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Biochar has gained significant attention in agricultural and environmental research over the last two decades. This comprehensive review evaluates the effects of biochar on soil organic carbon (SOC), emission of non-CO2 greenhouse gases, and crop yield, including related mechanisms and major influencing factors. The impacts of biochar on SOC, methane and nitrous oxide emissions, and crop yield are controlled by biochar and soil properties and management practices. High-temperature biochar produced from lignin-rich feedstocks may decrease methane and nitrous oxide emissions in acidic soils and strengthen long-term carbon sequestration due to its stable aromatic structure. In contrast, low-temperature biochar from manure may increase crop yield in low-fertility soils. Applying biochar to farmlands in China can increase SOC content by 1.9 Pg C and reduce methane and nitrous oxide emissions by 25 and 20 Mt CO2-eq year−1, respectively, while increasing crop yields by 19%. Despite the increasing evidence of the positive effects of biochar, future research needs to explore the potential factors that could weaken or hinder its capacity to address climate change and secure crop production. We conclude that biochar is not a universal solution for global cropland; however, targeted applications in fields, landscapes, or regional scales, especially in low fertility and sandy soils, could realize the benefits of biochar as a climate-smart measure. Highlights The findings of research on biochar's effects on soil C sequestration, GHG mitigation, and crop production were summarized. The factors influencing the impact of biochar on soil functioning were reviewed. The effects of biochar on soil C sequestration and GHG mitigation in farmlands of China were quantified. [ABSTRACT FROM AUTHOR]

A 3-year field experiment was conducted to investigate the effects of different organic fertilization strategies for rice–wheat annual rotation systems on net global warming potential (net GWP) and greenhouse gas intensity (GHGI) by incorporating methane, nitrous oxide emissions, the changes in soil organic carbon (SOC) derived from the net ecosystem carbon budget (NECB), and the CO 2 equivalent emissions from manure and chemical nitrogen (N) fertilizer manufacturing. Six fertilization strategies were studied, including control (CK), N fertilizer (CF), pig manure compost + N fertilizer (MC), straw + N fertilizer (SC), straw + pig manure compost + N fertilizer (SM), and straw + straw-decomposing inoculant + N fertilizer (SI). The results indicated that the application of organic amendments did not change the seasonal pattern of GHG emissions but significantly affected their seasonal quantities. Averaged over the 3 cycles, the annual SOC sequestration rates contributed significantly to the net GWPs and were estimated to be 1.01 t C ha −1  yr −1 for the control and 1.13–1.27 t C ha −1  yr −1 for the fertilized plots. Compared to CF, the MC strategy significantly increased SOC while had similar size of net GWP and GHGI, thus deserving recommendation regarding sustainable soil productivity and GHGs mitigations. However, the other proposed organic strategies of SC, SM, and SI significantly increased net GWP and GHGI as well as SOC thus requiring further researches for GHGs mitigations. Therefore, we recommend that the application of manure substituting half chemical fertilizer be an effective strategy while straw returning in any currently studied strategies should be re-examined in the rice–wheat annual rotation system. [ABSTRACT FROM AUTHOR]

The fruit has become the third-largest agricultural planting industry after cereals and vegetables in China. Fertilization regimes (e.g., application rate and method) in fruit orchards typically differ from cereal croplands, which would incur a pronounced difference in fertilizer-induced nitrous oxide (N 2 O) emissions between them. However, fertilizer-induced direct N 2 O emissions from orchard fields remain poorly understood. We conducted a field experiment in a peach orchard and a global meta-analysis of N 2 O emissions from fruit orchards. The emission factor (EF) of fertilizer N for N 2 O averaged 0.81%, with a background N 2 O emission of 3.4 kg N ha–1 yr-1 in our field study. A global meta-analysis suggested that the linear regression model was the best to fit N 2 O emissions by fertilizer N input for most fruit types compared to the nonlinear models. When averaging all global data, the linear model projected the EF of N 2 O from orchards to be 0.84%, with the background emission of 1.96 kg N ha–1. The estimate of direct N 2 O derived from the orchard-specific nonlinear model was substantially lower than those from the nonlinear model with global cropland measurements. The fertilizer-induced direct N 2 O emission from Chinese orchards during the 2000s was estimated to be 32–49 Gg N yr–1, equivalent to about 14% of total direct N 2 O emissions from Chinese uplands. Therefore, orchard cultivation constitutes a hotspot of N 2 O emissions in the agricultural sector, and priority should be given to emissions reduction to achieve the transition to climate-smart agriculture. [Display omitted] • N 2 O emissions from global orchards were summarized and meta-analyzed. • N 2 O emission was 32–49 Gg N yr–1 from Chinese orchards during the 2000s. • Orchard cultivation is one of the hotspots of agricultural N 2 O emissions. • Orchard N 2 O emissions were similar to emissions from vegetables and tea cultivation. [ABSTRACT FROM AUTHOR]