Assessment Of Grain Yields And Soil Carbon And Nitrogen Stocks Of Water-saving Ground Cover Rice Production System At Regional Scale

Traditional irrigated rice production will suffer from unprecedented challenges due to increasing population and associated water demands for urban and industrial use and the reduction of arable land. Therefore, to develop and promote water-saving technology is of high priority for the future rice production worldwide. Ground cover rice production system is one of the water-saving technologies in areas where seasonal water shortage and low temperature during early growth stage were the restricting factors for rice production. However, a sound assessment of yield and yield performances in GCRPS at regional scale and applicability of GCRPS in cold region with high content on soil organic carbon have so far not been reported. Additionally, it has been speculated that reduction of soil moisture, increased soil aeration and temperature and Eh under GCRPS will increase the decomposition of soil organic carbon, thus threatening the stability and sustainability of the production system. Therefore, a better and more comprehensive understanding on the effects of GCRPS on yields, yield components and soil organic carbon stocks at regional scales as well as the effect of GCRPS on yield and nitrogen use efficiency in cold region of rice production is beneficial to promote and maintain the stability and sustainability of GCRPS.This study was conducted at Shiyan, Central China and Heilongjiang Province, Northeast China. In this study, we compared grain yield and yield components, stable carbon isotopic composition of plant leaves and characterized soil physical-chemical properties and content of soil carbon and nitrogen of0-90cm between GCRPS and Paddy systems by sampling paired adjacent farmer fields at representative sites in the region of Shiyan, central China, in order to classify the effect of GCRPS on yields, soil organic carbon and nitrogen stocks. Furthermore, the field experiments were carried out with two cultivation system (GCRPS and Paddy) at three rates of N fertilizer for two years in cold region of rice production with high content on soil organic matter. The grain yield, yield components, crop growth rate and nitrogen use efficiency were analyzed to assess the effect of GCRPS in cold region of rice production. Our study revealed the following findings:1. Across all sites, GCRPS significantly increased grain yield by on average18%, which suggests that the observed increase in yield for GCRPS is mainly due to the increase in soil temperature as compared to Paddy, which resulted in higher shoot dry matter, productive tiller numbers, spikelets per square meter and percentage of filled grains.2. Statistical analysis allowed us to classify yield performance of the36(n=108) paired sites into three different groups:a) group of significant increase (SI; n=66), with increase in yield by32%on average, b) group showing no significant increase (NI; n=27), which yield increased on average by6%, and c) sites with grain yields showing a small (-8%) but non significant decrease (ND; n=15). In-detail analyses of yield components, soil temperature, soil redox potential and stable carbon isotopic composition of plant leaves among groups between GCRPS and Paddy revealed the lack of significant effect observed in GCRPS of ND group, which strongly suggested that unnecessary excess water was used, thus hampering GCRPS-induced increases in soil temperature and grain yields, and unequivocally signaling that appropriate water management by farmers is crucial for the successful implementation of GCRPS.3. On the contrary to the original expectations, our study showed that based on a pair wise comparison of49neighbouring fields at regional scale management using either GCRPS or Paddy cultivation, the water-saving GCRPS significantly increased soil organic C and N stocks within a few year (5-20) following conversion of production systems. This suggests that the observed increase in soil organic carbon stock for GCRPS is mainly due to the increasing photosynthetic products into plant root and soil stable small aggregates as well as more stable structure of organic material allocated into the soil, which revealed decreased mineralization potential for soil organic C.4. Lower δ15N in the soils and plant leafs under GCRPS indirectly indicated less NH3volatilization in GCRPS than in Paddy.5. Compared to Paddy, GCRPS significantly increased grain yield by31%,14%and10%at N fertilizer rate of0,90and135kg N ha-1respectively in cold region of rice production with high content on soil organic matter.6. The significant higher number of filled grains and grain yield in GCRPS indicated that crop growth rate during the reproductive stage was improved, which is likely to be caused by a positive effect of higher mineralization of organic N even at low N fertilizer rate.