Asian Research Thesis Index

Abstract

The present study was planned to investigate the effect of agronomic practices on the yield and quality of forage sorghum under rainfed condition, in an effort to strengthen livestock industry in dry areas of the country, and to improve the livelihood of rural masses. The study comprised of two field and two greenhouse experiments. In the first field experiment, three sorghum cultivars, viz., JS-2002, Chakwal sorghum and Local sorghum (check) were sown with three seeding rates (75, 100 and 125 kg ha -1 ) and three nitrogen levels (0, 60 and 120 kg ha -1 ) following RCBD split- split plot design in three replications, during the years 2008 and 2009. Sorghum cultivar JS-2002 performed better with regard to morphology, yield and quality traits as compared to other cultivars. The cultivar JS-2002 also had low hydrocyanic acid (HCN) content at pre-booting, booting as well as 50% heading stage during both years of study. Increasing the nitrogen rate had a positive impact on forage yield as well as quality traits except neutral detergent fibre. HCN increases with the increase of nitrogen levels. The increase of HCN content was 38 and 63% higher with the application of nitrogen at 60 and 120 kg ha -1 when compared with control treatment. Increase in seed rate resulted in an increase in forage yield, while inverse relationships with quality traits were recorded. Second field experiment comprised of three levels of phosphorus (0, 30 and 60 kg P 2 O 5 ha -1 ), in combination with three levels of sulphur (0, 20 and 40 kg SO 4 ha -1 ), which were tested at three harvest times (35, 45 and 55 DAE). At different growth xxxstages, morphological, functional growth, yield and quality traits were assessed. The combined effect of delayed harvest, P and S fertilization on sorghum seemed to have significantly increased forage longevity and succulence under rainfed conditions. A third pot experiment was conducted using three sorghum cultivars with three soil moisture levels (30, 50 and 70 percent field capacity) to examine the response of forage sorghum cultivars. Three cultivars significantly differed in their response to moisture. At low moisture (30% FC), they showed very similar crop growth rate, net assimilation rate, specific leaf area, leaf succulence, root and shoot dry weight at harvest. Conversely, at high moisture (70% FC) JS-2002 showed a higher potential than Chakwal sorghum, which in turn surpassed local sorghum. The HCN content was considerably reduced with the progressive increase in soil moisture level and with the advancement of crop growth stage. Local sorghum also showed a higher yield response factor to water, meaning a stronger yield decrease under water deficit. The fourth and last experiment consist of a glasshouse study, carried out in the Department of Agricultural Sciences, University of Bologna, Italy. The three genotypes (JS-2002, Trudan-8 and Local sorghum) significantly differed under different water regimes with regard to bio-physical, gas exchange, water relation and growth measurements. The cv. JS-2002 proved superior to the other two genotypes in terms of number of leaves, stem diameter, relative water content, leaf area and leaf dry weight, although the hybrid Trudan-8 gave better results for plant height, number of tillers, transpiration rate, stomatal conductance, SPAD chlorophyll content, stem dry weight and specific leaf area; while chlorophyll fluorescence, leaf water potential and osmotic potential values were found higher in local sorghum. Bio-physical, gas xxxiexchanges, water relation and growth traits were significantly greater at higher water regime compared to the lower water regime. On the basis of field and glasshouse studies, it is recommended that the livestock producers should be encouraged to use seed of approved cultivars (e.g., JS- 2002) instead of old local races. Beside the agronomic benefits, the approved cultivars possess lower HCN content and thus are safe to feed livestock under dryland conditions. Delayed harvesting will produce safe and good quality feed for livestock. Application of nitrogen fertilizer @ 120 kg ha -1 although enhanced the yield as well as quality of sorghum fodder but the livestock producers are warned to use sorghum forage carefully before at booting stage because of high HCN content.

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