[Effects of Straw in Combination with Reducing Fertilization Rate on Soil Nutrients and Enzyme Activity in the Paddy-Vegetable Rotation Soils].

The effects of straw returning combined the reducing application of chemical fertilizer for crop yield, soil nutrients and enzyme activity were studied in a typical southwestern hilly area of China in a rice-vegetable ( var. Lin.) cropping system. The purple soil was selected as the target type of soil, and the Pioneer Town, Jiangjin District, Chongqing, China was selected as the typical southwestern hilly area during 2013 and 2014.Scientific basis based on the optimized fertilization strategy and the recyclable utilization of straw was provided through a field in-situ experiment in this study. There were five treatments in the field experiment: F (conventional fertilizer), 90% F+AS (100% straw with 90% conventional fertilizer), 80% F+AS (100% straw with 80% conventional fertilizer), 70% F+AS (100% straw with 70% conventional fertilizer), 50% F+DS (200% straw with 50% conventional fertilizer), and the 100% straw was 7500 kg·hm. The results showed that the yields of rice and vegetable were all increased in straw with reduced fertilizer treatments (3.0%-17.9% in rice yield and 12.2%-36.4% in vegetable yield) compared with conventional fertilizer (F) treatment. Moreover, the yield of rice in the second season was also increased by 820-1240 kg·hm. Soil pH values in straw with reduced fertilizer treatments raised by 0.06-0.55 compared with F treatment, especially in straw with 70% and 80% of conventional fertilizer dosage which increased by 6.74-6.88 and 6.52-6.84, respectively. The highest content of soil organic matter was 41.01 g·kg in straw with 80% of conventional fertilizer treatment. For the aspect of soil available nutrients, straw with 80% of conventional fertilizer treatment increased 110-178 mg·kg content of soil available nitrogen and 31.3-64.0 mg·kg content of soil available phosphorus. However, the excessive application of straw had negative effect on the accumulation of soil available phosphorus. In the same cultivation period, the contents of soil urease increased significantly in straw with 70% and 80% of conventional fertilizer treatments, which increased by 13.6%-76.4% and 20.1%-75.0% compared with F treatment. The contents of soil catalase in straw with reduced fertilizer treatments were significantly higher than F treatment; in first two seasons, soil catalase contents increased by 0.37 and 0.31 mL·(h·g) relative to F treatment in straw with reduced fertilizer treatment (80% of conventional fertilizer). With the increasing time of planting, the soil phosphatase content in the third season was higher than those in first two seasons. Straw with 70% and 80% of fertilizer treatments increased the activity of soil phosphatase by 45.2% and 48.2% compared with F treatment. It was concluded that straw application with 70% or 80% dosage of conventional fertilizer could benefit the rice-vegetable rotation in the southwest hilly area of China.