Effect of integrated rice-crayfish farming system on soil physico-chemical properties in waterlogged paddy soils

Integrated rice-crayfish system is a complex ecological system based on waterlogged paddy field cultivation characterized with crayfish fed by rice straw. Using rice monoculture system as the control, a 10-year (2005-2015) field experiment was conducted to study the effects of integrated rice-crayfish system on rice yield and soil physico-chemical properties at soil depths of 0-10 cm, 10-20 cm, 20-30 cm and 30-40 cm. The economic benefit of integrated rice-crayfish system was evaluated using the input-output method. The results indicated that long-term integrated rice-crayfish system significantly reduced soil compaction at the 15-30 cm layer. The soil compaction in 15 cm, 20 cm, 25 cm and 30 cm soil was lower in integrated rice-crayfish system than in rice monoculture system by 20.9%, 29.9%, 24.8% and 14.7%, respectively. Long-term integrated rice-crayfish system increased soil water-stable aggregates (>0.25 mm) content, aggregate mean weight diameter (MWD) and geometric mean diameter (GMD) in the 0-40 cm layer, but decreased aggregate fractal dimension (D) in the 0-20 cm layer. Compared with rice monoculture system, long-term integrated rice-crayfish system significantly increased the contents of soil organic carbon, total K and available N in the 0-40 cm layer, then total N in the 0-30 cm layer, total P and available P in the 0-10 cm layer and available K in the 20-40 cm layer. The total amount of reducing matter in the 0-10 cm soil layer of the long-term integrated rice-crayfish system was lower than that in the monoculture rice system, but it was higher in the 20-30 cm soil layer. Rice yield in integrated rice-crayfish system significantly increased by 9.5% than that in the monoculture rice system. The output, profit and ratio of output to input in integrated rice-crayfish system were higher than those in the monoculture rice system by 46 818.0 ￥·hm^-2, 40 188.0 ￥·hm^-2 and 100.0%, respectively. It was therefore clear that integrated rice-crayfish system improved soil structure, enhanced soil nutrient and increased rice yield and economic benefit. However, it also increased the risk of soil gleying in the 10 cm depth.