High Nitrogen Input Research Articles

Deficit irrigation combined with reduced N-fertilizer rate can mitigate the high nitrous oxide emissions from Chinese drip-fertigated maize field

Agricultural soils are major sources of the greenhouse gas N2O, particularly under maize with high nitrogen (N) inputs and excessive irrigation. To determine how N and water management can mitigate N2O emissions from drip-irrigated maize fields, a field study was carried out in the North China Plain during the maize growing season. The objective of the study was to investigate the individual and combined effects of irrigation level and N input on N2O emissions and grain yields, as well as N and water use efficiency (WUE), under drip-fertigation management. The main treatments were two irrigation levels: 50 mm/event (sufficient irrigation, WH) and 25 mm/event (limited irrigation, WL), with four N application rates: 0 (N0), 90 (N1), 180 (N2), and 270 (N3) kg N ha−1. Pulses of N2O emissions were recorded every 2–3 d following each irrigation or fertigation (irrigation + fertilization) event. N input, irrigation, and their interactions all significantly influenced N2O emissions. A significant exponential relationship (P < 0.05) was observed between N application rate and cumulative and yield-scaled N2O emissions in both irrigation treatments. The cumulative N2O emission fluxes from the N0, N1, N2, and N3 levels of fertilizer with WL were 11.4, 13.8, 27.2, and 58.8% lower, respectively, than those from the same N levels with WH; this occurred because high pulses of N2O were avoided during low irrigation conditions. Under WH, denitrification was the likely source of the high amounts of N2O, whereas nitrification was likely the main source of N2O emissions under WL. The variations in the water-filled pore space (WFPS) between the two irrigation treatments may explain these results. The effect of N fertilizer on grain yield and WUE depended on the availability of soil water. Based on the available soil water content, the regulation of N fertilizer application can increase yield and also reduce cumulative and yield-scaled N2O emissions.

Germany’s Excessive Agricultural Nitrogen Emissions and the Need for Improving Existing Regulatory Concepts

For decades, German agriculture has been responsible for high nitrogen inputs into the environment. Recent reductions in nitrogen surpluses that were originally caused by fertilization are not sufficient to meet European requirements. In the case of ammonia emissions, there has even been an upward trend despite contradicting national emission targets due to the expansion of animal husbandry. Both developments are not surprising, since German agricultural policy has for years been unable to adopt stricter measures that would reduce nitrogen surpluses and ammonia emissions and modernise existing regulatory concepts in line with European requirements. This paper presents the state of current emissions in section 1. Subsequently, sections 2 to 4 present the regulatory concepts for livestock facilities, agricultural fertilisation as well as the protection of Natura 2000 areas from agricultural intervention and identify their shortcomings in the light of recent rulings by the European Court of Justice. The paper offers a summary assessment that includes the most important areas for improvement.

Biochar amendment in reductive soil disinfestation process improved remediation effect and reduced N2O emission in a nitrate-riched degraded soil

ABSTRACTGreenhouse cultivation with high nitrogen inputs is extensively used in the vegetable production in China, leading to severe soil degradation. To effectively improve the quality of degraded soils, reductive soil disinfestation (RSD) has been adopted as a reliable remediation method but high N2O emission would occur in nitrate-riched soils during RSD treatment. This study aimed to apply biochar amendment to reduce N2O emission during the RSD remediation of degraded vegetable soils. The remediation effect and N2O emission were investigated during the RSD process followed by tomato cultivation in pot culture experiment. Results showed that RSD treatments with and without biochar amendment both significantly increased soil pH from 4.0 to 6.1 and decreased NO3− content in degraded soil from 180 to less than 20 mg kg−1. These RSD treatments also promoted the plant growth and vegetable production in the following cultivation. Biochar amendment decreased N2O emission during the RSD treatment stage with a reduction of cumulative emission of 39%. The inhibitive effect of biochar on N2O emission was potentially realized through the increase of soil pH. Biochar amendment may be an effective means to mitigate N2O emission in the RSD application with promoting effects for vegetable growth.

Analysis of durum wheat proteome changes under marine and fungal biostimulant treatments using large-scale quantitative proteomics: A useful dataset of durum wheat proteins

Durum wheat requires high nitrogen inputs to obtain the high protein concentration necessary to satisfy pasta and semolina quality criteria. Optimizing plant nitrogen use efficiency is therefore of major importance for wheat grain quality. Here, we studied the impact on grain yield, protein concentration, and for the first time on protein composition of a marine (DPI4913) and a fungal (AF086) biostimulants applied to plant leaves. A large-scale quantitative proteomics analysis of wheat flour samples led to a dataset of 1471 identified proteins. Quantitative analysis of 1391 proteins revealed 26 and 38 proteins with a significantly varying abundance after DPI4913 and AF086 treatment, respectively, with 14 proteins in common. Major effects affected proteins involved in grain technological properties like grain hardness, in storage functions with the gluten protein gamma-gliadin, in regulation processes with transcription regulator proteins, and in stress responses with biotic and abiotic stress defense proteins. The involvement of biostimulants in the abiotic stress response was further suggested by an increase in water-use efficiency for both DPI4913 (15.4%) and AF086 (9.9%) treatments. Overall, our work performed in controlled conditions showed that DPI4913 and AF086 treatments promoted grain yield while maintaining protein concentration, and positively affected protein composition for grain quality.Data are available via ProteomeXchange with identifier PXD012469.

Intercropping N-fixing shrubs in pine plantation forestry as an ecologically sustainable management option

We explored the ecological impact of a nitrogen-fixing shrub (Ulex europaeus, common gorse) cultivated as an intercrop species in the interlines of a young stand of maritime pine (Pinus pinaster). Nitrogen fixing species are well-known for their advantage of increasing the soil fertility in agriculture. Nevertheless, in forest ecosystems, their use is uncommon except in some associations in the tropics. The Landes de Gascogne forest range (SW France) has soil fertility issues and Ulex europaeus is a vigorous plant, native to this region. Therefore, an investigation of the association of this N-fixing species with trees is worthwhile.To this end, we compared a standard pine plantation management (control) with a treatment where gorse seeds were sown in the interlines at tree plantation (gorse sowing). This factor was combined with a phosphorus supply (control versus P-fertilisation), resulting in four treatments. The forestry practices evaluated here distinguish two main periods: a first period of six years after tree plantation when gorse individuals grew as an intercrop and formed dense vegetation, and a second period of three years after crushing this vegetation in the interlines.In the first period, pine mortality in the gorse sowing treatment was higher during the dry season than in the control treatment, suggesting competition for water. Pine diameter growth was reduced, but not height growth, indicating avoidance of light competition with gorse. In the presence of gorse, pine foliar-N was appreciably enhanced relative to the control, and natural pine pruning occurred, while pine browsing by animals was limited due to the protection of the thorny gorse thickets surrounding the trees. In the second period, soon after crushing the gorse vegetation in the interlines, enrichment of nitrogen in needles continued, suggesting a fertilising effect of the gorse remnants. Crushing also freed the pines from shrub competition and a “catch-up growth” was identified regarding diameter and stem volume growth. Two years after the gorse crushing, tree size and biomass were similar in the experimental treatments regardless of gorse sowing or not.Overall, during the first nine years after tree plantation, gorse introduction in the pine tree forests had various effects. On the one hand, gorse induced competition for light and water. On the other hand, it resulted in high inputs of nitrogen and organic matter into the ecosystem which could lead to sustained soil fertility and this might improve tree nutritional status. We recommend continuing the assessment of such pine-gorse forestry associations for longer observation periods and in very nutrient-poor sites in this forest range.

Direct and indirect effects of nitrogen enrichment on soil organisms and carbon and nitrogen mineralization in a semi‐arid grassland

Abstract Semi‐arid grasslands on the Mongolian Plateau are expected to experience high inputs of anthropogenic reactive nitrogen in this century. It remains unclear, however, how soil organisms and nutrient cycling are directly affected by N enrichment (i.e., without mediation by plant input to soil) vs. indirectly affected via changes in plant‐related inputs to soils resulting from N enrichment. To test the direct and indirect effects of N enrichment on soil organisms (bacteria, fungi and nematodes) and their associated C and N mineralization, in 2010, we designated two subplots (with plants and without plants) in every plot of a six‐level N‐enrichment experiment established in 1999 in a semi‐arid grassland. In 2014, 4 years after subplots with and without plant were established, N enrichment had substantially altered the soil bacterial, fungal and nematode community structures due to declines in biomass or abundance whether plants had been removed or not. N enrichment also reduced the diversity of these groups (except for fungi) and the soil C mineralization rate and induced a hump‐shaped response of soil N mineralization. As expected, plant removal decreased the biomass or abundance of soil organisms and C and N mineralization rates due to declines in soil substrates or food resources. Analyses of plant‐removal‐induced changes (ratios of without‐ to with‐plant subplots) showed that micro‐organisms and C and N mineralization rates were not enhanced as N enrichment increased but that nematodes were enhanced as N enrichment increased, indicating that the effects of plant removal on soil organisms and mineralization depended on trophic level and nutrient status. Surprisingly, there was no statistical interaction between N enrichment and plant removal for most variables, indicating that plant‐related inputs did not qualitatively change the effects of N enrichment on soil organisms or mineralization. Structural equation modelling confirmed that changes in soil communities and mineralization rates were more affected by the direct effects of N enrichment (via soil acidification and increased N availability) than by plant‐related indirect effects. Our results provide insight into how future changes in N deposition and vegetation may modify below‐ground communities and processes in grassland ecosystems. A plain language summary is available for this article.

High nitrogen input reduces yield loss from low temperature during the seedling stage in early-season rice

Early transplanting of the first crop is often attempted by farmers to increase rice yields in double-season rice cropping systems in central China. The risk of yield loss from low temperature is high with early transplanting; heavy application of nitrogen (N) fertilizer is commonly practiced to minimize this risk. However, whether the negative effects of low temperature on rice growth and yield can be mitigated by applying more N fertilizer is unclear. To address this question, we conducted field experiments on early-season rice in Wuxue county, Hubei province, China with two transplanting dates (early and normal) and two N rates (low and high) in 2016 and 2017. Transplanting was advanced by 9 days in the early compared with that in the normal transplanting date, and the high N treatment received 70 kg ha−1 more basal N than did the low N treatment. Early transplanting reduced the grain yield of early-season rice by 20.1% in 2016 and by 7.0% in 2017 at the low N rate, but there was no difference in grain yield between transplanting dates at the high N rate in both years. The high N rate increased the grain yield of early transplanting by 21.9%, averaged across the two years. Both the reduction in grain yield due to early transplanting and the increase in grain yield due to the high N rate under early transplanting were explained by the number of spikelets m-2 and dry weight production. The high N rate promoted N uptake, tillering, and leaf area development under low temperature. Thus, we conclude that the negative effects of low temperature on early-season rice can be mitigated by applying more basal N fertilizer. Environmental concerns about the practices of early transplanting and heavy basal N application for early-season rice are discussed.

Nitrate leaching from open-field and greenhouse vegetable systems in China: a meta-analysis.

The potential for nitrate leaching in Chinese vegetable systems is substantial because of high inputs of nitrogen (N) fertilizer and water. To quantify the nitrate leaching and identify the key controlling factors in Chinese vegetable systems, we conducted a meta-analysis that included 221 data sets from 18 field studies. The results revealed that nitrate leaching over the entire crop growing season in Chinese vegetable systems was very high and averaged 79.1kgNha-1 and primarily resulted from extremely high N fertilizer inputs (in average 423kgNha-1). Nitrate leaching was, on the average, 63.9% greater in the greenhouse systems (98.0kgNha-1) than in open-field systems (59.8kgNha-1). The leaching factor, defined as the proportion of the quantity of N applied to soils that was lost due to nitrate leaching, averaged 14.6% overall and was significantly lower in greenhouse systems (10.9%) than in open-field systems (18.4%). This difference appears to be due to lower of the total water inputs (irrigation + precipitation) in greenhouse systems. Nitrate leaching increased with water input, the number of growing days, and the N rate. The nitrate leaching response to increasing N rate was linear. The leaching factor significantly increased with water input but was not affected by the N rate or the number of growing days. Compared with application of synthetic fertilizer alone, the application of manure alone or manure plus synthetic fertilizer significantly reduced both the nitrate leaching and the leaching factor in open-field and greenhouse systems. These results suggest that nitrate leaching in Chinese vegetable systems can be reduced by optimizing rates of N and water supply to synchronize crop needs. Application of mixed synthetic N fertilizer and manure is more effective in reducing nitrate leaching, compared to synthetic N only.

Impact of Exogenous Nitrogen Import on Sediment Denitrification and N2O Emissions in Ditches Under Different Land Uses

Farmland drainage ditch soil can consume part of the agricultural non-point nitrogen through nitrification-denitrification processes. Paddy fields, vegetable land, and orchards are the main types of land uses in the Taihu Lake region, and many drainage ditches are distributed across these lands. The way exogenous nitrogen is imported to drain ditches under different land uses differs significantly, which can directly affect the nitrogen consumption ability of the channels. A soil incubation experiment was conducted under laboratory conditions to study the denitrification loss and N2O emissions of drainage ditch soil under different land uses. In this study, drainage ditch sediment was collected from orchards, paddy fields, and vegetable land in the Taihu Lake region. Five different NO3--N content import levels were set:0, 0.5, 1.0, 5.0, and 10 mg·L-1, which were denoted as N0, N1, N2, N3, and N4, respectively. The results showed that exogenous nitrogen input stimulated sediment denitrification in the drainage ditches. The sediment denitrification rates of the three types of channels increased significantly with the increase of input NO3--N concentration (P<0.05). There was a significant linear positive correlation between the cumulative denitrification loss and input NO3--N concentration (R2>0.75). Excluding for the vegetable land sediment, the N2O emission rate and cumulative emissions did not increase significantly with the increase of input NO3--N concentration (P>0.05). There was no significant difference in the denitrification and N2O emissions among the three kinds of channel sediment, with no or low exogenous nitrogen input (N0and N1) (P>0.05). As the input NO3--N concentration increased, especially under the condition of high exogenous nitrogen input (N3and N4), the nitrogen consumed via denitrification in orchard and paddy field sediment was significantly higher than that in vegetable land sediment (P<0.05), whereas the N2O emissions of drainage ditch sediment from the vegetable land was significantly higher than that of the other two channel sediments (P<0.05). The mineralization rate of ditch soil organic carbon had a positive correlation with denitrification rate (n=15), and microbial mineralization (CO2-C) promoted the nitrification and denitrification of the drainage ditch soils.

Comparison of perennial ryegrass,Lolium perenneL., ploidy and white clover,Trifolium repensL., inclusion for herbage production, utilization and nutritive value

AbstractIncreasing herbage dry‐matter (DM) production and utilization on‐farm improves efficiency and sustainability. The objective of this study was to investigate the effect of perennial ryegrass,Lolium perenneL., ploidy and white clover,Trifolium repensL., inclusion on herbageDMproduction and utilization in an intensive animal grazing system, with high nitrogen (N) inputs (250 kg N ha−1) and a high stocking rate (2.75 livestock units ha−1). The study was a 2 × 2 factorial design, consisting of diploid and tetraploid cultivars sown as grass‐only and grass‐white clover to give four sward treatments (diploid‐only, tetraploid‐only, diploid‐white clover, tetraploid‐white clover). These were evaluated at each grazing occasion (8–10 per year) for 3 years (2014–2016). Tetraploid‐white and grass‐white clover swards had a lower sward density (−9 and −8 kg DM cm−1, respectively) and perennial ryegrass tiller density (−820 and −1,436 tillers m−2, respectively) leading to lower postgrazing sward heights (−0.15 and −0.41 cm, respectively), and maintained a superior nutritive value when compared with diploid‐only and grass‐only swards respectively. White clover inclusion resulted in higher productivity characterized by increased herbageDMproduction (+1,468 kg DM ha−1), improved nutritive value and increased utilization across the three grazing seasons. Varying sward composition with perennial ryegrass ploidy led to improved nutritive value and favourable grazing characteristics in tetraploid swards.

The relative importance of autochthony along the longitudinal gradient of a small South African river influenced by agricultural activities

Generalisations about the sources of organic matter that support aquatic consumers are usually focussed on certain parts of the world (particularly the northern hemisphere) and large rivers, and therefore may not include the full spectrum of food webs that occur in the southern hemisphere (particularly those with high nitrogen inputs). We studied the relative importance of organic matter sources to macroinvertebrate consumers in a small South African river. Based on previous observations of our system of interest and other agricultural streams, we hypothesised that (a) the carbon fuelling consumers is primarily derived from autochthonous (in situ) food sources regardless of sampling time and, (b) the contribution of autochthonous basal resources to consumers increases in importance as the river widens (from upper to downstream reaches). To test these predictions, stable carbon (δ13C) and nitrogen (δ15N) isotopes were used to estimate the contributions of local algal and land-based production to aquatic macroinvertebrates over space (six sites) and time (four sampling occasions between November 2012 and September 2013) along the Kowie River, South Africa. Mixing models revealed that consumers in the upper reaches assimilated terrestrially-derived allochthonous organic matter, and consumers in the middle and lower reaches assimilated primarily autochthonous basal resources (macrophytes and algae). The isotopic values of consumers and their food sources changed over time, indicating that food sources and consumers should be analysed many times throughout the year to capture that variability and ensure that ephemeral components of the food web are not missed. Our results enhance the growing body of literature on the dynamics of riverine systems and indicate the importance of autochthony in a small temperate river with high nitrogen inputs.

Community Composition of Nitrous Oxide-Related Genes in Salt Marsh Sediments Exposed to Nitrogen Enrichment.

Salt marshes provide many key ecosystem services that have tremendous ecological and economic value. One critical service is the removal of fixed nitrogen from coastal waters, which limits the negative effects of eutrophication resulting from increased nutrient supply. Nutrient enrichment of salt marsh sediments results in higher rates of nitrogen cycling and, commonly, a concurrent increase in the flux of nitrous oxide, an important greenhouse gas. Little is known, however, regarding controls on the microbial communities that contribute to nitrous oxide fluxes in marsh sediments. To address this disconnect, we generated profiles of microbial communities and communities of micro-organisms containing specific nitrogen cycling genes that encode several enzymes (amoA, norB, nosZ) related to nitrous oxide flux from salt marsh sediments. We hypothesized that communities of microbes responsible for nitrogen transformations will be structured by nitrogen availability. Taxa that respond positively to high nitrogen inputs may be responsible for the elevated rates of nitrogen cycling processes measured in fertilized sediments. Our data show that, with the exception of ammonia-oxidizing archaea, the community composition of organisms involved in the production and consumption of nitrous oxide was altered under nutrient enrichment. These results suggest that previously measured rates of nitrous oxide production and consumption are likely the result of changes in community structure, not simply changes in microbial activity.

Economic and environmental linear optimization model of crop production in selected regions of Slovakia

Abstract For the agricultural industry in Slovakia, the dominating sector is crop production. The major part of arable land is devoted to the cultivation of cereals (57%), feed crops (20%) and industry crops (19%).The aim of this paper is to model the distribution of crop management practices in selected regions of Slovakia and identify the net return for four selected crops in these regions. We use integrated modelling framework which incorporates bio-physical and economic data to identify opportunity costs of agricultural production choices. We delineate homogenous response units (HRU) and aggregate them on regional level as the model is constrained by land endowment in particular region. The results suggest that highest yields and thus high returns are achieved in case of management practice with high nitrogen input and irrigation. The high input management causes environmental pressures on soils, therefore its enforcement in regions is not desirable. The solution might appear in policy premiums for low input management practices.

Implications of grass–clover interactions in dairy pastures for forage value indexing systems. 5. Southland

ABSTRACTThis experiment, implemented at a Southland site representative of the lower South Island, New Zealand, and monitored for three full years from 2012/2013 to 2015/2016, was one of four throughout New Zealand that investigated the yield and nutritive value rankings of perennial ryegrass cultivars sown with or without white clover and with high (225 kg N/ha/annum) or low (50 kg N/ha/annum) application rates of nitrogen fertiliser. High inputs of nitrogen (N) fertiliser increased annual total dry matter (DM) yields and seasonal yield in 12 out of 18 measurement occasions. Adding white clover increased both annual dry matter yield and seasonal yield in 7 out of 18 measurement occasions. An interaction between clover and N input occurred on 10 occasions. Over time, the low N minus clover treatment became progressively lower yielding compared with the other three treatments. Ryegrass cultivar by clover interactions occurred in the latter half of the experiment. When analysed using ryegrass characteristics, early- and late-heading ryegrass cultivars produced similar yields when sown without clover, but late-heading ryegrass cultivars had a higher yield than early-heading pastures when sown with white clover (P < .001). Tetraploid ryegrasses had lower yields than diploid ryegrasses when sown without clover (P = .001). This difference was reduced when white clover was included. There was no significant interaction with ryegrass morphology when sown with white clover, as dense ryegrass cultivars always had a higher yield than open ryegrass cultivars (P = .005). Interactions occurred between N input levels and ryegrass cultivar. These occurred in early spring or late spring of each year. Analysis by ryegrass characteristics identified consistent interactions. Ryegrass cultivars with a late-heading date were higher yielding than early-heading cultivars at low N inputs (P = .029), but they were not different at high N inputs. Diploid and tetraploid ryegrass cultivars were similar with low N inputs, but diploid cultivars out-yielded tetraploid cultivars at high N inputs (P = .005). Significant interactions between N inputs and white clover addition affected herbage nutritive value but this did not extend to consistent interactions with ryegrass cultivar. Invertebrate pest numbers were generally low and unlikely to have influenced clover/ryegrass interactions or cultivar ranking. Results from this site suggest that ranking of ryegrass cultivars needs to account for both the inclusion of clover and variation in N fertiliser input.

Green manure effects on zinc and cadmium accumulation in wheat grains (Triticum aestivum L.) on high and low zinc soils

Zinc (Zn) deficiency is a global problem in human nutrition due to imbalanced diets based on staple foods of low Zn contents. This study investigated the potential of using clover (Trifolium alexandrinum L.) and mustard (Sinapis alba L.) green manure crops to increase soil Zn uptake by wheat (Trifolium aestivum L.) without enhancing cadmium (Cd) accumulation. A factorial pot experiment with wheat was performed with three green manure treatments (clover, mustard or no green manure) and three soil treatments which were a high-Zn soil (FYM), a low-Zn soil (TURK) and the TURK soil with mineral Zn fertilization (TURK+ZN). Green manure crops were grown first and then incorporated into the soils before wheat. In contrast to mustard, clover increased grain Zn concentrations in the FYM and TURK+ZN soils, but not in the TURK soil. The effect appeared to be due to high soil nitrogen inputs and concurrent pH decrease, root biomass increase, and the release of organic ligands mobilizing soil Zn and Cd. However, the high N inputs also induced Cd accumulation above critical thresholds. The study suggests that on Zn sufficient soils or in combination with Zn fertilizer, leguminous green manure can increase soil Zn accumulation by wheat.

Root system characterization and water requirements of ten perennial herbaceous species for biomass production managed with high nitrogen and water inputs

Although several studies have investigated the aboveground production of perennial herbaceous species for biomass production, only a few details are available on their root systems and water balance. This paper provides a root system characterization and a water balance calculation for ten perennial herbaceous species (Arctium lappa L., Arundo donax L., Carex acutiformis Ehrh., Carex riparia Curtis, Glyceria maxima (Hartm.) Holmb., Helianthus tuberosus L., Iris pseudacorus L., Lythrum salicaria L., Miscanthus x giganteus Greef et Deu., Symphitum x uplandicum Nyman) cultivated with high fertilizer and water inputs in a four-year study. Crop evapotranspiration (ETc) maintained the same seasonal trend for all studied species, with the highest cumulative seasonal average water losses for A. donax (1675.1mm) and the lowest for G. maxima (1406.0mm). During the growing season, crop coefficients followed a similar trend to that reported for ETc, with average seasonal values ranging from 1.9 for A. lappa and G. maxima to 2.6 for M. x giganteus. For all species soil moisture was higher in the deeper soil layers (20–50 and 50–90cm) than in the upper (0–20cm) where a high root system biomass was observed. At the end of the study, different root system biomass productions were found between species with the highest median value at 0–50cm depth for M. x giganteus (62.6Mgha−1) and the lowest for S. x uplandicum (0.5Mgha−1). Since these topics have not been well investigated in other studies, our initial results need to be confirmed in different climatic conditions.

Plastic mulch: Tradeoffs between productivity and greenhouse gas emissions

One of humanity's contemporary challenges is continuously satisfying the need for global food and environmental security. Numerous individual reports have emphasized the importance of soil surface plastic mulch (PM) as an auxiliary means of increasing crop yields, but a comprehensive assessment of yields and environmental benefits on a national scale has not been performed. A meta-analysis was conducted to compare PM and no-mulch (NM) cropping patterns in China, the largest plastic film consumer in the world. Overall, PM positively influenced crop yields, particularly in semi-arid regions with medium and high nitrogen (N) input. The mean yield increased by 18% for wheat and 27% for maize; these changes were explained by the capacity of PM to increase water use efficiency (17% for wheat and 30% for maize). Notably, PM always increased greenhouse gas (GHG) emissions, and the mean yield-scaled GHG emissions increased by 32% for wheat and 10% for maize on a countrywide scale. In detail, compared to NM, PM resulted in a 2–113% increase in yield-scaled GHG emissions, which was lower in semi-arid regions with medium and high N inputs. For PM systems, yield-scaled GHG emissions in medium N input decreased by 19–31% compared to high N input. Importantly, the yield-scaled GHG emissions in maize was always lower than in wheat. In future, in order to achieve global food and environmental security, it may be advisable to adopt PM in semi-arid regions with medium N input, especially for maize production, based on managing the tradeoffs among yield increase, yield-scaled GHG emissions, and increase in yield-scaled GHG emissions.

Direct and indirect greenhouse gas emissions from two intensive vegetable farms applied with a nitrification inhibitor

Nitrification inhibitors are effective in decreasing direct nitrous oxide (N2O) emission from agricultural soils but may stimulate ammonia (NH3) volatilization. Part of the NH3 deposited to land is converted to N2O and emitted to the atmosphere, termed indirect N2O emission. While vegetable production systems entail a considerable risk of NH3 and N2O loss from high nitrogen (N) input to the soil, the simultaneous effects of nitrification inhibitors on these N loss pathways have rarely been examined. We conducted paddock-scale (ca. four hectares) measurements using micrometeorological techniques to simultaneously quantify the effects of a nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate) on NH3 and N2O emissions from two intensive vegetable farms. We found that DMPP decreased direct N2O emission by 37–38% (2.2–7.3 kg N ha−1) across the farms during the most intensive period of N input (18 days), but could increase NH3 volatilization by 3–39% (1.6–4.8 kg N ha−1). The results highlight the importance of considering multiple N loss pathways when developing a strategy for mitigating agricultural greenhouse gas emissions.

Reducing N2O and NO emissions while sustaining crop productivity in a Chinese vegetable-cereal double cropping system

High nitrogen (N) inputs in Chinese vegetable and cereal productions played key roles in increasing crop yields. However, emissions of the potent greenhouse gas nitrous oxide (N2O) and atmospheric pollutant nitric oxide (NO) increased too. For lowering the environmental costs of crop production, it is essential to optimize N strategies to maintain high crop productivity, while reducing the associated N losses. We performed a 2 year-round field study regarding the effect of different combinations of poultry manure and chemical N fertilizers on crop yields, N use efficiency (NUE) and N2O and NO fluxes from a Welsh onion-winter wheat system in the North China Plain. Annual N2O and NO emissions averaged 1.14–3.82 kg N ha−1 yr−1 (or 5.54–13.06 g N kg−1 N uptake) and 0.57–1.87 kg N ha−1 yr−1 (or 2.78–6.38 g N kg−1 N uptake) over all treatments, respectively. Both N2O and NO emissions increased linearly with increasing total N inputs, and the mean annual direct emission factors (EFd) were 0.39% for N2O and 0.19% for NO. Interestingly, the EFd for chemical N fertilizers (N2O: 0.42–0.48%; NO: 0.07–0.11%) was significantly lower than for manure N (N2O: 1.35%; NO: 0.76%). Besides, a negative power relationship between yield-scaled N2O, NO or N2O + NO emissions and NUE was observed, suggesting that improving NUE in crop production is crucial for increasing crop yields while decreasing nitrogenous gas release. Compared to the current farmers’ fertilization rate, alternative practices with reduced chemical N fertilizers increased NUE and decreased annual N2O + NO emissions substantially, while crop yields remained unaffected. As a result, annual yield-scaled N2O + NO emissions were reduced by > 20%. Our study shows that a reduction of current application rates of chemical N fertilizers by 30–50% does not affect crop productivity, while at the same time N2O and NO emissions would be reduced significantly.

Effects of soil heterogeneity on the uncertainty in modelling the fate of urinary nitrogen deposited during winter forage grazing

Despite the importance of soil physical properties on loss pathways from high nitrogen (N) inputs quantitative information on the effect of soil heterogeneity on the fate of N is lacking. To quantify how changes in the physical description of soil layers, used as model inputs, affect various outputs of the biophysical APSIM model regarding the fate of urinary nitrogen (N) following winter grazing, a modelling sensitivity analysis was performed. APSIM was set up according to a field experiment on a poorly drained Flaxton soil in the Canterbury region of New Zealand. Soil profile descriptions were based on various measured datasets, with and without compacted soil surface layers due to treading during grazing of the winter forage crop. The effect of the inclusion of more permeable sandy layers within the subsoil, a common occurrence in the study region, was also examined. By systematically replacing soil layers with different physical properties, the effect of these layers on the N loss pathways was evaluated. The analysis identified that the bottom layer (1–1.5m depth) had the greatest impact. With a low-permeability bottom layer nitrate leaching was 20% lower, whereas pasture N uptake, denitrification and nitrous oxide emissions were greater (by 5%, 58% and 43%). This is due to the effect of the bottom layer on water movement and storage within the soil profile. This description of the bottom layer had a substantially greater effect than compaction of the top soil layers due to treading. These results highlight the need for accurate soil physical descriptions for adequate model parameterisation, when such models are used for assessing management practices aimed at reducing environmental impacts.