[Rational range and optimum proportion of energy input in farmland]

There exists a rational range of artificial supplemental energy inputs in fields. In the range, the inputs can improve the yield and the output/input ratio. The rational range of energy input in total energy output is bigger than that in the output/input ratio. It is bigger in low yield fields than high yield fields, which suggests that increasing artificial supplemental energy input can increase the production of low yield fields as same as high yield fields. In the rational range of energy input, there exist high efficient lines in water and fertilizer inputs. The highest efficiency occurs when the rational inputs of water and fertilizer occur in these two lines. There also exist optimum lines of energy and economy input proportions. In the two lines, the proportions of energy and economy output/input of water and fertilizer inputs are the highest, which are the optimum of water and fertilizer inputs. Water and fertilizer may replace each other for equal yields, but would result in a decrease in the output/input ratio.