Showing papers in "Nutrient Cycling in Agroecosystems in 2011"

Agronomic and environmental aspects of phosphate fertilizers varying in source and solubility: an update review

Abstract: This review discusses and summarizes the latest reports regarding the agronomic utilization and potential environmental effects of different types of phosphate (P) fertilizers that vary in solubility. The agronomic effectiveness of P fertilizer can be influenced by the following factors: (1) water and citrate solubility; (2) chemical composition of solid water-soluble P (WSP) fertilizers; (3) fluid and solid forms of WSP fertilizers; and (4) chemical reactions of P fertilizers in soils. Non-conventional P fertilizers are compared with WSP fertilizers in terms of P use efficiency in crop production. Non-conventional P fertilizers include directly applied phosphate rock (PR), partially acidulated PR (PAPR), and compacted mixtures of PR and WSP. The potential impacts of the use of P fertilizers from both conventional (fully acidulated) and non-conventional sources are discussed in terms of (1) contamination of soils and plants with toxic heavy metals, such as cadmium (Cd), and (2) the contribution of P runoff to eutrophication. Best practices of integrated nutrient management should be implemented when applying P fertilizers to different cropping systems. The ideal management system will use appropriate sources, application rates, timing, and placement in consideration of soil properties. The goal of P fertilizer use should be to optimize crop production without causing environmental problems.

Effectiveness of recycled P products as P fertilizers, as evaluated in pot experiments

Abstract: World phosphorus (P) resources are limited and may be exhausted within 70–175 years. Therefore recycling of P from waste materials by chemical or thermal processes is important. This study evaluated the effectiveness of recycled P products from sewage sludge and animal wastes as P fertilizer. Four products were obtained from chemical processes, three magnesium-ammonium-phosphates (MAP) of different sewage treatment plants and a Ca phosphate precipitated from wastewater (Ca-P) and four from thermal processes, an alkali sinter phosphate (Sinter-P), a heavy metal depleted sewage sludge ash (Sl-ash), a cupola furnace slag made from sewage sludge (Cupola slag) and a meat-and-bone meal ash (MB meal ash). The effectiveness of these products as P fertilizers compared with triple superphosphate (TSP) and phosphate rock (PR) was determined in a 2-year pot experiment with maize (Zea mays L., cv. Atletico) in two soils with contrasting pH (pH(CaCl2) 4.7 and 6.6). The parameters used to evaluate the effectiveness were P uptake, P concentration in soil solution (CLi) and isotopically exchangeable P (IEP). MAP products were as effective as TSP in both soils, while Ca-P was only effective in the acid soil. Sinter-P was as effective as TSP in the acid soil, while Cupola slag was in the neutral soil. The products Sl-ash and MB meal ash were of low effectiveness and were comparable to PR. The effect of the fertilizers on IEP, but not on CLi, described their effectiveness. Recycled P products obtained by chemical processes, especially MAP, could be directly applied as P fertilizers, while products such as Sl-ash and MB meal ash are potential raw materials for P fertilizer production.

Using the DSSAT-CERES-Maize model to simulate crop yield and nitrogen cycling in fields under long-term continuous maize production

Abstract: Simulation models, such as the DSSAT (Decision Support System for Agrotechnology Transfer) Crop System Models are often used to characterize, develop and assess field crop production practices. In this study, one of the DSSAT Cropping System Model, CERES-Maize, was employed to characterize maize (Zea mays) yield and nitrogen dynamics in a 50-year maize production study at Woodslee, Ontario, Canada (42°13′N, 82°44′W). The treatments selected for this study included continuous corn/maize with fertilization (CC-F) and continuous corn/maize without fertilization (CC-NF) treatments. Sequential model simulations of long-term maize yield (1959–2008), near-surface (0–30 cm) soil mineral nitrogen (N) content (2000), and soil nitrate loss (1998–2000) were compared to measured values. The model did not provide accurate predictions of annual maize yields, but the overall agreement was as good as other researchers have obtained. In the CC-F treatment, near-surface soil mineral N and cumulative soil nitrate loss were simulated by the model reasonably well, with n-RMSE = 62 and 29%, respectively. In the CC-NF treatment, however, the model consistently overestimated soil nitrate loss. These outcomes can be used to improve our understanding of the long-term effects of fertilizer management practices on maize yield and soil properties in improved and degraded soils.

Mineralizable soil nitrogen and labile soil organic matter in diverse long-term cropping systems

Abstract: Sustainable soil fertility management depends on long-term integrated strategies that build and maintain soil organic matter and mineralizable soil N levels. These strategies increase the portion of crop N needs met by soil N and reduce dependence on external N inputs required for crop production. To better understand the impact of management on soil N dynamics, we conducted field and laboratory research on five diverse management systems at a long-term study in Maryland, the USDA- Agricultural Research Service Beltsville Farming Systems Project (FSP). The FSP is comprised of a conventional no-till corn (Zea mays L.)–soybean (Glycine max L.)–wheat (Triticum aestivum L.)/double-crop soybean rotation (NT), a conventional chisel-till corn–soybean–wheat/soybean rotation (CT), a 2 year organic corn–soybean rotation (Org2), a 3 year organic corn–soybean–wheat rotation (Org3), and a 6 year organic corn–soybean–wheat–alfalfa (Medicago sativa L.) (3 years) rotation (Org6). We found that total potentially mineralizable N in organic systems (average 315 kg N ha−1) was significantly greater than the conventional systems (average 235 kg N ha−1). Particulate organic matter (POM)–C and –N also tended to be greater in organic than conventional cropping systems. Average corn yield and N uptake from unamended (minus N) field microplots were 40 and 48%, respectively, greater in organic than conventional grain cropping systems. Among the three organic systems, all measures of N availability tended to increase with increasing frequency of manure application and crop rotation length (Org2 < Org3 ≤ Org6) while most measures were similar between NT and CT. Our results demonstrate that organic soil fertility management increases soil N availability by increasing labile soil organic matter. Relatively high levels of mineralizable soil N must be considered when developing soil fertility management plans for organic systems.

Influence of topography and land management on soil nutrients variability in Northeast China

Abstract: It is well recognized that soil nutrient content varies across the landscape, but the nature and degree of that variability with respect to landscape position is still poorly understood and documented. Slope steepness and aspect, climate and land management are known to affect soil nutrient distribution in a field, but the relative and cumulative strengths of these effects are less well investigated. Four hundred and thirty-five topsoil samples collected from a typical Mollisol under intensive crop management in Northeast China were used to analyze the influence of landscape position, climate and land management on the spatial variability of soil organic matter (SOM), total nitrogen (TN) and total phosphorus (TP). Both geo-statistics and traditional statistics were used to analyze the data, and significant spatial variability was found for SOM (22.5–86.6 g kg−1), TN (0.98–4.26 g kg−1) and TP (0.26–1.80 g kg−1). The distribution of all 3 nutrients was found to be influenced by human activity and by landscape. When both slope degree and slope aspect were considered, the results differed from when only aspect or steepness was considered independently. In a northern aspect, SOM and TN were significantly higher on slopes of 0–2% than on steeper slopes, in a south-eastern aspect they were significantly higher on slopes of 0–2, 2–3 and 3–4% than on slopes >4% and in a south-western aspect those nutrients on slopes of 2–4% were significantly higher than on slopes of >5%. Cross-slope tillage effectively increased SOM, TN and TP by 33.8, 23.3 and 22.4%, respectively compared to down-slope tillage, indicating the potential for adoption of a nutrient-retaining management practice in the Mollisol region of northeast China.

Assessing internal crop nitrogen use efficiency in high-yielding irrigated cotton

Abstract: Improving the efficiency of nitrogen (N) fertiliser use is one means of reducing greenhouse gas emissions, particularly in irrigated crops such as cotton (Gossypium hirsutum L.). Internal crop N use efficiency (iNUE) was measured within two N fertiliser rate experiments that covered a wide range of N fertility over six cropping seasons. Crop iNUE was determined by dividing lint yield by crop N uptake. No nutrients other than N limited cotton growth or yield and the crops were irrigated to avoid drought stress. The optimal N fertiliser rates were determined from fitted quadratic functions that related lint yields with N fertiliser rates for each cropping system in each year. When the optimal N fertiliser rate was applied, crop iNUE averaged 12.5 ± 0.2 kg lint/kg crop N uptake. The crop iNUE was then used to determine the degree to which N fertiliser was under or over-applied, with respect to the economic optimum N fertiliser rate. Low iNUE values were associated with excessive N fertiliser application. Crop iNUE was determined in 82 commercial cotton crops in six valleys over the final 4 years of this study. The crop iNUE value was high in 8 fields (10%), optimal in 9 fields (11%) and low in 65 fields (79%). Crop N uptake averaged 247 kg N/ha, yield 2,273 kg lint/ha and crop iNUE 10.1 kg lint/kg crop N uptake for these sites. Averaged over all sites and years, about 49 kg N/ha too much N fertiliser was applied. Apparent N fertiliser recovery by cotton in the N rate experiments ranged from <20% in N-fertile treatments where legume crops had been grown, to more than 60% following winter cereal crops. Information on crop iNUE will enable cotton producers to assess their N fertiliser management and adjust N fertiliser rates for future crops. This study has demonstrated that there is scope to substantially reduce N fertiliser inputs to Australian cotton fields without reducing yields.

Managing soil fertility diversity to enhance resource use efficiencies in smallholder farming systems: a case from Murewa District, Zimbabwe

Abstract: Smallholder farms in sub-Saharan African exhibit substantial heterogeneity in soil fertility, and nutrient resource allocation strategies that address this variability are required to increase nutrient use efficiencies. We applied the Field-scale resource Interactions, use Efficiencies and Long-term soil fertility Development (FIELD) model to explore consequences of various manure and fertilizer application strategies on crop productivity and soil organic carbon (SOC) dynamics on farms varying in resource endowment in a case study village in Murewa District, Zimbabwe. FIELD simulated a rapid decline in SOC and maize yields when native woodlands were cleared for maize cultivation without fertilizer inputs coupled with removal of crop residues. Applications of 10 t manure ha−1 year−1 for 10 years were required to restore maize productivity to the yields attainable under native woodland. Long-term application of manure at 5 and 3 t ha−1 resulted in SOC contents comparable to zones of high and medium soil fertility observed on farms of wealthy cattle owners. Targeting manure application to restore SOC to 50–60% of contents under native woodlands was sufficient to increase productivity to 90% of attainable yields. Short-term increases in crop productivity achieved by reallocating manure to less fertile fields were short-lived on sandy soils. Preventing degradation of the soils under intensive cultivation is difficult, particularly in low input farming systems, and attention should be paid to judicious use of the limited nutrient resources to maintain a degree of soil fertility that supports good crop response to fertilizer application.

Vertical distribution of heavy metals in wastewater-irrigated vegetable garden soils of three West African cities

Abstract: Application of untreated wastewater to irrigate urban vegetable gardens is raising serious concern about possible health risks associated with the consumption of these vegetables particularly with regard to the concentrations of heavy metals (HM) in their edible portions. The soil concentrations of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn), were investigated in seven vegetable gardens from the three West African cities of Kano (Nigeria), Bobo Dioulasso (Burkina Faso) and Sikasso (Mali). Also determined were input–output balances of Cd and Zn from five vegetable gardens under 30 years of wastewater irrigation in Kano. In these gardens Cd (2.3–4.8 mg kg−1) and Zn (13–285 mg kg−1) concentrations throughout the profile attained unsafe levels. The concentrations of Cu (0.8–18 mg kg−1), Cr (1.8–72 mg kg−1), Ni (0–17 mg kg−1) and Pb (0.6–46 mg kg−1) were below the safety thresholds for arable soils. Overall, concentrations of Zn, Cd, Pb and Ni were higher in Kano than in Bobo-Dioulasso and Sikasso. Input–output analyses in Kano indicated that irrigation wastewater contributed annually 400–3,700 g Cd ha−1 and 7,200–22,300 g Zn ha−1, fertilizer 30–2,100 g Cd ha−1 50–17,600 g Zn ha−1, harmattan dust 0.02–0.4 g Cd ha−1 and 40–200 g Zn ha−1 while 300–500 g Cd ha−1 and 2,700–4,700 g Zn ha−1 came from rainwater inputs. Input–output calculations subtracting the amounts of HM taken out in vegetable biomass and that lost to leaching from total inputs yielded an annual net positive balance of 700–4,160 g Cd ha−1 and 9,350–39,700 g Zn ha−1. If such balances remain unchanged for another 10–20 years vegetables raised in these garden fields are likely to be unsuitable for human consumption.

Long-term tillage, straw management and N fertilization effects on quantity and quality of organic C and N in a Black Chernozem soil

Abstract: Soil, crop and fertilizer management practices may affect the amount and quality of organic C and N in soil. A long-term field experiment (growing barley, wheat, or canola) was conducted on a Black Chernozem (Albic Argicryoll) loam at Ellerslie, Alberta, Canada, to determine the influence of 19 (1980 to 1998) or 27 years (1980 to 2006) of tillage (zero tillage [ZT] and conventional tillage [CT]), straw management (straw removed [SRem]and straw retained [SRet]) and N fertilizer rate (0, 50 and 100 kg N ha−1 in SRet and 0 kg N ha−1 in SRem plots) on total organic C (TOC) and N (TON), and light fraction organic C (LFOC) and N (LFON) in the 0–7.5 and 7.5–15 cm or 0–5, 5–10 and 10–15 cm soil layers. The mass of TOC and TON in soil was usually higher in SRet than in SRem treatment (by 3.44 Mg C ha−1 for TOC and 0.248 Mg N ha−1 for TON after 27 years), but there was little effect of tillage and N fertilization on these parameters. The mass of LFOC and LFON in soil tended to increase with SRet (by 285 kg C ha−1 for LFOC and 12.6 kg N ha−1 for LFON with annual rate of 100 kg N ha−1 for 27 years), increased with N fertilizer application (by 517 kg C ha−1 for LFOC and 36.0 kg N ha−1 for LFON after 27 years), but was usually higher under CT than ZT (by 451 kg C ha−1 for LFOC and 25.3 kg N ha−1 for LFON after 27 years). Correlations between soil organic C or N fractions were highly significant in most cases. Linear regressions between crop residue C input and soil organic C or N were significant in most cases. The effects of tillage, straw management and N fertilizer on soil were more pronounced for LFOC and LFON than TOC and TON, and also in the surface layers than in the deeper layers. Tillage and straw management had little or no effect on C:N ratios, but the C:N ratios in light organic fractions significantly decreased with increasing N rate (from 20.06 at zero-N to 18.91 at 100 kg N ha−1). Compared to the 1979 results, in treatments that did not receive N fertilizer (CTSRem0, CTSRet0, ZTSRem0 and ZTSRet0), CTSRem0 resulted in a net decrease in TOC concentration (by 1.9 g C kg−1) in the 0–15 cm soil layer in 2007 (after 27 years), with little or no change in the CTSRet0 and ZTSRem0 treatments, while there was a net increase in TOC concentration (by 1.2 g C kg−1) in the ZTSRet0 treatment. Straw retention and N fertilizer application at 50 and 100 kg N ha−1 rates showed a net positive effect on TOC concentration under both ZT (ZTSRet50 by 2.3 g C kg−1 and ZTSRet100 by 3.1 g C kg−1) and CT (CTSRet50 by 3.5 g C kg−1 and CTSRet100 by 1.6 g C kg−1) treatments in 2007 compared to 1979 data. In conclusion, the findings suggest that retention of straw, application of N fertilizer and elimination of tillage would improve soil quality, and this might increase the potential for N supplying power of the soil and sustainability of crop productivity.

Assessment of trace gases, carbon and nitrogen emissions from field burning of agricultural residues in India

Abstract: Field burning of crop residue (FBCR) is becoming a growing environmental concern in developing countries. In this instance, a comprehensive crop-wise and spatially distributed study on the FBCR emissions from India for the period 1980 through 2010 have been undertaken, that covers: residue generation, its types, use pattern, and estimates of carbon, nitrogen, CH4, CO, N2O and NOX emissions; along with associated uncertainties. FBCR contributed about 44 and 14% of the non-biofuel biomass and total biomass burning, respectively in India in the year 2000. The total dry residue generated are estimated as 217, 239 and 253 Tg, of which 45, 60 and 63 Tg of dry biomass are estimated to be subjected to FBCR in the years 1994, 2005 and 2010, respectively. Wheat and rice crops together accounted for about 76% of this. Burning of such huge amount of biomass is estimated to emit 22.4, 24.4 and 26.1 Tg of carbon; 0.30, 0.33 and 0.35 Tg of nitrogen; 4.18, 4.59 and 4.86 Tg carbon dioxide equivalent of greenhouse gases (GHG, viz., CH4 and N2O; which is over 1% of the Indian agriculture sector GHG emissions); 2951, 3,240 and 3,431 Gg of CO; and 120.8, 132.9 and 140.6 Gg NOx emissions in 1994, 2005 and 2010, respectively. Further, the Indian states of U.P, Punjab, Haryana, M.P, Maharashtra, T.N, Karnataka, Andhra Pradesh, Bihar and W.B have been found to contribute maximum to the Indian FBCR emissions. FBCR avoidance and optimum utilization of crop-residue resource is urgently required for agro-ecosystem sustainability in the region.

Relationship between residue quality, decomposition patterns, and soil organic matter accumulation in a tropical sandy soil after 13 years

Abstract: The objectives of this study were to investigate decomposition patterns and soil organic matter (SOM) accumulation of incorporated residues (10 Mg ha−1 year−1) of different quality, and identify microbiological parameters sensitive to changes in SOM dynamics, in a 13-year-old field experiment on a sandy soil in Northeast Thailand. Mass loss was fastest in groundnut stover (high N), followed by rice straw (high cellulose) and tamarind (intermediate quality), and slowest in dipterocarp (high lignin and polyphenol) following a double exponential pattern. The decomposition rate k 1 (fast pool) was positively correlated with cellulose (r = 0.70*) while k 2 (slow pool) was negatively related to lignin (r = −0.85***) and polyphenol (r = −0.81**) contents of residues. Residue decomposition was sensitive to indigenous soil organic nitrogen (SON), particularly during later stages (R 2 = 0.782**). Thirteen years’ addition of tamarind residues led to largest soil organic carbon (SOC) (8.41 Mg ha−1) accumulation in topsoil (0–20 cm), while rice straw yielded only 5.54 Mg ha−1 followed by the control (2.72 Mg ha−1). The highest SON (0.78 Mg N ha−1) was observed in the groundnut treatment. Increases in SOC were negatively correlated with cellulose content of residues (r = −0.92***) and microbial respiration (CO2-C) losses, while SON was governed by organic N added. During later decomposition stages, there was a high efficiency of C utilization (low qCO2) of decomposer communities especially under tamarind with the lowest qCO2 and CO2-C evolution loss. This study suggests that N-rich residues with low cellulose and moderate lignin and polyphenol contents are best suited to improve SOM content in tropical sandy soils.

Nutrient release during the decomposition of mowed perennial ryegrass and white clover and its contribution to nitrogen nutrition of grapevine

Abstract: Sustainable management of mineral nutrition in vineyards, as well as in other fruit plantations, should aim at exploiting the use of internal sources of nutrients, in order to reduce the need for external nutrient inputs. In this paper we explore the potential of the grassed alleys to provide nutrients to the vines. We followed for one vegetative season the decomposition of ryegrass and clover, frequently present as floor vegetation in vineyards, using litter bags filled with 15N-enriched grass material. In addition, we quantified the amount of nitrogen (N) transferred from the decomposing litter to field-grown grapevines. Ryegrass and clover had a relatively rapid decomposition rate, with a loss of C approaching 80% in only 16 weeks. The release of nutrients was particularly fast for potassium (95% in 16 weeks) followed by nitrogen (80%), calcium (70–80%), phosphorous (65–85%), magnesium (70–75%), and sulfur (60–70%). In spite of the rapid release of N from decomposing material, the N uptake by grapevines was on average less than 4% of the initial amount of N present in the litter of ryegrass and clover. Even if N release during the decomposition of mowed perennial ryegrass and white clover little contributed to the N nutrition of grapevine in the same growing season, most N from mowed grassed was still recovered in the soil.

Effects of ten year application of empty fruit bunches in an oil palm plantation on soil chemical properties

Abstract: The oil palm empty fruit bunches (EFB), a major waste product of the palm oil mills, were earlier incinerated at the mills and had contributed to air quality problems in Malaysia. This lead to the introduction of the Malaysian Environmental Air Quality Regulation in 1978 which prompted mills to look for alternative management methods in disposal of the EFB. A convenient method is applying the EFB to the oil palm field near the mill for nutrient cycling. A study was conducted to investigate the effects of 10 years of EFB yearly application in an oil palm plantation, as a source of nutrients, on the chemical properties of a well-drained, highly weathered acidic soil, classified as Typic Kandiudult. The experimental plots receiving 3 treatments, i.e. chemical fertilization, without EFB application (CHEM)), application of 150 kg EFB palm−1 year−1 (EFB150) and application of 300 kg EFB palm−1 year−1 (EFB300) with four replications, from 1983 to 1992. The EFB was applied in heaps in the middle of every 4 palms. The cumulative addition of EFB had increased the soil pH by two units with application of EFB300 and a one unit increase with EFB150 in the 0–60 cm soil layer, compared to CHEM. The application of EFB even at the lower rate decreased significantly exchangeable Al contents and the cation exchange capacity increased up to 60 cm soil depth. Overall increases in exchangeable bases were also observed in soils treated with EFB. The increase was more evident in EFB300 compared to EFB150. Organic C in the topsoil increased from 1.49 to 2.50% and 2.73% in EFB150 and EFB300, respectively. There was also an increase in total nitrogen with EFB application but only in the topsoil. An overall analysis of the yield response in the 10 year-period shows that EFB300 resulted in higher fresh fruit bunch (FFB) yield than EFB150 and CHEM while the yield of EFB150 was not significantly different from CHEM. This study showed that it is beneficial to dispose the EFB by applying them in the oil palm fields around the mills.

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

Abstract: Long-term use of soil, crop and fertilizer management practices alters some soil properties, but the magnitude of change depends on soil type and climatic conditions. A field experiment with a barley (Hordeum vulgare L.)–wheat (Triticum aestivum L.)–canola (Brassica napus L.) rotation was conducted on a Gray Luvisol (Typic Cryoboralf) loam soil at Breton, Alberta, Canada. 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 [SRem] and straw retained [SRet]) and N fertilizer rate (0, 50 and 100 kg N ha−1 in SRet, and 0 kg N ha−1 in SRem plots) were determined on total organic C (TOC) and N (TON), light fraction organic C (LFOC) and N (LFON), macro organic matter C (MOM-C) and N (MOM-N), microbial biomass C (MB-C), and mineralizable C (Cmin) and N (Nmin) in the 0–7.5 and 7.5–15 cm or 0–5, 5–10 and 10–15 cm soil layers. Zero tillage and SRet tended to have higher, and N fertilizer treatment usually had higher mass of TOC, TON, LFOC, LFON, Cmin and Nmin in soil compared to the corresponding CT, SRem and zero-N control treatments, especially in the surface soil layers. Soil MB-C, MOM-C and MOM-N in soil generally tended to be higher with SRet than SRem, and also with N fertilizer than zero-N. There was no additional beneficial effect of ZT in increasing MB-C in soil. There were close and significant correlations among most soil organic C or N fractions, except for MB-C which did not correlate with MOM-N, and Nmin did not correlate with MOM-C. Linear regressions between crop residue C input and soil organic C or N were significant in most cases, except for MB-C and Nmin. Compared to the 1979 data, all treatments that did not receive N fertilizer (CTSRem0, CTSRet0, ZTSRem0 and ZTSRet0) showed a decrease in TOC concentration in the 0–15 cm soil layer over time, with the highest decrease in the CTSRem0 treatment. Straw retention and N fertilizer application at 50 and 100 kg N ha−1 under both ZT (ZTSRet50 and ZTSRet100) and CT (CTSRet50 and CTSRet100) resulted in a strongest increase in TOC during the first 11 years, and since then the TOC decreased under both N rates but 50 kg N ha−1 rate under CT (CTSRet50) showed the strongest negative effect on TOC in soil. In conclusion, elimination of tillage, straw retention and N application all improved organic C and N in soil, and generally differences were more pronounced for light fraction organic C and N, and between the most extreme treatments (CTSRem0 vs. ZTSRet100) for each dynamic organic fraction. This may be better for the long-term sustainability of soil quality and productivity.

Effect of timing and duration of midseason aeration on CH4 and N2O emissions from irrigated lowland rice paddies in China

Abstract: Midseason aeration (MSA) of rice paddy fields functions to mitigate CH4 emission by a large margin, while simultaneously promoting N2O emission. Alternation of timing and duration of MSA would affect CH4 and N2O emissions from intermittently irrigated rice paddies. A pot trial and a field experiment were conducted to study the effect of timing and duration of MSA on CH4 and N2O emissions from irrigated lowland rice paddy soils in China. Four different water regimes, i.e., early aeration, normal aeration (the same as the local practice in timing and duration of aeration), delayed aeration, and prolonged aeration, were adopted separately and compared with respect to global warming potential (GWP) of CH4 and N2O emissions and rice yields as well. Total emission of CH4 from the rice fields ranged from 28.6 to 64.1 kg CH4 ha−1, while that of N2O did from 1.71 to 6.30 kg N2O–N ha−1 during the study periods. Compared with the local practice, early aeration reduced CH4 emission by 13.3–16.2% and increased N2O emission by 19.1–68.8%, while delayed aeration reduced N2O emission by 6.8–26.0% and increased CH4 emission by 22.1–47.3%. The lowest GWP of CH4 and N2O emissions occurred in prolonged aeration treatment, however, rice grain yield was reduced by 15.3% in this condition when compared with normal practice. It was found in the experiments that midseason aeration starting around D 30 after rice transplanting, just like the local practice, would optimize rice yields while simultaneously limiting GWPs of CH4 and N2O emissions from irrigated lowland rice fields in China.

Maize silage for dairy cows: mitigation of methane emissions can be offset by land use change

Abstract: Increasing the digestibility of cattle rations by feeding grains and whole plant silages from maize have been identified as effective options to mitigate greenhouse gas emissions. The effect of ploughing grassland for maize crops have not been taken into account yet. A intensive dairy farm is used as an example to demonstrate the trade offs by this type of land use change when more maize silage is fed to dairy cows. The model DAIRY WISE has been used to calculate the mitigation by the changed ration, the Introductory Carbon Balance Model to calculate the changes in soil organic carbon and nitrogen caused by ploughing grassland for maize crops. The losses of soil carbon and the loss of sequestration potential are much larger than the annual mitigation by feeding more maize. The ecosystem carbon payback time defines the years of mitigation that are needed before the emissions due to land use change are compensated. For ploughing grassland on sandy soils, the carbon payback time is 60 years. A higher global warming potential for methane can reduce the carbon payback time with 30%. Ploughing clay soils with a higher equilibrium level of soil organic matter increases the payback time by maximally 70%. The payback times occur only in the case of permanent maize cropping, grass maize rotations cause annual losses of nitrous oxide that are larger than the mitigation by feeding more maize.

Nitrogen fixation of red clover interseeded with winter cereals across a management-induced fertility gradient

Abstract: The incorporation of legume cover crops into annual grain rotations remains limited, despite extensive evidence that they can reduce negative environmental impacts of agroecosystems while maintaining crop yields. Diversified grain rotations that include a winter cereal have a unique niche for interseeding cover crops. To understand how management-driven soil fertility differences and inter-seeding with grains influenced red clover (Trifolium pratense) N2 fixation, we estimated biological N2 fixation (BNF) in 2006 and 2007, using the 15N natural abundance method across 15 farm fields characterized based on the reliance on BNF derived N inputs as a fraction of total N inputs. Plant treatments included winter grain with and without interseeded red clover, monoculture clover, monoculture orchardgrass (Dactylis glomerata), and clover-orchardgrass mixtures. Fields with a history of legume-based management had larger labile soil nitrogen pools and lower soil P levels. Orchardgrass biomass was positively correlated with the management-induced N fertility gradient, but we did not detect any relationship between soil N availability and clover N2 fixation. Interseeding clover with a winter cereal did not alter winter grain yield, however, clover production was lower during the establishment year when interseeded with taller winter grain varieties, most likely due to competition for light. Interseeding clover increased the % N from fixation relative to the monoculture clover (72% vs. 63%, respectively) and the average total N2 fixed at the end of the first growing season (57 vs. 47 kg N ha−1, respectively). Similar principles could be applied to develop more cash crop-cover crop complementary pairings that provide both an annual grain harvest and legume cover crop benefits.

Nutrient recycling potential of rock phosphate and waste mica enriched compost on crop productivity and changes in soil fertility under potato–soybean cropping sequence in an Inceptisol of Indo-Gangetic Plains of India

Abstract: This manuscript focuses on the nutrient recycling potential of enriched compost prepared using rice straw, low-grade rock phosphate (RP) and waste mica along with Aspergillus awamori and their effect on crop productivity and changes in soil fertility under potato–soybean cropping sequence in an Inceptisol of Indo-Gangetic Plains of India. Enriched composts had higher total as well as bioavailable P and K content than ordinary compost. Data emanated from the field study revealed that yield and uptake of N, P and K by potato tubers were significantly increased due to application of inorganic fertilizer and enriched compost over control. Application of 50% recommended dose of NPK fertilizers (RDF) along with 4.0 Mg ha−1 of enriched compost product-C prepared by rice straw + RP @ 4% P + waste mica 4% K + Aspergillus awamori resulted in 43.3% additional yield and 102.3, 67.0 and 62.2% additional N, P and K uptake by potato over control, respectively. Significant increase in yield and uptake of N, P and K by soybean grown on residual fertility were also observed over control. Post-harvest soil analysis indicated a significant build-up in soil organic C, available N, P and K due to application of enriched compost in combination with inorganic fertilizer over 100% RDF. The results clearly showed that enriched compost could be an alternative and cost effective option to prepare a value added product using agricultural wastes and low-grade minerals like RP and waste mica in place of costly chemical fertilizer for crop production and maintaining soil fertility.

Runoff capture through vegetative barriers and planting methodologies to reduce erosion, and improve soil moisture, fertility and crop productivity in southern Orissa, India

Abstract: Use of perennial grasses as vegetative barriers to reduce soil erosion from farm and non-farm lands is increasing world-over. A number of perennial grasses have been identified for their soil conserving properties, but their effectiveness varies with location and method of planting. Installing vegetative barriers in combination with suitable mechanical measures, like bunds or trenches or both, on the appropriately spaced contours may enhance their conservation potential. Hence, the effect of vegetative barriers, viz., sambuta (Saccharum spp.)—a local grass, vetiver (Vetiveria zizanioides) and lemongrass (Cymbopogon citratus) planted in combination with trench-cum-bund, on runoff, soil loss, nutrient loss, soil fertility, moisture retention and crop yield in the rainfed uplands, was studied in Kokriguda watershed in southern Orissa, India through 2001–2005. However, runoff, soil and nutrient losses were studied for 2002, 2003 and 2004 only. Analysis of the experimental data revealed that on a 5% slope, the lowest average runoff (8.1%) and soil loss (4.0 Mg ha−1) were observed in the sambuta + trench-cum-bund treatment followed by vetiver + trench-cum-bund (runoff 9.8%, soil loss 5.5 Mg ha−1). Lemongrass permitted the highest runoff and soil loss. Further, the conservation effect of grass barriers was greater under bund planting than berm planting. Minimum organic C (50.02 kg ha−1), available N (2.49 kg ha−1) and available K (1.56 kg ha−1) loss was observed under sambuta with bund planting. The next best arrester of the soil nutrients was vetiver planted on bund. Significantly better conservation of nutrients under sambuta and vetiver resulted in the soil fertility build-up. Soil moisture content was also higher in the sambuta and vetiver than lemongrass treated plots. Increase in the yield of associated finger millet (Eleusine coracana (L.) Gaertn.) due to vegetative barriers ranged from 18.04% for lemongrass to 33.67% for sambuta. Further, the sambuta and vetiver treated plots produced 13.23 and 11.86% higher yield, respectively, compared to the plots having lemongrass barrier (1.17 Mg ha−1). Considering the conservation potential, and crop yield and soil fertility improvements, the sambuta barrier with trench-cum-bund is the best conservation technology for treating the cultivated land vulnerable to water erosion. Farmers also showed greater acceptance for the sambuta barrier as it is erect growing and available locally. Vetiver with-trench-cum bund can be the second best option.

Legume cover crops and mulches: effects on nitrate leaching and nitrogen input in a pepper crop ( Capsicum annuum L.)

Abstract: 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 (R2 = 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.

Nitrogen, phosphorus and potassium balances and cycles of Swiss agriculture from 1975 to 2008

Abstract: Intensification of Swiss agriculture after 1950 led to an increase in productivity and a range of environmental and health problems provoked by growing inputs of nitrogen (N), phosphorus (P) and potassium (K) into the agricultural cycle. In 2008, farm-gate balances showed surpluses of 108 kg N ha−1, 5.5 kg P ha−1 and 28 kg K ha−1 for Swiss agriculture. Nutrient surpluses rose between 1975 and 1980 and then decreased significantly until 2008, with percentage reductions being higher for P (80%) and K (54%) than for N (27%). The introduction of direct payments for ecological programmes such as integrated production in 1993 led to a more pronounced decrease in nutrient surpluses for several years, until most farmers had joined these programmes. Lower surpluses could primarily be attributed to reductions in mineral fertilizer use and N deposition. Biological N fixation and atmospheric deposition contributed most to the uncertainty in calculating nutrient balances. N cycle was characterized by substantial inputs into and outputs out of the agricultural sector, whereas P and K cycles were more closed. In future, nutrient balances at a regional level are required to identify areas with high surpluses. In Switzerland, a further reduction in surpluses could be achieved by better feeding strategies and an improved fertilizer management, mainly of animal manure.

Decomposition, nitrogen and phosphorus mineralization from winter-grown cover crop residues and suitability for a smallholder farming system in South Africa

Abstract: Increasing land degradation has prompted interest in conservation agriculture which includes growing cover crops. Besides providing soil cover, decaying cover crops may release substantial amounts of nutrients. Decomposition, N and P release from winter cover crops [grazing vetch (Vicia darsycarpa), forage peas (Pisum sativum) and oats (Avena sativa)] were assessed for suitability in a cropping system found in the smallholder irrigation sector of South Africa. Nitrogen and P contribution to maize growth by cover crop residues was also estimated. Decrease in mass of cover crop residues was highest in grazing vetch (7% remaining mass after 124 days) followed by forage peas (16%) and lastly oats (40%). Maximum net mineralized N and P were higher for grazing vetch (84.8 mg N/kg; 3.6 mg P/kg) than for forage peas (66.3 mg N/kg; 2.7 mg P/ha) and oats (13.7 mg N/kg; 2.8 mg P/kg). Grazing vetch and forage pea residues resulted in higher N contribution to maize stover than oat residues. Farmers may use grazing vetch for improvement of soil mineral N while oats may result in enhancement of soil organic matter and reduction land degradation because of their slow decomposition. Terminating legume cover crops a month before planting summer crops synchronizes nutrient release from winter-grown legume cover crops and uptake by summer crops.

Yield response models to phosphorus application: a research synthesis of Finnish field trials to optimize fertilizer P use of cereals

Abstract: Fertilizer applications should be based on relevant yield response models and be economically justified. In this study, we defined the yield response models of cereals to phosphorus (P) fertilization on the major Finnish soil types by the means of a research synthesis and meta-analysis. We also calculated economically optimum P rates under different price combinations of P fertilizer (1–3 € kg−1) and cereal yields (100–300 € tn−1), for 1-year decision interval of P applications. Our material consisted of data on P fertilizer experiments conducted in Finland during the last 60 years on clay, coarse-textured mineral and organic soils, with variable soil test P (STP) status at the start of the experiments. The cereals cultivated were spring barley, oats, spring and winter wheat, and winter rye. The applied P rates ranged between 6 and 100 kg ha−1. For low STP classes, Mitscherlich-type exponential models were appropriate for all soil groups, predicting 17–27% higher maximum yields when compared to the controls without added P. In contrast, for medium and high STP classes, the yield responses to increasing P rates were scattered around zero in most soils. Phosphorus fertilization had also negligible effect on 1,000-seed and test weights. On Finnish cereal farms, when P fertilizer is purchased, the present P rates allowed by the Agri-Environmental Programme are uneconomically high. It appears that P fertilization can be substantially reduced on majority of Finnish fields, or even omitted for years, without economic loss under current (2 € kg−1) or higher P fertilizer prices.

Nitrate loss via overland flow and interflow from a sloped farmland in the hilly area of purple soil, China

Abstract: Nitrate losses through runoff (both overland flow and interflow) represent a significant portion of the nitrogen (N) biogeochemical cycle. The mechanisms of this cycle have been well documented for flat agricultural lands. It is unclear, however, how nitrate loss takes place in sloping farmlands of purple soil. This paper reports the finding of a field experiment examining nitrate losses due to overland flow and interflow along sloping farmland sites dominated by a regosol known as purple soil in the Sichuan Basin, Southwest China. During rainfall events, the nitrate contents in the overland flow initially increased and then decreased gradually, however, the nitrate contents in the interflow increased and then approached to a steady status. The average nitrate concentrations in the overland flow and the interflow were 0.7 +/- A 0.2 and 21.7 +/- A 2.1 mg N L-1, respectively. The annual nitrate loss loads through the overland flow and the interflow were 0.9 +/- A 0.1 and 33.5 +/- A 2.7 kg N ha(-1), respectively accounting for 0.6 and 22% of the fertilizer applied in the growing season. Nitrate was predominantly lost via interflow in the sloping farmland in Sichuan Basin, Southwest China. The experimental farmland was located in the upper stream of the Yangtze River, and the conclusions yielded from this study can be applied to interpreting the eutrophication and groundwater pollution patterns that are currently occurring in this watershed.

Fate of labeled urea-15N as basal and topdressing applications in an irrigated wheat–maize rotation system in North China Plain: I winter wheat

Abstract: A field micro-plot experiment for summer maize was conducted in an irrigated winter wheat (Triticum aestivum)-summer maize (Zea mays L.) rotation system in Mazhuang, Xinji of Hebei province in the North China Plain, using the 15N isotope method to determine the effects of N application (rates and timing) on urea-15N fate, residual N effects and N recovery efficiency (NRE) by maize. The experiment included three N rates (90, 180, and 270 kg ha−1), divided by two 15N-labeled groups of basal-15N (30, 60, and 90 kg ha−1, respectively) and topdress-15N (60, 120, and 180 kg N ha−1, respectively). All of the treatments were irrigated two times, once at seeding time and once at topdressing time. The absorbed N in the maize plant derived from basal-N (6.8–13%) and topdress-N (17–30%) was identified. The residual N in the 0–150-cm soil depth ranged from 45 to 60% at the first maize harvest, mainly retained in the top 20-cm layers. Both NRE in grain and total N recovery in plant in the first maize crop were higher from topdress-15N (26–31 or 41–51%, respectively) than from basal-15N (18–23 or 34–43%, respectively). The residual N in the 0–150-cm soil layer was lower from topdress-15N (45–47%) than from basal-15N (55–60%) after the first maize harvest. Residual N recovery was 6–11% in the second and 1.5–3.5% in the third crop. Cumulative N recovery in the maize-wheat-maize rotations was higher from the topdress-15N (49–59%) than from basal-15N and (45–55%). The unaccounted N loss was 14–24% from the basal-15N and 20–33% from the topdress-15N, with a double dose of basal-15N application. An N rate of approximately 180 kg ha−1 appears to be an effective application rate to optimum maize yield and NRE on North China Plain, depending on the residual N and the crop yield potential.

Effect of drainage in the fallow season on reduction of CH4 production and emission from permanently flooded rice fields

Abstract: Field and incubation experiments were conducted during 2007–2009 to study the effect of drainage in the fallow season on CH4 production and emission from permanently flooded rice fields. It was found that drainage in the fallow season significantly affected the temporal variations of CH4 production and emission from permanently flooded rice fields. CH4 production and emission from permanently flooded rice fields (Treatment FF) mainly occurred during the rice season, where they were found to be much lower in the late fallow season. No CH4 flux was detected from drained fields (Treatment DF) in the fallow season. Compared with Treatment FF, Treatment DF was delayed not only its onset of CH4 production and emission, but also appearance of the highest peak of CH4 production during the rice season. A significant positive relationship was observed between CH4 production rates of paddy soil and corresponding CH4 fluxes (P < 0.01). CH4 production in rice roots was the highest in rate at the rice booting stage, but was obviously lower at the rice tillering, grain filling and ripening stages, and the highest value reached at the same time as the peak of CH4 production occurred in the paddy soil. Drainage in the fallow season significantly decreased CH4 production and emission from Treatment FF. Compared with Treatment FF, Treatment DF was about 42–61% lower in mean CH4 production rate in the paddy soil during the rice season, and was reduced by approximately 56% in mean CH4 production rate in rice roots. Accordingly, Treatment DF was 20.6–30.2 g CH4 m−2, 39–52% lower than Treatment FF in total CH4 emission during the rice season, and 44–57% lower in annual total CH4 emission. Rice yield in Treatment DF tended to be 4–7% lower than that in Treatment FF.

Conservation Tillage, Local Organic Resources, and Nitrogen Fertilizer Combinations Affect Maize Productivity, Soil Structure and Nutrient Balances in Semi-arid Kenya

Abstract: 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 (tillage system and low quantities of organic resources) 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 involving tied ridges (under reduced tillage), no-till and conventional tillage, and organic resource (manure and/or crop residue) combinations in the main plots, and chemical nitrogen fertilizer in subplots. Although yield in no-till was lower than conventional and tied ridges during initial two seasons, it achieved higher yields than did the other tillage systems by season 4. 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 57 to 190 kg N ha–1, 11 to 26 kg P ha–1, and 95 to 195 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. There were higher total nutrient NPK uptake treatments under tied ridges than in those under no-till and conventional tillage systems. We conclude that even with modest organic resource application, conservation tillage can be effective in improving crop yield and soil structure and that farmers are better off applying 1 t ha–1 each of crop residue and manure rather than sole manure.

Nitrous oxide emissions from fertilized and unfertilized grasslands on peat soil

Abstract: Emissions of nitrous oxide (N2O) from managed and grazed grasslands on peat soils are amongst the highest emissions in the world per unit of surface of agriculturally managed soil. According to the IPCC methodology, the direct N2O emissions from managed organic soils is the sum of N2O emissions derived from N input, including fertilizers, urine and dung of grazing cattle, and a constant ‘background’ N2O emission from decomposition of organic matter that depends on agro-climatic zone. In this paper we questioned the constant nature of this background emission from peat soils by monitoring N2O emissions, groundwater levels, N inputs and soil NO3 −–N contents from 4 grazed and fertilized grassland fields on managed organic peat soil. Two fields had a relatively low groundwater level (‘dry’ fields) and two fields had a relatively high groundwater level (‘wet’ fields). To measure the background N2O emission, unfertilized sub-plots were installed in each field. Measurements were performed monthly and after selected management events for 2 years (2008–2009). On the managed fields average cumulative emission equaled 21 ± 2 kg N ha−1y−1 for the ‘dry’ fields and 14 ± 3 kg N ha−1y−1 for the ‘wet’ fields. On the unfertilized sub-plots emissions equaled 4 ± 0.6 kg N ha−1y−1 for the ‘dry’ fields and 1 ± 0.7 kg N ha−1y−1 for the ‘wet’ fields, which is below the currently used estimates. Background emissions were closely correlated with groundwater level (R 2 = 0.73) and accounted for approximately 22% of the cumulative N2O emission for the dry fields and for approximately 10% of the cumulative N2O emissions from the wet fields. The results of this study demonstrate that the accuracy of estimating direct N2O emissions from peat soils can be improved by approximately 20% by applying a background emission of N2O that depends on annual average groundwater level rather than applying a constant value.

Dynamics of methane emission, active soil organic carbon and their relationships in wetland integrated rice-duck systems in Southern China

Abstract: A randomized field experiment with three replicates was conducted in the subtropical region of China to investigate the effects of integrated rice-duck system (RD) on methane (CH4) emission, active soil organic carbon fractions and their relationships in 2007 and 2008, compared with conventional rice system (CK). Methane emissions were measured at 7–9 days intervals using a closed static chamber technique, and two fractions of active soil organic carbon, namely, dissolved organic carbon (DOC) and microbial biomass carbon (MBC), were analyzed simultaneously. Soil DOC and MBC in RD and CK had similarly distinct seasonal variation patterns within the 2 years. During this time DOC and MBC concentrations were low at the early growth stage, increased during panicle differentiation and heading period, and dropped during grain filling period of rice. CH4 emission fluxes from RD and CK followed a similar seasonal variation pattern both in 2007 and 2008. Two peaks of CH4 emission were observed, the first at the tillering stage, second at panicle differentiation and heading stage. The CH4 cumulative emission was reduced in RD by 19.3 and 19.6% in 2007 and 2008, respectively, compared with CK. Seasonal variation pattern of CH4 emission was regulated by soil DOC, MBC and soil temperature, all of which were significantly positively correlated with methane emissions. Improvement in soil redox status was the predominant reason for significant reduction of CH4 emission in RD. These results clearly indicate that integrated rice-duck system could be an effective mode of rice farming for decrease in methane emission in southern China.

Leaching losses of nitrate nitrogen and dissolved organic nitrogen from a yearly two crops system, wheat-maize, under monsoon situations

Abstract: A large amount of nitrogen (N) fertilizers applied to the winter wheat-summer maize double cropping systems in the North China Plain (NCP) contributes largely to N leaching to the groundwater. A series of field experiments were carried out during October 2004 and September 2007 in a lysimeter field to reveal the temporal changes of N leaching losses below 2-m depth from this land system as well as the effects of N fertilizer application rates on N leaching. Four N rates (0, 180, 260, and 360 kg N ha(-1) as urea) were applied in the study area. Seasonal leachate volumes were 87 and 72 mm in the first and second maize season, respectively, and 13 and 4 mm during the winter wheat and maize season in the third rotational year, respectively. The average seasonal flow-weighted NO(3)-N concentrations in leachate for the four N fertilizer application rates ranged from 8.1 to 103.7 mg N l(-1), and seasonal flow-weighted dissolved organic nitrogen (DON) concentrations in leachate varied from 0.8 to 6.0 mg N l(-1). Total amounts of NO(3)-N leaching lost throughout the 3 years were in the range of 14.6 to 177.8 kg ha(-1) for the four N application rates, corresponding to N leaching losses in the range of 4.0-7.6% of the fertilizers applied. DON losses throughout the 3 years were 1.4, 2.1, 3.6, and 6.3 kg N ha(-1) for the four corresponding fertilization rates. The application rate of 180 kg N ha(-1) was recommended based on the balance between reducing N leaching and maintaining crop yields. The results indicated that there is a potential risk of N leaching during the winter wheat season, and over-fertilization of chemical N can result in substantial N leaching losses by high-intensity rainfalls in summer.