Effects of pre-anthesis drought, nitrogen fertilizer rate, and variety on grain yield, yield components, and harvest index of tropical maize

Abstract

Water and nitrogen (N) are the most limiting factors for grain yield of maize ( Zea mays L.) in the tropics. In Thailand, the risk of water shortage is highest during the vegetative stages of maize development. A 3-year study with two water regimes (pre-anthesis drought versus irrigation throughout the vegetation cycle), three levels of N fertilization (0, 80, and 160 kg N ha −1), two open-pollinated varieties (Suwan 1 and La Posta Sequia), and two hybrids (KTX2602 and DK888) was conducted to determine the interactive effects of pre-anthesis water supply, N fertilizer rate, and variety on the grain yield, yield components, and harvest index of maize in the tropical lowlands of Thailand. Averaged across the N rates and varieties, drought-stressed maize yielded 32% (1995), 13% (1996), and 21% (1997) less than well-watered maize. Irrespective of variety, 80 kg N ha −1 was sufficient to achieve maximum grain yield under pre-anthesis drought, whereas 160 kg N ha −1 resulted in the highest yield under well-watered conditions. Pre-anthesis drought significantly reduced the number of kernel rows, the number of kernels per row, as well as the 1000-kernel weight. The effect of the water regime on the ear number of DK888 varied from year-to-year. Water stress consistently resulted in increases in the harvest index. There were significant effects of the water regime × variety interaction on grain yield in two of the three cropping seasons. KTX2602 was more affected by drought than Suwan 1 in all the years and, in 2 of the 3 years, than La Posta Sequia. This was attributed to the fact that KTX2602 was the earliest variety. In 1996, DK888, the top yielder, produced almost the same grain yield under drought stress and continuous irrigation. Unfavorable weather conditions shortly after silking in 1996 (low irradiation in combination with relatively high temperature) seemed to have limited the grain yield of well-watered DK888. It is hypothesized that the adverse effects of pre-anthesis drought on grain yield can be mitigated if varieties are selected for roots which rapidly penetrate the soil and exploit the water resources in deep soil layers.