Variation Characteristics and Expression State of Nitrogen and Phosphorus Metering Ratio of Rice in Black Soil under Film Mulching and Irrigation Methods

In order to investigate the effects of film mulching and water-saving methods on soil inorganic nitrogen, nitrogen content of rice organs, nitrogen-phosphorus metering ratio, and nutrient limitation during rice yield formation, two water-saving irrigation methods and black biodegradable film mulching were adopted. The effects of water-saving film mulching on NH4+-N and NO3--N in 0 to 60 cm soil, nitrogen accumulation and ratio, and nitrogen-phosphorus metering ratio in rice organs were analyzed. The nitrogen-phosphorus-limiting state of rice growth under water-saving film mulching was determined. The results showed that water-saving and film mulching methods could weaken the leaching of NH4+-N and NO3--N and enhance the nitrogen uptake of rice. The water-saving method of mulching could reduce the metering ratio of nitrogen and phosphorus in rice organs. The panicle maturity process had been in a state of nitrogen limitation, and the effect was gradually enhanced. The nitrogen and phosphorus metering ratio of panicles was positively correlated with NH4+-N accumulation in the 0 to 60 cm soil layer and nitrogen accumulation of rice organs, and negatively correlated with soil NO3--N accumulation under film mulching and water-saving methods. The correlation between stems and leaves' nitrogen and phosphorus metering ratios and influencing factors was basically opposite to that of panicles' nitrogen and phosphorus metering ratio. This study can provide a reference for the formulation of a fertilization system under film mulching in the black soil region of northeast China.