Study Of Effects Of Different Rice Genotypes On Nitrogen Use Efficiencies Under Fertilizer-N And Zero-N Conditions

With the dramatic economic increases and irreversible increases of China's population, and declines of arable land, the feasible way to increase food production is to increase the grain yield per unit area. These result in the huge increases of nitrogen fertilizer application, and reducing nitrogen-use efficiency, lower economic profit, poor grain quality and environmental contamination by nitrogen. Selection of rice genotype with high nitrogen use efficiency is one feasible way of methods to improve nitrogen use efficiency. The aim of this paper was to provide theoretical basis and experimental evidence in selecting new rice genotype with high-N use efficiency (e.g. high rates of N utilization and reallocation in plant), and high fertilizer-N response (e.g. high yield can be achieved with higher fertilizer-N rate), and improving growth characters with high-yield potential and appraisal of rice variety resources.A pot experiment was carried out to study the effects of zero-N and fertilizer-N on growth characteristics of 8 rice genotypes in Jilin province. These included analysis of relationships between yield characteristics, nitrogen use efficiency of different rice genotypes, plants uptake and transformation of phosphorous and potassium under zero-N and fertilizer-N condition, and the uptake rate (the amount of N-uptake by plant per unit soil), utilization rate (unit organic matter produced by unit N uptake) and translocation efficiency (ratio of N in yield to N in plant biomass) of different rice genotypes.The results shown that under fertilizer-N condition, main differences of growth characteristics of rice were length of root, tillers and ratio of the aboveground biomass to root, suggesting that these characters can be optimized by improving varieties so that the best agronomical characters can be obtained, then nitrogen use efficiencies can be reached and the high-yield can be gained. There were strong correlations among yield characters in rice genotypes, and nitrogen fertilizer had significant effect on the yield characters. The correlations between the yield and characters showed that the order of effect of yield characters on yield were 1000-grain weight > number grain per panicle > panicle-bearing tiller under fertilized-N condition. Therefore, attention should be paid in the order of 1000-grain weight, number of grain per panicle and panicle-bearing tiller when selecting high-yield genotypes of rice. It was found that some effects of N levels on transportation andreallocation of P and K nutrients of rice genotype. Fertilizer-N promoted the accumulations of P and K in the root system after nitrogen fertilizer application and facilitates the available utilization of P and K Fertilizer-N accelerated transportation of P and K to grain. Under balanced nutrient condition, the maximum uptake of K by plant was in tillering stage and ear forming stage. Under imbalance N condition, the maximum uptake of K by plants was from ear forming stage to harvesting stage. JF10 has the highest yield under low N condition, indicating that this variety can be grown under a low soil-N with a reasonable yield, and a higher yield can be obtained under high-N condition. Yields of JD16, JF8 and FY301 are not sensitive to nitrogen fertilizer, and of these, JF8 has the lowest yield. This indicates that in practice less nitrogen fertilizer is needed for this genotype. For all rice genotypes, the maximum uptake of N is in tillering stage, indicating that attention should be paid for fertilizer-N application and management in this stage in practice.To summarize, eight rice genotypes can be grouped into 4 classes according to their characteristics and abilities to fertilizer-N uptake;Lower N use efficiency with lower fertilizer-N response: This class includes ND3, ND8 and JF8, and they are not good varieties for future application in practices.Higher N use efficiency with lower fertilizer-N response: This class includes JD16, FY301, JF3, and they are suitable for lower soil-N condition and they can be used as variety-resourc...