Dynamics of Nutrient Accumulation in Maize Plants Under Different Water and N Supply Conditions

The dynamics of accumulations of plant dry matter, nutrient uptake and N fertilizer recovery were studied under different water and N supply, using summer maize(Zea mays L.var. Shandan9)as an indicating crop. The total dry matter (including roots) and N, P, K uptake amounts were continuously increased with plant growth, and their accumulations with time during plant growing period were shaped in S curves that could be described by exponential regression equations. Differentiating the regression equations fitting the curves over time for first derivatives, the momentary rate of the dry matter and nutrient uptake was obtained. Results show that the rate of dry matter accumulation and nutrient uptake were not in the same at all time, but changed from one time to another. Usually, the rate was increased fast at early stages, and gradually decreased after reaching their peak. Of N, P and K, the uptake rate of N and K was higher, and their increase and decrease were both fast while P was in reverse case. The time of the maximum absorptive rate appeared earlier for K, followed by N, and then by P. In any case, the time of maximum nutrient uptake rate appeared earlier than did the dry matter. The momentrary N recovery rate was similar in trend to those of dry matter and N uptake, and its maximum momentary recovery rate occurred almost at the same time as its maximum uptake rate. Supplemental irrigation raised the accumulative and momentary rates of N. Although water and N supplies increased dry matter and nutrient uptake rates, they did not alter their changing trends during the plant growing period.