| A field experiment was conducted during the wet seasons of 2013 and 2014 at the research farm Institute for Agricultural research, Samaru (11 11N 7 38 E 686m above sea level) in the northern Guinea savanna and the Experimental farm of Hassan Usman Katsina Polytechnic, Katsina (12 56 N, 7 36 E 465m above sea level) in the Sudan savanna ecology of Nigeria to determine the effects of integrating nitrogen fertilizer and organic manures on sorghum varieties grown on Striga- infested field. The treatments consisted of two varieties of sorghum (SAMSORG-40 AND SAMSORG-41), three levels of nitrogen (0, 40 and 80kgNha-1) and four levels of organic manure (Cassia obtusifolia green manure at 0, 7.5 and 15t ha-1 and cowdung at 10t ha-1). The experiment was laid in a split-plot design and replicated three times; with nitrogen assigned to the main plot while factorial combinations of crop variety and organic manure were assigned to the sub-plots. The experimental sites were inoculated with Striga at the rate of 25 g seeds per Kg ha-1 of fine sand to boostStriga level. The experimental soil wereStriga infested and low in organic matter, nitrogen and available phosphorus at Katsina (0.37 % N, 3.69 % P), (0.54 % N, 3.20 % P) at Samaru. Analysis of the soil after harvest showed that application of green manure at 15t ha-1(46.0 % P, 0.59 %, N) with nitrogen at 80kg Nha-1(0.46 % N, 14.2 % P) improved fertility status of the soil with respect to total N, available P and exchangeable K. SAMSORG-40 recorded moreStriga shoot count, plant height, number of leaves, LAI, shoot dry weight and yield and yield attributes than SAMSORG-41 in both locations and seasons. Nitrogen application at 80kgN ha-1 reduced Striga count, number of infested plants with Striga and Striga crop reaction score compared to the untreated control. Nitrogen at 80kgN ha-1 improved plant height, number of leaves, LAI and shoot dry weight compared to zero and 40kgN ha-1,however, the use of 40kgN ha-1 increased grain yield over 80kgN ha-1 .Strigashoot count was found to be low to moderate with the use of green manure and cowdung when compared to the untreated control;however, application of cowdung at 10t ha-1 resulted in higher stand count, number of leaves, plant height and LAI when compared to treatment that receive of 0, 7.5 and 15t ha-1 of green manure for same parameters. Complementary application of 15tha-1 green manure with 80kgN ha-1 resulted in higher grain yield than cowdung at 10t ha-1 with 80kgN ha-1 at Katsina and Samaru respectively. Positive and significant relationship was recorded in Katsina between sorghum grain yield and stand count, number of leaves, LAI, shoot dry weight, panicle weight, 100- grain weight, grain weight, Stover yield, as the primary determinants for yield in combined years. In Samaru, grain yield was negative and not significantly correlated to LAI and Striga shoot count in combined years. Growth parameters, such as plant height, shoot dry weight and number of leaves showed significantdirect effectto yield. The highest individual percent contributions to yield wereby panicleweight and the highest combined contributions were by panicle weight via shoot dry weight. Sorghum grain yield showed linear response to the applied green manure from 0 – 15t ha-1 and N from 0 – 80kgha-1, an indication that optimum levels were not attained. In both locations, highest gross margin was recorded by SAMSORG-40 under 10t ha-1 with 0kgN ha-1, while the gross margin per naira invested was in SAMSORG-41 from untreated control in Katsina, and SAMSORG-40 with 0t ha-1 organic manure and 40kg Nha-1 in Samaru. The total variable cost (TVC) of sorghum production in Samaru (N441, 669) was higher when compared to the TVC in Katsina site (N 422,219)in thetwo years of study. In conclusion, the study revealed that, the highest grain yield of sorghum was by the application of 15 t ha-1 green manureand 80 kg N ha-1 with SAMSORG-40 grown on Strigainfested field, viii irrespective of location. Improving soil fertility, especially N will reduce the effect of Strigaon sorghum. Application of 15 t ha-1 green manure delayed Striga emergence at Samaru and reduced Striga shoot count and crop reaction score at Katsina. In contrast, grain yield was insignificantly and negatively correlated to Striga shoot count at Samaru. Panicle weight and panicle weight via shoot dry weight gave the highest percent contribution to sorghum grain yield. Grain yield showed linear response to the applied green manure from 0- 15 t ha-1 and from 0- 80 kg N ha-1, an indication that work still needs to be carried out in order to determine their optimum levels. The highest returns per Naira invested was obtained with SAMSORG-40 supplied with Cassia green manure at 15 t ha-1 and 80 kg N ha-1 at Katsina; and SAMSORG-40 supplied with 10 t ha-1 of cow dung, without any N input |
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