Crop residue returning is a common practice in agricultural system that consequently influences nitrous oxide (N2O) emissions. Much attention has been focused on the effects of crop residue on N2O ...release. However, no systematic result has yet been drawn because environmental factors among different studies vary. A meta-analysis was described to integrate 112 scientific assessments of crop residue returning on N2O emissions in this study. Results showed that crop residue returning, when averaged across all studies, had no statistically significant effect on N2O release compared with control treatments. However, the range of effects of crop residue returning on N2O emission was significantly affected by synthetic nitrogen (N) fertilizer application, type of crop residue, specific manner in which crop residue has returned, and type of land-use. N2O release was significantly inhibited by 11.7% and 27.1% (P < 0.05) when crop residue was with synthetic N fertilizer and when type of land-use was paddy, respectively. While N2O emissions were significantly enhanced by 42.1% and 23.5% (P < 0.05) when crop residue was applied alone and when type of land-use was upland, respectively. N2O emissions were likewise increased when crop residue with lower C/N ratio was used, mulching of crop residue was performed, and type of land-use was fallow. Our study provides the first quantitative analysis of crop residue returning on N2O emissions, indicating that crop residue returning has no statistically significant effect on N2O release at regional scale, and underlining that the Intergovernmental Panel on Climate Change guidelines should take the opposite effects of crop residue returning on upland and paddy into account when estimating the N2O emission factor of crop residue for different land-use types. Given that most of data are dominated by certain types of crop residue and specific application methods, more field data are required to reduce uncertainty.
► Effects of crop residue returning on N2O release are evaluated by meta-analysis. ► Crop residue returning has no obvious effect on N2O release compared with controls. ► Effects of crop residue on N2O emission is significantly affected by land-use types.
Recycling of livestock manure in agroecosystems to partially substitute synthetic fertilizer nitrogen (N) input is recommended to alleviate the environmental degradation associated with synthetic N ...fertilization, which may also affect food security and soil greenhouse gas (GHG) emissions. However, how substituting livestock manure for synthetic N fertilizer affects crop productivity (crop yield; crop N uptake; N use efficiency), reactive N (Nr) losses (ammonia (NH3) emission, N leaching and runoff), GHG (methane, CH4; and nitrous oxide, N2O; carbon dioxide) emissions and soil organic carbon (SOC) sequestration in agroecosystems is not well understood. We conducted a global meta-analysis of 141 studies and found that substituting livestock manure for synthetic N fertilizer (with equivalent N rate) significantly increased crop yield by 4.4% and significantly decreased Nr losses via NH3 emission by 26.8%, N leaching by 28.9% and N runoff by 26.2%. Moreover, annual SOC sequestration was significantly increased by 699.6 and 401.4 kg C ha–1 yr–1 in upland and paddy fields, respectively; CH4 emission from paddy field was significantly increased by 41.2%, but no significant change of that was observed from upland field; N2O emission was not significantly affected by manure substitution in upland or paddy fields. In terms of net soil carbon balance, substituting manure for fertilizer increased carbon sink in upland field, but increased carbon source in paddy field. These results suggest that recycling of livestock manure in agroecosystems improves crop productivity, reduces Nr pollution and increases SOC storage. To attenuate the enhanced carbon source in paddy field, appropriate livestock manure management practices should be adopted.
The effective use of biochar as biomass recycling in agriculture to improve both crop production and environmental performance requires an understanding of its effects on soil nutrients, i.e., ...nitrogen (N) and phosphorus (P) and soil structure and soil carbon stocks. Thus, crop yield, soil aggregate stability and N and P use efficiencies (NUE and PUE, respectively) were investigated in a rice-wheat rotation field experiment 6 years after biochar amendment (20 and 40 t ha−1). Biochar application increased crop (rice and wheat) root (by 3–19%), straw (by 10–19%) and grain (by 10–16%) biomasses, as well as grain NUE (by 20–53%) and PUE (by 38–230%) compared with N fertilization only, whereas decreases in the N stocks in the root (2–5%), straw (13–17%) and grain (0–2%) occurred after biochar addition in the rice growth stage. No differences were observed between 20 and 40 t ha−1 biochar with respect to root, straw and grain biomasses as well as NUE and PUE. Biochar improved soil organic carbon (by 26–53%), total N (by 14–16%) and P (by 6–19%) compared to N fertilization only and positively affected the 250–2000 μm aggregate class (by 87–93%) and aggregate stability (by 43–48%). Based on structural equation modeling (SEM), this additional carbon affected aggregate stability by improving the aggregate structure, whereas P affected aggregate stability directly in biochar-fertilized soils. Improvement of soil carbon stocks and nutrient pools (i.e., N, P), promoted root growth, uptake of N and P fertilizers and crop production. Thus, biochar application is an effective strategy to increase crop yield, even in the long-term, and is connected not only with the improvement of soil structure and carbon stocks but also with increases in nutrient use efficiency.
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•Effects of long-term direct straw incorporation in a rice–wheat cropping system were appraised.•Long-term direct straw incorporation increased net GWP.•Long-term direct straw incorporation produced ...positive net economic benefit due to grain yield increase.
Straw incorporation has multiple effects on greenhouse gas emissions and soil productivity. However, few studies have comprehensively evaluated the effects of long-term straw incorporation. An ongoing long-term straw incorporation experiment in a rice–wheat cropping system in China was established in 1990 and was used in the present study to evaluate the net global warming potential (NGWP) and the net economic benefit (NEB) of the straw return. The following four field treatments were included: a control (CK); N, P and K fertilization (NPK); fertilization plus a moderate rate of straw application (NPKS1); and fertilization plus a high rate of straw application (NPKS2). We calculated the increase in the soil organic carbon (SOC) and the straw-induced emissions of CH4 and N2O, which were expressed as the global warming potential (GWP) in units of CO2-equivalent (CO2-eq) at the 100-year scale. The straw-induced NEB was defined as the difference between the economic income, which was calculated by multiplying the increase in straw-induced crop grain yield by the grain price, and the economic loss was computed by multiplying the increase in straw-induced CO2-eq emissions by the carbon price. The results showed that long-term straw incorporation significantly increased the CH4 emissions and the topsoil SOC density. The GWP of the straw-induced CH4 emissions was 3.21–3.92 times that of the straw-induced SOC sequestration rate, suggesting that long-term direct straw incorporation in the rice–wheat systems worsens rather than mitigates the climate change. Additionally, continuous straw incorporation slightly enhanced the rice and wheat grain yields, contributing to the production of the NEB. We determined that under the current carbon price, ranging from 2.55 to 31.71 EUR per ton CO2-eq, the direct straw incorporation will produce a positive NEB, ranging from 156 to 658 RMBha−1year−1, if the grain yield prices do not fluctuate, which does not provide a significant incentive for farmers to change from their traditional direct straw incorporation pattern. Considering the other benefits that the straw application produced, such as improving soil fertility and the water retention capacity, we recommend that the government should establish an incentive for ecological compensation to encourage farmers to implement proper straw incorporation, such as composting straw under aerobic conditions before application.
The Intergovernmental Panel on Climate Change (IPCC) regularly publishes guidelines for national greenhouse gas inventories and methane emission (CH4) from rice paddies has been an important ...component of these guidelines. While there have been many estimates of global CH4 emissions from rice fields, none of them have been obtained using the IPCC guidelines. Therefore, we used the Tier 1 method described in the 2006 IPCC guidelines to estimate the global CH4 emissions from rice fields. To accomplish this, we used country‐specific statistical data regarding rice harvest areas and expert estimates of relevant agricultural activities. The estimated global emission for 2000 was 25.6 Tg a−1, which is at the lower end of earlier estimates and close to the total emission summarized by individual national communications. Monte Carlo simulation revealed a 95% uncertainty range of 14.8–41.7 Tg a−1; however, the estimation uncertainty was found to depend on the reliability of the information available regarding the amount of organic amendments and the area of rice fields that were under continuous flooding. We estimated that if all of the continuously flooded rice fields were drained at least once during the growing season, the CH4 emissions would be reduced by 4.1 Tg a−1. Furthermore, we estimated that applying rice straw off season wherever and whenever possible would result in a further reduction in emissions of 4.1 Tg a−1 globally. Finally, if both of these mitigation options were adopted, the global CH4 emission from rice paddies could be reduced by 7.6 Tg a−1. Although draining continuously flooded rice fields may lead to an increase in nitrous oxide (N2O) emission, the global warming potential resulting from this increase is negligible when compared to the reduction in global warming potential that would result from the CH4 reduction associated with draining the fields.
Molybdenum disulfide (MoS2) with excellent properties has been widely reported in recent years. However, it is a great challenge to achieve p-type conductivity in MoS2 because of its native stubborn ...n-type conductivity. Substitutional transition metal doping has been proved to be an effective approach to tune their intrinsic properties and enhance device performance. Herein, we report the growth of Nb-doping large-area monolayer MoS2 by a one-step salt-assisted chemical vapor deposition method. Electrical measurements indicate that Nb doping suppresses n-type conductivity in MoS2 and shows an ambipolar transport behavior after annealing under the sulfur atmosphere, which highlights the p-type doping effect via Nb, corresponding to the density functional theory calculations with Fermi-level shifting to valence band maximum. This work provides a promising approach of two-dimensional materials in electronic and optoelectronic applications.
Using soil slurry-based 15N tracer combined with N2/Ar technique, the potential rates of denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium ...(DNRA), and their respective contributions to total nitrate reduction were investigated in 11 typical paddy soils across China. The measured rates of denitrification, anammox, and DNRA varied from 2.37 to 8.31 nmol N g–1 h–1, 0.15 to 0.77 nmol N g–1 h–1 and 0.03 to 0.54 nmol N g–1 h–1, respectively. The denitrification and anammox rates were significantly correlated with the soil organic carbon content, nitrate concentration, and the abundance of nosZ genes. The DNRA rates were significantly correlated with the soil C/N, extractable organic carbon (EOC)/NO3 – ratio, and sulfate concentration. Denitrification was the dominant pathway (76.75–92.47%), and anammox (4.48–9.23%) and DNRA (0.54–17.63%) also contributed substantially to total nitrate reduction. The N loss or N conservation attributed to anammox and DNRA was 4.06–21.24 and 0.89–15.01 g N m–2 y–1, respectively. This study reports the first simultaneous investigation of the dissimilatory nitrate reduction processes in paddy soils, highlighting that anammox and DNRA play important roles in removing nitrate and should be considered when evaluating N transformation processes in paddy fields.
Previous studies of long-term manure applications in paddy soil mostly focused on the effects on denitrification, occurrence of antibiotics and antibiotic resistance genes (ARGs) without considering ...the effects on anaerobic ammonium oxidation (anammox). Here, we investigated the potential rates of anammox and denitrification, occurrence of antibiotics and AGRs in response to three fertilization regimes (C, no fertilizer; N, mineral fertilizer; and NM, N plus pig manure) in six long-term paddy experiment sites across China. The potential rates of anammox (0.11–3.64 nmol N g−1 h−1) and denitrification (1.5–29.05 nmol N g−1 h−1) were correlated with the abundance of anammox genes (hzsB) and denitrification functional genes (narG, nirK, nirS and nosZ), respectively. The anammox and denitrification rates were affected by soil organic carbon (SOC) and significantly (p < 0.05) increased in NM treatments relative to those in N treatments. Although pig manure application increased antibiotic concentrations and abundance of ARGs compared with N treatments, the increased antibiotics did not directly affect the anammox and denitrification rates. Our results suggested that long-term pig manure application significantly increased antibiotic concentrations, abundance of ARGs, and rates of anammox and denitrification, and that the effects of pig manure-derived antibiotics on anammox and denitrification were marginal. This is the first report that investigates the effects of long-term pig manure application on anammox in paddy soils. More attention should be paid to the potential ecological risk of increased ARGs caused by pig manure application in paddy soils.
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•Long-term pig manure application increased anammox and denitrification rates.•Antibiotics concentrations, anammox and denitrification rates were affected by SOC.•Anammox and denitrification rates were not affected by manure-derived antibiotics.•ARGs, anammox, and denitrification genes were increased in pig manure-applied soil.
Agricultural soils in China have been estimated to have a large potential for carbon sequestration, and modelling and literature survey studies have yielded contrasting results of soil organic carbon ...(SOC) stock change, ranging from −2.0 to +0.6% yr⁻¹. To assess the validity of earlier estimates, we collected 1394 cropland soil profiles from all over the country and measured SOC contents in 2007-2008, and compared them with those of a previous national soil survey conducted in 1979-1982. The results showed that average SOC content in the 0-20 cm soil increased from 11.95 g kg⁻¹ in 1979-1982 to 12.67 g kg⁻¹ in 2007-2008, averaging 0.22% yr⁻¹. The standard deviation of SOC contents decreased. Four major soil types had statistically significant changes in their mean SOC contents for 0-20 cm. These were: +7.5% for Anthrosols (paddy soils), +18.3% for Eutric Cambisols, +30.5% for Fluvisols, and −22.3% for Chernozems. The change of SOC contents showed a negative relationship with the average SOC contents of the two sampling campaigns only when soils in the region south of Yangtse River were excluded. SOC contents of the two major soil types in the region south of Yangtse River, i.e., Haplic Alisols/Haplic Acrisols and Anthrosols (paddy soils), changed little or significantly increased, though with a high SOC content. We suggest that the increase of SOC content is mainly attributed to the large increase in crop yields since the 1980s, and the short history as cropland establishment is mainly responsible for the decrease in SOC content for some soil types and regions showing a SOC decline.
Yan and Akiyama believe that the conclusion reached by Kritee et al in their study regarding reduction of nitrous oxide in rice paddy fields with nitrogen management not playing a central role could ...potentially mislead readers by exaggerating the data, causing inaccurate interpretation. Kritee et al revealed that rice greenhouse gas emissions could be reduced by up to 90%, implying that the reduction can be achieved by water management and not by nitrogen management. However, rice yields using "alternate" practices were severely reduced compared with those using "baseline" practices in their study. Kritee et al defend their study citing that they do not claim that 90% mitigation can be achieved everywhere, but rather that this was the maximum mitigation observed in their study. They have already pointed out that more research is needed to minimize climate impacts per unit yield.
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