Water pH, water temperature, and soil elements in the paddy fields under the integrated Azolla-Duck-Rice farming system and its manuring effects

摘要

The present study was carried out to examine the influences of the integrated Azolla-Duck-Rice farming system on water pH, water temperature and soil elements in the paddy fields, and the manuring effects of the farming system. It was shown that the water pH was not changed, but the water temperature was lowered by 1-2 deg C; however, this temperature drop was not severe enough to affect the tiller of rice plant. Measurement of the soil elements in the paddy fields indicated that, at the harvest stage, the nitrogen (T-N) of Azolla-Aigamo ducks plot was significantly higher than those of Control, Azolla, and Aigamo ducks plots (P<0.05), and it was also higher than before the experiment was applied, compared to the other 3 plots which were lower. The same results were obtained from soil carbon (T-C). The amount of phosphorus (P_2O_5) in Azolla-Aigamo ducks plot was significantly higher than those of Control and Azolla plots or that before the experiment though it was significantly lower in comparison with Aigamo ducks plot (P<0.01). The soil potassium content also appeared increased in each trial plot when compared to the experiment which was done before. The N concentration of the leaf, stem, and ear of the rice plant in Azolla-Aigamo ducks plot were significantly higher compared with the other plots. Nitrogen fixation by the Azolla was estimated to be greater than 4.78g/m~2 in Azolla-Aigamo ducks plot. Moreover, the interactions of Azolla and Aigamo ducks on the T-N and P_20_5 were shown at the havesting stage of the rice plant (P<0.05). The differences between the treatments due to inoculation of the Azolla or the free-ranging of the Aigamo ducks were greater, suggesting that the effect of the Azolla was enhanced with the free-ranging of the Aigamo ducks.