Forage Sorghum Production on a Witchweed-Infested Soil in Relation to Cutting Height and Nitrogen
Little is known about forage sorghum [Sorghum bicolor (L.) Moench] and forage sorghum-sudangrass [S. bicolor × S. sudanense] hybrid production in soil infested with witchweed [Striga hermonthica (Del.) Benth]. The objective of the present study was to evaluate the immediate effects (first harvest) and aftereffects (second and third harvest) of two cutting heights (0.1 and 0.3 m) and five N treatments (0,60 + 60,120,120 + 120, and 240 kg N ha−1) on witchweed management in forage sorghum (cv. Abu Sabeen) and forage sorghum-sudangrass (cv. Pioneer 988) hybrid. Field studies were conducted at Shambat, Sudan, in 1984 and 1985 on a heavy alluvial clay soil (montmorillonitic, isohyperthermic Vertic Camborthid) heavily infested with witchweed. Pioneer 988 was more tolerant of witchweed than Abu Sabeen at first harvest, but less tolerant of witchweed at later harvests. The shorter cutting height resulted indirectly in a larger number of tillers (26%) and a higher forage greenchop yield (37%) at first harvest. Nitrogen increased forage tiller density approximately twofold and forage greenchop yield by approximately ten-fold at the first harvest. There was a concurrent, approximately fivefold reduction in witchweed shoot weight. At second harvest, forage tiller density, forage greenchop yield, and witchweed shoot weight were increased with N. Both forage sorghum and witchweed were dead in the zero N plots at third harvest. No differences were detected between single and split applications of N, or between low (120 kg N ha−1) and high (240 g N ha−1) rates of N. Forage tiller density, forage greenchop yield and witchweed shoot weight were reduced at the second and third harvests compared to the first harvest.
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