A meta-analysis of conservation tillage management effects on soil organic carbon sequestration and soil greenhouse gas flux.

Conservation tillage practices, including reduced tillage (RT), no-tillage (NT) and straw return (SR), have been widely adopted to enhance soil organic carbon density (PSOC) and improve the soil quality while mitigating the negative environmental impacts of intensive farming. However, current studies on the effects of these practices on SOC sequestration and N2O flux show considerable variability, making it challenging to draw definitive conclusions about the individual and combined impacts of conservation tillage practices and introducing substantial uncertainty in estimating the agricultural sector's potential to mitigate climate change. To address this gap, we conducted a meta-analysis of 902 pairwise comparisons from 90 peer-reviewed publications to evaluate the effects of five conservation tillage practices (straw return (SR), reduced tillage (RT), no-tillage (NT), straw return combined with tillage reduction (SR + RT) and straw returning combined with no-tillage (SR + NT)) on C sequestration and N2O emissions from agricultural soils. The results show that SR was the most effective practice for increasing SOC content (23.7 %), followed by RT + SR (5.5 %) and NT + SR (4.4 %). Additionally, RT (12.3 %) and NT (14.3 %) significantly reduced soil N2O emissions. This study also identified key drivers, including climatic factors, soil properties, and agricultural management practices, that influence SOC content and N2O emissions under different conservation tillage practices. For example, the mean annual precipitation, mean annual temperature, soil type, pH, soil total nitrogen content, N application rate, and experiment duration were identified as the key factors affecting SOC content and N2O emissions Specifically, suitable temperature, lower rainfall and alkaline soil environment significantly enhanced the C sequestration efficiency of SR, while suitable climatic conditions and soil texture combined with an alkaline environment contributed to a significant reduction in long-term NT soil N2O emissions. These results provide a robust scientific foundation for the strategic implementation of conservation tillage to reduce greenhouse gas emissions, mitigate global warming, and enhance soil C sequestration capacity.

Nitrous oxide (N2O) emission characteristics of farmland (rice, wheat, and maize) based on different fertilization strategies.

Fertilizer application is the basis for ensuring high yield, high quality and high efficiency of farmland. In order to meet the demand for food with the increasing of population, the application of nitrogen fertilizer will be further increased, which will lead to problems such as N2O emission and nitrogen loss from farmland, it will easily deteriorate the soil and water environment of farmland, and will not conducive to the sustainable development of modern agriculture. However, optimizing fertilizer management is an important way to solve this problem. While, due to the differences in the study conditions (geographical location, environmental conditions, experimental design, etc.), leading to the results obtained in the literatures about the N2O emission with different nitrogen fertilizer application strategies have significant differences, which requiring further comprehensive quantitative analysis. Therefore, we analyzed the effects of nitrogen fertilizer application strategies (different fertilizer types and fertilizer application rates) on N2O emissions from the fields (rice, wheat and maize) based on the Meta-analysis using 67 published studies (including 1289 comparisons). For the three crops, inorganic fertilizer application significantly increased on-farm N2O emissions by 19.7-101.05% for all three; and organic fertilizer increased N2O emissions by 28.16% and 69.44% in wheat and maize fields, respectively, but the application of organic fertilizer in rice field significantly reduced N2O emissions by 58.1%. The results showed that overall, the application of inorganic fertilizers resulted in higher N2O emissions from farmland compared to the application of organic fertilizers. In addition, in this study, the average annual temperature, annual precipitation, soil type, pH, soil total nitrogen content, soil organic carbon content, and soil bulk weight were used as the main influencing factors of N2O emission under nitrogen fertilizer strategies, and the results of the study can provide a reference for the development of integrated management measures to control greenhouse gas emissions from agricultural soils.

The effect of biochar types on carbon cycles in farmland soils: A meta analysis.

Application of biochar has been demonstrated to be a successful strategy for boosting soil carbon sequestration and altering the agricultural soil carbon cycle. However, in the studies involving biochar worldwide, the effects of different types of biochar on the soil carbon component response direction and increase are not consistent. Therefore, to assess the effects of applying four types of biochar during the soil carbon cycle on carbon components on a farmland, we performed a meta-analysis of 1150 comparisons from 86 peer-reviewed publications. Generally speaking, the types of biochar raw materials have a significant impact on soil carbon cycle. The application of chaff biochar significantly inhibited (10.0 %) soil respiration, while the application of manure biochar (47.0 %), straw biochar (11.2 %) and wood biochar (8.7 %) showed a strong promotion effect on CO2 emission. In addition, although the soil organic C, microbial biomass C and dissolved organic C all had positive responses to the application of the four biochar types, the degree and increase in their response varied greatly due to the differences in biomass raw materials. Moreover, by increasing the biochar rates applied to coarse-textured soils with low average annual rainfall and an average temperature under controlled circumstances, the relative increase in SOC was encouraged. Meanwhile, applying low temperature pyrolytic biochar (≤400 °C) at a lower rate (<25 t/ha) in the long-term experiment (>3 years) is more beneficial to soil C sequestration and emission reduction. Hence, climatic conditions, agricultural management practices, and initial soil properties jointly constrained and influenced the ability of biochar to alter the soil C cycle. Based on this, our research offers a fresh viewpoint for making a profound study biochar-enhanced soil C cycle.

Response of Wheat, Maize, and Rice to Changes in Temperature, Precipitation, CO2 Concentration, and Uncertainty Based on Crop Simulation Approaches.

The influence of global climate change on agricultural productivity is an essential issue of ongoing concern. The growth and development of wheat, maize, and rice are influenced by elevated atmospheric CO2 concentrations, increased temperatures, and seasonal rainfall patterns. However, due to differences in research methodologies (e.g., crop models, climate models, and climate scenarios), there is uncertainty in the existing studies regarding the magnitude and direction of future climate change impacts on crop yields. In order to completely assess the possible consequences of climate change and adaptation measures on crop production and to analyze the associated uncertainties, a database of future crop yield changes was developed using 68 published studies (including 1842 samples). A local polynomial approach was used with the full dataset to investigate the response of crop yield changes to variations in maximum and minimum temperatures, mean temperature, precipitation, and CO2 concentrations. Then, a linear mixed-effects regression model was utilized with the limited dataset to explore the quantitative relationships between them. It was found that maximum temperature, precipitation, adaptation measure, study area, and climate model had significant effects on changes in crop yield. Crop yield will decline by 4.21% for each 1 °C rise in maximum temperature and increase by 0.43% for each 1% rise in precipitation. While higher CO2 concentrations and suitable management strategies could mitigate the negative effects of warming temperatures, crop yield with adaptation measures increased by 64.09% compared to crop yield without adaptation measures. Moreover, the uncertainty of simulations can be decreased by using numerous climate models. The results may be utilized to guide policy regarding the influence of climate change and to promote the creation of adaptation plans that will increase crop systems' resilience in the future.

Genotypic Variation in a Breeding Population of Yellow Sweet Clover (Melilotus officinalis).

Yellow sweet clover is a widely spread legume species that has potential to be used as a forage crop in Western China. However, limited information is available on the genetic variation for herbage yield, key morphological traits, and coumarin content. In this study, 40 half sib (HS) families of M. officinalis were evaluated for genotypic variation and phenotypic and genotypic correlation for the traits: LS (leaf to stem ratio), SV (spring vigor), LA (leaf area), PH (plant height), DW (herbage dry weight), SD (stem diameter), SN (stem number), Cou (coumarin content), SY (seed yield), across two locations, Yuzhong and Linze, in Western China. There was significant (P < 0.05) genotypic variation among the HS families for all traits. There was also significant (P < 0.05) genotype-by-environment interaction for the traits DW, PH, SD, SN, and SV. The estimates of HS family mean repeatability across two locations ranged from 0.32 for SN to 0.89 for LA. Pattern analysis generated four HS family groups where group 3 consisted of families with above average expression for DW and below average expression for Cou. The breeding population developed by polycrossing the selected HS families within group 3 will provide a significant breeding pool for M. officinalis cultivar development in China.

Co-transforming bar and CsALDH Genes Enhanced Resistance to Herbicide and Drought and Salt Stress in Transgenic Alfalfa (Medicago sativa L.).

Drought and high salinity are two major abiotic factors that restrict the productivity of alfalfa. By application of the Agrobacterium-mediated transformation method, an oxidative responsive gene, CsALDH12A1, from the desert grass Cleistogenes songorica together with the bar gene associated with herbicide resistance, were co-transformed into alfalfa (Medicago sativa L.). From the all 90 transformants, 16 were positive as screened by spraying 1 mL L(-1) 10% Basta solution and molecularly diagnosis using PCR. Real-time PCR analysis indicated that drought and salt stress induced high CsALDH expression in the leaves of the transgenic plants. The CsALDH expression levels under drought (15 d) and salt stress (200 mM NaCl) were 6.11 and 6.87 times higher than in the control plants, respectively. In comparison to the WT plants, no abnormal phenotypes were observed among the transgenic plants, which showed significant enhancement of tolerance to 15 d of drought and 10 d of salinity treatment. Evaluation of the physiological and biochemical indices during drought and salt stress of the transgenic plants revealed relatively lower Na(+) content and higher K(+) content in the leaves relative to the WT plants, a reduction of toxic on effects and maintenance of osmotic adjustment. In addition, the transgenic plants could maintain a higher relative water content level, higher shoot biomass, fewer changes in the photosystem, decreased membrane injury, and a lower level of osmotic stress. These results indicate that the co-expression of the introduced bar and CsALDH genes enhanced the herbicide, drought and salt tolerance of alfalfa and therefore can potentially be used as a novel genetic resource for the future breeding programs to develop new cultivars.