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Appropriate nitrogen (N) fertilization in vegetable-maize rotations is effective in improving agricultural production and mitigating environmental impacts to ensure sustainable food security. The dynamic and sustainability of crop yields, crop root biomasses, and accumulations and sequestration rates of soil organic C (SOC) and total N (STN) were explored and analyzed under four N application rates (kg N ha−1 year−1): 0 (Control), 285 (Low-N), 480 (Medium-N), and 720 (High-N). The Low-N and Medium-N applications increased Chinese cabbage yield by 22% and 20.7% than the High-N application, respectively. The Medium-N application gained the highest grain yield and root biomass in the maize season when compared with the Low-N application. The sustainable yield index had no difference between Low-N and Medium-N treatments in Chinese cabbage-maize rotation. Compared to the Low-N application, the Medium-N application improved the storage and sequestration rates of SOC and STN. Simultaneously, the Medium-N application significantly enhanced the soil C:N ratio than the High-N application. In conclusion, the Medium-N application is a promising fertilization strategy in the Chinese cabbage-maize cropping system as it increases the yield and root biomass of crops, improves the accumulation and sequestration rates of SOC and STN, and maintains a high soil C:N ratio. [ABSTRACT FROM AUTHOR]

The quantification of soil organic carbon (SOC) and N fractions under the influence of long-term fertilisation is useful to understand soil organic matter (SOM) stabilization mechanism and to develop optimal management practices. This study was to investigate the responses of different SOC and N fractions to long-term fertilisation and their contributions to the total change in the bulk soil under a rice-wheat cropping system. Compared with soil with no fertilisation, the 22-year fertilisation improved the C and N content of the bulk soil and different fractions with the greatest increase in NPK fertilisers and rice straw treatment. The SOC and N changes of heavy fraction accounted for 92% and 88% of the total SOC increases, while the Fe/Al-bound organic carbon and humic organic carbon in heavy fraction accounted for 43% and 48%, respectively. The SOC and N contents of each fraction were positively correlated with the bulk soil and the others. It is concluded that the NPK fertilisers plus straw returning was efficient to enhance SOC and N accumulation; the chemical binding of Fe and Al in organic-mineral complexes and the further formation of recalcitrant humin might be the potential mechanism for SOM accumulation in the rice-wheat cropping system. Abbreviations: SOM: soil organic matter; SOC: soil organic carbon; STN: soil total nitrogen; POM: particulate organic matter; MOM: mineral associated organic matter; LF: light fraction; HF: heavy fraction; Ca-OC: Ca-bound organic carbon; Fe/Al-OC: Fe- or Al-bound organic carbon; Humin-OC: humic organic carbon [ABSTRACT FROM AUTHOR]

In the present study, soil samples collected from 20-year (1993‒2013) long-term tobacco plantation and perennial fallow were analyzed to study the influence of soil acidification on soil physicochemical and mineralogical properties. Results showed a significant decrease of soil pH, Ca2+, Mg2+, Na+and total exchangeable cations, except K+, under tobacco plantation than under fallow land. Further X-ray diffraction (XRD) analysis for 1 mm soil size demonstrated an increase of vermiculite and kaolinite, but an obvious decrease of original potassium-bearing mica and potassium feldspar, under tobacco plantation than under fallow. For the <2 μm soil clay fraction, the XRD patterns showed an obvious desilication and accumulation of Al and Fe under tobacco plantation than under fallow. Other potassium-bearing minerals, such as illite and chlorite, had also visibly weathered and slaked under tobacco plantation than under fallow, resulting in an increase of vermiculite and hydroxy-Al-vermiculite, and an accelerated decomposition of 2:1 minerals and formation of 1:1 minerals. These results demonstrated that long-term continuous tobacco plantation has exerted negative effects on soil acidification and maintenance of soil potassium-bearing minerals. [ABSTRACT FROM AUTHOR]