Effect of conservation tillage on soil fertility under rice-rape rotation system

In this study, the long-term effects of straw returning and no-tillage on physical properties and nutrient content of soils were assessed by continuous monitoring of soil bulk density, porosity, pH, organic matter, total nitrogen, total potassium, available nitrogen, available phosphorus and available potassium. The study considered different soil layers (0-20 cm and 20-40 cm) under rice-rape rotation system in Wuxue, Jingzhou and Wuhan Cities in Hubei Province for various farming years (9, 5 and 3 years) and cultivation systems. Also the Nemoro index method was used to evaluate soil fertility in different soil layers. The aim of the study was to provide the scientific basis for application of conservation tillage measures and optimization of field management. Results showed that:1) straw returning reduced soil bulk density by 2.00%-16.54% and increased total porosity by 1.00%-15.07% in rice and rape seasons. The changes in rape season were reversed under no-tillage treatment, while no significant changes were noted in the rice season. 2) Straw returning treatment increased the contents of organic matter (4.76%-35.07%), total nitrogen (1.80%-32.03%), available phosphorus (20.95%-65.82%), available nitrogen (5.97%-37.00%) and available potassium (8.71%-133.04%) in the 0-20 cm soil layer across the three sites. Compared with other nutrients, the greatest increase was recorded in available potassium. No significant differences were observed in no-tillage, although it had the best effect in terms of increase in soil nutrients compared with the other treatments after straw returning. The effect of each treatment on the 20-40 cm soil layer was similar to that on the 0-20 cm soil layer, but the total effect in terms of increase in the investigated parameters was not significant. 3) The no-tillage + straw returning and the nitrogen, phosphorus, potassium fertilizers application + straw returning treatments led to more increase in soil fertility with higher increase in integrated fertility index (7.56%-25.93%), they were good choice for improvement of soil fertility in the study sites.