Search

Many Chinese croplands are suffering from soil acidification, defined as a decrease in soil acid neutralizing capacity (ANC), due to over-application of nitrogen (N) fertilizer and removal of base cations (BCs) in crop harvest. The contribution of fertilization and harvesting on soil acidification rates for different cropping systems is, however, seldom quantified under field conditions. Here, field experiments were conducted on a moderately acid silty clay soil in southwest China to quantify proton (H+) production rates under three fertilization management regimes, including control (non-N), optimized fertilization and farmers' practices (i.e. over fertilization), by measuring the inputs and outputs of major element in three cropping systems, i.e. rice-fallow, rice-wheat and maize-wheat. The maize-wheat cropping system had the highest proton production rates (2.3–10.2 kmol c H+ ha−1 yr−1), followed by rice-fallow (3.2–4.6 kmol c H+ ha−1 yr−1) and rice-wheat (2.2–4.5 kmol c H+ ha−1 yr−1) systems. Crop removal, dominated by straw removal, was the main driver of proton production in all three cropping systems, contributing over 50% of the total H+ production. Compared to the control, N fertilizer application enhanced soil acidification rates among three cropping systems, but had no significant effects on H+ production per kg grain in the rice-fallow and rice-wheat systems. The same was true for the maize-wheat system in case of optimized fertilization, but over fertilization increased both soil acidification rate and H+ production per kg grain, while grain yield was comparable to that with optimized fertilization. The change in soil ANC was dominated by accumulation of SO 4 2− (leading to potential soil acidification) that was mainly added to the soil with superphosphate containing high concentrations of both Ca2+ and SO 4 2− sometimes even causing an increase in the base cation pool, despite BC crop removal. The low contribution of N transformation processes to the total H+ production (3–47%) was due to high denitrification in this specific soil. The soil pH and base saturation did not change significantly among the three fertilization management regimes, largely due to the large BCs pools in the soil. Although the common farmers' practice does not strongly increase proton production in rice-fallow and rice-wheat systems, it still implies a waste of N fertilizer as the excess N input is either enhancing straw production or lost to air in this silty clay soil. Hence, optimized fertilization and localized BCs-rich straw return are suggested to reduce costs of N fertilizer without yield losses and mitigate soil acidification in those systems. [Display omitted] • Soil acidification rates were quantified in three cropping systems in China. • Maize-wheat rotations had higher acidification rates than rice-wheat and rice-fallow. • Optimized N fertilization reduced soil acidification rates without yield loss. • Base cation removal by crop harvesting was the main driver of soil acidification. • Low contribution of N cycle to soil acidification was due to high denitrification. [ABSTRACT FROM AUTHOR]

Excessive N fertilizer application contributes to a surge in reactive N (Nr) emissions from agroecosystems, consequently threatening global ecosystems' quality and security. Adding functional microorganisms to agricultural soils, namely microbial inoculants (MI), is a promising method for ensuring sustainable agriculture, but general assessment of microorganism-driven N losses and mediating factors (such as climate conditions, soil properties, and field management practices) remains unclear. Therefore, a comprehensive meta-analysis on the effect of MI addition on NH 3 volatilization, N 2 O emissions, and N leaching in soil-crop systems was conducted by integrating 50 published articles (188 paired observations). The MI application significantly reduced N 2 O emissions and NH 3 volatilization by 29.8% and 24.9%, respectively. The boosted regression tree model showed that the soil organic carbon (SOC) and soil pH significantly affected the efficacy of MI application on both NH 3 and N 2 O loss mitigation. The effects of MI application on N leaching were not clear due to limited data points. Additionally, MI addition significantly increased the abundance of denitrification functional genes (nir K, nir S, and nos Z). In conclusion, MI application presented a high potential to reduce Nr from croplands, future adoption of MI techniques should consider the effects of soil properties and field practices on its efficacy in order to achieving sustainable N management in crop production systems. [Display omitted] • MI amendment mitigated N 2 O and NH 3 losses from fertilized soils. • N fertilizer management had great contribution to variation of MI efficacy. • Soil pH had significant impact on mitigation efficiency of N 2 O and NH 3 by MI. • MI amendment increased denitrification genes abundance. [ABSTRACT FROM AUTHOR]

• Soil pH decreased by 0.07 annually after 20 years of applying NPK fertilizers. • Long-term application of organic fertilizer increased soil SOC content. • Organic fertilizer resulted in higher grain yield than NPK alone. • Applying organic fertilizer alone prevents soil acidification. Long-term fertilization causes declines in soil quality and crop yield, hindering current agricultural development. This paper is about the effect of long-term fertilization (20 years) in Hunan's Qiyang County. It was found that chemical nitrogen, phosphorus, and potassium (NPK) fertilizer lowered soil pH by an annual average of 0.07, while organic fertilizer increased soil pH by about 0.04. Furthermore, organic fertilizer and chemical fertilizer both increased total soil organic carbon (SOC). Long-term chemical NPK and organic fertilizer increased straw and grain yield of wheat and maize to a greater extent than did other fertilization methods. Thus, our results suggest that mixing organic fertilizer with chemical NPK fertilizer should prevent soil acidification and elevate crop yield. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is the key nutrient for crop growth in most agricultural systems, but excessive N fertilizer applications have led to very large ammonia (NH 3) and greenhouse gas (GHG), especially nitrous oxide (N 2 O), emissions, resulting in severe air pollution and making a major contribution to global warming. To clarify the effects of improved N management on NH 3 and N 2 O emissions and crop production, a 2-year field experiment was carried out in a maize-wheat rotation in the North China Plain (NCP), testing four optimized N management practices including reducing the fertilizer (urea) N rate and using N 'synergists' with the fertilizer. NH 3 emissions were significantly reduced only by the urease inhibitor (UI) LIMUS®, with an average reduction of 66.9 % relative to emissions from the untreated urea. At the same N rate, N 2 O emissions were reduced by 30.8–76.7 % by all the synergists (UI, a nitrification inhibitor DMPP (NI) and urea with a bacterial agent (UB)), and crop yields were improved by 14.4 % and 15.2 % under the UI and UB treatments, respectively. An 15N tracer experiment showed that using N synergists decreased the total N loss by 10.9–58.7 %, and significantly increased the recovery efficiency of N (RE N) by 16.9–44.8 % over the whole rotation. Reducing the N rate reduced the GWP and yield-scaled GWP (GHGI) by 10.6 % and 8.4 %, respectively. Using the N synergists, GHGI was significantly decreased by 19.2–26.7 % (P < 0.05), while GWP was reduced by 13.2–18.1 % only by the application of DMPP or LIMUS®. Overall, the study showed that reducing N 2 O and NH 3 emissions is important for increasing N utilization and mitigating global warming. Reducing N rate and using synergists can address the joint problems of environmental pollution and agricultural efficiency. In particular, the application of the optimal amount of urea (33% reduction over rates typically applied by farmers) amended with the urease inhibitor LIMUS® to maize-wheat rotations in the NCP proved to be the most effective method for the 'green' and sustainable development of agriculture and the mitigation of global warming in that region of China. • Optimizing N rate decreased environmental impact while maintaining crop yield. • Cropland NH 3 emissions were halved by incorporating a urease inhibitor. • A nitrification inhibitor reduced cropland N 2 O emissions. • Both inhibitors increased the recovery efficiency of fertilizer N by 16.9–44.8 %. • Optimizing fertilizer N rate plus appropriate inhibitor mitigated GWP and GHGI. [ABSTRACT FROM AUTHOR]

The North China Plain (NCP) is an intensive agricultural area and ammonia (NH 3) emission hotspot in China. Urgent mitigation actions are needed to reduce its environmental impact. A field trial was conducted, and results combined with a synthesis of existing data to assess the NH 3 loss and mitigation potentials in a wheat-maize double-crop rotation, a dominant crop production system in the NCP. Ammonia volatilization losses from N fertilizer applied to summer maize and winter wheat were 9.1% and 5.0%, respectively, based on the data synthesis, and were significantly affected by fertilizer application method and N fertilizer type. From the field trial, optimized reduction in N application rate, compared with conventional practice, had great efficiency for NH 3 mitigation. Despite their high NH 3 reduction potential, the higher input costs associated with the use of controlled-release fertilizers, replacement of urea with calcium ammonium nitrate or inclusion of double inhibitors (urease and nitrification inhibitors) with urea limited their applicability from an economic perspective. The inclusion of a urease inhibitor with urea achieved over 70% reduction in NH 3 emission and also gave a significant improvement in grain yield, net income and N use efficiency. Future adoption of NH 3 mitigation options in the NCP should focus on establishing a reduction target and consider the cost-benefits of simultaneous implementation of multiple mitigation techniques. [Display omitted] • Placement of fertilizer and fertilizer types significantly influence NH 3 emissions. • High cost of fertilizer amendment compromised economic benefits. • Using urease inhibitor showed good economic and environmental performance. [ABSTRACT FROM AUTHOR]

• Three crop rotations were studied in Chongqing over five years. • Reduced fertilizer promoted grain yields and environmental and economic benefit. • The rice-wheat rotation produced the highest grain yield and economic benefit. • The maize-wheat rotation was not suitable for Chongqing. • The rice-flooded fallow rotation is the most suitable system for Chongqing. A suitable crop rotation with optimum fertilizer application can balance the need for high crop yields with minimal environmental risk. This has not yet been achieved in China, and the Chinese Government now requires rotations that include a fallow period with the aim of improving soil quality. As a step towards achieving these aims, a 5-year field experiment was carried out to evaluate the effects of different rates of nitrogen (N) fertilizer in three typical and acceptable crop rotations on grain yield, nitrogen use efficiency (NUE), N balance and economic benefit at Jiangjin, Chongqing, China. The rotations were rice-flooded fallow (RF), rice-wheat (RW) and maize-wheat (MW). Three fertilizer treatments were tested over five years. The RW rotation with reduced fertilizer application had the highest grain yield and generated the highest economic benefit. The MW rotation was not suitable for the region that we studied because high precipitation can cause serious disease problems for the wheat. The RF rotation with reduced fertilizer application proved to be the best system for ensuring food security, increasing economic benefit and reducing environmental risk. [ABSTRACT FROM AUTHOR]

Large uncertainties and challenges remain in the quantification of land-atmosphere exchanges of ammonia (NH 3), mainly due to limitations in measurement techniques. In this study, the eddy covariance (EC) technique based on an open-path quantum cascade laser (QCL) spectrometer was used to measure the NH 3 fluxes at a typical cropland in the North China Plain, one of the global NH 3 hotspots. It is the first attempt of measuring both NH 3 volatilization and deposition fluxes at an agricultural ecosystem using the open-path instrument-based EC technique. During the one-month experimental period, the NH 3 fluxes were characterized by enhanced emissions after fertilizer application and persistent dry depositions after ploughing practice, with the flux magnitude varying from −0.293 to 7.29 (median: −0.042) mg N m−2 h−1. Nearly 93% of the half-hourly fluxes (absolute values) exceeded the mean instrumental flux detection limit of 9.6 μg N m−2 h−1. Nitrogen loss rate from the wheat field through NH 3 volatilization was 0.57–0.71% relative to the applied nitrogen fertilizers. Ammonia deposition dominated the period after the ploughing practice, showing an average deposition rate of 0.014 kg N ha−1 d−1 with a significant diurnal pattern. Both the local emission sources and meteorological conditions influenced the variation of NH 3 dry deposition. The deposition fluxes measured by the EC technique were nearly one third the results modelled by the widely used inferential model method, but the difference needs to be validated by more observations that includes different surface and meteorological conditions. This study suggests that this open-path QCL-based EC instrument is an effective tool for long-term and high-frequency measurements of ecosystem NH 3 exchanges. It also enables cross-validation between different methods to improve the understanding in the atmospheric reactive nitrogen cycling. • The open-path QCL-based eddy covariance instrument can detect small NH 3 fluxes. • Nitrogen loss rate from the wheat field through NH 3 volatilization was 0.57–0.71%. • NH 3 dry deposition averaged to 0.014 kg N ha−1 d−1 with a significant diurnal pattern. • Depositions estimated by inferential model were two times larger than the observed. [ABSTRACT FROM AUTHOR]

Nitrogen (N) stabilizers such as urease inhibitors (UI) and nitrification inhibitors (NI) are promising tools to mitigate N losses from fertilized soils. To better understand the efficacy of UI and NI, a 2-year field trial was carried out in the North China Plain (NCP) to analyze the impact of UI and NI on NH 3 loss and N transformations following urea fertilizer application. Additionally, a laboratory study using an automated continuous-flow incubation system was conducted under controlled conditions, using the same soil, to evaluate the mitigation potential of the N stabilizers on NO, N 2 O and CO 2 emission. The results showed that a novel UI product, Limus® (BASF, Germany), containing active ingredients N-(n-butyl) thiophosphoric triamide (NBPT) and N-(n-propyl) thiophosphoric triamide (NPPT), limited ammonium formation rate and reduced NH 3 loss in both maize (by 85 and 96% for year 1 and 2, respectively) and wheat (by 41 and 64%, for year 1 and 2, respectively) seasons. The 3, 4-dimethypyrazole phosphate (DMPP) amendment significantly retarded nitrate formation rate but the effectiveness was compromised by high ambient temperature; additionally, the NI amendment increased NH 3 emission (by 16 and 24% for maize and wheat year 2, respectively). In the laboratory incubation experiment, addition of the UI reduced emissions of NO, N 2 O and CO 2 by 89, 73 and 19%, respectively, while the addition of the NI reduced the respective emissions by 95, 83 and 24% over the 16 d incubation period. These results suggest that N stabilizers can play a significant role in the mitigation of the environmental impacts of intensive agriculture, and, in particular, that the UI amendment may have the better potential to reduce N losses in the climatic and soil conditions of the NCP, and that the NI should be avoided under high ambient temperatures. Image 1 • Urease inhibitor amendment of urea reduced NH 3 , NO and N 2 O emissions. • Nitrification inhibitor amendment of urea reduced NO and N 2 O but increased NH 3 emissions. • Efficacy of the nitrification inhibitor was compromised by high ambient temperature. • Urease and nitrification inhibitor amendment of urea reduced CO 2 emissions. [ABSTRACT FROM AUTHOR]