Influence of cultivar, nitrogen and plant density on production of sorghum planted under different environmental conditions
Sorghum is an important cereal crop in the semi-arid regions of sub-Saharan Africa. This study was conducted in the 2016/17 and 2017/18 planting seasons at Mafikeng and Taung, North West Province, South Africa. The main objective of the study was to evaluate the yield and quality of sorghum cultivars as influenced by different nitrogen rates and plant density under different environmental conditions. The experimental design was a split-split plot arrangement fitted into a randomized complete block design with four replicates. The main plot factor comprised of high (33 333 plants/ha) and low (22 222 plants/ha) plant densities. The nitrogen fertiliser rates were 0, 100 and 150 kg N/ha as the sub plot factor. The sub-sub plot factor consisted of two sorghum cultivars, PAN 8625 and PAN 8816. Parameters measured for the study included, plant height, stem diameter, number of leaves per plant, chlorophyll content index, leaf area index, days to 50 and 100 percent flowering, panicle length, panicle mass per plant, panicle mass/ha, 1000 seed mass, biomass yield, grain yield, protein, sugar, starch, oil, fibre, and ash content. In both planting seasons, the cultivar had a significant effect (P < 0.05) on the plant height and stem diameter of the sorghum plant. Sorghum cultivar PAN 8625 had a significantly taller plant and larger stem diameter than PAN 8816. The cultivar also had a significant effect on sorghum panicle mass per plant and sorghum biomass yield in both seasons. Sorghum cultivar PAN 8625 had a significantly higher panicle mass per plant and higher biomass yield than PAN 8816. Significant effects were also obtained on the cultivars for protein and starch content. Sorghum cultivar PAN 8816 had a significantly higher protein and starch content than PAN 8625. Plant density had a significant effect (P < 0.05) on the sorghum leaf area index (LAI), panicle mass per plant and sorghum biomass yield in both seasons. Sorghum planted under high density had a significantly higher value of LAI than those planted under low density. Sorghum planted under high plant density had a significantly higher panicle mass per plant and a higher biomass yield than sorghum under low density. Location had a significant effect (P < 0.05) on the sorghum chlorophyll content index and days to the 50 and 100% flowering in both seasons. Sorghum planted at Mafikeng had a significantly higher chlorophyll content index value than those recorded at Taung during the 2016/17 planting season while in 2017/18 planting season reverse was the case. During the 2016/17 planting season, sorghum planted at Mafikeng flowered significantly earlier than sorghum planted at Taung and contrary in the following season. Location had a significant effect (P < 0.05) on the sorghum 1000 seed mass and grain yield in both seasons. Sorghum planted at Mafikeng had a significantly higher 1000 seed mass than sorghum planted at Taung in both seasons. Grain yield obtained in Mafikeng was significantly higher than value from Taung in 2016/17 planting season. With regards to the oil and starch content of sorghum, location had a significant effect in 2017/18 season; where Sorghum planted at Mafikeng had a significantly higher oil and starch content than sorghum planted at Taung. Mafikeng offers a better nutritive value for the sorghum produced than the one planted in Taung due to favourable weather conditions especially the rainfall. It is therefore recommended that sorghum is cultivated in Mafikeng.