Maize Yield Response to Increased Assimilate Supply

The capacity of the maize (Zea mays L.) ear to accept greater assimilate supplies is an important parameter in some strategies to increase grain yield. This problem was studied by increasing assimilate supply at several growth stages and determining the effects on grain yield, yield components and partitioning ratios. During a 2-year period, a single-eared hybrid was grown at a control density of 64,500 plants/ha and was thinned to 43,000 and 21,500 plants/ha at growth stages ranging from soon after emergence to 3 weeks after silk emergence. In a second experiment, light reflectors were placed between rows of three different hybrids for 2-week intervals ranging from about 3 weeks before to about 6 weeks after silk emergence. Both thinning and reflector treatments were designed to increase assimilate supply to the ear. In thinning experiments, control densities yielded about 10,700 kg/ha during 1978 and 1979. Thinning at 2.5 weeks before silking increased yield per plant up to 41% while thinning at 3 weeks after silking caused an 11% increase. Increased kernel number and weight/kernel accounted for the yield increase, and the relative contribution of each shifted from one year to the next even though yields were similar both years. Ear number, kernel row number and duration of grain fill were unaffected by increased assimilate supply. Yield increases obtained by thinning to the intermediate density occurred with little change in partitioning ratio of dry weight and N. Thinning to the lowest density caused a decline in the partitioning ratios. Reflector experiments in spite of some heat stress demonstrated that increased assimilate supply for short, discrete periods could cause similar results. We conclude that under our U.S. Corn Belt conditions, increasing assimilate supply can result in a grain yield increase per plant and can do this without altering the length of grain-filling or the partitioning ratios.