Effect of Different Macro-nutrient Combinations on Growth, Yield and Fibre Quality of Cotton (Gossypium Hirsutum L.) in Machakos County, Kenya

Abstract

Cotton (Gossypium hirsutum L) requires large quantities of nitrogen (N), phosphorus (P) and potassium (K), and these nutrients are frequently limiting in cotton growing areas in Kenya. Nitrogen, P and K nutrition affects cotton growth, yield and lint quality but the peak demand for either nutrient is crop stage specific. As cotton successively goes through vegetative and reproductive growth, there is considerable shift in the relative demand among the macronutrients. It is only partially understood which among the combinations of N, P and K increases cotton growth and yield, as well as improves fibre quality. This study was carried out to investigate the effect of different combinations of N, P and K macro-nutrients on: (i) growth, yield of cotton, and (ii) water and nutrient use efficiency, and fibre quality of cotton. Experiments were conducted in Machakos County of southeastern Kenya at the Farmers’ Training Centre in Machakos and in a farmer’s field in Ndalani village. Treatments comprising two cotton varieties (conventional variety (HART 89M) and genetically modified variety (Bt-C571 BGII) and varying nutrient combinations of N, P, and K and unfertilized control were set out in a randomized complete block design with a split plot arrangement. Variety was assigned to the main plots while nutrient combinations formed the subplots. In the first objective, cotton growth and yield parameters were determined through the number of days taken to attain 50% branching, squaring, boll formation and boll opening, as well as the corresponding number of branches, squares and bolls per plant. Plant height and stem girth were measured during branching, flowering and at boll opening, whereas chlorophyll content was measured at branching and flowering. At harvesting, data on cotton yield and root length and angle were measured. In the second objective, water use efficiency (WUE), N, P, and K nutrient uptake, agronomic efficiency and fibre quality traits were measured. Generally, both cotton varieties grown in NP, NK, NPK, and NPK, Zn, S fertilized soils matured earlier than those grown in soils fertilized with PK and in the unfertilized soils. Notably, cotton grown under NK, NP, NPK, NPK, Zn, S nutrient combinations were significantly (P≤0.05) taller, thicker and greener than cotton grown in plots without N nutrient but fertilized with PK and unfertilized control. In addition, cotton grown in plots where N was combined with P and K produced larger biomass and yield compared with crops in treatments excluding N or unfertilized control. Similarly, cotton grown under N nutrient combinations had advanced uptake of N, P, and K compared with unfertilized crops. While the varieties did not differ in the majority of the measured quality traits, Bt-C571 BGII recorded higher strength and Rd than HART 89M, whereas HART 89M had higher +b. Compared with control, addition of nutrients did not affect maturation, fibre xiii attributes such as length uniformity index, upper half mean length, elongation and the number of short fibres. However, cotton grown in the soils fertilized with N nutrient had significantly (P<0.05) higher strength, micronaire, Rd and +b than those grown in unfertilized soils and PK plots. Overall, N nutrient combinations were observed to enhance maturity period, biomass, yield, WUE, uptake of N, P, and K, agronomic efficiency and fibre quality of cotton. This implies that the use of nitrogenous fertilisers guarantees efficient water and nutrients use consequently enhancing cotton growth, yield and fibre quality