Potentiality Analysis of Grain Productivity and Its Security in Changwu County in the Loess Plateau Gully Region against the Background of "Grain for Green" Projection

The issues of grain,population and resources are now becoming increasingly serious in the loess gully area in China,especially under the background of Grain for Green projection from 1999.It is important to evaluate the impacts of Grain for Green projection on the grain productivity and security in the area.In this study,the data of agricultural meteorology in Changwu county in 1993 and 2009 were used to evaluate the grain productivity potentiality.The farmland area and its geographical distribution in 1993 and 2009 were used to check the farmland change and the grain security in the county.The potential productivity for each meterological factor limitation level for main grain plants and the degree of potentiality exploited was calculated using mechanism methodology.Compared with 1993,the achievable potential productivity in 2009 reduced by 7.8%,while the actual grain productivity increased by 4.0%,so the fulfilling rate of the potential natural productivity increased from 61.58% in 1993 to 68.59% in 2009.During the past 17 years,the planting area of main grain plants decreased by 27.8%,grain yield per hectare improved by 44.1%,population increased by 12.5%,the grain planting area per capital decreased 35.9%,the grain yield per capital declined by 7.5% from 320.1 kg to 296.0 kg.The potential productivity was promoted due to the raise of effective coefficient of temperature and land,while the actual grain yield was restricted by the quantity of farmland.Farmland shrinking and population accretion are two core problems in the grain security in the area.So improvement of per capital grain yield is the guarantee for grain security.At the last,the paper was suggested that it be exploited grain potential productivity further and settled down the serious grain security problem in the area,it was requisite to scientifically input assistant energy,to extensively build basic farmland,to conserve cultivated land and popularize the sustainable and efficient modern agriculture technology.