Forage yield potential of the secondary crop of sorghum bicolor L. moench, cv abu sabein as influenced by some agronomic practices of the primary crop

Three experiments were conducted at the Gezira Research Farm during 2005 and 2006 to study the effect of agronomic practices of the primary crop on forage yield potential of the secondary (2 deg) crop of Abu Sabein. Experiment 1 involved variation in cutting ages and heights of the primary crop of September 2005 and June 2006 sown Abu Sabein. The treatments involved cutting the primary crop at ages of 6, 7, 8, 9 and 10 weeks and at heights of 5, 10, 15 and 20 cm above ground. Experiment II and III were sown on August 2005 and December 2005. Experiment II involved growing the primary crop at four seed rates and four urea levels. The seed rates were 12, 24, 36 and 48 kg/ha and the urea levels were 0, 93, 186 and 279 kg/ha. Experiment III involved four seed rates 12, 24, 36 and 48 kg/ha and four P2O5 levels, 0, 93, 186 and 279 kg P2O5/ha. The results of experiment 1 showed that June sowing resulted in dramatic increase in the dry matter yields of the 2 deg crop of Abu Sabein. Cutting the 1 deg crop of Abu Sabein at the age of 6 or 7 weeks of June sown crop resulted in 2 deg crop dry matter yield equal or even higher than those of the 1 deg crop. Based on the cumulative yields, adequately high and good dry matter yields could be obtained when 1 deg crop was harvested at the age of 8 weeks in June sown crop. Cutting the 1 deg crop at the height of 20 cm above ground increased plant height, culm density and yields of the 2 deg crop. The results of experiment II showed that the 1 deg crop yields and plant height of Abu Sabein were higher in August sown crop while those of the 2 deg crop were higher in December sown crop. The effect of urea fertilization and the seed rates on the 1 deg crop were significant in December sowing only. The highest yield of the 1 deg crop of Abu Sabein was associated with 186 kg urea/ha. Regarding the seed rate, the highest seed rate (48 kg/ha) resulted in the highest dry matter yield of the 1 deg crop of Abu Sabein. Nitrogen fertilization had significant negative effects on all yield attributes of the 2 deg crops of Abu Sabein in both seasons as reductions in plant height, culm densities and fresh dry matter yield of 2 deg crop of Abu Sabein with the increase in nitrogen fertilizer. The increase in the seed rate resulted in the increase of the culm densities in both seasons and the fresh and dry matter yields of the 2 deg crop in December sown crop. The results of the experiment III showed that the 2 deg crop yields of December were higher than those of August sown crop. Phosphorus however, did not result in any increase in the 2 deg crop yield of Abu Sabein in both seasons. Increasing the seed rate of the 1 deg crop resulted in increase of the fresh and dry matter yields and culm densities of the 2 deg crop