Nitrogen leaching and crop availability in manured catch crop systems in Sweden

Results are presented from five years (1990–1995) of a field leaching experiment on a sandy soil in south-west Sweden. The aim was to study N leaching, change in soil organic N and N mineralization in cropping systems with continuous use of liquid manure (two application rates) and catch crops. N leaching from drains, N uptake in crops and mineral N in the soil were measured. Simulation models were used to calculate the N budget and N mineralization in the soil and to make predictions of improved fertilization strategies in relation to manure applications and changing the time for incorporation of catch crops. In treatments without catch crops, a normal and a double application of manure increased average N leaching by 15 and 34%, respectively, compared to treatment with commercial fertilizer. Catch crops reduced N leaching by, on average, 60% in treatments with a normal application of manure and commercial fertilizer, but only by 35% in the treatment with double the normal application rate of manure. Incorporation of catch crops in spring increased simulated net N mineralization during the crop vegetation period, and also during early autumn. In conclusion, manured systems resulted in larger N leaching than those receiving commercial fertilizer, mainly due to larger applications of mineral N in spring. More careful adaptation of commercial N fertilization with respect to the amounts of NH₄-N applied with manure could, according to the simulations, reduce N leaching. Under-sown ryegrass catch crops effectively reduced N leaching in manured systems. Incorporating catch crop residues in late autumn instead of spring might be preferable with respect to N availability in the soil for the next crop, and would not increase N leaching.     

Effects of a catch crop and reduced nitrogen fertilization on nitrogen leaching in greenhouse vegetable production systems

Greenhouse vegetable cultivation has greatly increased productivity but has also led to a rapid accumulation of nitrate in soils and probably in plants. Significant losses of nitrate–nitrogen (NO₃-N) could occur after heavy N fertilization under open-field conditions combined with high precipitation in the summer. It is urgently needed to improve N management under the wide spread greenhouse vegetable production system. The objective of this study was to evaluate the effects of a summer catch crop and reduced N application rates on N leaching and vegetable crop yields. During a 2-year period, sweet corn as an N catch crop was planted between vegetable crops in the summer season under 5 N fertilizer treatments (0, 348, 522, 696, and 870 kg ha⁻¹) in greenhouse vegetable production systems in Tai Lake region, southern China. A water collection system was installed at a depth of 0.5 m in the soil to collect leachates during the vegetable growing season. The sweet corn as a catch crop reduced the total N concentration from 94 to 59 mg l⁻¹ in leached water and reduced the average soil nitrate N from 306 to 195 mg kg⁻¹ in the top 0.1-m soil during the fallow period of local farmers’ N application rate (870 kg ha⁻¹). Reducing the amount of N fertilizer and using catch crop during summer fallow season reduced total N leaching loss by 50 and 73%, respectively, without any negative effect on vegetable yields.     

Effect of climate on the recovery in crop and soil of15N-labelled fertilizer applied to wheat

Data was assembled from experiments on the fate of¹⁵N-labelled fertilizer applied to wheat (Triticum spp.) grown in different parts of the world. These data were then ranked according to the annual precipitation-evaporation quotient for each experimental location calculated from the average long-term values of precipitation and potential evaporation. Percentage recovery of¹⁵N fertilizer in crop and soil varied with location in accordance with the precipitation-evaporation quotient. In humid environments more¹⁵N fertilizer was recovered in the crop than in the soil, while in dry environments more¹⁵N fertilizer was recovered in the soil than in the crop. Irrespective of climatic differences between locations 20% (on average) of the¹⁵N fertilizer applied to wheat crops was unaccounted for at harvest. Most of the¹⁵N fertilizer remaining in the soil was found in the 0–30 cm layer. The most likely explanation of these differences is that wheat grown in dry environments has a greater root:shoot ratio than wheat grown in humid environments and, further, that the residue of dryland crops have higher C/N ratios. Both factors could contribute to the greater recovery of¹⁵N fertilizer in the soil in dry environments than in humid ones.     

Recovery of 15N-labelled fertilizer applied to winter wheat and perennial ryegrass crops and residual 15N recovery by succeeding wheat crops under different crop residue management practices

The recovery of ¹⁵N-labelled fertilizer applied to a winter wheat (120 kg N ha^–1) and also a perennial ryegrass (60 kg N ha^–1) crop grown for seed for 1 year in the Canterbury region of New Zealand in the 1993/94 season was studied in the field. After harvests, ryegrass and wheat residues were subjected to four different residue management practices (i.e. ploughed, rotary hoed, mulched and burned) and three subsequent wheat crops were grown, the first succeeding wheat crop sown in 1994/95 to examine the effects of different crop residue management practices on the residual ¹⁵N recovery by succeeding wheat crops. Total ¹⁵N recoveries by the winter wheat and ryegrass (seed, roots and tops) were 52% and 41%, respectively. Corresponding losses of ¹⁵N from the crop-soil systems represented by un-recovered ¹⁵N in crop and soil were 12% and 35%, respectively. These losses were attributed to leaching and denitrification. The proportions of ¹⁵N retained in the soil (0-400 mm depth) at the time of harvest of winter wheat and ryegrass were 36% and 24%, respectively. Although the soil functioned as a substantial sink for fertilizer N, the recovery of this residual fertilizer by subsequent three winter wheat crops was low (1-5%) and this was not affected by different crop residue management practices.     

Nitrogen management in organic farming: comparison of crop rotation residual effects on yields,N leaching and soil conditions

After 3 years of different crop rotations in an organic farming experiment on a sandy soil in northwest Germany, spring triticale was cultivated on all plots in the fourth year to investigate residual effects on yield, nitrogen (N) leaching and nutrient status in the soil. Previous crop rotations differed in the way N was supplied, either by farmyard manure (FYM, 100 and 200 kg N ha⁻¹ year⁻¹) or by arable legumes like grass-red clover and field beans, or as a control with no N. Other crops in the rotations were maize, winter triticale and spring barley. Additional plots had a 3-year grass-clover ley, that was ploughed-in for spring triticale in the fourth year. Yields of spring triticale were moderate and largest for ploughed-in grassland leys and grass-red clover and plots that had previously received farmyard manure. The former crop rotation, including grassland break-up, had a significant effect on most yield and environmental parameters like residual soil mineral nitrogen (SMN) and N leaching and on the level of available K in the soil. The single crop harvested in the year before spring triticale had a significant effect on yield parameters of spring triticale, less so on SMN and N leaching in the fourth year and no effect on available nutrients (P, K, Mg) and pH in the soil. We conclude that the effects of arable legumes were rather short lived while ploughing of 3-year grassland leys had a profound influence on mineralization processes and subsequently on yield and N losses.     

Measurement and simulation of the effects of N-fertilizer on growth,plant composition and distribution of soil mineral-N in nationwide onion experiments

To aid the development of simulation models for N-response, N-fertilizer experiments with onions (Allium cepa L.) were carried out on 5 different sites. In each experiment, there was little loss of fertilizer-N in soil during the period between application and rapid crop growth and little loss of mineral N by leaching at any time. Even so, a substantial proportion of the N applied as fertilizer could not be accounted for in the crop and soil at harvest; the sum of soil mineral-N plus crop N (excluding fibrous roots) was always linearly related to N rate applied over the entire range (0–300 kg N ha^–1) and the gradient was always approximately the same, 0.64, irrespective of soil type or the amount of nitrate remaining in soil at harvest. Evidence was obtained that the phenomena resulted from roots retaining N and inducing immobilization at a rate proportional to soil nitrate concentration and that the proportionality constant was similar on all sites.Throughout plant growth there was little luxury consumption of N and the critical %N was related to plant mass by an equation previously deduced for other C3 crops (Plant and Soil 85, 163); plant nitrate concentration in the early stages increased with soil mineral-N (0–30 cm) to a maximum which varied from site to site but the nitrate concentration in the mature crop was always negligible. Plant yield in the early stages of growth generally declined with increase in fertilizer-N, despite the crops having been planted as sets and no more than 150 kg N ha^–1 broadcast at one time; but at maturity, yield always increased asymptotically with increase in fertilizer-N. Mineralization rates were approximately the same in the first as in the second half of each experiment. At harvest, residual soil mineral-N in the upper 30, 60 and 90 cm of soil increased with increase in fertilizer-N even when crop demand for N exceeded supply. At harvest in every experiment, the ratio of crop dry weight in the absence of added N to the maximum obtained was approximately equal to the ratio of plant %N (with no fertilizer) to critical %N.The various phenomena concerning yields, plant-N contents, and values of soil mineral-N at harvest were quite well simulated by a slightly modified version of a previously published model (Fert. Res. 18, 153) with few site-dependent inputs.     

Effect of climate change on greenhouse gas emissions from arable crop rotations

The DAISY soil–plant–atmosphere model was used to simulate crop production and soil carbon (C) and nitrogen (N) turnover for three arable crop rotations on a loamy sand in Denmark under varying temperature, rainfall, atmospheric CO₂ concentration and N fertilization. The crop rotations varied in proportion of spring sown crops and use of N catch crops (ryegrass). The effects on CO₂ emissions were estimated from simulated changes in soil C. The effects on N₂O emissions were estimated using the IPCC methodology from simulated amounts of N in crop residues and N leaching. Simulations were carried out using the original and a revised parameterization of the soil C turnover. The use of the revised model parameterization increased the soil C and N turnover in the topsoil under baseline conditions, resulting in an increase in crop N uptake of 11 kg N ha^–1 y^–1 in a crop rotation with winter cereals and a reduction of 16 kg N ha^–1 y^–1 in a crop rotation with spring cereals and catch crops. The effect of increased temperature, rainfall and CO₂ concentration on N flows was of the same magnitude for both model parameterizations. Higher temperature and rainfall increased N leaching in all crop rotations, whereas effects on N in crop residues depended on use of catch crops. The total greenhouse gas (GHG) emission increased with increasing temperature. The increase in total GHG emission was 66–234 kg CO₂-eq ha^–1 y^–1 for a temperature increase of 4°C. Higher rainfall increased total GHG emissions most in the winter cereal dominated rotation. An increase in rainfall of 20% increased total GHG emissions by 11–53 kg CO₂-eq ha^–1 y^–1, and a 50% increase in atmospheric CO₂ concentration decreased emissions by 180–269 kg CO₂-eq ha^–1 y^–1. The total GHG emissions increased considerably with increasing N fertilizer rate for a crop rotation with winter cereals, but remained unchanged for a crop rotation with spring cereals and catch crops. The simulated increase in GHG emissions with global warming can be effectively mitigated by including more spring cereals and catch crops in the rotation.     

Comparing the effectiveness of radish cover crop, oilseed rape volunteers and oilseed rape residues incorporation for reducing nitrate leaching

The soil water and N dynamics have been studied during two long fallow periods (between wheat or oilseed rape and a spring crop) in a field experiment in Châlons-en-Champagne (eastern France, 48°50 N, 2°15 E). The experiment involved frequent measurements of soil water, soil mineral N, dry matter and N uptake by cover crops. Water and N budgets were established using Ritchie's model for calculating evapotranspiration in cropped soils and a model (LIXIM) for calculating water drainage, N leaching and N mineralisation in bare soils. During the first autumn and winter, a radish cover crop (grown from September 1994 to January 1995) was compared to a bare soil. During the second period (July 1995 to April 1996), a comparison was carried out between (i) oilseed rape volunteers, (ii) bare soil with two types of oilseed rape residues incorporated into the soil (R0 and R270 residues) and (iii) bare soil without residues incorporation. R0 and R270 residues came from two preceding oilseed rape crops which received two rates of N fertilizer (0 and 270 kg N ha^-1).Soil mineral N content was markedly reduced by the presence of radish cover crop or oilseed rape volunteers during autumn. The calculated actual evapotranspiration (AET) did not differ much between treatments, meaning that the transpiration by the cover crop or volunteers was relatively low (100–150 L kg^-1 of dry matter). Consequently, nitrate leaching was reduced during the rest of the winter and spring as well as nitrate concentration in the percolating water: 45 vs. 91 mg NO₃ ^- L^-1 for radish cover crop and bare soil, respectively. The incorporation of oilseed rape residues to soil also exerted a beneficial but smaller action on reducing the nitrate content in the soil. This effect was due to extra N immobilisation which reached a maximum of about 20 kg N ha^-1 in mid-autumn for both types of residues. Nine months after the incorporation of the oilseed rape residues, and comparing to the control soil without residues incorporation, N rich residues induced a significant positive N net effect (+ 9 kg N ha^-1) corresponding to 10% of N added whereas for N poor residues no net effect was still obtained at the end of experiment (–3 kg N ha^-1, not significantly different from 0).To reduce nitrate leaching during long fallow periods, it is necessary to promote techniques leading to decrease mineral-N contents in the soil during autumn before the drainage period, such as (i) residue incorporation after harvest (without fertiliser-N) and (ii) allowing volunteers to grow or sowing a cover crop just after the harvest of the last main crop.     

Minimizing nitrogen losses from a corn–soybean–winter wheat rotation with best management practices

Best management practices are recommended for improving fertilizer and soil N uptake efficiency and reducing N losses to the environment. Few year-round studies quantifying the combined effect of several management practices on environmental N losses have been carried out. This study was designed to assess crop productivity, N uptake from fertilizer and soil sources, and N losses, and to relate these variables to the fate of fertilizer 15N in a corn (Zea mays L.)-soybean (Glycine max L.)-winter wheat (Triticum aestivum L.) rotation managed under Best Management (BM) compared with conventional practices (CONV). The study was conducted from May 2000 to October 2004 at Elora, Ontario, Canada. Cumulative NO₃ leaching loss was reduced by 51% from 133 kg N ha⁻¹ in CONV to 68 kg N ha⁻¹ in BM. About 70% of leaching loss occurred in corn years with fertilizer N directly contributing 11–16% to leaching in CONV and <4% in BM. High soil derived N leaching loss in CONV, which occurred mostly (about 80%) during November to April was attributable to 45–69% higher residual soil derived mineral N left at harvest, and on-going N mineralization during the over-winter period. Fertilizer N uptake efficiency (FNUE) was higher in BM (61% of applied) than in CONV (35% of applied) over corn and wheat years. Unaccounted gaseous losses of fertilizer N were reduced from 27% of applied in CONV to 8% of applied in BM. Yields were similar between BM and CONV (for corn: 2000 and 2003, wheat: 2002, soybean: 2004) or higher in BM (soybean: 2001). Results indicated that the use of judicious N rates in synchrony with plant N demand combined with other BMP (no-tillage, legume cover crops) improved FNUE by corn and wheat, while reducing both fertilizer and soil N losses without sacrificing yields.     

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.     

Legume cover crops and mulches: effects on nitrate leaching and nitrogen input in a pepper crop (<Emphasis Type="Italic">Capsicum annuum</Emphasis> L.)

There is not sufficient knowledge concerning the risks involved in NO₃–N leaching in relation to the use of cover crops and mulches. A 2 year field experiment was carried out in a pepper (Capsicum annuum L.) crop transplanted into different soil management treatments which involved the addition of mulch of three different types of winter cover crops (CC) [hairy vetch (Vicia villosa Roth.), subclover (Trifolium subterraneum L.), and a mixture of hairy vetch/oat (Avena sativa L.)], and an un-mulched plot. At the time of CC conversion into mulch, the hairy vetch/oat mixture accumulated the highest aboveground biomass (5.30 t ha⁻¹ of DM), while hairy vetch in pure stand accumulated the highest quantity of N (177 kg ha⁻¹) and showed the lowest C/N ratio (12). The marketable pepper yield was higher in mulched than in conventional (on average 33.5, 28.9, 27.7 and 22.2 t ha⁻¹ of FM for hairy vetch, subclover, hairy vetch/oat mixture, and conventional, respectively). Generally, the NO₃–N content of the soil was minimum at CC sowing, slightly higher at pepper transplanting and maximum at pepper harvesting (on average 15.2, 16.8, and 23.3 mg NO₃-N kg⁻¹ of dry soil, respectively). The cumulative leachate was higher during the CC period (from October to April) than the pepper crop period (from April to September), on average 102.1 vs 66.1 mm over the years, respectively. The cumulative NO₃–N leached greatly depended on the type of mulch and it was 102.3, 95.3, 94.7, and 48.2 kg ha⁻¹ in hairy vetch, subclover, hairy vetch/oat mixture, and conventional, respectively. A positive linear correlation was found between the N accumulated in the CC aboveground biomass and the NO₃–N leached during pepper cultivation (R ² = 0.87). This research shows that winter legume cover crops, especially hairy vetch in pure stand, converted into dead mulch in spring could be used successfully for adding N to the soil and increasing the yield of the following pepper crop although the risks of N losses via leaching could be increased compared to an un-mulched soil. Therefore when leguminous mulches are used in the cultivation of a summer crop, appropriate management practices of the system, such as a better control of the amount of irrigation water and the cultivation of a graminaceous or a cruciferous catch crop after the harvesting of the summer crop, should be adopted in order to avoid an increase in NO₃–N leaching.     

Long-term simulations of nitrate leaching from potato production systems in Prince Edward Island,Canada

LEACHN was employed to simulate nitrate leaching from a representative potato production system in Prince Edward Island (PEI), Canada and enhance the understanding of impacts of potato (Solanum tuberosum L.) production on groundwater quality. The model’s performance on predicting drainage was examined against water table measurements through coupled LEACHN and MODFLOW modeling. LEACHN was calibrated and verified to data from tile-drain leaching experiments of potato grown in rotation with barley (Hordeum vulgare L.) and red clover (Trifolium pratense L.) during 1999–2008. Long-term simulations using the calibrated model were performed to evaluate the effects of climate and N fertilization for the potato crop on nitrate leaching. The modeling suggests LEACHN can be an effective tool for predicting nitrate leaching from similar cropping systems in PEI. Both measurements and simulations showed nitrate leaching primarily occurred during the non-growing season when crop uptake diminishes, and nitrate from mineralization and residual fertilizer coexists with excessive moisture from rainfall and snowmelt infiltration. Annual average nitrate leaching following potato, barley and red clover phases was predicted to be 81, 54 and 35 kg N ha⁻¹, respectively, and the corresponding leached concentrations were 15.7, 10.1 and 7.3 mg N l⁻¹. Increased N input for potato alone increased nitrate leaching not only during potato phase but also during the rotation crop phases. To reduce the risk of nitrate leaching, practices should be developed to minimize nitrate accumulation in soil both during and outside of the growing season and in both the potato and the rotation crop phases.     

Nitrogen supply from fertilizer and legume cover crop in the transition to no-tillage for irrigated row crops

In spite of potential benefits and positive assessments of reducing primary tillage operations, only a small part of irrigated row crops is currently managed using reduced tillage, for reasons that include concerns about its agronomic suitability for certain crop rotations. Three years of a tomato/corn rotation under standard and no-tillage management were used to understand the fate of a fertilizer and cover crop nitrogen (N) application. Uptake of both inputs was reduced under no-tillage during the year of application, in this case a tomato crop. As a result, more input N was retained in the soil in this system. The initial challenge of reduced tomato yields diminished as no-tillage management remained in place and the soil N reservoir developed. Corn production was not affected by tillage treatment. Inclusion of a legume cover crop increased the amount of fertilizer N retained in the soil over time, more so under no-tillage than under standard tillage, emphasizing the benefit of cover crops in reducing the amount of fertilizer required to maintain productivity. While acceptance of reduced tillage ultimately depends on economic performance, the results of this study support its agronomic viability for irrigated row crops.     

Nitrogen use and losses in agriculture in subtropical Australia

This review examines the use of nitrogen (N) fertilizer on sugar-cane, summer and winter grain crops, cotton, tropical fruit crops and pastoral areas in the four subtropical zones in eastern Australia. The pathways for N loss from the various crops grown in these zones are also examined and estimates of N loss given.Sugar-cane is the most important crop grown in the subtropical humid northern and southern zones, using 77% of all N fertilizer applied in 1988–89. Urea is the most widely used form of N fertilizer with about 50% of the applied N often lost via ammonia volatilization, denitrification and leaching. Losses of N via ammonia volatilization can be reduced by either irrigating after application, applying urea in subsurface bands or delaying application until after canopy development. Denitrification losses of 20% of applied N have been measured on clay soils in sugar- cane areas while leaching losses may occur by movement of solutes down preferential pathways (e.g. soil fauna, root channels and structural weaknesses in the soil profile). Tropical fruit crops also make a significant contribution to the economy of the humid northern and southern zones. The livestock industry is well established in the subtropical northern zones, with beef and dairy production relying on leguminous as well as N fertilized pastures. Urea is again the most widely used form of N and is susceptible to large losses via ammonia volatilization. Over a 12 month period, losses of between 9% and 42% of the N applied were recorded from a subtropical pasture.Wheat is the major winter crop of the sub-humid northern and southern zones with grain sorghum the main summer crop. Urea is the principal form of N fertilizer applied to both crops and is essential for increasing or maintaining economic yields from both regions. This decrease in soil fertility in grain producing areas is due mainly to a decrease in the amount of soil organic matter available for mineralization. Cotton is another major crop of both areas and relies heavily on N fertilizer application. Nitrogen fertilizer losses have been recorded from all cropping areas, although nitrification inhibitors such as wax coated calcium carbide and 2-ethynylpyridine have reduced denitrification losses from soils growing wheat and cotton respectively.Subtropical agriculture relies heavily on N fertilizer, principally urea, to maintain and increase crop yields. Losses of N from soils sown to crops and from native and sown pasture occur although management practices are being developed to help minimize this loss.     

Conservation tillage,local organic resources and nitrogen fertilizer combinations affect maize productivity,soil structure and nutrient balances in semi-arid Kenya

Smallholder land productivity in drylands can be increased by optimizing locally available resources, through nutrient enhancement and water conservation. In this study, we investigated the effect of tillage system, organic resource and chemical nitrogen fertilizer application on maize productivity in a sandy soil in eastern Kenya over four seasons. The objectives were to (1) determine effects of different tillage-organic resource combinations on soil structure and crop yield, (2) determine optimum organic–inorganic nutrient combinations for arid and semi-arid environments in Kenya and, (3) assess partial nutrient budgets of different soil, water and nutrient management practices using nutrient inflows and outflows. This experiment, initiated in the short rainy season of 2005, was a split plot design with 7 treatments involving combinations of tillage (tied-ridges, conventional tillage and no-till) and organic resource (1 t ha⁻¹ manure + 1 t ha⁻¹ crop residue and; 2 t ha⁻¹ of manure (no crop residue) in the main plots. Chemical nitrogen fertilizer at 0 and 60 kg N ha⁻¹ was used in sub-plots. Although average yield in no-till was by 30–65% lower than in conventional and tied-ridges during the initial two seasons, it achieved 7–40% higher yields than these tillage systems by season four. Combined application of 1 t ha⁻¹ of crop residue and 1 t ha⁻¹ of manure increased maize yield over sole application of manure at 2 t ha⁻¹ by between 17 and 51% depending on the tillage system, for treatments without inorganic N fertilizer. Cumulative nutrients in harvested maize in the four seasons ranged from 77 to 196 kg N ha⁻¹, 12 to 27 kg P ha⁻¹ and 102 to 191 kg K ha⁻¹, representing 23 and 62% of applied N in treatments with and without mineral fertilizer N respectively, 10% of applied P and 35% of applied K. Chemical nitrogen fertilizer application increased maize yields by 17–94%; the increases were significant in the first 3 seasons (P < 0.05). Tillage had significant effect on soil macro- (>2 mm) and micro-aggregates fractions (<250 μm >53 μm: P < 0.05), with aggregation indices following the order no-till > tied-ridges > conventional tillage. Also, combining crop residue and manure increased large macro-aggregates by 1.4–4.0 g 100 g⁻¹ soil above manure only treatments. We conclude that even with modest organic resource application, and depending on the number of seasons of use, conservation tillage systems such as tied-ridges and no-till can be effective in improving crop yield, nutrient uptake and soil structure and that farmers are better off applying 1 t ha⁻¹ each of crop residue and manure rather than sole manure.     

Effect of seasonal rainfall,N fertilizer and tillage on N utilization by dryland wheat in a semi-arid environment

Crop yield and N uptake in semi-arid environments are typically limited by available water and/or N. Since remobilization of shoot N is a major source of grain N, an understanding of how it is influenced by soil N and water supply, and tillage, is required. In 2003, 2005 and 2006, we determined the influence of N supply (0 or 60 kg fertilizer N ha⁻¹) and tillage [no tillage (NT) or conventional tillage (CT)] on N translocation and N use efficiency of wheat (Triticum aestivum L.) at Scott, Saskatchewan, Canada. Wheat production and N use, and their response to N fertilizer or tillage, were largely influenced by water availability. Wheat N uptake and remobilization were strongly correlated with normalized rainfall in May and June (r = 0.985 and 0.935, respectively, both significant at the P = 0.01 level). In a moisture-stressed year (2003), grain yield was higher under NT than CT, and fertilizer N was ineffective due to low N demand. Nitrogen application increased shoot dry matter (DM), and N uptake and remobilization only in 2006, a year with near-average precipitation. In a wet and cool year (2005), wheat showed no response to tillage or fertilizer N as available soil N was high. Root DM and N content varied slightly only with year or treatment. When N uptake at heading was substantially greater than 100 kg ha⁻¹, N loss occurred during plant senescence, and it was higher with N fertilization: in 2005 and 2006, N-fertilized wheat lost 33–35 kg N ha⁻¹. Nitrogen use efficiency was: (1) higher under NT than CT, due to higher N utilization efficiency, (2) higher with no added N due to higher uptake and utilization efficiencies, and (3) low when water availability was low or excessive. Tillage system had little effect on the uptake, remobilization or loss of N. Fertilizer N application in a year with average rainfall increased wheat production, N accumulation and remobilization, and N loss during senescence.     

Erratum to: Long-term tillage,straw and N rate effects on quantity and quality of organic C and N in a Gray Luvisol soil

Long-term use of soil, crop residue and fertilizer management practices may affect some soil properties, but the magnitude of change depends on soil type and climatic conditions. Two field experiments with barley, wheat, or canola in a rotation on Gray Luvisol (Typic Cryoboralf) loam at Breton and Black Chernozem (Albic Argicryoll) loam at Ellerslie, Alberta, Canada, were conducted to determine the effects of 19 or 27 years (from 1980 to 1998 or 2006 growing seasons) of tillage (zero tillage [ZT] and conventional tillage [CT]), straw management (straw removed [S_Rem] and straw retained [S_Ret]) and N fertilizer rate (0, 50 and 100 kg N ha⁻¹ in S_Ret, and 0 kg N ha⁻¹ in S_Rem plots) on pH, extractable P, ammonium-N and nitrate–N in the 0–7.5, 7.5–15, 15–30 and 30–40 cm or 0–15, 15–30, 30–60, 60–90 and 90–120 cm soil layers. The effects of tillage, crop residue management and N fertilization on these chemical properties were usually similar for both contrasting soil types. There was no effect of tillage and residue management on soil pH, but application of N fertilizer reduced pH significantly (by up to 0.5 units) in the top 15 cm soil layers. Extractable P in the 0–15 cm soil layer was higher or tended to be higher under ZT than CT, or with S_Ret than S_Rem in many cases, but it decreased significantly with N application (by 18.5 kg P ha⁻¹ in Gray Luvisol soil and 20.5 kg P ha⁻¹ in Black Chernozem soil in 2007). Residual nitrate–N (though quite low in the Gray Luvisol soil in 1998) increased with application of N (by 17.8 kg N ha⁻¹ in the 0–120 cm layer in Gray Luvisol soil and 23.8 kg N ha⁻¹ in 0–90 cm layer in Black Chernozem soil in 2007) and also indicated some downward movement in the soil profile up to 90 cm depth. There was generally no effect of any treatment on ammonium-N in soil. In conclusion, elimination of tillage and retention of straw increased but N fertilization decreased extractable P in the surface soil. Application of N fertilizer reduced pH in the surface soil, and showed accumulation and downward leaching of nitrate–N in the soil profile.     

Effects of soil and crop management practices on yields,income and nutrients losses from upland farming systems in the Middle Mountains region of Nepal

On-farm runoff plots were established during 2004 and monitored for 4 years in the Pokhare Khola watershed (Nepal) in a completely randomized design with four replications of each three treatments: traditional Farmer Practice (FP) (Zea mays–Eleusine coracana), Reduced Tillage (RT; Z. mays–Vigna ungeuculata), and Commercial Vegetable with double dose of farm yard manure (CV; Z. mays–Capsicum species) to evaluate treatment effects on soil nutrient losses, nutrient balances and crop income on Bari land (rainfed terraces). Nutrient removal due to crop harvest was found to be significantly higher than nutrient loss through soil erosion, and CV treatment exhibited a significantly higher N uptake (123 kg ha⁻¹ year⁻¹) through crop harvest than other treatments. Moreover, the CV treatment produced significantly higher income per unit area of Bari land than the other treatments. Soil organic carbon and major nutrients losses (NPK) through soil erosion were minimal [25.5 kg ha⁻¹ year⁻¹ soil organic carbon (SOC) and 5.6:0.02:0.12 kg ha⁻¹ year⁻¹ nitrogen (N), phosphorus (P), potassium (K), respectively]. Result showed that no nutrients were lost through leaching. Nutrient losses due to soil erosion and runoff were lower than previously reported in the Middle Mountain region, indicating a need to re-evaluate the soil erosion and nutrient loss problems in this region. Interventions such as reduced tillage and double dose of FYM with vegetable production were found to be effective in maintaining soil fertility and increasing farm income compared to the traditional maize-millet production system. The nutrient balance calculations suggest that integrated nutrient management techniques such as residue incorporation and application of FYM with a minimum application of chemical fertilizer are potentially sustainable production approaches for the Mid-hills of Nepal.     

Nutrient cycling in a cropping system with potato, spring wheat, sugar beet, oats and nitrogen catch crops. II. Effect of catch crops on nitrate leaching in autumn and winter

The Nitrate Directive of the European Union (EU) forces agriculture to reduce nitrate emission. The current study addressed nitrate emission and nitrate-N concentrations in leachate from cropping systems with and without the cultivation of catch crops (winter rye: Secale cereale L. and forage rape: Brassica napus ssp. oleifera (Metzg.) Sinksk). For this purpose, ceramic suction cups were used, installed at 80 cm below the soil surface. Soil water samples were extracted at intervals of ca 14 days over the course of three leaching seasons (September – February) in 1992–1995 on sandy soil in a crop rotation comprising potato (Solanum tuberosum L.), spring wheat (Triticum aestivum L.), sugar beet (Beta vulgaris L.) and oats (Avena sativa L.). Nitrate-N concentration was determined in the soil water samples. In a selection of samples several cations and anions were determined in order to analyze which cations primarily leach in combination with nitrate. The water flux at 80 cm depth was calculated with the SWAP model. Nitrate-N loss per interval was obtained by multiplying the measured nitrate-N concentration and the calculated flux. Accumulation over the season yielded the total nitrate-N leaching and the seasonal flux-weighted nitrate-N concentration in leachate. Among the cases studied, the total leaching of nitrate-N ranged between 30 and 140 kg ha^–1. Over the leaching season, the flux-weighted nitrate-N concentration ranged between 5 and 25 mg L^–1. Without catch crop cultivation, that concentration exceeded the EU nitrate-N standard (11.3 mg L^–1) in all cases. Averaged for the current rotation, cultivation of catch crops would result in average nitrate-N concentrations in leachate near or below the EU nitrate standard. Nitrate-N concentrations correlated with calcium concentration and to a lesser extent with magnesium and potassium, indicating that these three ion species primarily leach in combination with nitrate. It is concluded that systematic inclusion of catch crops helps to decrease the nitrate-N concentration in leachate to values near or below the EU standard in arable rotations on sandy soils.     

N application to winter wheat at tillering and shooting: N balance at different growth stages

At two sites, microplots under winter wheat were given 140 kg N ha^–1 as labelled ammonium nitrate split in 80 kg N ha^–1 at tillering and 60 kg N ha^–1 at shooting. Soil and plant samples were analyzed at shooting, after anthesis and at grain harvest and a¹⁵N balance was established. The average recovery rate of 95% indicates that there were no marked N losses due to leaching and denitrification, which is attributed to the low rainfall in the two months after fertilizer application. Between 19 and 23% of the fertilizer N remained in the 0–30 cm soil layer as organically bound soil N. Up to 64% was taken up by the above-ground crop. On the loamy sand, 4% of the fertilizer N at harvest remained in the roots in the 0–30 cm layer and only 3% was found as inorganic N in the 0–90 cm soil layer. The fertilizer N applied diminished plant uptake of soil N in the period between fertilizer application and harvest. As compared with the control, the fertilized plants extracted 25 and 28% less soil N from loamy sand and loess soil, respectively. The results show that application of mineral N fertilizer helps to maintain the mineralizable N content of the soil, which has been accumulated in the course of long-term intensive crop production, by adding N to the soil organic pool and simultaneously reducing the supply of soil N to the plants.