Differences In The Productivity And Stress Resistance Of Double Rice Cropping System Between Different Fertilization Regimes In Jiangxi Province

Fertilization is an important way to increase crop yield and contributes more than 50% to food production increment in China. However, unreasonable fertilization can lead to soil degradation and soil quality decline, and thus may influence the sustainable increase in crop yield. The hilly areas south of the Yangtze River are the main production areas for double rice and play a key role in the long-term food security in our country. Jiangxi is a typical region of the tested areas. It is of important significance for sustainable double rice production and food security in our country to study the long-term impact of different fertilization regimes on the productivity of double cropping rice systems. Therefore, through a 29-year (1981-2009) fertilization experiment in fields and a 4-year (2006-2009) nutrient depletion experiment with pots in Jiangxi province, we analyzed and compared the differences of crop productivity and dry matter production efficiency among different fertilization management. Through investigating the trends of crop productivity, coefficient of variation, and sustainable yield index (SYI) in the double rice cropping system, we elucidated the integrated effects of long term different fertilization regimes on the productivity and stress resistance of the agroecosystems. The main results were as follows:1. Only under N, P, and K fertilization, the yield of the double rice increased significantly in the short term. The chemical N could increase yield within 16 years, but the effects decreased with years. After 29 years, the yield of N, P and K treatments were close to the control by 9.8%,-6.1%,-1.0%. and there was no significant difference between them. The productivity of the treatment without N fertilizer (PK) was lower than NP, NK treatment significantly, whose mean value of yield was lower than the above two treatments by 15.0% and 14.8%. The balanced fertilization treatment (NPK and NPK+OM) had the significant biomass and yield in all the treatments all over the experiment. The application of NPK+OM gained both the highest mean aboveground biomass and mean grain yield that were 24.5% and 20.2% higher than those in the NPK treatment, respectively. The annual grain yield only in NPK+OM treatment and P treatment showed increasing trends, which inclined by 6.9 kg hm-2 a-1 and 5.2 kg hm-2 a-1 respectively.2. Compared with other treatments, only N fertilizer treatment decreased the annual biomass coefficient of variation (CV) of double rice, increased the annual biomass sustainable index of double rice. The next effects are NPK treatment. In balanced fertilizer treatments (NPK. NPK+OM), no matter early rice or late rice, the yield CV was the least and the sustainable yield index (SYI) was the highest. Although the stability of biomass production was higher the productivity was lower. Therefore, only balanced fertilizer can assure the high and stable yield in double rice ecosystem.3. In the soil nutrient depletion experiment, the tolerance ability of paddy ecosystem was higher in the only N fertilizer treatment than in only P or only K fertilizer treatment. The annual biomass was 3.5% and 3.7% higher in only N fertilizer treatment than in only P or only K fertilizer treatment and the annual yield mean was 6.2% and 8.0% higher. The paddy ecosystem under only P fertilizer degraded seriously and had lower tolerance ability. The yield significantly decreased at -5.0 g pot-1 a -1 in partial application of NK. So. the only long term P fertilizer application or long term P fertilizer absence had negative impacts on paddy ecosystem. Therefore, reasonable combined application of P fertilizer can effectively increase the tolerance ability in red soil paddy ecosystem. After four years operation of soil nutrient depletion experiment, the seasonal or annual biomass and yield of rice was the highest in NPK+OM treatment. And the biomass and yield means was also the highest in NPK+OM treatment. These results indicated that the tolerance ability under combined organic fertilizer and inorganic fertilizer was the highest. Therefore, the combined application of organic and inorganic fertilizer can not only maintain high productivity in paddy ecosystem but also increase the stress resistance of paddy ecosystem, facilitating the high and stable yield of double rice system in Jiangxi.4. The N harvest index was significantly reduced by N fertlizaiotn. which was highest in the PK treatment significantly higher than that in the N,NPK+OM,NP. and NPK treatments. Under application of the same amount of N, N use efficiendy (NUE) increased with the increasing application of P and K fertilizers, which was in the order:NPK> NP, NK> N. Application of NPK combined with organic manure can increase the NUE as well.