Comparative effects of soybean, grain amaranth (Amaranthus spp) and nitrogen on Striga (Striga hermonthica) and maize yield in western Kenya

Western Kenya, the area considered the grain basket of the country, is heavily infested by Striga, reducing maize yields by up to 30-100%. On-farm trials were conducted in two cropping seasons between August 2014 to July 2015 at Ugunja, Siaya County, western Kenya to (i) evaluate the effects of grain amaranth and nitrogen (N) fertilizer on Striga (Striga hermonthica) weed control through suicidal germination as compared to soybean; and to (ii) determine treatment effects on grain yields. The treatments consisted of rotational cropping of maize with maize, soybean with maize and grain amaranth with maize at different rates of N i.e. 0, 50, 100, 150, and 200 kg ha-1. The treatments were replicated three times in a randomized complete block design in three different sites. Results showed that soybean-maize rotation at 0 N fertilizer resulted into 41.2% reduction on Striga count while amaranth-maize rotation at the same rate of N fertilizer resulted in 34.4% reduction 12 weeks after planting. These reductions were pegged on the reductions Striga counts in maize-maize rotation. There was significant difference (P<0.05) due to crop rotation systems, nitrogen and their interaction on maize yield. Despite the relatively higher counts of Striga under amaranth-maize rotation than the soybean-maize rotation in all N levels, the amaranth-maize rotation treatment gave a generally higher maize yields in treatment with similar N levels. Grain amaranth-maize rotation at 200 kg ha-1 N resulted in 10.5 % maize yield increase while soybean-maize system at 200 kg ha-1 N resulted in 25.7% maize yield increase. These results show that crop rotation involving maize and grain amaranth can be adopted by farmers as an efficient cropping system strategy to reduce Striga infestation and increase maize yields.