Mechanism Of Saving Water And Increasing Yield And Optimization Of Management In Ground Cover Rice Production System

Rice is an important food crop. It is necessary to ensure a further increase of food production to meet the growing demand of global people. However, with the rapid growth of industrial water and urban water,agricultural water is gradually decreasing which has threatened the production and stability of conventional flooded cultivation. In order to solve the contradiction between supply and demand of irrigation water, ground cover rice production system (GCRPS) emerged as the times require. In the region of low water availability and low temperature at early spring, GCRPS can improve grain yield and resource use efficiency with reducing the amount of irrigation water. Previous studies on GCRPS were mostly focused on the agronomic performance of aboveground. Photosynthetic characteristics and root characteristics of rice were rarely reported which are critical to understand the condition of water and nutrient use efficiency, the mechanism of increasing production efficiency, the optimization of nitrogen management and maintain the sustainability and stability of GCRPS.In this study, the experiment was conducted in Shiyan City, Hubei Province. We designed a three-year field experiment to compare the effects of conventional flooding (Paddy, P) and GCRPS (G) on rice root growth and photosynthetic characteristics. Leaf and canopy photosynthetic rate, root dry weight, length,surface area, at the maximum tillering stage and flowering stage, grain yield and water use efficiency were measured to explain the reason of increased grain yield and resource use efficiency. In this experiment, ?13C value of rice plants were measured to explore more simple and effective method to characterize water use efficiency of rice plants. Another two-year experiment is using the degradable film instead of the commonly plastic film, and applying nitrogen split to verify whether this method can be used to optimize the management of nitrogen in GCRPS to further improve yield and nitrogen use efficiency. The above studies get the following results:(1) Leaf and canopy photosynthetic rate at the maximum tillering stage were significantly increased in GCRPS, while which was lower in GCRPS than that in Paddy. Leaf and canopy photosynthetic rate of rice at maximum tillering stage was positively correlated to shoot dry weight, grain yield and water use efficiency which indicated that GCRPS increased photosynthetic rate of rice and product higher yield and resource use efficiency. Optimizing nitrogen fertilizer management to improve the photosynthetic rate at the later growth stage could further improve grain yield in GCRPS.(2) Root dry weight, length and surface area in the 0-10, 10-20, 20-40 cm soil layer of GCRPS were significantly higher than those of Paddy. Greater root dry matter, length and root surface area at the flowering stage were positively correlated to grain yield and water use efficiency. GCRPS could promote growth and development of rice root system which is very important to improve grain yield. In addition,GCRPS promote root development can also avoid rice lodging, improve soil organic carbon, thereby improving soil function.(3) Compared to basal application of all N fertilizer in GCRPS, split application of N or a basal combination of urea plus manure in conjunction with the use of biodegradable film could significantly increase rice grain yield, number of productive tillers, and spikelets per square meter, improve crop growth rate and N uptake rate from panicle initiation to maturity, significantly increase agronomic efficiency of N fertilizer and recovery efficiency of N in grains. Our results highlight that using biodegradable film instead of standard plastic film allows for split application of fertilizers, which increases yield and N use efficiency as well as significantly reduce environmental pollution with plastic film in GCRPS(4) ?13C value of plant shoot at maximum tillering stage was positively correlated to irrigation and total water use efficiency. However, the relationship was not found at flowering stage. The ?13C values in 2013 were significantly higher than those in 2014. This may because solar radiation from transplanting to maximum tillering stage in 2013 was significantly higher than that in 2014. While other meteorological and soil factors were not significantly different. The results showed that the ?13C value of shoot at maximum tillering stage can better characterize field water use efficiency. The big difference of ?13C value between years was mainly due to the difference of solar radiation between years.(5) When the gray scale threshold of WinRhizo software is set 225, the rice root length is significant positively correlated with the actual measured value, and the absolute difference between them is smallest.