Modeling the impact of crop rotation with legume on nitrous oxide emissions from rain-fed agricultural systems in Australia under alternative future climate scenarios

Land use modified impacts of global change factors on soil microbial structure and function: A global hierarchical meta-analysis

Nitrogen cycling in terrestrial ecosystems is critical for biodiversity, vegetation productivity and biogeochemical cycling. However, little is known about the response of functional nitrogen cycle genes to global change factors in soils under different land uses. Here, we conducted a multiple hierarchical mixed effects meta-analyses of global change factors (GCFs) including warming (W+), mean altered precipitation (MAP+/-), elevated carbon dioxide concentrations (eCO2), and nitrogen addition (N+), using 2706 observations extracted from 200 peer-reviewed publications. The results showed that GCFs had significant and different effects on soil microbial communities under different types of land use. Under different land use types, such as Wetland, Tundra, Grassland, Forest, Desert and Agriculture, the richness and diversity of soil microbial communities will change accordingly due to differences in vegetation cover, soil management practices and environmental conditions. Notably, soil bacterial diversity is positively correlated with richness, but soil fungal diversity is negatively correlated with richness, when differences are driven by GCFs. For functional genes involved in nitrification, eCO2 in agricultural soils and the interaction of N+ with other GCFs in grassland soils stimulate an increase in the abundance of the AOA-amoA gene. In agricultural soil, MAP+ increases the abundance of nifH. W+ in agricultural soils and N+ in grassland soils decreased the abundance of nifH. The abundance of the genes nirS and nirK, involved in denitrification, was mainly negatively affected by W+ and positively affected by eCO2 in agricultural soil, but negatively affected by N+ in grassland soil. This meta-analysis was important for subsequent research related to global climate change. Considering data limitations, it is recommended to conduct multiple long-term integrated observational experiments to establish a scientific basis for addressing global changes in this context.

Exploring adaptation responses of maize to climate change scenarios in southern central Rift Valley of Ethiopia

In this study, we assessed responses of adaptation options to possible climate change scenarios on maize growth and yield by using projections of 20 coupled ensemble climate models under two representative concentration pathways (RCPs) 4.5 and 8.5 by means of a DSSAT model. Growth and yield simulations were made across present and future climate conditions using the hybrid maize variety (Shone). Subsequently, simulated yields were compared with farmer' average and on-farm trial yields. Results showed that on-farm trial yield (5.1-7.3 t ha-1) lay in between farmers' average yield (2.9-5 t ha-1) and water-limited potential yield (6.3-10.6 t ha-1). Maize yields achieved in farmers' fields are projected to decline towards mid-century and further towards the end of the century regardless of the adaptation options compared with baseline in low potential clusters. Results of a combination of adaptation options including February planting, use of 64 kg ha-1 N and conservation tillage provided yield advantage of 5.8% over the 30 cm till under medium GHGs emission scenario during mid-century period at Shamana. Mulching with 5 t ha-1 was projected to produce a 4-5% yield advantage in the Hawassa cluster during the mid-century period regardless of changes in tillage or planting window. Under a high GHGs emission scenario, over 13.4% yield advantage was projected in the Bilate cluster due to conservation tillage and June planting during the mid-century period. In the Dilla cluster, the use of 10 t ha-1 mulch, conservation tillage and early planting (February) would result in a 1.8% yield advantage compared with the control either in medium or high GHGs emission scenarios. Thus, the most promising and least risky practices among simulated strategies were the use of nitrogen and mulching in combination with tillage or planting date adjustment. However, adaptation options remained least promising and highly risky if not integrated with mulching or nitrogen use. Hence, the negative impacts of future climate change and subsequent yield gaps would be reduced by optimizing the application of nitrogen, mulch and their interaction with planting date and tillage in high and low potential areas of maize production.

SPL12 Regulates AGL6 and AGL21 to Modulate Nodulation and Root Regeneration under Osmotic Stress and Nitrate Sufficiency Conditions in Medicago sativa

The highly conserved plant microRNA, miR156, affects root architecture, nodulation, symbiotic nitrogen fixation, and stress response. In Medicago sativa, transcripts of eleven SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE, SPLs, including SPL12, are targeted for cleavage by miR156. Our previous research revealed the role of SPL12 and its target gene, AGL6, in nodulation in alfalfa. Here, we investigated the involvement of SPL12, AGL6 and AGL21 in nodulation under osmotic stress and different nitrate availability conditions. Characterization of phenotypic and molecular parameters revealed that the SPL12/AGL6 module plays a negative role in maintaining nodulation under osmotic stress. While there was a decrease in the nodule numbers in WT plants under osmotic stress, the SPL12-RNAi and AGL6-RNAi genotypes maintained nodulation under osmotic stress. Moreover, the results showed that SPL12 regulates nodulation under a high concentration of nitrate by silencing AGL21. AGL21 transcript levels were increased under nitrate treatment in WT plants, but SPL12 was not affected throughout the treatment period. Given that AGL21 was significantly upregulated in SPL12-RNAi plants, we conclude that SPL12 may be involved in regulating nitrate inhibition of nodulation in alfalfa by targeting AGL21. Taken together, our results suggest that SPL12, AGL6, and AGL21 form a genetic module that regulates nodulation in alfalfa under osmotic stress and in response to nitrate.

Recent trends in nitrogen cycle and eco-efficient nitrogen management strategies in aerobic rice system

Rice (Oryza sativa L.) is considered as a staple food for more than half of the global population, and sustaining productivity under a scarcity of resources is challenging to meet the future food demands of the inflating global population. The aerobic rice system can be considered as a transformational replacement for traditional rice, but the widespread adaptation of this innovative approach has been challenged due to higher losses of nitrogen (N) and reduced N-use efficiency (NUE). For normal growth and developmental processes in crop plants, N is required in higher amounts. N is a mineral nutrient and an important constituent of amino acids, nucleic acids, and many photosynthetic metabolites, and hence is essential for normal plant growth and metabolism. Excessive application of N fertilizers improves aerobic rice growth and yield, but compromises economic and environmental sustainability. Irregular and uncontrolled use of N fertilizers have elevated several environmental issues linked to higher N losses in the form of nitrous oxide (N2O), ammonia (NH3), and nitrate (NO3 -), thereby threatening environmental sustainability due to higher warming potential, ozone depletion capacities, and abilities to eutrophicate the water resources. Hence, enhancing NUE in aerobic rice has become an urgent need for the development of a sustainable production system. This article was designed to investigate the major challenge of low NUE and evaluate recent advances in pathways of the N cycle under the aerobic rice system, and thereby suggest the agronomic management approaches to improve NUE. The major objective of this review is about optimizing the application of N inputs while sustaining rice productivity and ensuring environmental safety. This review elaborates that different soil conditions significantly shift the N dynamics via changes in major pathways of the N cycle and comprehensively reviews the facts why N losses are high under the aerobic rice system, which factors hinder in attaining high NUE, and how it can become an eco-efficient production system through agronomic managements. Moreover, it explores the interactive mechanisms of how proper management of N cycle pathways can be accomplished via optimized N fertilizer amendments. Meanwhile, this study suggests several agricultural and agronomic approaches, such as site-specific N management, integrated nutrient management (INM), and incorporation of N fertilizers with enhanced use efficiency that may interactively improve the NUE and thereby plant N uptake in the aerobic rice system. Additionally, resource conservation practices, such as plant residue management, green manuring, improved genetic breeding, and precision farming, are essential to enhance NUE. Deep insights into the recent advances in the pathways of the N cycle under the aerobic rice system necessarily suggest the incorporation of the suggested agronomic adjustments to reduce N losses and enhance NUE while sustaining rice productivity and environmental safety. Future research on N dynamics is encouraged under the aerobic rice system focusing on the interactive evaluation of shifts among activities and diversity in microbial communities, NUE, and plant demands while applying N management measures, which is necessary for its widespread adaptation in face of the projected climate change and scarcity of resources.

Modelling adaptation strategies to reduce adverse impacts of climate change on maize cropping system in Northeast China

Maize (Zea mays L.) production in Northeast China is vulnerable to climate change. Thus, exploring future adaptation measures for maize is crucial to developing sustainable agriculture to ensure food security. The current study was undertaken to evaluate the impacts of climate change on maize yield and partial factor productivity of nitrogen (PFPN) and explore potential adaptation strategies in Northeast China. The Decision Support System for Agrotechnology Transfer (DSSAT) model was calibrated and validated using the measurements from nine maize experiments. DSSAT performed well in simulating maize yield, biomass and N uptake for both calibration and validation periods (normalized root mean square error (nRMSE) < 10%, -5% < normalized average relative error (nARE) < 5% and index of agreement (d) > 0.8). Compared to the baseline (1980-2010), the average maize yields and PFPN would decrease by 7.6-32.1% and 3.6-14.0 kg N kg^-1 respectively under future climate scenarios (2041-2070 and 2071-2100) without adaptation. Optimizing N application rate and timing, establishing rotation system with legumes, adjusting planting dates and breeding long-season cultivars could be effective adaptation strategies to climate change. This study demonstrated that optimizing agronomic crop management practices would assist to make policy development on mitigating the negative impacts of future climate change on maize production.

Prediction of future carbon footprint and ecosystem service value of carbon sequestration response to nitrogen fertilizer rates in rice production

There is concern for variations of the carbon footprint (CF) and ecosystem service value of carbon sequestration (ESVCS) related to nitrogen (N) fertilizer rate in rice production under future climate change. To explore possible future ecological effects of N fertilizer rate, a DeNitrification-DeComposition (DNDC) model combined with Representative Concentration Pathway (RCP) projections (RCP 4.5 and RCP 8.5) were used to predict the CF and ESVCS of rice production. The model was validated by a two-year field experiment, and then seven N fertilizer levels (0, 75, 150, 190, 225, 300, and 375 kg N/ha) were set for prediction from 2015 to 2050. The validation results indicated a good fit between the DNDC-simulated and observed data of GHG emission and rice yield. Under RCP 8.5, the mean CF was 4.5-8.7% higher and the average ESVCS was 3.6-7.4% lower than those under RCP 4.5. The effects of N fertilizer rate on CF and ESVCS were consistent between the two climate change scenarios. In both RCPs, it was found that CF and ESVCS were mainly influenced by N fertilizer rate due to the latter's effect on CH₄ emissions and crop carbon fixation. CH₄ was the main contributor to CF during 2015-2050, accounting for 43.9-58.3% of the total CF. Agricultural inputs were also large contributors to CF, and N fertilizer increased the indirect GHG emissions by 24.6-122.2% compared with no N fertilization treatment. Among the studied N fertilizer rates, 190 kg N/ha was the optimal rate, obtaining the lowest CF and highest ESVCS. These results indicate that, under future climate change, an N fertilizer rate of 190 kg N/ha could achieve a trade-off between high yield, reduction of CF, and improvement of ESVCS in rice production.

Biological nitrification inhibitor for reducing N2O and NH3 emissions simultaneously under root zone fertilization in a Chinese rice field

Rice fields significantly contribute to the global N₂O and NH₃ emissions. Nitrification inhibitors (NIs) show promise in decreasing N₂O emission, but they can increase NH₃ volatilization under traditional broadcasting. Root zone fertilization (RZF) can mitigate NH₃ volatilization, but it may pose a high risk to N₂O emission. Additionally, most chemical NIs have limited availability and potential for environmental contamination, in contrast, biological NIs, such as methyl 3-(4-hydroxyphenyl) propionate (MHPP), are easily available and eco-friendly. However, the effects of RZF combined with MHPP on N₂O and NH₃ emissions are unknown. Therefore, a field experiment was conducted in a Chinese rice field with five treatments at 210 kg urea-N ha^-1 (BC: 3-split surface broadcasting; BC + MHPP: BC with MHPP; RZ, root zone fertilization; RZ + MHPP, RZF with MHPP; RZ + MHPP + NBPT, RZF with MHPP and NBPT). The results showed that although RZ eliminated NH₃ volatilization, it significantly increased total N₂O emission by 761% compared with BC due to the stimulation of nitrification by mid-season aeration (MSA) and the trigger of denitrification by a large amount of NO₃^-. Nearly 90% N₂O was emitted at MSA stage for RZF treatments, and their N₂O fluxes were exponentially related to the soil NO₃^--N concentrations in the 7-20 cm deep soil layer. RZ + MHPP greatly reduced the peak values of N₂O flux due to the suppression of nitrification by MHPP and then less production of NO₃^- for denitrification, its total N₂O emission was 79% lower compared with that of RZ. However, RZ + MHPP + NBPT further increased the total N₂O emission by 1044% compared with that of BC. Compared to BC, the RZF practice reduced total NH₃ volatilization by 88-92% regardless use of NIs. RZF had no influence on CH₄ emissions and enhanced the rice yields. In conclusion, RZF + MHPP is a promising strategy for simultaneously reducing N₂O and NH₃ emissions in rice fields.

Combined effects of nitrogen fertilizer and biochar on greenhouse gas emissions and net ecosystem economic budget from a coastal saline rice field in southeastern China

Biochar amendment has complex impacts on greenhouse gas emissions, crop production and economic benefit. However, few studies have comprehensively investigated the effects of biochar amendment in coastal saline rice fields. Thus, a biochar amendment field experiment was established in a coastal saline rice field in China to estimate the CH₄ and N₂O emissions, global warming potential (GWP), greenhouse gas intensity (GHGI), and net ecosystem economic budget (NEEB) of the biochar amendment during the rice growing season in 2017. There were six treatments (N0B0, N0B1, N0B2, N1B0, N1B1, N1B2) with different N fertilizer levels of 0 and 300 kg N ha^-1 and biochar rates of 0, 20, and 40 t ha^-1. The results showed that the application of N fertilizer increased N₂O emissions and rice yield by 128.3% (p < 0.001) and 44.4% (p < 0.001), respectively, while decreased the GHGI by 20.5% (p < 0.01); additionally, there were no significant effects on the CH₄ emissions and GWP compared with the treatments without N fertilizer. Although biochar amendment significantly increased the N₂O emissions and rice yield by 13.7-38.1% and 31.5-34.9%, respectively, biochar amendment had no significant effects on CH₄ emissions, GWP, and GHGI relative to the treatments without biochar amendment. From an economic perspective, N fertilizer significantly increased the NEEB by 135.5%, relative to the treatments without N fertilizer. Due to the high price of biochar and the large quantity applied, biochar amendment significantly reduced the NEEB by 99.8-229.3% compared with the treatments without biochar amendment. Considering the different characters between field-aged biochar and fresh biochar. Thus, long-term observations are needed to evaluate the environmental and economic profits affected by biochar and N fertilizer.

Carbon Footprint of Mediterranean Pasture-Based Native Beef: Effects of Agronomic Practices and Pasture Management under Different Climate Change Scenarios

Simple Summary

The livestock sector requires a significant amount of natural resources and has an important role in climate change. Although the carbon footprint has become a widely accepted indicator for assessing the greenhouse gases emitted per unit of product, due to the lack of a commonly accepted methodology, there are still few studies that have included soil organic carbon sequestration in their calculations. In this study, by including soil organic carbon dynamics, the carbon footprint of a Mediterranean pasture-based beef cattle farm was estimated using current weather data and farming management policies. Subsequently, different soil management strategies, grazing systems, and climate scenarios were compared to the current ones to investigate the effects of these variables on the greenhouse gases emitted. The results showed that the current beef carbon footprint could be significantly reduced by switching to reduced tillage systems. The modeled combination of no-tillage practices with higher organic fertilizer application rates showed a greater potential carbon footprint reduction. No significant differences were found between carbon footprint values modeled under different climate scenarios and grazing systems. By including a process-based model into its carbon footprint calculations, this study highlights the climate mitigation potential of different farming practices and the importance of considering soil carbon sequestration.

Abstract

A better understanding of soil organic carbon (SOC) dynamics is needed when assessing the carbon footprint (CFP) of livestock products and the effectiveness of possible agriculture mitigation strategies. This study aimed (i) to perform a cradle-to-gate CFP of pasture-based beef cattle in a Mediterranean agropastoral system (ii) and to assess the effects on the CFP of alternative tillage, fertilizing, and grazing practices under current (NCC) and future climate change (CC) scenarios. Minimum (Mt) and no-tillage (Nt) practices were compared to current tillage (Ct); a 50% increase (Hf) and decrease (Lf) in fertilization was evaluated against the current (Cf) rate; and rotational grazing (Rg) was evaluated versus the current continuous grazing (Cg) system. The denitrification–decomposition (DNDC) model was run using NCC as well as representative concentration pathways to investigate the effects of farm management practices coupled with future CC scenarios on SOC dynamics, N₂O fluxes, and crop yield. Within NCC and CtCf, an emission intensity of 26.9 ± 0.7 kg CO_2eq per kg live body weight was estimated. Compared to Ct, the adoption of Mt and Nt reduced the CFP by 20% and 35%, respectively, while NtHf reduced it by 40%. Conservation tillage practices were thus shown to be effective in mitigating greenhouse gas emissions.

Effects of warming and elevated O3 concentrations on N2O emission and soil nitrification and denitrification rates in a wheat-soybean rotation cropland

The effects of warming and elevated ozone (O3) concentrations on nitrous oxide (N2O) emission from cropland has received increasing attention; however, the small number of studies on this topic impedes understanding. A field experiment was performed to explore the role of warming and elevated O3 concentrations on N2O emission from wheat-soybean rotation cropland from 2012 to 2013 using open-top chambers (OTCs). Experimental treatments included ambient temperature (control), elevated temperature (+2 °C), elevated O3 (100 ppb), and combined elevated temperature (+2 °C) and O3 (100 ppb). Results demonstrate that warming significantly increased the accumulative amount of N2O (AAN) emitted from the soil-winter wheat system due to enhanced nitrification rates in the wheat farmland and nitrate reductase activity in wheat leaves. However, elevated O3 concentrations significantly decreased AAN emission from the soil-soybean system owing to reduced nitrification rates in the soybean farmland. The combined treatment of warming and elevated O3 inhibited the emission of N2O from the soybean farmland. Additionally, both the warming and combined treatments significantly increased soil nitrification rates in winter wheat and soybean croplands and decreased denitrification rates in the winter wheat cropping system. Our results suggest that global warming and elevated O3 concentrations will strongly affect N2O emission from wheat-soybean rotation croplands.

The combined effects of nitrogen fertilizer, humic acid, and gypsum on yield-scaled greenhouse gas emissions from a coastal saline rice field

In coastal saline rice fields, rice production shows high greenhouse gas (GHG) emissions but low nitrogen use efficiency (NUE). However, few studies have focused on the combined effects of nitrogen (N) fertilizer and soil ameliorants on GHG emissions. Thus, a field experiment was conducted to study the combined effects of N fertilizer, humic acid, and gypsum on the global warming potential (GWP), yield-scaled greenhouse gas intensity (GHGI), rice grain yield, and NUE in coastal saline rice fields in southeastern China. The experiment was conducted with eight treatments: N0, N1, N0H1, N1H1, N0G1, N1G1, N0H1G1, and N1H1G1. The codes N0, N1, H1, and G1 represented treatments without N (0 kg N ha^-1), with N (300 kg N ha^-1), with humic acid (0.6 t ha^-1), and with gypsum (0.6 t ha^-1), respectively. Compared with the treatments without N addition, the application of N fertilizer significantly increased N₂O emissions and grain yield by 41.9~130.6% and 32.8~57.5%, respectively, while significantly decreased the yield-scaled GHGI by 9.4~31.9%. Humic acid amendment significantly increased N₂O emissions and grain yield as compared with the treatments without humic acid. Gypsum addition had no significant effects on CH₄ and N₂O emissions, GWP, yield-scaled GHGI, and grain yield in relation to the treatments without gypsum. In addition, compared with the N1 treatment, the N1H1, N1G1, and N1H1G1 treatments increased the grain yield by 18.3% (p < 0.05), 2.3%, and 10.4%, and decreased yield-scaled GHGI by 9.6%, 20.5%, and 31.2% (p < 0.05), despite similar GWPs, respectively. Overall, the N1H1 and N1H1G1 treatments are the appropriate fertilizer management to realize high yield together with low environmental impacts in coastal saline rice fields in China.

Indirect N2O emissions from groundwater under high nitrogen-load farmland in eastern China

Current estimates of global indirect N₂O emissions are based on a relatively small dataset and remain a major source of uncertainly in the global N₂O budget. Nitrogen (N)-enriched groundwater from agricultural fields may act as an important source of indirect N₂O emissions as it discharges to adjacent watershed areas. During 2015-2017, dissolved N₂O concentrations in groundwater were measured and indirect N₂O emission factors (EF_5g) calculated under three typical high-N land-use types (vineyard, vegetable field and paddy field) in eastern China. The average dissolved N₂O concentrations in groundwater were 58.1 ± 40.4, 18.5 ± 11.5 and 0.72 ± 0.27  μg N L^-1 for vineyard, vegetable field and paddy field, respectively. The dissolved N₂O was over-saturated and was therefore a net source of N₂O to the atmosphere. The indirect N₂O emission factors (EF_5g) of vineyard (0.0091) and vegetable (0.0092) fields were much higher than the current Intergovernmental Panel on Climate Change (IPCC) default value of 0.0025 which indicated that these land-uses may have led to indirect N₂O emissions from the underlying groundwater. In contrast, the EF_5g of the paddy field (0.0019) was slightly lower than the default EF_5g proposed by IPCC (2006) and contributed minimal indirect N₂O emissions to the atmosphere. However, the current IPCC method may have overestimated the contribution of groundwater N₂O to the global N cycle because it took residual but not initial groundwater NO₃^--N concentration into account when calculating EF_5g. Therefore, we proposed the adoption of an improved method for calculating the EF_5g and compared it to the current IPCC (2006) method using data from the present study and other published data. The results of the comparison showed that the improved method was more scientifically appropriate measurement for calculating EF_5g.

Heat Priming During Early Reproductive Stages Enhances Thermo-Tolerance to Post-anthesis Heat Stress via Improving Photosynthesis and Plant Productivity in Winter Wheat (Triticum aestivum L.)

Heat stress during grain filling substantially decreases wheat productivity; thus, to ensure food security, heat tolerance in wheat needs to be developed. In this study, we evaluated the effect of heat priming applied during the stem-elongation stage, booting and anthesis, followed by 5 days of severe heat stress (a 7.86°C rise in temperature) during the grain-filling stage on physiological activities and grain yield of winter wheat in pot experiments during the 2015-2017 growing seasons using the winter wheat cultivars Yangmai 18 (a vernal type) and Yannong 19 (a facultative type). Compared with the damage observed in non-primed plants, heat priming during the stem-elongation stage and booting significantly prevented the grain-yield damage caused by heat stress during grain filling. Heat-primed plants displayed higher sucrose contents and sucrose-phosphate activity in leaves and greater above-ground dry matter than non-primed plants. Priming during stem elongation and booting led to increased photosynthetic capacity, stomatal conductance and chlorophyll contents in comparison with non-priming. Improved tolerance to heat stress due to the enhanced activities of antioxidant enzymes superoxide dismutase and peroxidase and reductions in reactive oxygen species and malondialdehyde production was observed in primed plants compared with non-primed plants of both cultivars. The positive effect of heat priming on the response to heat stress during grain filling was more pronounced in plants primed at the booting stage than in those primed at the stem-elongation or anthesis stage. Moreover, the vernal-type Yangmai 18 benefited more from heat priming than did Yannong 19, as evidenced by its higher productivity. We conclude that heat priming during early reproductive-stage growth can improve post-anthesis heat tolerance in winter wheat.