Effect of rice straw on the physicochemical properties of field surface solution under waterlogged incubation

The objective of this research was to determine the effect of different rates of rice straw returned to soil on field surface solution properties via experimental simulation. Under four rice straw rates (0 g·pot^-1, 100 g·pot^-1, 200 g·pot^-1 and 300 g·pot^-1), with 15 kg soil and 2.8 g urea of a pot, electrical conductivity (EC), pH, total nitrogen (TN), total phosphorus (TP) and total potassium (TK) were determined in the experiment. The results show an obvious increase in EC at the beginning, and peaks of 960 μs·cm^-1, 1 150 μs·cm^-1, 1 467 μs·cm^-1 and 1 620 μs·cm^-1 after 36 days of the experiment for the four straw treatments, which are then followed by a slight decrease. EC for the four rice straw rates at the end of the incubation are 683 μs·cm^-1, 910 μs·cm^-1, 1 083 μs·cm^-1 and 1 277 μs·cm^-1 respectively. pH slowly decreases in 3 days of the experiment, the decrease is negatively related with rice straw rate, and then increases rapidly till 16 days, after which it gets relatively stable. The treatments have high TN concentration at the beginning of the experiment caused by urea application. However, TN declines rapidly from the 20th to the 76th day. Less effect of rice straw application on TN is observed. Rice straw return increases TP. There is an obvious increases in TK on the 1st day with 6.87 mg·L^-1, 36.10 mg·L^-1, 60.27 mg·L^-1, and 114.23 mg·L^-1 TK in surface soil solution. TK is steady during the entire experimentation period. Returning rice straw to field increases field surface solution EC, TP and TK concentration. While there is a positive correlation between rice straw rate and the above variables, rice straw return has little effect on pH and TN. In terms of nutrient loss, the critical time for controlling N, P and K loss is 30 days after straw application.