Subsequent Cereals Research Articles

Nitrogen supply by cut-and-carry biomass for vegetable crops and subsequent cereals

Nitrogen supply by cut-and-carry biomass for vegetable crops and subsequent cereals

Nitrogen rhizodeposition from corn and soybean, and its contribution to the subsequent wheat crops

Nitrogen (N) is a key factor in the positive response of cereal crops that follow leguminous crops when compared to gramineous crops in rotations, with the nonrecyclable rhizosphere-derived N playing an important role. However, quantitative assessments of differences in the N derived from rhizodeposition (NdfR) between legumes and gramineous crops are lacking, and comparative studies on their contributions to the subsequent cereals are scarce. In this study, we conducted a meta-analysis of NdfR from leguminous and gramineous crops based on 34 observations published worldwide. In addition, pot experiments were conducted to study the differences in the NdfR amounts, distributions and subsequent effects of two major wheat (Triticum aestivum L.)-preceding crops, corn (Zea mays L.) and soybean (Glycine max L.), by the cotton wick-labelling method in the main wheat-producing areas of China. The meta-analysis results showed that the NdfR of legumes was significantly greater by 138.93% compared to gramineous crops. In our pot experiment, the NdfR values from corn and soybean were 502.32 and 944.12 mg/pot, respectively, and soybean was also significantly higher than corn, accounting for 76.91 and 84.15% of the total belowground nitrogen of the plants, respectively. Moreover, in different soil particle sizes, NdfR was mainly enriched in the large macro-aggregates (>2 mm), followed by the small macro-aggregates (2–0.25 mm). The amount and proportion of NdfR in the macro-aggregates (>0.25 mm) of soybean were 3.48 and 1.66 times higher than those of corn, respectively, indicating the high utilization potential of soybean NdfR. Regarding the N accumulation of subsequent wheat, the contribution of soybean NdfR to wheat was approximately 3 times that of corn, accounting for 8.37 and 4.04% of the total N uptake of wheat, respectively. In conclusion, soybean NdfR is superior to corn in terms of the quantity and distribution ratio of soil macro-aggregates. In future field production, legume NdfR should be included in the nitrogen pool that can be absorbed and utilized by subsequent crops, and the role and potential of leguminous plants as nitrogen source providers in crop rotation systems should be fully utilized.

Effects of Forage Legumes Sowing in the Fallow Year on Silage Yield and Quality Characteristics of Subsequent Cereals

In this study, the effect of P. arvense-H. vulgare mixture and V. pannonica grown in the fallow year on silage yield and quality of subsequent cereals were investigated in the arid condition of Eskişehir, Turkey. The fresh weight of P. arvense-H. vulgare mixture with 2750 kg/da was found two-fold high than V. pannonica. P. arvense-H. vulgare mixture significantly increased the fresh and dry hay weights of cereals except for H. vulgare cv. İnce. In addition, the highest grain yield was obtained by growing Triticosecale cv. Karma in P. arvense-H. vulgare mixture plots. Due to the high pH and low dry matter content of triticale samples, the Fleig scores were very low, which is a quality indicator in silage. ADF and NDF ratios were the highest in A. sativa cv. Checato as a negative quality factor. Top-dressing of nitrogen had a positive effect on the crude protein ratio. It was concluded that production of quality roughage can be sustainably increased by growing P. arvense-H. vulgare mixture in barren areas in the fallow year and followed by sowed cvs. Karma, Müfitbey, and Checato in the cereal growing season.

Cereal and oil seed crops response to organic nitrogen when grown in rotation with annual aerial-seeded pasture legumes

AbstractNitrogen fixation from pasture legumes is a fundamental process that contributes to the profitability and sustainability of dryland agricultural systems. The aim of this research was to determine whether well-managed pastures, based on aerial-seeding pasture legumes, could partially or wholly meet the nitrogen (N) requirements of subsequent grain crops in an annual rotation. Fifteen experiments were conducted in Western Australia with wheat, barley or canola crops grown in a rotation that included the pasture legume species French serradella (Ornithopus sativus), biserrula (Biserrula pelecinus), bladder clover (Trifolium spumosum), annual medics (Medicago spp.) and the non-aerial seeded subterranean clover (Trifolium subterraneum). After the pasture phase, five rates of inorganic N fertilizer (Urea, applied at 0, 23, 46, 69 and 92 kg/ha) were applied to subsequent cereal and oil seed crops. The yields of wheat grown after serradella, biserrula and bladder clover, without the use of applied N fertilizer, were consistent with the target yields for growing conditions of the trials (2.3 to 5.4 t/ha). Crop yields after phases of these pasture legume species were similar or higher than those following subterranean clover or annual medics. The results of this study suggest a single season of a legume-dominant pasture may provide sufficient organic N in the soil to grow at least one crop, without the need for inorganic N fertilizer application. This has implications for reducing inorganic N requirements and the carbon footprint of cropping in dryland agricultural systems.

Effects of Rotations With Legume on Soil Functional Microbial Communities Involved in Phosphorus Transformation.

Including legumes in the cereal cropping could improve the crop yield and the uptake of nitrogen (N) and phosphorus (P) of subsequent cereals. The effects of legume-cereal crop rotations on the soil microbial community have been studied in recent years, the impact on soil functional genes especially involved in P cycling is raising great concerns. The metagenomic approach was used to investigate the impacts of crop rotation managements of soybean-wheat (SW) and maize-wheat (MW) lasting 2 and 7years on soil microbial communities and genes involved in P transformation in a field experiment. Results indicated that SW rotation increased the relative abundances of Firmicutes and Bacteroidetes, reduced Actinobacteria, Verrucomicrobia, and Chloroflexi compared to MW rotation. gcd, phoR, phoD, and ppx predominated in genes involved in P transformation in both rotations. Genes of gcd, ppa, and ugpABCE showed higher abundances in SW rotation than in MW rotation, whereas gadAC and pstS showed less abundances. Proteobacteria, Acidobacteria, and Gemmatimonadetes played predominant roles in microbial P cycling. Our study provides a novel insight into crop P, which requires strategy and help to understand the mechanism of improving crop nutrient uptake and productivity in different rotations.

Combining crop diversification practices can benefit cereal production in temperate climates

Diversifying cropping systems by increasing the number of cash and cover crops in crop rotation plays an important role in improving resource use efficiency and in promoting synergy between ecosystem processes. The objective of this study was to understand how the combination of crop diversification practices influences the performance of arable crop sequences in terms of crop grain yield, crop and weed biomass, and nitrogen acquisition in a temperate climate. Two field experiments were carried out. The first was a 3-year crop sequence with cereal or grain legume as the first crops, with and without undersown forage legumes and forage legume-grass crops, followed by a cereal crop. The second experiment was a 2-year crop sequence with cereal or legume as the first crops, a legume cover crop, and a subsequent cereal crop. For the first time, crop diversification practices were combined to identify plant-plant interactions in spatial and temporal scales. The results partly confirm the positive effect of diversifying cereal-based cropping systems by including grain legumes and cover crops in the crop sequence. Legume cover crops had a positive effect on subsequent cereal grain yield in one of the experiments. Using faba beans as the first crop in the crop sequence had both a positive and no effect on crop biomass and N acquisition of the subsequent cereal. In cover crops composed of a forage legume-grass mixture, the grass biomass and N acquisition were consistently increased after the grain legume, compared to the cereal-preceding crop. However, differences in the proportion of legume to grass in mixture did not influence crop yield or N acquisition in the subsequent cereal. In conclusion, these results support that increased crop diversity across spatial and temporal scales can contribute to resource-efficient production and enhance the delivery of services, contributing to more sustainable cropping systems.

Nitrogen rhizodeposition by legumes and its fate in agroecosystems: A field study and literature review

AbstractQuantification of legume nitrogen (N) rhizodeposition (N derived from roots) and its fate in agroecosystems is crucial for managing soil fertility, land productivity, and agriculture sustainability. In contrast to forage legumes, the N rhizodeposition by grain legumes is nearly unknown. Therefore, N rhizodeposition of four grain legumes and its transfer to subsequent wheat crops was quantified using the 15N stem labeling method under field conditions. The N rhizodeposition of the grain legumes: peanut, soybean, mungbean, and adzuki bean amounted to 25, 51, 20, and 63 kg N ha−1, respectively. N rhizodeposition was not affected by fertilization, and it was 53–257% more accumulated in topsoil (0–20 cm) than that in subsoil (20–40 cm). However, N rhizodeposition per unit of root biomass in subsoil was 3.5‐times as much as that in topsoil (p < 0.05), indicating the importance of legumes for soil fertility and exploration in subsoil. Remarkably, subsequent wheat utilized 13–85% of legume N rhizodeposition, which contributed to 4–20% of total wheat N uptake. Combining the present data with the literature review, the average N rhizodeposition of legumes (both grain and forage legumes) is 83 kg N ha−1 (n = 75), and one‐fourth of which was utilized by subsequent cereals. Increasing root biomass by 1 g increases rhizodeposition by 53 mg N. In conclusion, legume N rhizodeposition is crucial for the sustainability of legume‐based crop rotations resulting in soil N build‐up and is an important N source for subsequent crops.

N supply and pre-cropping benefits to triticale from three legumes in rainfed and irrigated Mediterranean crop rotations

Including pulses in crop rotations can improve the productivity of subsequent crops due to increased soil available N and other agronomic benefits. However, the magnitude of this effect can vary with environmental conditions, agricultural management practices and legume genotypes. We aimed to measure the N supply and pre-crop benefits from pulses introduced in different crop rotations with cereals in a Mediterranean climate. Two three-year field trials were set with non N-fertilized fodder triticale (× Triticosecale ‘Alter’) as a monoculture, and in rotation with irrigated cowpea (Vigna unguiculata’ Fradel’) as replacement of summer fallow, or rainfed faba bean (Vicia faba ‘Favel’) or pea (Pisum sativum ‘Grisel’) as ‘break’ crops. Two legume residue managements were tested: incorporation into the soil and removal from the system. Triticale monocultures with three levels of synthetic N fertilization were included for estimation of N-fertilizer equivalence from rainfed pulse pre-crops. Yields and N contents were measured for each plant fraction and crop, including weeds. Biologically fixed N was estimated by an N-difference method and residual fixed N (RFN) was calculated. Cowpea fixed between 62–127 kg N ha−1 and provided up to 61 kg N ha−1 to soil as RFN. Faba bean and pea fixed between 0–72 kg N ha−1 but RFN was negative overall, as low as −52 kg N ha−1. However, the apparent N benefit of these ‘break’ crops was largely positive (up to 70 kg N ha−1) in comparison with the reference crop (triticale). Agricultural intensification with irrigated cowpea did not affect the productivity of subsequent cereal, likely due to a combined effect of low residue mineralization potential of its residues, and to increased nitrate leaching and weed infestation in cereal. However, the overall productivity of the agroecosystem was increased with minimal inputs. Rainfed faba bean and pea improved cereal productivity similarly, but only when grown in wet conditions with no weed control (30–59% yield increase, equivalent to 72–153 kg fertilizer-N ha−1). Removal of legume residue did not affect the productivity of subsequent cereal. This study identifies cowpea as a suitable crop for sustainable intensification in Mediterranean conditions.

Leguminous pre-crops improved quality of organic winter and spring cereals

ABSTRACTThe aim of this research was to assess the effect of leguminous pre-crop species on quality characteristics of subsequent spring and winter cereals. The experiment was carried out in an organic crop rotation in north-eastern Europe. The influence of biomass dry matter yield, carbon and nitrogen content of perennial red clover (Trifolium pratense L.), alsike clover (Trifolium hybridum L.), Washington lupin (Lupinus polyphyllus Lindl.), biennial white sweet clover (Melilotus albus L.), annual crimson clover (Trifolium incarnatum L.) and Alexandria clover (Trifolium alexandrinum L.) on protein concentration, bulk density and thousand grain weight of subsequent cereals were assessed. Barley, oats, winter rye, spring and winter wheat were grown in the first post-legume year and barley and oats in the second post-legume year. In the first year after perennial and biennial pre-crops, the protein concentration of the cereals, except for rye, increased by 0.8–2.6 percentage points compared with the control. The largest increases in protein concentration of the cereals were after red and alsike clovers. The legumes increased the bulk density of all of the cereals, while thousand kernel weights were increased only for barley, spring and winter wheat. All the legume species had a positive second-year after-effect on the protein concentration of barley and oats, with the largest effect after red and alsike clover at 1.0–1.3 percentage points. The results showed that all of the leguminous pre-crops were suitable for increasing the quality of cereals. The effect was greater after perennial and biennial species compared with the annual species.

Preceding cultivation of grain legumes increases cereal yields under low nitrogen input conditions

The European Union (EU) has advised to increase the production of grain legumes, both to reduce EU dependency on soybean imports from the Americas and to reduce pollution from intensive cereal production. Several studies have indicated that preceding grain legume had a positive effect on the yields of subsequent cereals; this argument being often used to promote cultivation of grain legumes. However, no quantitative synthesis of the data has been performed on a global scale to estimate the relative increases in cereal yields arisen from cultivation of preceding grain legumes. Here, we performed a meta-analysis of 1181 yields of cereals cultivated in 15 countries. The results show that the yields of cereals cultivated after grain legumes were, on the average, + 29% higher than the yields of cereals cultivated after cereals. Our findings also show that the positive effect of grain legumes decreased with the nitrogen (N) fertilization applied to subsequent cereals, then became negligible when the mean N fertilization exceeded 150 kg N ha−1. This threshold is often exceeded in European conventional cereal systems.

Removal of phosphorus in residues of legume or cereal plants determines growth of subsequently planted wheat in a high phosphorus fixing soil

Legumes have been shown to improve the phosphorus (P) uptake and growth of subsequent cereals even when all legume residues (including roots) are removed, but the mechanism(s) responsible have not been elucidated. Further, this phenomenon has not been investigated in high P-fixing soils, which are prevalent in tropical and subtropical regions where P deficiency in soils is a major global issue. We tested the hypothesis that carbon (C) inputs into the soil from the roots of legumes may increase labile organic C pools and microbial biomass in soil cf. wheat (Triticum aestivum L.), with consequences for subsequent wheat growth. The hypothesis was tested by cultivating wheat after pre-cropping of the soil with either wheat, faba bean (Vicia faba L.), chickpea (Cicer arietinum L.) or an unplanted fallow in a high-P-fixing Ferralsol, with or without P fertiliser addition to the pre-crop, under glasshouse conditions. The addition of P fertiliser resulted in significantly higher P concentrations in the NaHCO3-Pi, NaOH-Pi and HCl-Po pools in the bulk soil after the pre-crop phase, but resulted in significantly lower water-Po, NaHCO3-Po, NaOH-Po and total organic C (TOC) concentrations. Neither of the legumes nor wheat changed the soil P pools, with the exception of the water-Pi pool, which was significantly higher following chickpea where P fertiliser was applied. While the faba bean pre-crops resulted in higher total microbial biomass under nil-P fertiliser conditions, these changes did not result in enhanced growth of the subsequent wheat crop. Notably, a strong negative correlation between subsequent wheat growth and the amount of P removed by the pre-crop was observed both with (r = −0.60) and without (r = −0.80) P fertiliser, suggesting that in high P-fixing soils the depletion of P pools by pre-crops limits the growth of subsequent cereals. Any benefits of legumes to P cycling in rotations on high P-fixing soils likely relies on contributions from the mineralisation of root residues (and shoot residues where these are retained) to soil P availability, rather than any rhizosphere-specific changes in soil P pools induced by legumes.

Different leguminous pre-crops increased yield of succeeding cereals in two consecutive years

ABSTRACTLeguminous pre-crops are an important source of green manure in organic crop rotations for improving soil fertility and achieving high yields of cereals. We aimed to study the potential of various leguminous species, other than the traditionally cultivated red clover (Trifolium pratense L.), as green manure pre-crops for subsequent cereals. The use of different legume species enables to exploit advantages of specific legumes in organic cereal production. In order to test the legumes as pre-crops for cereals, we carried out trials located in the temperate climate zone of northeast Europe (58°44′59.41″ N, 26°24′54.02″ E). We sowed the following perennial legumes as pre-crops: red clover, alsike clover (Trifolium hybridum L.) and Washington lupine (Lupinus polyphyllus Lindl.), biennial white sweet clover (Melilotus albus Medik.) and annual Alexandria clover (Trifolium alexandrinum L.), and crimson clover (Trifolium incarnatum L.). Timothy (Phleum pratense L.) was used as a control. The leguminous pre-crops were followed by three spring cereals (barley, oat and spring wheat) and two winter cereals (rye and winter wheat). We tested the first-year after-effect (all cereals) and second-year after-effect (only barley and oat) of pre-crops on the grain yield of cereals. Perennial and biennial legume species produced the highest dry matter yield and contained the highest amount of nutrients, especially nitrogen, compared to annual species. All subsequent cereals produced significant extra yields after each leguminous pre-crop in the following two years, although the effect was smaller in the second year. The most suitable pre-crops for spring cereals were red and alsike clover followed by lupine, whereas the best pre-crops for winter cereals were sweet clover and annual clovers. Our results show the potential of various leguminous pre-crop species as valuable sources of green manure in organic crop rotation.

Break-crop effects on wheat production across soils and seasons in a semi-arid environment

In low-rainfall environments, a high frequency of cereal crops has been favoured for optimising productivity and risk. However, cereals at high intensity often lead to declining water-use efficiency and increasing inputs to cope with emergent nutritional, disease and weed problems. The value of including breaks in the cropping sequence can involve a high level of uncertainty in low-rainfall areas where non-cereal crops are more risky and profitability is largely determined by the subsequent benefit to cereal productivity. In this study, we aimed to improve understanding of the magnitude and primary source of break benefits such as nutrition, water and disease management in a low-rainfall environment where a high level of within-field soil variability can also contribute to uncertainty about the value of breaks. In on-farm field experiments near Karoonda in the South Australian Mallee, breaks were grown in 2009 or 2010 on four distinct soil types across a dune–swale catena. The effect of these breaks on subsequent cereal production was measured for up to 3 years. In addition, the effect of breaks on nutrition and water available, along with disease infection in subsequent cereal crops, was explored and actual yields were compared with nitrogen and water-limited potential yields. Consistent cumulative benefits to subsequent cereal crops of at least 1 t ha–1 after 3 years accrue from breaks grown on the different soil types. The inclusion of breaks had beneficial effects on the cycling and supply of nutrients along with some short-term impacts on infection by Rhizoctonia solani AG8 in subsequent cereals, whereas there were no conclusive effects of breaks on the supply of water to subsequent crops. This study suggests that the inclusion of both legume and brassica breaks is likely to be beneficial to subsequent cereal production where nitrogen is a factor limiting productivity in low-rainfall, semi-arid environments.

Diversity of Rhizobium leguminosarum from Pea Fields in Washington State

Rhizobia-mediated biological nitrogen (N) fixation in legumes contributes to yield potential in these crops and also provides residual fertilizer to subsequent cereals. Our objectives were to collect isolates of Rhizobium leguminosarum from several pea fields in Washington, examine genetic diversity among these isolates and several commercial isolates of R. leguminosarum, and compare genetically distinct isolates for their ability to fix N in a range of pea hosts. Seventy-nine isolates were collected from pea root from four noninoculated pea fields. Sequence-related amplified polymorphism (SRAP) markers generated by PCR were used to discriminate among isolates. Isolates fell into 17 clusters with robust bootstrap support values. Nearly half of the isolates fell into a single large cluster, but smaller clusters were also detected for isolates from all four field locations. The majority of commercial isolates fell into a distinct cluster. Four genetically distinct isolates were compared for their efficiency in fixing N in a greenhouse experiment. Host plant variety effects were significant for plant biomass due to N fixation and also for the quantity of N fixed per variety. Significant effects of R. leguminosarum isolates were observed for the quantity of N fixed per isolate, plant biomass, and the quantity of N per plant.

Grass-clover undersowing affects nitrogen dynamics in a grain legume–cereal arable cropping system

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

The effect of elevated atmospheric carbon dioxide concentration on the contribution of residual legume and fertilizer nitrogen to a subsequent wheat crop

This study investigated the residual contribution of legume and fertilizer nitrogen (N) to a subsequent crop under the effect of elevated carbon dioxide concentration ([CO2]). Field pea (Pisum sativum L.) was labeled in situ with 15N (by absorption of a 15N-labeled urea solution through cut tendrils) under ambient and elevated (700 μmol mol–1) [CO2] in controlled environment glasshouse chambers. Barley (Hordeum vulgare L.) and its soil were also labeled under the same conditions by addition of 15N-enriched urea to the soil. Wheat (Triticum aestivum L.) was subsequently grown to physiological maturity on the soil containing either 15N-labeled field pea residues (including 15N-labeled rhizodeposits) or 15N-labeled barley plus fertilizer 15N residues. Elevated [CO2] increased the total biomass of field pea (21 %) and N-fertilized barley (23 %), but did not significantly affect the biomass of unfertilized barley. Elevated [CO2] increased the C:N ratio of residues of field pea (18 %) and N-fertilized barley (19 %), but had no significant effect on that of unfertilized barley. Elevated [CO2] increased total biomass (11 %) and grain yield (40 %) of subsequent wheat crop regardless of rotation type in the first phase. Irrespective of [CO2], the grain yield and total N uptake by wheat following field pea were 24 % and 11 %, respectively, higher than those of the wheat following N-fertilized barley. The residual N contribution from field pea to wheat was 20 % under ambient [CO2], but dropped to 11 % under elevated [CO2], while that from fertilizer did not differ significantly between ambient [CO2] (4 %) and elevated [CO2] (5 %). The relative value of legume derived N to subsequent cereals may be reduced under elevated [CO2]. However, compared to N fertilizer application, legume incorporation will be more beneficial to grain yield and N supply to subsequent cereals under future (elevated [CO2]) climates.

Legume residue influence arbuscular mycorrhizal colonisation and P uptake by wheat

Legumes have been shown to increase growth and P uptake of the following cereal. This could, in part, be due to nutrients released by the decomposing legume residues. To investigate the effect of P added with legume residues on wheat growth, P uptake and arbuscular mycorrhizal (AM) colonisation, a number of experiments were conducted with different legume residues added to a soil with low P availability under conditions in which N was not limiting. Young and mature faba bean shoots (FYS, FMS) and mature chickpea shoots (CP) were added to soil at different rates (0.5–2%, w/w) with the P concentration being the greatest in the young faba bean shoots and least in the mature chickpea residues. Other treatments included addition of inorganic P at different rates (0–80 mg P kg−1). Available P, growth and P uptake and AM colonisation of wheat were measured after 6 weeks. As expected, inorganic P addition increased growth and P uptake but decreased AM colonisation. The effect of the residues was more complex. AM colonisation was not correlated with available P in the soil amended with residues, whereas there was significant negative correlation between available P and AM colonisation in the treatments with inorganic P. Addition of FYS increased wheat shoot growth and P uptake and decreased AM colonisation. However, FMS and CP addition not only decreased wheat growth and P uptake but also AM colonisation despite low soil P availability. It is concluded that addition of some legume residues can improve the growth of subsequent cereals, but others have a negative effect on wheat growth and AM colonisation which cannot be explained solely by soil P availability.

Pea–barley intercropping and short-term subsequent crop effects across European organic cropping conditions

Grain legumes are known to increase the soil mineral nitrogen (N) content, reduce the infection pressure of soil borne pathogens, and hence enhance subsequent cereals yields. Replicated field experiments were performed throughout W. Europe (Denmark, United Kingdom, France, Germany and Italy) to asses the effect of intercropping pea and barley on the N supply to subsequent wheat in organic cropping systems. Pea and barley were grown either as sole crops at the recommended plant density (P100 and B100, respectively) or in replacement (P50B50) or additive (P100B50) intercropping designs. In the replacement design the total relative plant density is kept constant, while the additive design uses the optimal sole crop density for pea supplementing with ‘extra’ barley plants. The pea and barley crops were followed by winter wheat with and without N application. Additional experiments in Denmark and the United Kingdom included subsequent spring wheat with grass-clover as catch crops. The experiment was repeated over the three cropping seasons of 2003, 2004 and 2005. Irrespective of sites and intercrop design pea–barley intercropping improved the plant resource utilization (water, light, nutrients) to grain N yield with 25–30% using the Land Equivalent ratio. In terms of absolute quantities, sole cropped pea accumulated more N in the grains as compared to the additive design followed by the replacement design and then sole cropped barley. The post harvest soil mineral N content was unaffected by the preceding crops. Under the following winter wheat, the lowest mineral N content was generally found in early spring. Variation in soil mineral N content under the winter wheat between sites and seasons indicated a greater influence of regional climatic conditions and long-term cropping history than annual preceding crop and residue quality. Just as with the soil mineral N, the subsequent crop response to preceding crop was negligible. Soil N balances showed general negative values in the 2-year period, indicating depletion of N independent of preceding crop and cropping strategy. It is recommended to develop more rotational approaches to determine subsequent crop effects in organic cropping systems, since preceding crop effects, especially when including legumes, can occur over several years of cropping.

Nitrogen dynamics following grain legumes and subsequent catch crops and the effects on succeeding cereal crops

The effects of faba bean, lupin, pea and oat crops, with and without an undersown grass-clover mixture as a nitrogen (N) catch crop, on subsequent spring wheat followed by winter triticale crops were determined by aboveground dry matter (DM) harvests, nitrate (NO3) leaching measurements and soil N balances. A 2½-year lysimeter experiment was carried out on a temperate sandy loam soil. Crops were not fertilized in the experimental period and the natural 15N abundance technique was used to determine grain legume N2 fixation. Faba bean total aboveground DM production was significantly higher (1,300 g m−2) compared to lupin (950 g m−2), pea (850 g m−2) and oat (1,100 g m−2) independent of the catch crop strategy. Faba bean derived more than 90% of its N from N2 fixation, which was unusually high as compared to lupin (70–75%) and pea (50–60%). No effect of preceding crop was observed on the subsequent spring wheat or winter triticale DM production. Nitrate leaching following grain legumes was significantly reduced with catch crops compared to without catch crops during autumn and winter before sowing subsequent spring wheat. Soil N balances were calculated from monitored N leaching from the lysimeters, and measured N-accumulation from the leguminous species, as N-fixation minus N removed in grains including total N accumulation belowground according to Mayer et al. (2003a). Negative soil N balances for pea, lupin and oat indicated soil N depletion, but a positive faba bean soil N balance (11 g N m−2) after harvest indicated that more soil mineral N may have been available for subsequent cereals. However, the plant available N may have been taken up by the grass dominated grass-clover catch crop which together with microbial N immobilization and N losses could leave limited amounts of available N for uptake by the subsequent two cereal crops.

Residual effect of clover-rich leys on soil nitrogen and successive grain crops

Legume-based leys form the basis for crop rotations in organic farming as they fix nitrogen (N) from the atmosphere for the succeeding crops. The age, yield, C:N, biological N fixation (BNF) and total N of red clover-grass leys were studied for their influence on yields, N uptake and N use efficiency (NUE) of the two sequential cereal crops planted after the leys. Mineral N in deeper soil (30-90 cm) was measured to determine N leaching risk. Altogether, four field experiments were carried out in 1994-1998 at two sites. The age of the ley had no significant effect on the yields and N uptake of the two subsequent cereals. Surprisingly, the residual effect of the leys was negligible, at 0–20 kg N ha-1yr-1. On the other hand, the yield and C:N of previous red clover-grass leys, as well as BNF-N and total-N incorporated into the soil influenced subsequent cereals. NUEs of cereals after ley incorporation were rather high, varying from 30% to 80%. This might indicate that other factors, such as competition from weeds, prevented maximal growth of cereals. The mineral N content deeper in the soil was mostly below 10 kg ha-1 in the sandy soil of Juva, but was 5-25 kg ha-1 in clayey soil of Mietoinen.;