Variation Of Crop Productivity With Size And Proportion Of Soil Nutrient Pools And The Balancing Fertilization Design

Cereals production in China has experienced several stages of development due to cultivar innovation and fertilizer application.High input of chemical fertilizers has been overspread in China for high yielding since 1990's.However,high rates of of fertilizer application may have resulted in decreasing use efficiency and increasing runoff loss as a source of non-point source pollution from farmplands.Therefore,formulated or precise fertilization had been a new frontier for nutrition and fertilization technology development in agriculture.There had been numerous studies on the rational fertilization for dry croplands of North China since 1990's.This dissertation deals with rational fertilization with dry crops by field experiments concerned with both the pool and proportion of nutrients in supply,taking examples of corn and wheat production in drycropland soils from Shanxi province,China.The fertilization schemes were developed from the hypothesis of "minimum nutrient control' and with improved design concerning both the nutrient supply rate and proportion.The experiments had been conducted in a series of soils from different locations and crops of tobacco,corn,and wheat with different nutrient demands.The response of crop yield to different fertilization schemes were studied for deducing the best total fertilization rate and proper proportion for high yielding production.In addition, uptake and utilization of soil nutrients by different types of crops and the effect of the phyllogenetic nature of crop culticvars were also discussed.The main results were as follows:1,The status of soil nutrient supply could be divided into two main types of balancing and non-balancing supply of the soils studied.This was especially true when soil nutrient pool was exausted under continuous cultivation.Therefore,dry crops should be supplied not only a rational total amount of fertilizsers but a proper proportion of the nutrients applied with N,P and others when seeking high yielding producitivity of corn,wheat and tobacco as well.In this means,fertilization is aimed to adjust the supply rate of soil in an enough amount to meet the crop requirements so that crop could use efficiently for a potentially high yield.Whereas,the fertilization rate is only to meet the requirement at the seedling stage for the potential growth for biomass buid-up.The proportion of nutrient supply affects not only the total uptake of crops but the maximum yield.The use efficientcy of nutrient fertilized could be increased under a proper ratio of N to P as a high N use efficiency of 44.8%～48.2%was observed under balanced fertilization for corn and a contribution to grain yield of per kg of N turned to be as high as 38.9～41.4kg.Inproper N to P ratio could result in reduced nutrient uptake by corn and accumulation of excess of P in soil after harvest,thus reducing P use efficiency;2,Difference in the maximum fertilization rates for corn was observed between using N application rate following P rate and using consistent proportion of N to P in fertilizer application.The maximum application rate of N and P for highest yield depends on the ratio of N to P.The marginal yield response could be described with different type of regression functions.The marginal yield response seemed small variation with application rates under a fertilization rate loewer than the maximum rate.However,the marginal response turned smaller when the application rates in excess of the maximum rates.The response to nutrient supply rates could be staitisatically modeled with two linear curves with the corss point at the maximum fertilization rate,which may reflect the actual marginal effect of supplied nutrients in a proper proportion.It is concerned as a real demand of nutrient for high yielding production in the field.It is likely that the maximum fertilization rates were determined by soil fertility and the nutrient proportion in supply of the soils under cultivation.Nevetheless,meterological conditions may have effects on the agronomicial efficient of the supplied soil nutrients.3,An experiment with a series of new cultivars in a regional test was also conducted with the balabcing fertilization schemes,demonstrating a potential control of phylogenetic properties on the nutrient uptake and the marginal yield response.High potential yield may be obtained of some cultivars breeded under imbalanced soil nutrient supply when grown under balanced supply of fertilizer nutrients;Whereas,some cultivars adapting to both balancing and imbalancing soil nutrients may have higher yield potential when grown under imbalanced soil nutrient status;However,limited yield increase would be expected when grown under balanced soil nutrient status of some cultivars breeded under imbalanced status.The yield potential seemed to be controlled in a great deal by the soil nutrient supply when they were breeded,which may in turn affect the genetic stability of the productivity of the cultivars under breeding.Therefore,a new approach for cultivars breeding by adjusting soil nutrient supply status could be developed.This study may offer a new insight into the actual yield response curve when using nutrient supply rate and proportion in field experiments of fertilization schemes in classical soil-plant nutrition study.It is suggested that the marginal response would be characterized by a decreasing yield unless an improper ration of N to P be applied.The response curve may be interpreted with a cross point of a maximum yield of two linear response curve both an increasing and a decreasing trend turning at the maximum rate,which reflect the different marginal yield response depending on the rational maximum rate and the balancing status.This offers a scientific base for recommending a high yielding and high use effiency fertilization shceme for dry croplands of North China.