Abstract
A two-year field experiment was conducted to investigate the response of soil carbon sequestration, crop yield and economic benefit to rates of NPK application and straw returning under rice–wheat rotation from 2015 to 2017. The experiment included five treatments: application of NPK without straw returning (SN+NPK), application of NPK with straw returning (S+NPK), application of NPK with decayed straw returning (SD+NPK), application of NPK with 15% reduction plus decayed straw returning (SD+85%NPK) and application of NPK with 15% reduction plus decayed straw returning (SD+70%NPK). Compared with SN+NPK, total organic carbon (TOC) and active organic carbon (LOC) in 0–15 cm depth increased by 3.62%–25.07% and 23.01%–46.79% in the treatments of straw returning plus different returned NPK application, respectively. Both S+NPK and SD+NPK treatments increased organic carbon storage (SCS) in 0–30 cm soil layer by 4.67% and 18.20%, but SD+85%NPK and SD+70%NPK decreased the SCS by 8.31% and 9.83%, respectively. Compared with SN+NPK, both S+NPK and SD+NPK increased grain yields for wheat and rice. However, SD+85%NPK and SD+70%NPK treatments significantly reduced grain yields for wheat and rice. Compared with SN+NPK treatment, the increase in annual average yield was 3.47% for S+NPK, 8.70% for SD+NPK, –3.65% for SD+85%NPK, and –8.12% for SD+70%NPK, while the increase of annual net profit in two years was 16.91%, 23.56%, 6.02%, and 1.06%, respectively. Soil organic carbon, crop yield and efficiency were the highest in the SD+NPK treatment, but lowest in SD+70%NPK. Compared with SD+70%NPK treatment, SD+85%NPK did not affect the annual average yield, but slightly increased the annual net profit due to a cost reduction caused by less fertilizer application with a total reduction of 80 kg ha–1. In conclusion, the combination of straw returning with NPK fertilization is an effective farming practice to improve soil carbon sequestration, crop yield and economic benefits in Hanzhong basin. Considering the environment and economic effects, decayed straw returning with 15% reduction in NPK application is more suitable to achieve the fertilizer reduction and green production.
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