 1.3–12.8. Increase in the vitality of larvae (L3) of entomopathogenic nematodes was studied. The survivability of the cultures of larvae increased during the use of solutions of vitamins С, В1, В6, В12. We determined the influence of 21 pigment colourings on larvae (L3), the lowest effect on the vitality of nematode larvae was exerted by pigment bases Abrikos (7.0–10.8% mortality during 24 h), Zolotoi Pesok (6.0–11.8%), Pudra Ananasa (7.7–13.4%), and complex DMAE (7.6–17.4%). The results we obtained allow development of recommendations for agriculturalists for combined use of entomopathogenic nematodes with various substances and also improving the vitality of invasive nematodes.

Effect of legume and legume-festulolium mixture and their mulches on cereal yield and soil quality in organic farming

ABSTRACT Research was conducted to determine the effects of perennial legume and their mulches on cereal grain yield and the alterations to clay loam Cambisol properties. The perennial legumes (Trifolium pratense L., Medicago sativa L.) as well as their mixtures with festulolium (x Festulolium) were studied in conjunction with their aboveground biomass management methods: removal from the field (cut twice for forage), mixed management (the first cut was for forage, the second and third cuts were mulched) and mulching (four times) in an organic arable farming system. Mulching of legumes biomass resulted in a higher total nitrogen (N) used for green manure. A similar amount of N was accumulated for lucerne and lucerne-festulolium mulch when using mulching and mixed management. Legumes used for mulching caused the amount of mineral N in soil to increase in late autumn (62.7–82.9 kg ha–1) and decrease in spring (39.5–64.0 kg ha–1). This mineral N had a positive impact on crop yield (r = 0.68–0.71*); however, mineral N in autumn had a negative impact on soil sustainable organic compounds (r = −0.71*). The results indicate that the most suitable treatment was the legume-festulolium mixture, which used the biomass under mixed management.

Environmental sustainability of conventional and organic farming: Accounting for ecosystem services in life cycle assessment

Today, there is an ongoing debate about the environmental sustainability of the products of organic farming. To compare the performance of conventional and organic farming systems regarding environmental impact and productivity, the comprehensive environmental assessment tool ‘life cycle assessment’ can be used. The lower crop yields attained by organic systems compared to conventional farming systems might, however, outweigh the benefits of the use of more environmental-friendly practices when evaluating the environmental impact per product unit. Although these practices are beneficial for the environment, which is reflected in the delivery of a range of ecosystem services (ES), the focus is traditionally put only on the (harvested) product. Because the agricultural product involves actually a bundle of ES, the impact should be allocated among the whole output of an agricultural system. In this study, we propose an allocation procedure based on the capacity of agricultural systems to deliver ES to divide the environmental impact over all agricultural outputs (i.e. provisioning and other ES). Allocation factors are developed for conventional and organic arable farming systems. Applying these allocation factors, we demonstrate that for about half of the studied food products (including maize, potato), organic farming has clear environmental benefits in terms of resource consumption in comparison to conventional cultivation methods. This allocation approach allows a more complete comparison of the environmental sustainability of organically and conventionally produced food.

Exchanging knowledge to improve organic arable farming: an evaluation of knowledge exchange tools with farmer groups across Europe

Organic farming is knowledge intensive. To support farmers in improving yields and organic agriculture systems, there is a need to improve how knowledge is shared. There is an established culture of sharing ideas, successes and failures in farming. The internet and information technologies open-up new opportunities for knowledge exchange involving farmers, researchers, advisors and other practitioners. The OK-Net Arable brought together practitioners from regional Farmer Innovation Groups across Europe in a multi-actor project to explore how online knowledge exchange could be improved. Feedback from the groups was obtained for 35 ‘tools’, defined as end-user materials, such as technical guides, videos and websites informing about practices in organic agriculture. The groups also selected one practice to test on farms, sharing their experiences with others through workshops, exchange visits and through videos. Farmers valued the same key elements in face-to-face exchanges (workshops and visits) as in online materials. These were the opportunity for visual observation, deeper understanding of the context in which a practice was being tried and details about what worked and what did not work. Videos, decision support tools and social media can provide useful mechanisms for taking knowledge exchange online, enabling farmers and researchers to share experiences and practical implications. Visual information, economics, details of the context, successes and failures were considered to be critical factors in good knowledge exchange tools. Online platforms and forums should not be expected to replace but rather to complement face to face knowledge exchange in improving organic farming.

Earthworm abundance response to conservation agriculture practices in organic arable farming under Mediterranean climate

Earthworms are one of the most important soil macrofaunal groups, and they play a major role in agricultural ecosystems. Agricultural practices, such as reduced tillage, the use of green manures and organic fertilization, can be beneficial for earthworm populations in agricultural systems. However, under a Mediterranean climate, not much is known regarding their response to agricultural management. The aim of this study was to analyse the effects of tillage type, organic fertilization, and green manures on the density and biomass of earthworms in organic arable dryland. The trial was conducted in a four-year crop rotation with a complete factorial design that combined tillage system (mouldboard ploughing vs. chisel), fertilization (composted farmyard manure vs. no fertilizer) and green manures (green manures vs. no green manures). Earthworms were assessed in each plot by the extraction of all individuals in three soil areas of 33cm×33cm that were excavated to a depth of 25cm. Only five earthworm species were found in this trial, and the earthworm community was dominated by such endogeic ecotypes as Aporrectodea rosea and Allolobophora georgii, and the anecic ecotype Aporrectodea trapezoides. Endogeic species can benefit from soil inversion because of the incorporation of organic matter, but the anecic ones can be negatively affected by it. The results show that plots with farmyard manure had higher density and biomass of earthworms. We observed that the type of tillage significantly affected earthworm populations: plots that had been ploughed with mouldboard ploughing (soil inversion) the year prior to sampling presented more juveniles. The biomass of earthworms was significantly lower in plots with green manures and chiselling. Our results indicated that the combination of chiselling and green manures were not optimal for earthworm populations, but organic fertilization played a considerably more important role and enhanced their abundances.

Integration of biogas production into organic arable farming systems: crop yield response and economic effects

There are several important differences between organic and conventional biogas production. One difference concerns the biomass production system (e.g., legume-grass instead of maize), and another difference is the way in which biogas plants are integrated into nutrient cycles, which results in different effects on soil fertility, crop yields, and the environment. The focus of this study is an analysis of the yield response and economic impact of biogas plant integration into an organic arable farming system. We compare two organic farming systems: the reference system (an arable farming system without biogas production) and the biogas system (an arable farming system with biogas production). Both farming systems underwent the same crop rotation, and the cash crops produced in the biogas system were sold identically to those in the reference system. In the reference system, the grass–legume mixture of the green fallow was mulched and left as green manure on the fields. In the biogas system, the grass–legume mixture was used for biogas production; therefore, electricity, heat, and the biogas slurry for fertilization of the cash crops were produced. The comparisons are based on a long-term field experiment and additional modeling data. This research approach was chosen to achieve reliable results on the basis of measured yield effects under comparable site and management conditions. Within the investigated period (2010–2014), the cereal yields of the biogas system were significantly (27–47%) higher than those of the reference system (arable farming). Case studies and model calculations on the basis of the experimental data showed higher entrepreneurial profits from the biogas systems as a result of the yield effects. The entrepreneurial profit of the arable farming in the biogas system was approximately 300 € ha−1 higher than that of the reference system. The higher revenues from the cash crops also compensated for the financial losses induced by the biogas plants. The dimensions of a biogas plant are important for improving the overall profit of a farm; the size must be adapted to the on-site supply of substrates and the need for biogas slurry. This study shows that suitable organic biogas production leads to synergistic effects between bioenergy and food production. The integration of a biogas plant into an organic farming system can ensure energy supply while increasing food output.

Effects of changing farm management and farm structure on energy balance and energy-use efficiency—A case study of organic and conventional farming systems in southern Germany

Abstract Fossil energy input, energy output, and energy use- efficiency (EUE) are important indicators of the environmental effects, resource consumption and economic performance of farming systems. In this study, the energy balance (process analysis) and EUE of different organic and conventional farming systems – mixed farming, arable farming, and agroforestry (AGFS) systems – were analyzed due to their importance in Germany. The analysis was based on long-term experiments at the Scheyern Research Farm in southern Germany. The results showed that the conversion from multi-structured organic mixed farming to a specialized organic arable farming system reduced the fossil energy input in crop production only marginally (from 5.9 to 5.5 GJ ha −1 yr −1 ), but considerably decreased dry matter yield (from 5.4 to 2.5 Mg ha −1 yr −1 ), energy output (from 99 to 46 GJ ha −1 yr −1 ) and EUE (from 16.8 to 8.3). Improved management in the conventional arable farming system (with high-yielding varieties and better N management) reduced the energy input from 14.0 to 12.2 GJ ha −1 yr −1 , increased the energy output from 155 to 179 GJ ha −1 yr −1 , and elevated the EUE from 11.1 to 14.6. The establishment of AGFS with short rotation trees (without fertilization and pesticide use) led to the reduction of energy input. Based on the results, we concluded that mixed farming is one of the best ways of producing food with high EUE under the conditions of organic farming. Therefore the conversion from organic mixed farming to an organic arable farming system is not recommended. Our AGFS results were from the first stage of a long-term experiment; it showed no negative effects on DM yield and energy output and positive effects on energy-use efficiency at this stage. However, further research is needed to know the long-term influence of AGFS.

An empirical analysis of risk in conventional and organic arable farming in The Netherlands

This paper assesses and compares risk in conventional and organic arable farming in The Netherlands with respect to family farm income and underlying price and production variables. To investigate the risk factors the farm accountancy data network was used containing unbalanced panel data from 196 conventional and 29 organic representative Dutch arable farms (for the period 2002 up to and including 2011). Variables with regard to price and production risk were identified using a family farm income analysis scheme. Price risk variables are input and output prices, while yield volatility of different crops is the main production risk variable. To assess risk, an error components implicit detrending method was applied and the resulting detrended standard deviations were compared between conventional and organic farms. Results indicate that the risk at the level of family farm income is higher in organic farming. The underlying variables show higher risk for organic farms in crop yields, crop prices and variable input costs per crop.

Nitrogen balances and nitrogen-use efficiency of different organic and conventional farming systems

Nitrogen (N) is the most important yield-limiting factor in agricultural systems, however, N application can lead to emissions and environmental problems such as global warming (N2O) and groundwater contamination (NO3 −). This study analyses the N balance, nitrogen-use efficiency, and N loss potential of conventional farming systems (arable farming, improved arable farming, and agroforestry) and organic farming systems (mixed farming, arable farming, and agroforestry) based on long-term field experiments in southern Germany. The effects of the conversion of farm structure and N management are identified. The conventional farming systems in this study were high N-input and high N-output systems. The conventional arable farming system had the lowest nitrogen-use efficiency and the highest N surplus. An optimised N management and the use of high-yielding crop varieties improved its nitrogen-use efficiency. The establishment of conventional agroforestry resulted in the reduction of N input, N output and N surplus, while maintaining high yields. The organic mixed farming system is characterised by a relatively high N input and N output, the accumulation of soil organic nitrogen, the highest nitrogen-use efficiency, and the lowest N surplus of all analysed systems. These good results can be attributed to the intensive farm N cycle between soil–plant–animal. The shift from organic mixed farming to organic arable farming system extensified the N cycle, reduced N input, crop yield and N output. The change from organic arable farming to organic agroforestry reduced the N input, increased the biomass yield, and remained the N surplus within an optimal range.

Knowledge Asymmetries Between Research and Practice: A Social Systems Approach to Implementation Barriers in Organic Arable Farming

AbstractThis article discusses the problem of implementing scientific knowledge in practice. The discussion is based on a case study of barriers to implementing research‐based principles of sustainable organic arable farming. The current literature tends to see this problem either as a dissemination issue (the linear approach) or as a failure of science to address real‐world problems (the co‐constructive approach). We argue that Luhmann's theory of social systems offers a way to understand the shortcomings of existing approaches and enables us to identify knowledge gaps that have often been overlooked so far. This theoretical claim is substantiated by an empirical analysis based on 10 in‐depth interviews with owners of organic arable farms. The farmers were interviewed about barriers to the implementation of research‐based knowledge in practice. The analysis points to the operational closure and the observational blindness of both research systems and farming systems as the keys to understanding knowledge gaps and suggests new ways of dealing with the problems of implementing research knowledge in practice.

Effects of green manure storage and incorporation methods on nitrogen release and N2O emissions after soil application

More efficient use of green manure-derived nitrogen (N) may improve crop yields and reduce environmental impacts in stockless organic arable farming. In this 3-month incubation study, we tested a new strategy where green manure leys are harvested and preserved until the following spring either as compost mixed with straw or as silage of harvested ley biomass. Grass-clover compost or silage was soil-incorporated by either simulated ploughing (green manure placed at 15 cm depth) or harrowing (green manure mixed into the upper 5-cm soil horizon) in order to assess treatment effects on net release of plant-available N, nitrous oxide (N2O) fluxes and soil respiration. Grass-clover silage provided the highest net N release with similar results for the two incorporation methods. Up to one third of the total N content in silage became plant-available during the 3 months. In contrast, no net N release was observed for the composted grass-clover and straw mixture. In fact, soil incorporation of compost by harrowing caused temporal immobilization of soil mineral N. Silage incorporated by ploughing gave rise to the largest N2O effluxes with silage-induced emissions corresponding to 0.3 % of applied total N. Possibly N2O production via denitrification was stimulated by oxygen-limited conditions near the decomposing silage. In contrast, compost incorporated by harrowing caused net N2O uptake, presumably an effect of reduced mineral N availability in this treatment. Overall, our study revealed that ensiled grass-clover was the best fertilizer product and that the method chosen for incorporation of green manure is likely to influence N2O emissions.

Seasonal nitrous oxide emissions from field soils under reduced tillage, compost application or organic farming

Soil management practices shown to increase carbon sequestration include reduced tillage, amendments of carbon and mixed rotations. As a means to mitigate greenhouse gases, however, the success of these practices will be strongly influenced by nitrous oxide (N2O) emissions that vary with soil wetness. Few seasonal data are available on N2O under different soil managements so we measured seasonal N2O emission in three field experiments between 2006 and 2009 in eastern Scotland. The experimental treatments at the three sites were (1) tillage: no-tillage, minimum tillage, ploughing to 20cm with or without compaction and deep ploughing to 40cm, (2) organic residue amendment: application of municipal green-waste compost or cattle slurry and (3) rotations: stocked and stockless (without manure) organic arable farming rotations. Most seasons were wetter than average with 2009 the wettest, receiving 20–40% more rainfall than average. Nitrous oxide emissions were measured using static closed chambers. There was no statistical evidence, albeit with low statistical power, that reduced tillage affected N2O emissions compared to normal depth ploughing. With organic residue amendments, only in the wet season in 2008 were emissions significantly increased by high rates of green-waste compost (4.5kgN2O-Nha−1) and cattle slurry (5.2kgN2O-Nha−1) compared to the control (1.9kgN2O-Nha−1). In the organic rotations, N2O emissions were greatest after incorporation of the grass/clover treatments, especially during conversion of a stocked rotation to stockless. Emissions from the organic arable crops (1.9kgN2O-Nha−1 in 2006, 3.0kgN2O-Nha−1 in 2007) generally exceeded those from the organic grass/clover (0.8kgN2O-Nha−1 in 2006, 1.1kgN2O-Nha−1 in 2007) except in 2008 when the wet weather delayed manure applications and increased emissions from the grass/clover (2.8kgN2O-Nha−1). Nevertheless, organic grassland was the land use providing the most effective overall mitigation. Although the magnitude of fluxes did not relate particularly well to rainfall differences between seasons, greater rainfall received during some growing seasons increased the differences between tillage, organic residue and crop rotation phase treatments, negating any possible mitigation by timing management operations in dry periods. This was partly attributed to applying tillage and manures late and/or in wet conditions. Of benefit would be different sampling strategies including closed chambers or eddy covariance with standardised methodology. Controlled soil management experiments with a wide geographic spread to specify land management for mitigation also important.