Experimental Study On Reducing Nitrogen And Phosphorus Loss In Paddy Field By Irrigation And Drainage Regulation

With the development of agriculture in China,the use of chemical fertilizers is increasing rapidly,and the risk of farmland non-point source pollution is also increasing.Production practice and research have shown that the loss of nitrogen and phosphorus caused by improper utilization of water and fertilizer is one of the main causes of agricultural non-point source pollution in China,among which the loss of nitrogen and phosphorus from rice fields is the main source of surface water pollution.Chemical fertilizers are the material basis for nitrogen and phosphorus loss in rice fields,while field water movement,especially rainfall runoff,is the driving force for non-point source pollution.Therefore,effective field water management is an important way to reduce nitrogen and phosphorus loss in the field,especially in the case of ensuring normal rice growth or not significantly reducing yield.Reasonable use of irrigation and drainage methods for regulation is of great significance for water conservation and emission reduction,and reducing nitrogen and phosphorus loss in rice fields.This study focuses on the dynamics of nitrogen and phosphorus in surface runoff of rice fields under different irrigation and drainage management after fertilization,as well as the physiological ecology of rice.Combining the growth process of rice,it investigates the nutrient absorption,transformation,and growth metabolism of rice,quantifies the water conservation,emission reduction,and production effects of different irrigation and drainage management,and proposes water management techniques that take into account rice growth and control of surface source pollution in rice fields.The main results are as follows:1.The dynamic characteristics of nitrogen and phosphorus concentration and loss rate of surface runoff in different growth stages of rice under different water management were clarified:①when the water storage duration was 3 d and 6 d,the concentration of TN and TP in the tillering stage was the lowest at the water storage depth of 16 cm,and the water storage depth was 20 cm at the jointing stage.The concentration of nitrogen and phosphorus increased gradually with the decrease of water storage depth,indicating that water storage at the tillering and jointing stages could significantly reduce the concentration of nitrogen and phosphorus in the water body,reduce the loss of nitrogen and phosphorus in the paddy field and the risk of non-point source pollution.②When the water storage was 3 d and 6 d,the loss rates of TN and TP at tillering and jointing stages were the highest at 16 cm and 20 cm,and the lowest at 8 cm and 10 cm.When the duration of water storage is constant,the greater the depth of water storage,the greater the displacement,which leads to the increase of nitrogen and phosphorus loss.Therefore,the greater the depth of water storage,the higher the loss rate,and the shallower the loss rate.When the water storage lasted for 3 d and 6 d,the nitrogen and phosphorus loss and loss rate were the smallest at the depth of 8 cm and 10 cm at tillering and jointing stages.2.The physiological and ecological response and nitrogen accumulation of rice under different water management were revealed:①The enzyme activity of rice flag leaf can reflect the metabolic activity of rice under adversity stress.At the tillering stage and jointing stage,on the end of 3 d and 6 d of water storage,the MDA,POD and CAT of 16 cm and 20 cm water storage were the largest,and there was a significant difference between normal treatment(CK)(p < 0.05).After 15 days of recovery after treatment,the enzyme activity of flag leaves at each water storage depth basically returned to normal level.②When the water storage was 3 d and 6 d,the plant height and SPAD value of rice at the jointing and tillering stages were the best at the storage depth of 16 cm and 20 cm,and the chlorophyll content was the highest.At the tillering stage,the ineffective tillers were the least at the storage depth of 12 cm and 8 cm.③Under 3 d and 6 d of water storage,the nitrogen accumulation at tillering and jointing stages was higher at 12 cm,8 cm and15 cm,10 cm of water storage,and the lowest at 16 cm and 20 cm of water storage,indicating that waterlogging at tillering and jointing stages of rice reduced plant nitrogen absorption capacity.3.In the risk period of nitrogen,phosphorus and sulfur in paddy field,the water management index with little effect on rice yield(less than 10 %)and the minimum loss of nitrogen and phosphorus in the field is: when the water storage is 3 days and 6 days,the water storage depth in the field is 12 cm and 10 cm at tillering stage,15 cm and 10 cm at jointing stage.