Edge effect of trench-pond pattern on rice grain and economic benefit in rice-fish co-culture
稻鱼系统中不同沟型边际弥补效果及经济效益分析

Rice-fish co-culture has been practiced for over 1 000 years and diverse models have been developed in China. The trench and pond model (which provides shelter for fish during low-irrigation period) may limit rice yield due to reduced rice-stand area. However, strengthened compensation effects from increased edge-zones make up for yield loss in smaller rice-stands. In this study, we conducted a field experiment to estimate the edge effect compensations for lost rice yields induced by trench-pond under different digging patterns. The production of rice and fish were also compared with economic output under different types of trenches. The study shows that average edge effect on first-row grain yield is 52.45%. The average marginal effect of trenches on grain yield is as high as 80%. The compensative effects of the three types of trenches are in the following order: peripheral-trench (95.89%) > cross-trench (85.58%) > straight-trench (58.02%). There is no significant difference between rice and fish yields for the three types of trenches. Economic output for the cross-trench is the highest among the three types of trenches. The results suggest that cross-trench is the best trench pattern for both rice and fish production in rice-fish co-culture.