Pig slurry fertilization in a double-annual cropping forage system under sub-humid Mediterranean conditions

In areas of Southern Europe with very intensive pig production, most of the pig slurry (PS) is applied as fertilizer. However, in the European Union, no more than 170 kg N ha⁻¹ year⁻¹ can be applied in nitrate vulnerable zones (NVZs) from livestock manures. In this context, a six-year trial was conducted for a maize-triticale double-annual forage cropping rotation under rainfed conditions. Four different N rates were applied (0, 170, 250 and 330 kg N ha⁻¹ year⁻¹), to evaluate their effect on crop yield, N uptake, unrecovered N and soil nitrate content. The corresponding PS rates were defined as zero (PS 0), low (PSL) medium (PSM) and high (PSH). The annual average dry matter (DM) yields (maize + triticale) for the PS fertilization treatments PS0, PSL, PSM and PSH were 12.6, 17.7, 20.2 and 22.0 Mg DM ha⁻¹, respectively. Maize DM yield was influenced mainly by weather conditions, and triticale DM yield was clearly influenced by initial soil NO₃⁻-N and PS fertilization rates. Unrecovered N was affected by PS fertilization rate and initial soil NO₃⁻-N content. A residual effect of the PS when applied to maize had an important effect on soil NO₃⁻-N and subsequent triticale DM yield. Moreover, total annual average unrecovered N, considering the sum of both crops (maize + triticale), were 91, 144, and 222 kg N ha⁻¹ in PSL, PSM and PSH, respectively. In order to avoid part of this unrecovered N, mainly by lixiviation of nitrates, PS fertilization in triticale should be applied as side dressing at tillering. The application of N, in the form of PS, at rates higher than the legally permitted maximum of 170 kg N ha⁻¹ year⁻¹, may result in better yields. However, high rates of PS fertilization may originate in significantly lower N use efficiency and a higher potential environmental impact in double-cropping systems, practiced in rainfed sub-humid Mediterranean conditions.     

Winter cereal yields as affected by animal manure and green manure in organic arable farming

The effect of nitrogen (N) supply through animal and green manures on grain yield of winter wheat and winter rye was investigated from 1997 to 2004 in an organic farming crop rotation experiment in Denmark on three different soil types varying from coarse sand to sandy loam. Two experimental factors were included in the experiment in a factorial design: (1) catch crop (with and without), and (2) manure (with and without). The four-course crop rotation was spring barley undersown with grass/clover – grass/clover – winter wheat or wheat rye – pulse crop. All cuttings of the grass–clover were left on the soil as mulch. Animal manure was applied as slurry to the cereal crops in the rotation in rates corresponding to 40% of the N demand of the cereal crops.Application of 50 kg NH₄–N ha^?1 in manure increased average wheat grain yield by 0.4–0.9 Mg DM ha^?1, whereas the use of catch crops did not significantly affect yield. The use of catch crops interacts with other management factors, including row spacing and weed control, and this may have contributed to the negligible effects of catch crops. There was considerable variation in the amount of N (100–600 kg N ha^?1 year^?1) accumulated in the mulched grass–clover cuttings prior to ploughing and sowing of the winter wheat. This was reflected in grain yield and grain N uptake. Manure application to the cereals in the rotation reduced N accumulation in grass–clover at two of the locations, and this was estimated to have reduced grain yields by 0.1–0.2 Mg DM ha^?1 depending on site. Model estimations showed that the average yield reduction from weeds varied from 0.1 to 0.2 Mg DM ha^?1. The weed infestation was larger in the manure treatments, and this was estimated to have reduced the yield benefit of manure application by up to 0.1 Mg DM ha^?1. Adjusting for these model-estimated side-effects resulted in wheat grain yields gains from manure application of 0.7–1.1 Mg DM ha^?1.The apparent recovery efficiency of N in grains (N use efficiency, NUE) from NH₄–N in applied manure varied from 23% to 44%. The NUE in the winter cereals of N accumulated in grass–clover cuttings varied from 14% to 39% with the lowest value on the coarse sandy soil, most likely due to high rates of N leaching at this location. Both NUE and grain yield benefit in the winter cereals declined with increasing amounts of N accumulated in the grass–clover cuttings. The model-estimated benefit of increasing N input in grass–clover from 100 to 500 kg N ha^?1 varied from 0.8 to 2.0 Mg DM ha^?1 between locations. This is a considerably smaller yield increase than obtained for manure application, and it suggests that the productivity in this system may be improved by removing the cuttings and applying the material to the cereals in the rotation, possibly after digestion in a biogas reactor.Cereal grain protein content was increased more by the N in the grass–clover than from manure application, probably due to different timing of N availability. Green-manure crops or manures with a relatively wide C:N ratio may therefore be critical for ensuring sufficiently high protein contents in high yielding winter wheat for bread making.     

Influence of sulfur on apparent N-use efficiency,yield and quality of oilseed rape (Brassica napus L.) grown on a calcareous soil

In the Lorraine region, major soils used for winter oilseed rape are calcareous. Across two pot and two field experiments, we studied the influence of sulfur applied at different levels on apparent N-use efficiency (ANU), yield, glucosinolate (GLS) and oil content of seeds. The soil received a constant dose of 200 kg N ha⁻¹ as ammonium nitrate, urea or cow slurry and three levels of S: 0, 30 and 75 kg ha⁻¹ as ammonium thiosulfate (ATS), MgSO₄ or ATS plus MgSO₄. Apparently, oilseed rape is a N-inefficient crop as revealed by low ANU values which varied within 36 and 53% from field experiment versus 25 and 61% under controlled conditions. In both cases, S additions improved N-use efficiency only at the highest dose of 75 kg S ha⁻¹, which is not attained by ATS with 35 kg S ha⁻¹ (10% v/v). S fertilization increased the GLS contents that were found to be negatively correlated with plant N/S uptake ratios observed at maturity. The most important increase in GLS content by 52% was noted with cow slurry in the pot experiment. But, as a whole, the GLS levels remain below the European norm of 18 μmol g seed⁻¹. Moreover, the oil content (% DM) of seeds decreased (but the total production increased) when the soil was fertilized with N and with or without S. The results showed that N and S nutrition during the growth were tightly linked. Their interactions, as reflected by plant uptake, are synergistic at optimum rates and antagonistic at excessive levels of one of the both. Collectively, the results indicate that S fertilization is required to improve N-use efficiency and thereby maintaining a sufficient oil level and fatty acid quality.     

Strategies to optimize nitrogen efficiency when fertilizing with pig slurries in dryland agricultural systems

In dryland agricultural systems, pig slurry (PS) is usually applied to cereal crops only at sowing, and slurries accumulate for the rest of the year in pits. In this context, a four-year experiment was established in order to evaluate the feasibility of PS applications at the barley or wheat tillering stage. The main treatments were PS either applied at sowing (25 Mg ha⁻¹) or not, but they alternated after a two-year period. Both were annually combined with eight side-dressing treatments at cereal tillering: mineral N as NH₄NO₃ (M; 60 or 120 kg N ha⁻¹ yr⁻¹), PS from fattening pigs (PSf; 17, 30, 54 Mg ha⁻¹ yr⁻¹), PS from sows (PSs; 25, 45, 81 Mg ha⁻¹ yr⁻¹) and a treatment without N. The combined fertilization treatments were 18 plus a control (no N applied). In the context of crop rotation, the biennial alternation of PS applied at sowing allowed the control of soil nitrate increments, while PS side-dressing improved N recovery compared with a unique application at sowing. The highest yields (>3.6 Mg ha⁻¹ yr⁻¹) were obtained with an annual average (4-yr) N rate close to 173 kg N ha⁻¹ (±40 kg N ha⁻¹). The best overall strategies corresponded to PSs side-dressings of 50–90 kg N ha⁻¹. These PSs rates also recorded the highest values on the five calculated N-efficiency indexes, which were higher than or similar to results from M side-dressings or those recorded in the literature. These similarities (M vs. PSs) were also shown by the reduction of unaccounted-for N inside the overall N balance. Thus, split PS application during the crop cycle is a sound fertilization option in dryland systems.     

Nitrogen fertilisation of irrigated maize under Mediterranean conditions

Nitrogen fertilisation of maize (Zea mays L.) has become an important economic and environmental issue, especially in high-yielding irrigated Mediterranean areas. Producers have traditionally applied more N fertiliser than required and, as a result, some environmental problems have appeared in recent decades. A 4-year study (2002–2005) was conducted and six N rates (0, 100, 150, 200, 250 and 300 kg N ha^?1 year^?1) were compared. Before planting 50 kg N ha^?1 were applied. The rest of the N was applied in two sidedresses, the first at V3–V4 developing stage and the second at V5–V6. Yield, biomass, grain N uptake, plant N uptake and SPAD-units were greatly influenced by both N fertilisation rate and soil NO₃^?-N content before planting and fertilising [Nini (0–90 cm)]. At the beginning of the experiment, Nini was very high (290 kg NO₃^?-N ha^?1) and there was therefore no yield response to N fertilisation in 2002. In 2003, 2004 and 2005, maximum grain yields were achieved with 96, 153 and 159 kg N ha^?1, respectively. Results showed that N fertilisation recommendations based only on plant N uptake were not correct and that Nini should always be taken into account. On the other hand, the minimum amount of N available for the crop [N applied with fertilisation plus Nini (0–90 cm)] necessary to achieve maximum grain yields was 258 kg N ha^?1. This value was similar to plant N uptake, suggesting that available N was able to predict N maize requirements and could be an interesting tool for improving maize N fertilisation.     

Effect of biogas digestate,animal manure and mineral fertilizer application on nitrogen flows in biogas feedstock production

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

Effect of spring fertilization on ecosystem services of organic wheat and clover relay intercrops

Nitrogen (N) deficiency and weed infestation are main factors limiting yield and yield stability in organic wheat. Organic fertilizers may be used to improve crop performance but off-farm input costs tend to limit profitability. Instead, forage legumes may be inserted into the crop rotation to improve the N balance and to control weed infestation. In opposition to simultaneous cropping, relay intercropping of legumes in organic winter wheat limits resource competition for the legume cover crop, without decreasing the performance of the associated wheat.The aim of this study is to evaluate the effect of spring organic fertilization on the performance of intercropped legumes and wheat, and on services provided by the legume cover.Two species of forage legumes (Trifolium pratense L. and Trifolium repens L.) were undersown in winter wheat (Triticum aestivum L. cv Lona) in five organic fields during two consecutive crop seasons. Organic fertilizer was composed of feather meal and applied on wheat at legume sowing. The cover crop was maintained after the wheat harvest and destroyed just before sowing maize.Spring organic nitrogen fertilization increased wheat biomass (+35%), nitrogen (+49%), grain yield (+40%) and protein content (+7%) whatever the intercropping treatment. At wheat harvest, red clover biomass was significantly higher than white clover one (1.4 vs. 0.7 t ha⁻¹). Nitrogen fertilization decreased forage legume above-ground biomass at wheat harvest, at approximately 0.5 t ha⁻¹ whatever the specie. No significant difference in forage legume biomass production was observed at cover killing. Nitrogen accumulation in legume above-ground tissues was significantly higher for white clover than for red clover. Both red and white clover species significantly decreased weed infestation at this date. Nitrogen fertilization significantly increased weed biomass whatever the intercropping treatment and decreased nitrogen accumulation in both clover species (−12%).We demonstrated that nitrogen fertilization increased yield of wheat intercropped with forage legume while the performance of legumes was decreased. Legume growth was modified by spring fertilization whatever the species.     

Delayed permanent water rice production systems do not improve the recovery of 15N-urea compared to continuously flooded systems

Crop recovery of nitrogen (N) fertiliser in flooded rice systems is low relative to fertiliser N recoveries in aerobic crops, and the N losses have environmental consequences. Recent water shortages across the globe have seen a move towards alternative water management strategies such as delayed permanent water (DPW, also known as delayed flood). To investigate whether N fertiliser regimes used in DPW systems result in greater recovery of N fertiliser than traditional continuously flooded (CF) rice systems, we conducted a multi-N rate field trial using ¹⁵N-labelled urea. Around 27% of the ¹⁵N-labelled fertiliser was recovered in aboveground biomass at maturity, regardless of water regime or N fertiliser rate, and approximately 20% recovered in the soil to 300 mm depth. Plants in the CF system accumulated more total N at each rate of applied N fertiliser than plants in the DPW system due to greater exploitation of native soil N reserves, presumably because the earlier application of N fertiliser in the CF systems led to greater early growth and higher crop N demand. The greater crop biomass production as a result of higher N uptake in the CF system did not increase grain yields above those observed in the DPW system, likely due to cold weather damage. In the following season at the same site, a single N rate (150 kg N ha⁻¹) trial found no significant differences in crop N uptake, biomass yields, grain yields or ¹⁵N-labelled urea recovery in DPW, CF and drill sown-CF (DS-CF) treatments. However, owing to higher ¹⁵N fertiliser recovery in the 0–100 mm soil horizon, total plant + soil recovery of ¹⁵N was significantly higher in the CF treatment (63%) than the DS-CF and DPW treatments (around 50% recoveries). The loss of 40–50% of the applied N (presumably as NH₃ or N₂) in both seasons regardless of watering regime suggests that new fertiliser N management strategies beyond optimising the rate and timing of urea application are needed, particularly in light of increasing N fertiliser prices.     

The new nitrification inhibitor 3,4-dimethylpyrazole succinic (DMPSA) as an alternative to DMPP for reducing N2O emissions from wheat crops under humid Mediterranean conditions

Nowadays agricultural practices are based in the use of N fertilizers which can lead to environmental N losses. These losses can occur as nitrous oxide (N₂O) emissions as result of the microbial processes of nitrification and denitrification. N₂O together with carbon dioxide (CO₂) and methane (CH₄) are the strongest greenhouse gases (GHG) associated with agricultural soils. Nitrification inhibitors (NI) have been developed with the aim of decreasing fertilizer-induced N losses and increasing N efficiency. One of the most popular NI is the 3,4-dimethylpyrazol phosphate (DMPP) which have proven to be an advisable strategy to mitigate GHG emissions while maintaining crops yield. A new NI, 3,4-dimethylpyrazole succinic (DMPSA), has been developed. The objective of this study was to compare the impact of the new nitrification inhibitor DMPSA on greenhouse gases emissions, wheat yield and grain protein with respect to DMPP. For this purpose a field-experiment was carried out for two years. Fertilizer dose, with and without NIs, was 180 kg N ha⁻¹ applied as ammonium sulphate (AS) split in two applications of 60 kg N ha⁻¹ and 120 kg N ha⁻¹, respectively. A single application of 180 kg N ha⁻¹ of AS with NIs was also made. An unfertilized treatment was also included. The new nitrification inhibitor DMPSA reduces N₂O emissions up to levels of the unfertilized control treatment maintaining the yield and its components. The DMPSA shows the same behavior as DMPP in relation to N₂O fluxes, as well as wheat yield and quality. In spite of applying a double dose of N at stem elongation than at tillering, N₂O losses from that period are lower than at tillering as a consequence of the influence of soil water content and temperature reducing the N₂O/N₂ ratio by denitrification. NI efficiency in reducing N₂O losses is determined by the magnitude of the losses from the AS treatment.     

Beet vinasse applied to wheat under dryland conditions affects soil properties and yield

The effect of six doses of beet vinasse (0, 3, 6, 10, 20 and 40 t ha⁻¹, respectively) on wheat (Triticum aestivum cv. Cajeme) yield in dryland conditions (Guadalquivir Valley, Andalusia, Spain) for 3 years on a Typic Xerofluvent was studied. The results showed that at low doses, beet vinasse is of agricultural interest due mainly to its organic matter concentration. The application of this byproduct to the soil increased soil microbial biomass and mineralization of its organic matter increased NO₃⁻–N concentrations in soil. This caused an increase in grain yield in the three seasons. When the vinasse was applied with high doses, NO₃⁻–N concentrations in soil, soil microbial biomass, soil structure, bulk density, electric conductivity, nutrient uptake, crop yield and grain quality were negatively affected. We assume that the high amounts of monovalent cations, particularly Na⁺, and of fulvic acids, which had been transported into the soil by the vinasse, destabilized the soil structure. This may have led to anaerobic soil conditions being presumably responsible for restricted N mineralization or even for denitrification. This explains the lower N supply to the crops reflected by the low N concentrations in the leaves of treatments A4 and A5.     

Contribution of green manure legumes to nitrogen dynamics in traditional winter wheat cropping system in the Loess Plateau of China

Excessive application of N fertilizer in pursuit of higher yields is common due to poor soil fertility and low crop productivity. However, this practice causes serious soil depletion and N loss in the traditional wheat cropping system in the Loess Plateau of China. Growing summer legumes as the green manure (GM) crop is a viable solution because of its unique ability to fix atmospheric N₂. Actually, little is known about the contribution of GM N to grain and N utilization in the subsequent crop. Therefore, we conducted a four-year field experiment with four winter wheat-based rotations (summer fallow-wheat, Huai bean–wheat, soybean–wheat, and mung bean–wheat) and four nitrogen fertilizer rates applied to wheat (0, 108, 135, and 162 kg N/ha) to investigate the fate of GM nitrogen via decomposition, utilization by wheat, and contribution to grain production and nitrogen economy through GM legumes. Here we showed that GM legumes accumulated 53–76 kg N/ha per year. After decomposing for approximately one year, more than 32 kg N/ha was released from GM legumes. The amount of nitrogen released via GM decomposition that was subsequently utilized by wheat was 7–27 kg N/ha. Incorporation of GM legumes effectively replaced 13–48% (average 31%) of the applied mineral nitrogen fertilizer. Additionally, the GM approach during the fallow period reduced the risk of nitrate-N leaching to depths of 0–100 cm and 100–200 cm by 4.8 and 19.6 kg N/ha, respectively. The soil nitrogen pool was effectively improved by incorporation of GM legumes at the times of wheat sowing. Cultivation of leguminous GM during summer is a better option than bare fallow to maintain the soil nitrogen pool, and decrease the rates required for N fertilization not only in the Loess Plateau of China but also in other similar dryland regions worldwide.     

Energy balance of winter oilseed rape (Brassica napus L.) cropping as related to nitrogen supply and preceding crop

Data from a field experiment (1995–2000) conducted on a fertile sandy loess in the Hercynian dry region of central Germany were used to determine the energy efficiency of winter oilseed rape (Brassica napus L.) as affected by previous crop and nitrogen (N) fertilization. Depending on the previous crop, winter oilseed rate was cultivated in two different crop rotations: (1) winter barley (Hordeum vulgare L.)–winter oilseed rape–winter wheat (Triticum aestivum L.), and (2) pea (Pisum sativum L.)–winter oilseed rape–winter wheat. Fertilizer was applied to winter oilseed rape as either calcium ammonium nitrate (CAN) or cattle manure slurry. The N rates applied to winter oilseed rape corresponded to 0, 80, 160 and 240 kg N ha⁻¹ a⁻¹.Results revealed that different N management strategies influenced the energy balance of winter oilseed rape. Averaged across years, the input of energy to winter oilseed rape was highly variable ranging from 7.42 to 16.1 GJ ha⁻¹. Lowest energy input occurred when unfertilized winter oilseed rape followed winter barley, while the highest value was obtained when winter oilseed rape received 240 kg N ha⁻¹ organic fertilization and followed winter barley. The lowest energy output (174 GJ ha⁻¹), energy from seed and straw of winter oilseed rape, was observed when winter oilseed rape receiving 80 kg N ha⁻¹ as organic fertilizer followed winter barley. The energy output increased to 262 GJ ha⁻¹ for winter oilseed rape receiving 240 kg N ha⁻¹ as mineral fertilizer followed pea. The energy efficiency was determined using the parameters energy gain (net energy output), energy intensity (energy input per unit grain equivalent GE; term GE is used to express the contribution that crops make to the nutrition of monogastric beings), and output/input ratio. The most favourable N rate for maximizing energy gain (250 GJ ha⁻¹) was 240 kg N ha⁻¹, while that needed for minimum energy intensity (91.3 MJ GE⁻¹) was 80 kg N ha⁻¹ and for maximum output/input ratio (29.8) was 0 kg N ha⁻¹.     

Sugar beet rotation effects on soil organic matter and calculated humus balance in Central Germany

In order to quantify the influence of land use systems on the level of soil organic matter (SOM) to develop recommendations, long-term field studies are essential. Based on a crop rotation experiment which commenced in 1970, this paper investigated the impact of crop rotations involving increased proportions of sugar beet on SOM content. To this end, soil samples were taken in 2010 and 2012 from the following crop rotation sequences: sugar beet–sugar beet–winter wheat–winter wheat (SB–SB–WW–WW = 50%), sugar beet–sugar beet–sugar beet–winter wheat (SB–SB–SB–WW = 75%), sugar beet–grain maize (SB–GM = 50%) and sugar beet-monoculture (SB = 100%); these were analysed in terms of total organic carbon (TOC) and microbial biomass carbon (MBC) content, MBC/TOC ratio and the TOC stocks per hectare. In addition, humus balances were created (using the software REPRO, reference period 12 years) in order to calculate how well the soil was supplied with organic matter. In the field experiment, harvest by-products (WW and GM straw as well as SB leaves) were removed. After 41 years, no statistically significant differences were measured between the crop rotations for the parameters TOC, MBC, MBC/TOC ratio and the TOC stock per hectare. However, the calculated humus balance was significantly affected by the crop rotation. The calculated humus balance became increasingly negative in the order SB–SB–WW–WW, SB–SB–SB–WW, SB monoculture and SB–GM, and correlated with the soil parameters. The calculated humus balances for the reference period did not reflect the actual demand for organic matter by the crop rotations, but instead overestimated it.     

Tillage,cover crops,and nitrogen fertilization effects on soil nitrogen and cotton and sorghum yields

Sustainable soil and crop management practices that reduce soil erosion and nitrogen (N) leaching, conserve soil organic matter, and optimize cotton and sorghum yields still remain a challenge. We examined the influence of three tillage practices (no-till, strip till and chisel till), four cover crops {legume [hairy vetch (Vicia villosa Roth)], nonlegume [rye (Secaele cereale L.)], vetch/rye biculture and winter weeds or no cover crop}, and three N fertilization rates (0, 60–65 and 120–130 kg N ha⁻¹) on soil inorganic N content at the 0–30 cm depth and yields and N uptake of cotton (Gossypium hirsutum L.) and sorghum [Sorghum bicolor (L.) Moench]. A field experiment was conducted on Dothan sandy loam (fine-loamy, siliceous, thermic, Plinthic Paleudults) from 1999 to 2002 in Georgia, USA. Nitrogen supplied by cover crops was greater with vetch and vetch/rye biculture than with rye and weeds. Soil inorganic N at the 0–10 and 10–30 cm depths increased with increasing N rate and were greater with vetch than with rye and weeds in April 2000 and 2002. Inorganic N at 0–10 cm was also greater with vetch than with rye in no-till, greater with vetch/rye than with rye and weeds in strip till, and greater with vetch than with rye and weeds in chisel till. In 2000, cotton lint yield and N uptake were greater in no-till with rye or 60 kg N ha⁻¹ than in other treatments, but biomass (stems + leaves) yield and N uptake were greater with vetch and vetch/rye than with rye or weeds, and greater with 60 and 120 than with 0 kg N ha⁻¹. In 2001, sorghum grain yield, biomass yield, and N uptake were greater in strip till and chisel till than in no-till, and greater in vetch and vetch/rye with or without N than in rye and weeds with 0 or 65 kg N ha⁻¹. In 2002, cotton lint yield and N uptake were greater in chisel till, rye and weeds with 0 or 60 kg N ha⁻¹ than in other treatments, but biomass N uptake was greater in vetch/rye with 60 kg N ha⁻¹ than in rye and weeds with 0 or 60 kg N ha⁻¹. Increased N supplied by hairy vetch or 120–130 kg N ha⁻¹ increased soil N availability, sorghum grain yield, cotton and sorghum biomass yields, and N uptake but decreased cotton lint yield and lint N uptake compared with rye, weeds or 0 kg N ha⁻¹. Cotton and sorghum yields and N uptake can be optimized and potentials for soil erosion and N leaching can be reduced by using conservation tillage, such as no-till or strip till, with vetch/rye biculture cover crop and 60–65 kg N ha⁻¹. The results can be applied in regions where cover crops can be grown in the winter to reduce soil erosion and N leaching and where tillage intensity and N fertilization rates can be minimized to reduce the costs of energy requirement for tillage and N fertilization while optimizing crop production.     

Effects of planting soybean in summer fallow on wheat grain yield,total N and Zn in grain and available N and Zn in soil on the Loess Plateau of China

Dryland wheat is the major contributor to wheat production in the world, where water deficiency and poor soil fertility are key factors limiting wheat grain yields and nutrient concentrations. A field experiment was carried out from June 2008 to June 2011 at Shilipu (latitude 35.12°N, longitude 107.45°E and altitude 1200 m above sea level) on the Loess Plateau (a typical dryland) in China, to investigate the effects of rotation with soybean (Glycine max) green manure (GM) on grain yield, total N and total Zn concentrations in subsequent wheat (Triticum aestivum L.), and on nitrate-N and available Zn in the soil. The benefits of crop rotation with soybean GM on wheat grain yields became more evident with time. In the second and third years, the grain yields of wheat rotated with soybean GM reached 4871 and 5089 kg ha⁻¹ at the 108 kg N ha⁻¹ rate. These yields were 21% and 12% higher than the highest yields of wheat under a fallow-winter wheat (FW) rotation. Rotation with soybean GM reduced the amount of N fertilizer required to obtain wheat grain yields and biomass levels similar to wheat grown in the FW rotation by 20–33%. In the first 2 years, average grain N concentrations over all N rates increased by 6% and 12%, and those of Zn increased by 26% and 14% under the soybean GM-winter wheat (SW) rotation, compared with the FW rotation. The increased grain N and Zn concentrations were found to be related to the increased concentrations of nitrate-N and available Zn in the soil, particularly at the sowing of winter wheat. However, grain N and Zn concentrations were not improved by rotation with soybean GM in the third year. This was attributed to the dilution effect caused by the more grain yield increase than its nutrient export. In conclusion, planting soybean for GM in fallow fields reduced the need for N fertilizer to enhance wheat yields in this dryland region. Change in wheat grain N and Zn concentrations was related to soil nutrient concentrations, and to the balance between increased grain yield and its nutrient export.     

Mechanical control of clover improves nitrogen supply and growth of wheat in winter wheat/white clover intercropping

The major objective for clover in a winter wheat/white clover intercropping system is to supply nitrogen (N) for the wheat. A field experiment was repeated in 2 years on a loamy sand in Denmark to investigate the possibilities for increasing N supply to the winter wheat by cutting and mulching the clover between the wheat rows. The clover was cut with a weed brusher on three different dates in each year.Intercropped wheat with unbrushed clover had a lower grain yield than wheat as a sole crop. Brushing increased wheat N uptake and wheat grain yields. Intercropping with two or three brushing dates gave higher wheat yields than wheat as the sole crop. The largest increases in grain N uptake, 21–25 kg N ha⁻¹, were obtained for the brushings around wheat flag leaf emergence. The highest yield increases with a single brushing, 0.98–1.11 Mg DM ha⁻¹, were obtained when brushing was performed during the stem elongation phase. The largest grain yields for treatments with two brushings were obtained with a first brushing at start of stem elongation and a second around flag leaf emergence. The first brushing probably provided N to increase the wheat leaf area index and thus the light interception, while the second brushing provided N to sustain the leaf area during grain filling and reduced clover biomass and therefore competition for water. Intercropping wheat and clover increased grain N concentrations by 0.11–0.39%-point compared with wheat as a sole crop. Intercropping may thus offer possibilities for improving the bread-making quality of organically grown wheat.     

Organic fertilizer effects on growth,crop yield,and soil microbial biomass indices in sole and intercropped peas and oats under organic farming conditions

In a field experiment, peas (Pisum sativum L.) and oats (Avena sativa L.) were grown as sole crops and intercrops, fertilized with horse manure and yard-waste compost derived from shrub and garden cuttings at 10 t C ha⁻¹ each. The objectives were to compare the effects of these organic fertilizer and cropping system in organic farming on (a) yield of peas and oats, grown as the sole crop or intercropped, as well as N₂ fixation and photosynthetic rates, (b) the yield of wheat as a succeeding crop, (c) microbial biomass indices in soil and roots, and (d) microbial activity estimated by the CO₂ evolution rate in the field and the amount of organic fertilizers, recovered as particulate organic matter (POM). In general, organic fertilizer application improved nodule dry weight (DW), photosynthetic rates, N₂ fixation, and N accumulation of peas as well as N concentration in oat grain. Averaged across fertilizer treatments, pea/oat intercropping significantly decreased nodule DW, N₂ fixation and photosynthetic rate of peas by 14, 17, and 12%, respectively, and significantly increased the photosynthetic rate of oats by 20%. However, the land equivalent ratio (LER) of intercropped peas and oats exceeded 1.0, indicating a yield advantage over sole cropping. Soil microbial biomass was positively correlated with pea dry matter yields both in sole and intercropped systems. Organic fertilizers increased the contents of microbial biomass C, N, P, and fungal ergosterol in soil and CO₂ production, whereas the cropping system had no effects on these microbial indices. According to the organic fertilizer recovered as POM, 70% (manure) and 64% (compost) of added C were decomposed, but only 39% (manure) and 13% (compost) could be attributed to CO₂–C during a 101-day period. This indicated that horse manure was more readily available to soil microorganisms than compost, leading to increased grain yields of the succeeding winter wheat.     

Long-term effects of lime and phosphogypsum application on tropical no-till soybean–oat–sorghum rotation and soil chemical properties

Root growth, nutrition and crop yield can be affected by soil chemical modifications caused by superficial limestone and phosphogypsum application in a no-till system. Using this approach, this study was conducted in southeastern Brazil, continuing an experiment that has been on-going since 2002 with the objective of evaluating the residual effects of the surface application of lime and phosphogypsum on the soil chemical characteristics and the root growth, nutrition and yield of soybean, black oat and sorghum in a dry winter region cultivated in 2008/2009 and 2009/2010. The experimental design was a randomized block with 4 replications. The treatments were applied in November 2004 and were as follows: original conditions, limestone application (2000 kg ha⁻¹), phosphogypsum application (2100 kg ha⁻¹), and limestone (2000 kg ha⁻¹) + phosphogypsum (2100 kg ha⁻¹) application. Superficial liming with or without phosphogypsum reduced the surface and subsurface soil acidity 5 years after application in the no-till system. The movement of Ca²⁺ and Mg²⁺ from the surface layer into the subsoil over time was evident. The phosphogypsum application associated with liming increased the Ca²⁺ levels throughout the soil profile. Liming maintained high levels of Mg²⁺ throughout the soil profile with or without phosphogypsum application. The organic matter content increased with liming with or without phosphogypsum, indicating that in the long term, these practices can increase the C accumulation. Phosphogypsum application had a residual effect on the SO₄-S levels, and high sulphate concentrations were observed in the subsoil after 5 years. Superficial liming improved crop nutrition and, when associated with phosphogypsum, increased Ca absorption by soybean and sorghum, as reflected in the increased yields of these crops.     

Low-input cropping systems to reduce input dependency and environmental impacts in maize production: A multi-criteria assessment

Intensification of cropping systems in recent decades has increased their productivity but affected air, soil and water quality. These harmful environmental impacts are exacerbated in Maize Monoculture (MM) and hasten the need for solutions to overcome the trade off between crop yield and environmental impacts. In a three-year cropping systems experiment, a conventional intensive maize monoculture (MM_Conv), with a winter bare fallow, deep soil tillage, non-limiting irrigation was compared to three Low Input Cropping Systems (LI-CS) designed as alternatives to the conventional system. They were managed with decision-rules implemented to reach specific objectives of input reduction. The LI-CS designed with Integrated Weed Management (IWM) techniques and other sustainable cropping practices, were:(i) MM_LI—an IWM Low Input MM; (ii) MM_CT—a Conservation Tillage combined with cover crop MM; and (iii) Maize-MSW—an IWM maize grown in rotation with soybean and wheat. A comprehensive multi-criteria assessment was carried out to quantify the agronomic, economic, social, and environmental performances of each system. A canonical discriminant analysis of performance metrics revealed large differences between the four systems. Yields were significantly higher in MM_Conv (11.0 Mg ha⁻¹) and MM_LI (10.3 Mg ha⁻¹) than in Maize-MSW (8.6 Mg ha⁻¹) and MM_CT (7.8 Mg ha⁻¹). MM_CT had the largest weed infestation (density and biomass) despite the greatest use of herbicides. The Herbicide Treatment Frequency Index (HTFI), used to indicate differences in herbicide use, revealed that the MM_LI (HTFI = 1.0) and Maize-MSW (1.1) halved the herbicide use as compared to the MM_Conv (2.1), despite having similar weed abundance levels. The LI-CS, especially MM_CT, produced high biomass winter cover crops and then less nitrogen fertilization was required as compared to MM_Conv. Gross margins in the MM_LI (1254 € ha⁻¹) and MM_Conv (1252 € ha⁻¹) were higher than the MM_CT (637 € ha⁻¹) and Maize-MSW (928 € ha⁻¹). MM_LI and MM_Conv had similar labour requirements. Water drainage, pesticide leaching, energy use, and estimated greenhouse gas emissions were higher in MM_Conv than in the LI-CS in most years. Results from this research show good potential for the MM_LI to reduce the environmental impacts of MM_Conv while maintaining its economic and social performance.     

Effect of elevated carbon dioxide and temperature on phosphorus uptake in tropical flooded rice (Oryza sativa L.)

A field experiment was carried out to assess the impact of elevated carbon dioxide (CO₂) and temperature on phosphorous (P) nutrition in relation to organic acids exudation, soil microbial biomass P (MBP) and phosphatase activities in tropical flooded rice. Rice (cv. Naveen) was grown under chambered control (CC), elevated CO₂ (EC, 550 μmol mol⁻¹) and elevated CO₂ + elevated temperature (ECT, 550 μmol mol⁻¹ and 2 °C more than CC) in a tropical flooded soil under open top chambers (OTCs) along with unchambered control (UC) for three years. Root exudates were analyzed at different growth stages of rice followed by organic acids determination. Rhizospheric soil was used for analysis of soil phosphatase, MBP and available P. The total organic carbon (TOC) in root exudates was increased by 27.5% and 30.2% under EC and ECT, respectively over CC. Four different types of organic acids viz. acetic acid (AA), tartaric acid (TA), malic acid (MA) and citric acid (CA) were identified and quantified as dominant in root exudates, concentration of these was in the order of TA > MA > AA > CA. The TA, MA, AA and CA content were increased by 34.4, 31.1, 38.7 and 58.3% under ECT compared to that of UC over the period of 3 years. The P uptake in shoot, root and grain under elevated CO₂ increased significantly by 29, 28 and 22%, respectively than CC. Soil MBP, acid and alkaline phosphatase activity was significantly higher under elevated CO₂ by 35.1%, 27 and 36%, respectively, compared to the CC. Significant positive relationship exists among the organic acid exudation, MBP, phosphatase activities and P uptake by rice. The enhanced organic acid in root exudates coupled with higher soil phosphatase activities under elevated CO₂ resulted in increased rate of soil P solubilization leading to higher plant P uptake.