Analytical determination of the effects of phosphatic fertilizers and manure on maize yields in acidic soils in Kisii and Rachuonyo districts.

Abstract

Maize production in sub-Saharan Africa remains low and the yields are on the decline. This has been attributed to a variety of factors which include soil nutrient depletion and Striga infestation. Soil phosphorous, nitrogen and Striga hermonthica are the major constraints to maize production in Nyanza Province of Kenya. The yields are typical of low input systems ranging below 1.0 t ha-1 against a potential of 5.0 t ha-1 per season. In an attempt to overcome these constraints, field trials were conducted at two on-farm sites, Bototo in Kisii Central district and Kabondo in Rachuonyo district, in Nyanza Province of Kenya. The trials were conducted during the long and short rains seasons in 2007. The study investigated the effects of phosphatic fertilizers and manure on nutrient uptake, nutrient use efficiency, maize yields and soil nutrients content at harvest in both sites. A Randomized Complete Block Design (RCBD) was used with the farmers as replicates. Farmers in Bototo plant H614 variety while those in Kabondo plant H513 maize variety. Plots were top dressed with Calcium Ammonium Nitrate (CAN) fertilizer at a uniform rate of 30 kg N ha.-1 Diammonium Phosphate (DAP), Minjingu Rock Phosphate (MRP) and Triple Super Phosphate (TSP) fertilizers were applied at a rate of 60 kg ha-1 P2O5 and farmyard manure (FYM) at 10 t ha-1. One rate of P (60 kg ha-1 P205) was applied on all the P sources and a no P treatment (check) plus lime only treatment was included in determining the effects due to the applied P in the acidic soils. Complete soil chemical analysis was done in all the plots. To assess the effects of phosphorus fertilizers and manure and estimate the nutrient content and uptake of major nutrients, plant and soil samples were analyzed using standard methods. There were significant (P_ 0.01) crop growth vigor response to the fertilizers and manure due to treatments at both sites. There were significant (P_ 0.01) grain yield, total dry matter yield and harvest index responses to phosphate fertilizers and manure treatments at both sites. Phosphate fertilizers and manure treatments had significant (P_ 0.01) effects on Striga emergence at both sites. Striga emergence correlated weakly with phosphate fertilizers and manure treatments and strongly with grain yield at both sites. Nutrient uptake and removal by the crop significantly (P_ 0.01) increased due to fertilizers and manure application, with a corresponding reduction in the total soil N, P, K, Ca and Mg. Phosphate fertilizers and manure application significantly (P_ 0.01) increased available soil hosphorus, agronomic phosphorus use efficiency (APUE) and physiological phosphorus use efficiency (PPUE) in both sites. The results indicate that phosphate fertilizers and manure applications are essential to improve maize yield, nutrient phosphorus use efficiency and the applied nitrogen reduced the impacts of Striga hermonthica damage to maize yields.