Abstract: In corn field ecosystem, precipitation is main factor to limit corn yield. Cornyield changes with the amount of precipitation, and gets its highest POint Underadequate water condition, but decreases when it is too dry or too waterlogged.The marginal yield effect of precipitation decreases with the increase ofprecipitation input. which are highly negative correlated, increases with the riseinaccumulated temperature and decreases with the increase of soil organic mattercontent. With the adequately incrasing input of N. P. K and manure, highinarginal yield effect of precipitation can be get. In the areas of enough precipitation and abundant heat resource, with the accordant combination of fertilizers andmanure, the corn yield potential can be thoroughly developed.

Key words: Maths model, Corn field, Precipitation, Marginal yield effect ofprecipitation