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Comparative Performance of Three Grain Sorghum [Sorghum bicolor (L.) Moench] Cultivars Grown under Rubber and in the Open Field as Affected by Nitrogen Level and Plant Density.
Dissertation Abstract:
Three grain sorghum cultivars were grown in the open field and under seven- and two-year-old rubbers at three levels of nitrogen fertilizer and plant population density, to determine the performance of both seed and ratoon crops in terms of agronomic characters and certain quality parameters.
The open field and under seven seven-year-old rubber plantation experiments were conducted at MIT, Kabacan, Cotacabato and the under two-year-old plantation experiment, at Malbas Rubber plantation, Kidapawan, Cotbato.
Results showed that the MIT open field seed and ratoon crops and the Kidapawan under two-year-old plantation crops gave higher grain and total dry-matter yields, 100-grain weight and number of grains per panicle, reduced number of days to blooming, short, plant height, higher leaf area index, greater leaf width and higher light utilization efficiency than those grown under the seven-year-old rubber trees.
Among the agronomic characters evaluated, the number of grains per panicle was found consistently associated with grain yield, indicating the importance of this component as yield determinant.
Nitrogen treatments increased grain yield, total dry-matter yield, plant height, leaf area index and number of grains per panicle. Plant population density reduced leaf size and panicle length in both seed and ratoon crops in all environments. Fertilizer rate of 50 kg N/ha and density of about 240,000 plants/ha seemed to be optimum for grain yield and grains per panicle.
Protein content was found inversely related to starch content. Sorghum cultivars grown under the seven-year-old rubber plantation had higher protein content than those raised in the open field and under the two-year-old rubber trees; however, the opposite was observed in the case of grain starch content.
Stem girth and latex yield of rubber were not affected by nitrogen, sorghum plant density nor cultivar.
The three sorghum cultivars studied exhibited productive potentials as intercops under two-year-old but not under seven-year-old rubber plantations.