作物生产、水分消耗与水分利用效率间的动态联系

DYNAMIC INTERRELATIONS OF CROP PRODUCTION,WATER CONSUMPTION AND WATER USE EFFICIENCY

在对水分消耗与产量（或同化物生产）关系剖析的基础上，引入边际水分利用效率与水分生产弹性系数概念，探讨具有动态特征的作物生产、水分消耗与水分利用效率间的内在联系。就作物产量层次上的水分利用效率而论，当Ｙ＝ｆ（ＥＴ）表现为线性时，ＷＵＥ随ＥＴ的变化趋势直接受常数项的取值条件的影响；当Ｙ＝ｆ（ＥＴ）表现为二次抛物线时，随着ＥＴ的增加，ＷＵＥ的最大值要先于Ｙ的最大值而提前达到，使ＷＵＥ达到最大值的ＥＴ值等于常数项与二次项系数之比的算术平方根，在其之前，ＷＵＥ渐增，在其之后，ＷＵＥ渐降。

This paper introduces the concepts of marginal water use efficiency (MWUE) and elasticity of water production (EWP),and reveals dynamic interrelations of crop production and water consumption and water use efficiency (WUE) based on the functional relation between water consumption and crop yield ( or photosynthate). Providing the relation of seasonal evapotranspiration (ET) and crop yield (Y) is as Y=f(ET),then WUE=Y/ET,MWUE=dY/dET,and EWP=MWUE/WUE.WUE increases with the rise of ET if EWP>1 and decreases with the rise of ET if EWP<1. Proper construction of the function of crop water production,Y=f(ET),serves as a basis for correct analysis of WUE. If the Y=f(ET) function is linear,the changing trend of WUE with ET is directly affected by the constant term. If the Y=f(ET) function is quadratic parabolic,the maximum WUE comes earlier than the maximum yield with the rise of ET. The ET that makes WUE reach to its maximum value equals the arithmetic square root of a ratio of the constant term to the coefficient of quadratic term(). WUE increases with the rise of ET when ,conversely WUE decreases with the rise of ET when . Field experiment on spring corn yield response to water and fertilizer in the loess tableland of China showed that the form of Y=f(ET) appeared parabolic relationships at both high and low fertility levels,and high fertility plots had higher WUE and ET than low fertility ones under the same level of water supply. At high fertility plots in 1987,WUE increased with the rise of ET when ET< 472mm,reached to the maximum value of 16 3kg/ha.mm when ET =472mm,and decreased with the rise of ET when ET<472mm. The yield reached the maximum of 8 111kg/ha when ET = 524mm. MWUE always decreased with the rise of ET within the experimental range and dropped to zero when ET = 524mm. At low fertility plots,WUE reached the maximum value of 11 6kg/ha.mm when ET =436mm,and the maximum yield of 5 298kg/ha was gained when ET = 485mm; the WUE and the MWUE were similar to the ones of high fertility plots in the aspect of the changing trend.