EFFECTS OF NITROGEN FERTILIZER AND HERBICIDE COATED MAIZE

Abstract

Striga hermonthica (witch weed) infestation and low soil fertility are two major constraints to maize production in western Kenya. The low inherent soil fertility and poor crop management practices result in subsequent Striga infestation thereby reducing maize productivity and driving several rural households into extreme poverty. Because of this, maize production averages 0.2 to 0.5 tons per hectare which is below the national potential average of 6 tons per hectare. Farmers in the region respond to the problem through various available Striga control methods developed by researchers. For instance, inorganic N fertilizers, resistant/tolerant maize varieties, hand pulling of witch weed, irrigation and use of cover crops have been tried by farmers. Each of these has been done on its own, not in combination with others, no significant effect on witch weed reported. The combination of two or more of these methods can bring a significant reduction of the weed. The main objective of the study was to evaluate the effect of two maize varieties (IR maize and DH04) in combination with inorganic N fertilizer in reducing Striga infestation and seed bank, improving soil fertility and increasing maize yields. Field experiments were conducted in Bondo, Siaya and Vihiga districts, western Kenya for two consecutive seasons (short rainy season, 2011 and long rainy season, 2012). Treatments included two maize varieties (IR maize and dry land hybrid maize (DH04)), two inorganic N fertilizer rates (0 Kg N ha-1 and 60 Kg N ha-1) and two soil fertility status, (low and high soil fertility status). The treatments were arranged in a split-split plot structure in a complete randomized block design (CRBD) replicated 30 times (using farms as replicates). soil fertility status and Maize varieties were assigned to the main and sub plot respectively while N fertilizer rates was assigned to sub-sub plots. Fertilizer N was applied at a rate of 60 kg N ha-1 in split application of 25 kg ha-1 at planting and 35 kg ha-1 at 6 weeks after planting. All treatments received basal phosphorus (P) and potassium (K) at rates of 30 kg ha-1. Results showed that the fertilized plots had significantly (P≤0.05) higher percentage nitrogen over the unfertilized plots in all the sites. In Bondo, Siaya and Vihiga, the percentage increase in total N was by 17%, 13% and 21%, respectively. The fertilized plots with IR maize significantly (P≤0.05) reduced Striga emergence by 38%, 20% and 29% in Bondo, Siaya and Vihiga, respectively. Striga emergence was significantly (P≤0.05) lower in the high fertility soils compared to low fertility soils. Addition of nitrogen fertilizer at 60 kg N ha-1 significantly (p<0.05) increased maize grain yield relative to control in all the sites. IR maize in the fertilized plots significantly (P≤0.05) reduced Striga seed bank density by more than 50% in all the sites across the rainy seasons. Combining resistant/tolerant maize varieties with N fertilizers is an effective strategy of controlling Striga and increasing maize yields in low fertility soils of western Kenya. It is recommended that farmers in western Kenya should practice combinations of IR maize with 60 kg ha-1 of N-fertilizer to reduce Striga density and increase maize grain yield. iii