Grain Yield ofPennisetum americanumAdjusts to Nitrogen Supply by Changing Rates of Grain Filling and Root Uptake of Nitrogen

Abstract

Coaldrake, P. D., Pearson, C. J. and Saffigna, P. G. 1987. Grain yield of Pennisetum americanum adjusts to nitrogen supply by changing rates of grain filling and root uptake of nitrogen.—J. exp. Bot. 38: 558-566. Pearl millet (Pennisetum americanum (L.) Leeke) was grown in containers at three constant rates of nitrogen supply or with the nitrogen supply increased from the lowest to the highest rate during panicle differentiation or at anthesis. We measured the rate and duration of nitrogen and dry weight gain by individual grains and nitrogen (15N) uptake by roots and its distribution during grain filling. The total amounts of nitrogen and dry weight in all grain per plant at the lowest nitrogen supply were 8% and 14% respectively of plants grown continuously at the highest rate of nitrogen. This was because low rates of nitrogen supply reduced grain number, mean grain weight and the nitrogen content of each individual grain. The amino acid composition of the grain protein was affected only slightly by nitrogen treatments. Rates of grain growth were sensitive to nitrogen supply whereas the duration of nitrogen movement to the grain was not. Nitrogen uptake by roots continued throughout grain filling; rates of uptake per g root in plants given least nitrogen were one-half those of plants given the highest amount of nitrogen. A change from lowest to highest nitrogen supply at panicle differentiation increased the uptake of nitrogen by roots and the rates of growth of individual grains, to the rates observed in plants which had been supplied continuously with the highest nitrogen. When the change in supply was made at anthesis there was rapid movement of nitrogen into the plant but this was not translated into more rapid grain growth.