Effect of Change of Agronomic Practices on Nutritive Value of Hybrid Fodder Sorghum Cultivated in Lowland Paddy Fields of the Dry Zone of Sri Lanka

This study was conducted to investigate the effect of low fertilizer rate and irrigation along with increased plant density on nutritive value of hybrid fodder sorghum cultivated in lowland fallowed paddy fields in dry zone during May to September. Seeds were sown in Yala season and continued as a ratoon crop to inter-monsoonal (Third) season. Four agronomic management packages (AMP1, AMP2, AMP3 and AMP4), which differ in fertilizer application rates, plant spacing, and irrigation intervals were tested with two fodder sorghum varieties (SX-17 and Dairygreen) in a split-plot design. The initial and first ratoon crops were harvested at dough grain stage. High fertilizer rate in combination with short irrigation interval, resulted in high (P<0.05) crude protein content in the initial harvest. AMP2 and AMP4 produced equally high (P<0.05) total dry matter yield (DMY) for SX-17 (24.7 and 20.9 MT/ha, respectively) and Dairygreen (27.7 and 25.7 MT/ha, respectively) varieties. Total digestible organic matter, crude protein and metabolizable energy yields were higher under AMP2 and AMP4 compared to other two packages for both varieties. Nutritive value was high in SX-17 under AMP1 for ratoon crop. In conclusion, AMP4 with plant spacing of 45 x 15 cm, low fertilizer rate (338-47-28 kg/ha, urea-TSP-MOP) and extended irrigation interval, could be recommended for cultivation of hybrid fodder sorghum in lowland paddy fields in the dry zone during Yala season. However, for cultivating SX-17 targeting to produce fodder with high nutritive level, AMP1 with spacing of 45 x 30 cm, high fertilizer rate (400-62-37 kg/ha of urea-TSP-MOP) and frequent irrigation could be recommended.