Studies On Nitrogen Cycle In Plant-soil System And On Physiological Basis Of Kernel Yield And Quality Formation In Winter Wheat

The studies were conducted on high-yield field which returning the crop straw into soil annually, using 6 wheat cultivars with strong gluten potential, to elucidate the rule of nitrogen transforming and using in wheat-soil system, physiological basis of kernel yield and quality formation of different wheat cultivars, effects and regulations of nitrogen fertilizer rate and soil fertility condition on them, in combing 15N isotope tracing method, enzymological method and the physiological and biochemical method. To clarify the relationship between kernel yield and quality further, and physiological mechanism of starch quality formation, experiments dealing with 32 wheat cultivars were also conducted. The principal results were as follows.1. Effects of nitrogen fertilizer rate on nitrogen cycle in wheat-soil systemEffects of nitrogen fertilizer rate on the amount of nitrogen accumulated in wheatWith the increasing of supplied nitrogen amount, the amount of nitrogen accumulated in wheat plant increased and reached the highest at nitrogen fertilizer rate of 150 kg·hm-2 and 195 kg·hm-2 respectively on fieldⅠ(organic matter content, 1.45%; total nitrogen content, 0.111%; alkali-hydrolysable nitrogen content, 102.78mg·kg-1; in 0～20cm soil layer) and on fieldⅡ(organic matter content, 1.33%; total nitrogen content, 0.082%; alkali-hydrolysable nitrogen content, 85.97mg·kg-1; in 0～20cm soil layer). Increasing supplied nitrogen amount further, the amount of nitrogen accumulation would not increase significantly. When the amount of supplied nitrogen was higher than 240 kg·hm-2, the amount of nitrogen accumulated in wheat decreased.1.2 Effects of nitrogen fertilizer rate on changes of nitrogen content in soilWith the increasing of supplied nitrogen amount, total nitrogen content, available nitrogen content, and microbe biomass nitrogen content in 0～40cm soil layer all showed increasing trend. At maturity, total nitrogen content and available nitrogen content in 0～40cm soil layer of these treatments, which supplied nitrogen more than150 kg·hm-2, were equal to or higher than that of before sowing, and microbe biomass nitrogen content of nitrogen-fertilized treatments was dramatically higher than that of not.NO3--N content in different soil layers showed obvious spatio-temporal variation. With the increasing of supplied nitrogen amount, NO3--N content in different soil layers increased dramatically, and along with wheat growth stage advancing, NO3--N tented to go down into deeper layer. When supplied with nitrogen of 105kg·hm-2, NO3--N were not founded accumulating largely in 0～100cm soil profile at maturity. When supplied with nitrogen of 195kg·hm-2, the amount of NO3--N accumulated in 60～100cm soil layer in field Ⅰand that in 40～80cm soil layer in field Ⅱincreased markedly, showing eluviations had occurred in both the Fields and NO3--N exuviated deeper in field Ⅰthan in field Ⅱ. When supplied with nitrogen of 240kg·hm-2, at maturity, the amount of NO3--N accumulated in 60～100cm soil layers in both the Fields was significantly larger than at wheat jointing, showing NO3--N had exuviated to these layers.After top dressed with nitrogen fertilizer, NH4+-N content, NO3--N content and microbe biomass nitrogen content in 0～40cm soil layers increased dramatically in short time, then decreased. With the increasing of supplied nitrogen amount, the effects marked up, and the effects on NO3--N content and microbe biomass nitrogen content lagged behind NH4+-N content, but continued for more time.1.3 Effects of nitrogen fertilizer rate on nitrogen using and lossThe results of 15N-isotope tracing showed that with the increasing of supplied nitrogen amount,fertilizer nitrogen recovery rate decreased but fertilizer nitrogen loss rate increased. Recovery rate and soil residual rate of basal nitrogen were lower than that of top dressed nitrogen, loss rate of basal nitrogen were higher than that of top dressed nitrogen. Compared with field Ⅰ, absorbing proportion of nitrogen derived from fertilizer...