Influence of plant population and nitrogen fertilization on corn yield variation in a black clayey soil

Experiment was conducted to study the influence of different plant population densities and nitrogen fertilizer rates on the variation of corn yields in a black clayey soil as guidelines to increase the yield of corns. Some researches have postulated that the yield of corns can be increased with the increase of plant populations to optimal densities. The seeds of corns, Nakornsawan 1 variety, were sown in the Lopburi soil (Very fine, montmorillonitic, isohyperthermic, Typic Pellustents). Randomized complete block design was employed with 4 replications. The treatments consisted of 2 factors combined in 3*4 factorial arrangements by 3 levels of plant populations densities (PPD) and 4 rates of N fertilizer. Then, the growth and yield of the corn influenced by the given factors were comparatively evaluated. The results showed that the plant hights of the treatments with 8,500 and 11,000 plants/rai (5.3 and 6.9 plant/square m, respectively) were not different from each other while they were higher than that of the treatment with 21,000 plants/rai (13.1 plants/square m). There was no difference in the plant hieght among the differnt rates of N application. The girdles of corn stalks were decreased with the increased of their PPD's. Conversely, the application of N fertilizer increased the stalk girdles, the N rates of 10 kg/rai and higher ones, however, did not significantly show any of their increment. The PPD greater than 11,000 plants/rai (6.9 plant/square m), especially, when N at 15 kg/rai or a higher rate was added. There was no significant difference in the seed yield of corns between the treatments with 8,500 and 11,000 plants/rai, but both treatments had higher seed yields than the one with 21,000 plants/rai. This is because the higher the PPD the lower the plant growth and the higher the lodging percentage. On the other hand, N applied at any rate had no effect on the seed yield. There might be soil N in a sufficient amount to meet the consumption of corn plants. However, ten kilograms per rai of N were recommended to maintain the fertility of the soil.