SOURCE-SINK LIMITATIONS OF MAIZE GROWING IN AN OUTDOOR HYDROPONIC SYSTEM
Experiments were conducted from 1983 to 1985 to test the hypothesis that rate of dry matter accumulation by maize (Zea mays L.) during grain filling can be enhanced by an increase in assimilate demand for grain filling (i.e., sink strength).The sink strength of maize plants grown in an outdoor hydroponic system was varied independently of the source strength by manipulating the plant spacing during the period in which final kernel number is established. The crop growth rate during grain filling, the dry matter of leaves, stems, ears and roots, and grain yield components were determined. In all 3 yr the crop growth rate during grain filling of plants that had been growing at a 20 000 plants ha−1 spacing for variable periods and were returned to the control density of 80 000 plants ha−1 at the start of the grain-filling period was lower than that of plants grown continuously at a spacing of 80 000 plants ha−1. In 1985, plants grown at 20 000 plants ha−1 from 3 wk preanthesis until 2 wk postanthesis and at 80 000 plants ha−1 thereafter had 50% more kernels per plant than the control plants. However, the net photosynthesis during grain filling was not increased; in fact it was somewhat lower. Final grain yield was not significantly different, mainly due to greater translocation from the stems to the grain in the spaced plants than in the controls. These studies indicate that maize growing in a nonlimiting below-ground environment is not sink limited. Hence adding sink capacity by maintaining kernel number while increasing plant density or by adding more kernels per plant would not appear to be a promising route for raising the yield potential.Key words: Sink strength, hydroponics, plant spacing, kernel number, yield components