Effect Of Nitrogen Fertilizer Rate On Yield And Nitrogen Uptake And Utilization Of Different Varieties Of Rice

Rice is one of the most important food crops in China, and its production is directly related to the food security of our country. With China’s economic and social development, rice production is faced with a series of new problems. Rice varieties with high-yielding are constantly emerged, not only the corresponding properties of nutrients uptake of different rice genotypes and nutrients resource management technologies still lag behind, but the fertilizer amount increases year by year and rice yield increase is not obvious. Current fertilization technology cannot provide guidance according to the fertilizer requisite characteristics of different rice varieties. This research selected9varieties of rice to study on its response under different nitrogen application, nitrogen absorption characteristics and nitrogen balance of rice field on field experiments in Honghu (2011yr) and Jingzhou (2012yr) in Hubei Province. The main results were shown as following:1. Rice yield increases significantly with nitrogen applicatied, but the increasing rate decreases with the increase of nitrogen application amount. Under the appropriate N fertilizer application amount (165kg/hm2), Honghu site had a higher yield and economic benefit,which got1609kg/hm2yield and5263yuan/hm2benefit more than Jingzhou site did in the average of9rice varieties. N fertilizer affects the yield components of different rice varieties, and increases the effective tiller number, the effective ear number, the spike length and the number of grain per ear. But it has less effect on the thousand seed weight of rice which related to different rice varieties. Using a quadratic equation with one unknown and linear platform model, we can get the optimum nitrogen fertilizer of each variety. The results showed that, in Honghu site the best N application for an average of9varieties was181kg/hm2, thus the rice yield will increase4899kg/hm2, a rate of growth77.6%, and the yield of11319kg/hm2at the same time can increase12248yuan/hm2. In Jingzhou site the best N application for an average of9varieties was160kg/hm2, thus the rice yield will increase2551kg/hm2, a rate of growth38.4%, and the yield of9311kg/hm2at the same time can increase6024yuan/hm2.2. The amount of Nitrogen accumulation of different rice varieties also significantly increases with nitrogen fertilization application. In Honghu (2011) site, those varieties accumulated nitrogen143.3,180.9,217.8,243.7kg/hm2for average with N72.5, N165, N247.5and N330treatments. Compared with No treatment, it increased49.7,87.3,124.3,150.2kg/hm2rice yield and the growth rate was53.1%、93.3%、132.8%、160.4%. Under the appropriate N fertilizer application amount (165kg/hm2), variety HA3and variety LY6326has higher N accumulation than other varieties. With N fertilization applied, amounts of N accumulated of different rice varieties in Jingzhou site respectively were lower than in Honghu site from17.9to66.4kg/hm2, lower amplitudes from19.2%to27.2%.The nitrogen fertilizer utilization rate presents a downward trend along with the increase of nitrogen fertilizer. And the difference of nitrogen fertilizer utilization rate between different rice varieties is big, as well as between seasons and years. In Honghu site, the nitrogen fertilizer utilization rate was36.8%-64.9%, with an average of52.3%. Nitrogen fertilizer utilization rate in variety HA3was highest and76.3%higher than that in variety XLY6which had lowest utilization rate. Under the same nitrogen level, nitrogen fertilizer utilization in Jingzhou site was lower than in Honghu site.3. Applying Nitrogen fertilizers can significantly increase the dry matter biomass and nitrogen accumulation amount in rice. During different growth stages, the growth of nitrogen accumulation amount was higher than that of dry matter biomass, and the difference in reproductive growth period change was bigger. Physiological growth of leaves is mainly in tillering stage to booting stage. Stem biomass in the jointing stage to booting stage increased rapidly and reached a maximum. In reproductive growth stage of rice, the biomass of rice panicle increased obviously in the booting to filling stage. In physiological growth stage of rice, nitrogen content in rice leaves kept at a high level from tillering stage to the booting stage. With the beginning of reproductive growth, nitrogen content in rice leaves decreased significantly and decreased more than100%in mature period, providing the formation of rice grains with large amount of nitrogen source. Nitrogen content in rice stem decreased significantly in jointing stage to booting stage, variety MH63and variety LY6326were decreased42.3%and38.1%respectively.4. Under the condition of the same nitrogen fertilizer inputs, the rice production levels, the increasing yield, the growth rate, the economic benefit, the nitrogen accumulation amount and the nitrogen utilization efficiency of two-line hybrid rice are all higher than those of conventional rice. In addition to the growth rate, other indicators of three-line hybrid rice are also higher than conventional rice. What’s more, the conventional rice needs more nitrogen fertilizer input per unit output than two-lines and three-line hybrid rice.5. Applying Nitrogen fertilizers increases ammonium nitrogen and nitrate nitrogen contents in paddy soil, and promote the N2O emission. In mature period, the siol nitrogen removed by rice in-N (0kgN/hm2) treatment was75.8kg/hm2,+N (165kg/hm2) treatment was147.7kg/hm2. Applying Nitrogen fertilizers with165kg/hm2, inorganic nitrogen surplus in soils was9.9kg/hm2. The rest did not absorbed by the rice and soil residual nitrogen was83.2kg/hm2, accounted for50.4%of total in the nitrogen input.To sum up, under the condition of different nitrogen fertilizer input, there were differences in yield, economic benefit, Nitrogen absorption characteristics, and nitrogen fertilizer amount of different rice varieties. So, in the process of actual production, we should apply nitrogen fertilizers according to yield potential of different varieties and nitrogen absorption properties.