| Rice is an important food crop in our country; nitrogen fertilizer played an important role for improving rice yield and stability of food production. However there are obvious problems of the higher nitrogen fertilizer inputs and lower fertilizer use efficiency in our rice production. Therefore high yield and high resource use efficiency has been the hot demand for rice production in China. Field trials were carried out with hybrid cultivars Lu liangyou996(early rice, E), and C Liang you396(late rice, L) in2011in Yong’an town of Liuyang City,Hunan province. The treatment without nitrogen fertilizer input (nitrogen blank, T1) and the treatments of farmers’practice (T2, CK), high yield and high N fertilizer use efficiency cultivation mode(T3), super-high-yield cultivation mode(T4), and further high-yield and N fertilizer use efficiency cultivation mode (T5) were designed in this experiment to explore the nitrogen fertilizer use efficiency and nitrogen metabolism under different rice yield levels in double cropping rice. The results obtained are as follows:1. Compared with that in farmers’practice, the average yield of double rice in treatments of T3,T4,and T5was significantly increased by26.7%,47.9%and37.6%, the nitrogen recovery use efficiency (RE) respectively increased by69.3%,55.2%,65.3%for early rice and141.1%210.7%,233.5%for late rice; the agronomic use efficiency (AE) of nitrogen fertilizer was increased by118.6%,92.2%,102.7%and165.1%,168.5%,169.4%, respectively, and the nitrogen partial factor productivity (PFP) for early rice and late rice was respectively increased by65.8%,30.9%,44.8%, and48.5%,18.4%,31.1%.Nitrogen fertilizer use efficiency had a significant linear correlation relationship with the yield, which indicated that yield enhancement was an effective approach for increasing rice nitrogen fertilizer use efficiency.2. Nitrogen accumulation amounts had highly significant linear relationship with biomass yield. The correlation coefficient (r) between above ground biomass and plant total nitrogen accumulation at mid-tillering stage (MT), panicle initiation stage (PI), booting stage (BT), heading stage (FL) and maturity (MA) were0.920**,0.896**,0.876**,0.863**and0.936**, respectively. SPAD value at full heading stage was significantly correlated with glutamine synthetase (GS), activity of nitrate reductase (NR), soluble protein and leaf nitrogen content (the correlation coefficient r values were0.634**,0.757**,0.645**0.608**for early rice;0.529*0.803**,0.869**and0.736**for late rice). 3. Relative to farmers’practice (T2), all the integrated and optimized cultivation modes T3, T4and T5enhanced SPAD value (relative chlorophyll content), activities of glutamine synthetase (GS) and nitrate reductase (NR), soluble protein and free amino acid content, amino acid content in root bleeding sap and root activity after heading, which promoted plant nitrogen absorption, accumulation and transportation, may be the direct physiological causes of nitrogen use efficiency enhancement in double rice.This study indicates that nitrogen fertilizer use efficiency can be increased in double cropping of rice production by promoting and increasing nitrogen metabolism through the integration and optimization of cultivation techniques. |
