Most General Circulation Models predict more infrequent but larger precipitation events in the eastern United States combined with a warmer climate. This could have a negative effect on maize production. To understand the sensitivity of maize production to future changes in precipitation, we analyzed growing season precipitation and average state maize yields in the eastern United States for the period 1963–2011. Growing season precipitation did not show a strong trend during this period. However, crop yields increased at 3.90% in the southern, 2.62% in the central, and 2.31% in the northern part of the eastern United States, which we attributed to technology and management. To separate technology and management effects from precipitation variability, we corrected maize yields for these yield trends. We then correlated maize yield corrected for advances in technology and management with total growing season precipitation and precipitation in the critical month of pollination, from the regional to state scale. Maize yield - precipitation relationships showed that moisture shortage rather than excess determined maize yield in the Eastern United States. The relationship between total growing season precipitation-maize yield was stronger in the southeastern than in the northeastern U.S., but the critical month precipitation-maize yield relationship was stronger in the northeastern than in the southeastern U.S. If climate model predictions are accurate and total growing season precipitation will not decrease in this region but variability will, it is likely that maize yields in the northeastern U.S. will be more significantly affected.

Fertilization plays a crucial role in enhancing tea production. However, it has been demonstrated that the long-term single application of chemical fertilizer will reduce soil nutrient content and the formation of soil aggregates, which is not conducive to the sustainable development of soil and agriculture. Many studies have shown that partial substitution of chemical fertilizer with organic fertilizer can improve soil physicochemical properties and soil nutrient content. This study compared the effects of different organic materials as substitutes for chemical fertilizer. We partially replaced chemical fertilizer with rabbit manure, wine lees and rapeseed cake, amounting to 30% of the total annual nitrogen application in the field experiment, and we set nine different fertilization methods to assess and analyze the soil nutrient condition, aggregate stability and enzyme activity. The results showed that the experimental soil aggregate mean weight diameter (MWD) and geometric mean diameter (GMD) were significantly increased compared with control (p < 0.05); the aforementioned fertilization methods also decreased the soil aggregate fractal dimension (D), disruption rate (PAD), average weight-specific surface area (MWSSA) and soil erodibility factor (K). The application of the fertilizer containing organic materials and microbial agent increased soil organic carbon (SOC) by 20.7% to 22.6% and total nitrogen (TN) by 34.6% to 38.1%; it also significantly promoted sucrase, urease and protease activities in all aggregate sizes (p < 0.05) and increased the 2–5 mm aggregate content. The correlation coefficients between the SOC and the enzyme activities were 0.18–0.95, and most of them showed an extremely significant positive correlation (p < 0.01). In conclusion, the application of fertilizers containing organic materials and microbial agents can improve soil aggregate stability, aggregate enzyme activity and soil structural stability.

Tillage modes and straw returning influence soil aggregate stability and the distribution of organic carbon (C) and nitrogen (N) in aggregates of different particle sizes. In the typical hilly regions of southwest China, the predominant soil type is purple soil, characterized by heavy texture and high stickiness, with relatively lower soil fertility compared to other soil types. The improper use of fertilizers and field management practices further exacerbates soil compaction. However, abundant straw resources in the region provide an opportunity for comprehensive straw utilization. The effective utilization of straw resources is of significant importance for stabilizing agricultural ecological balance, improving resource utilization efficiency, and alleviating ecological pressure. Previously, most studies have focused on the impact of different mechanized tillage systems on the physical and chemical properties of soil in hilly areas, while research on the preservation of water-stable aggregates’ organic C and N content remains limited. In this study, the soil properties of fields under a winter pea–summer corn rotation for two years were studied with regards to the effects of straw returning on its water-stable aggregate distribution, macroaggregate content (R_0.25), mean weight diameter (MWD), geometric mean diameter (GMD), and the organic C and N content in soil aggregates of different particle sizes and at different depths. The effects of five different tillage modes were assessed, namely rotary tillage with straw mixed retention (RTM), conventional tillage with straw burial retention (CTB), no-tillage with straw covered retention (NTC), subsoiling with straw covered retention (STC), and no-tillage without straw retention (NT). Based on the study results, under different tillage modes, straw returning effectively enhanced the soil organic carbon (SOC) and total nitrogen (TN) reserves at the plow layer (0–30 cm), SOC increased by 17.2% to 88%, and TN increased by 8.6% to 85.9%. At the same time, the content of 0.25–2 mm aggregates increased under the straw-return treatments under different tillage patterns. The NT treatment had the lowest R_0.25 and MWD and GMD values for soil aggregates at different depths, which were significantly different (p < 0.05) from the other treatment modes. The correlation coefficients between SOC and soil aggregate stability indices ranged from 0.68 to 0.90, with most of them showing highly significant positive correlations (p < 0.01). In conclusion, straw returning under different tillage systems has improved soil aggregate stability and promoted soil structure stability. Specifically, the STC treatment has shown more pronounced effects on soil improvement in the upper soil layer of the hilly regions in southwest China, while the RTM treatment is beneficial for improving the lower soil layer. Therefore, the comprehensive experimental results indicate that the combination of STC and RTM treatments represents the most promising mechanized tillage and straw returning practices for the hilly regions in southwest China.

In order to study the effects of different fertilization measures on spring tea soil in Southwest Sichuan, five treatments were set up, including no fertilization (CK), full chemical nitrogen fertilizer (CN), 50% nitrogen fertilizer +30% organic fertilizer +20% green fertilizer + microbial fertilizer (NOGM), 50% nitrogen fertilizer +30% organic fertilizer +20% green fertilizer (NOG), 50% nitrogen fertilizer +50% organic fertilizer + microbial fertilizer (NOM). Through the determination of the distribution, organic carbon and total nitrogen content of water stable aggregates, calculated the aggregate stability and carbon and nitrogen contribution rate. The results showed that :(1) compared with CK, fertilization could improve the organic carbon and total nitrogen of soil and the organic carbon and total nitrogen of the aggregates of all sizes. Different fertilization measures had different effects on the distribution of aggregates, but compared with CK, fertilization effectively promoted the stability of aggregates. Fertilization can obviously increased the content of organic carbon and total nitrogen in large aggregates. The contribution rate of organic carbon and total nitrogen in aggregates was mainly from macroaggregates, while that from micro-aggregates was very low. NOGM and NOM were better than other fertilization measures.

For the purpose of heavy metals’ spatial-temporal trends and source allocation in arable soil with the rapid urbanization in Western China, samples were collected in two stages (2008 and 2017) in Chengdu city which was chosen for the case study. Positive Matrix Factorization (PMF) receptor models and Multivariate statistical analysis were used to understand the heavy metals’ spatial-temporal variability. The results showed that Cd, Cr, and As in arable soil were presented with an increasing trend during the 10-year period. Semi-variation analysis showed that the block basis ratios of the five heavy metals (Pb, As, Cr, Hg, and Cd) showed an increasing trend, which suggests that the spatial distribution of heavy metals in arable soil is more influenced by human disturbances. The source analysis shows that the enrichment of As is closely related to agricultural activities in both phases (2008 and 2017). Further source analysis showed that source of As did not change, but the contribution increased significantly. The main sources of Hg pollution changed from agricultural activities to medical equipment manufacturing, Cd changed from soil parent material sources to chemical industry waste emissions, and the sources of Pb and Cr expanded from single transportation sources to multiple sources such as road traffic and human construction. In this study, the examining of the temporal and spatial patterns of heavy metal contamination in farmland of typical rapidly developing cities in China can also provide a basis for the conservation and management of arable soil in similar areas in the context of rapid urbanization in China.