Abstract:

To understand the effects of straw returning on the pollutants in the surface water of agricultural field and the possible non-point source pollution during the production of Zizania caduciflora, a simulation experiment was carried out to study the effects of straw returningof Zizania caduciflora as mulching or mixture with soil under flooded conditions (0%, 0.5%, 1%) on the concentrations of pollutants, such as COD, N, and P in surface water of agricultural field. The results showed that: the conductivity, COD, concentrations of P, K, Fe and Mn in surface water increased obviously at the beginning of the experiment, reached a peak on the 20 ^th-30 ^th day, and then gradually decreased to a relatively stable state; the peak concentration of NH₄ ⁺-N in surface water appeared in the first 10 days; the conductivity and the concentrations of COD, P, K, Fe and Mn increased with the increasing amount of straw returning, while the concentration of NH₄ ⁺-N decreased; the effects of straw returning of Zizania caduciflora as mulching on the conductivity, and concentrations of COD, P, K, Fe and Mn in surface water of field were greater than those of straw returning as mixture with soil; N application with straw returning could increase obviously the conductivity and NH₄ ⁺-N concentration of surface water. Straw returning of Zizania caduciflora as mixture with soil is better than straw returning as mulching, and the discharge of surface water should be controlled during the first 30 days of straw returning.

Key words: Straw of Zizania caduciflora, Returning, Non-point Pollution, DOC, Nitrogen, Phosphorus