Growing green manure, as a sustainable agricultural practice, is widely recognized for its role in improving soil structure and enhancing soil quality. However, despite the significant benefits of green manure, research on how its application specifically influences soil organic carbon content remains insufficient, especially in the context of complex and ever-changing agricultural management models and ecological environments. In this study, 59 papers published from January 1980 to May 2024 were collected, and a database containing 299 groups of comprehensive effects of green manure planting on soil organic carbon content and crop yield, as well as its key regulatory factors, was created through a meta-analysis system. The research is mainly conducted through several key elements: types of green manure, planting seasons, fallow periods of food crops, soil types, climate types, and planting years. The results show that compared with not growing green manure on fallow land, the cultivation of green manure significantly increased the soil organic carbon content (by 6.98%) and the yield of the next staple food crop (by 10.36%). In different planting seasons, both summer and winter planting of green manure can effectively increase the soil organic carbon (SOC) content and crop yield. Among them, the application effect during the fallow period of wheat and rice is particularly significant, while during the fallow period of maize, only the SOC content increases significantly. From the perspective of green manure types, both the single species of leguminous and the mixed species with cruciferous have shown good effects. The research also found that under soil types such as loam and clay loam, as well as climatic conditions like temperate continental climate, temperate monsoon climate, and subtropical monsoon climate, the effect of green manure planting on the increase of SOC and yield is more significant. In addition, the planting years are also an important influencing factor. Green manure planting for ≤3 a or >5 a can significantly improve the SOC content and crop yield. These findings provide important theoretical support for the scientific application and promotion of green manure in China.

Soil physicochemical properties, climate, and human activities can create barriers to arable land in varying degrees, affecting land quality. The Huanghuaihai Plain (HHHP) is an important agricultural region in China. To clarify the factors influencing the formation of barriers to arable land in this area and their spatial distribution characteristics, this study took the northern part of the HHHP as the research object, screened and quantified the factors influencing barriers to arable land, constructed a multifactor-based arable land barrier evaluation index system, and used the index system to spatially classify the barriers to arable land. The results showed that 1) 16 evaluation indicators including the five dimensions of chemical indicators, physical indicators, biological indicators, management measures, and plot environment were screened out through the random forest model; 2) the average rating of the multifactor barrier for arable land in the northern part of the HHHP was 5.3, exhibiting a medium level, and the area of grade 5 and grade 6 land accounted for the highest percentage, at up to 30%; 3) the order of barrier degree of main barrier factors from high to low was organic matter>salt content>available phosphorus>available potassium>irrigation capacity>soil texture class>soil bulk density; and 4) according to the idea of ranking barrier factors, 15 types of barriers were obtained and then divided into the three major barrier area categories of organic matter, irrigation capacity, and salinity, and the prioritization of cropland quality improvement was determined according to the sequential order of the combination of barrier factors. A preliminary multifactor barrier index system for croplands was constructed, which can provide a reference for cropland barrier abatement and the precise improvement of cropland quality in the HHHP area.

In order to ensure the most reasonable distribution of wheat seeds in the field to improve seeding quality and uniformity, a set of negative pressure precision seed-metering device was designed, which shares a hollow shaft. Every seed-metering device can sow two rows of wheat. By the STAR-CCM+, the analysis of nephogram, vectogram and streamline graph showed that more ideal structural parameters of the seed-metering device are 0.5 mm width of the slit sucking seed (WSS), 150-200 mm diameter of the seed-metering disc (DSD), 2.0 mm axial depth of air chamber in the seed-metering disc (ADS), and arc-shaped cross-section shape of the ring groove sucking seed (CSGS). Single-factor test on the JPS-12 test-bed analyzed the influence of the CSGS, WSS, DSD, and ADS on the qualified index (I_q), multiple index (I_mul), miss index (I_miss) and coefficient of variation of qualified seed spacing (CV). Through the orthogonal on the JPS-12 test-bed, it is found that the influence of vacuum negative pressure and seed-metering device shaft speed is significant on the I_q, I_miss and I_mul. Based on these, the structural parameters of the seed-metering device were optimized. The DSD is 180 mm, the WSS is 0.7 mm, the ADS is 2.5 mm, and the CSGS is arc-shaped. The optimization seed-metering device was tested on the JPS-12 test-bed. The I_q is 86.66%, the I_miss is 5.09%, the I_mul is 8.25%, and the CV is 24.50%. These testing results fully coincide with the standard JB/T 10293-2013 Specifications of single seed drill (precision drill). The seed-metering device meets fully the requirements for wheat precision seeding.