Agronomic And Economic Evaluation Of Phosphate Fertilizer Use In Maize -Bean Cropping Systems In Western Kenya

ABSTRACT Maize and beans are commonly grown as intercrops in western Kenya to maximize the utilization of the small land sizes per household, but their yields are low mainly due to deficiencies of nitrogen (N) and phosphorus (P) and inappropriate crop arrangements. A study was conducted at Bugeng‟i and Malanga sub locations in Busia and Siaya Counties respectively during the short rains (SR) of 2015, and Bugeng‟i and Ebusakami (Vihiga County) in long rains (LR) of 2016 to determine the effect of P fertilizer rate and cropping arrangement in maize-bean cropping systems on yields of the component crops and accruing economic benefits. The experiment was arranged as factorial in a split-plot design with 15 treatments replicated three times. The main plots consisted of five levels of maize-bean cropping arrangements (i) one row of maize alternating with one row of beans (conventional), (ii) maize planted in the same hole with beans, (iii) two rows of maize alternating with two rows of beans (Mbili), (iv) sole maize and (v) sole beans. The subplots consisted of three P fertilizer levels i.e. 0, 30, and 60 kg P ha-1. Leaf area index (LAI) of both crops and available soil P were determined at 6 weeks after planting (WAP) while maize height was measured at 8 WAP. Grain yield of the crops was determined at physiological maturity. All data were subjected to analysis of variance (ANOVA) and treatment means separated using least significance difference of means (p < 0.05). Land equivalent ratio (LER) was used to determine yield advantage of intercropping while benefit cost ratio (BCR) was used in economic evaluation. The available soil P generally increased with increasing P rate at all sites. The LAI of maize and beans was not significantly affected by crop arrangement at all sites. The LAI of beans was also not affected by P rate at all sites. However, LAI of maize significantly increased with increasing P rate at Bugeng‟i during the SR season but there was no significant effect of P rate at the same site in the LR and at Malanga (SR) and Ebusakami (LR). The LAI in all cases was however very low with the highest at 1.51 for beans and 1.93 for maize. Maize plant heights as affected by P rate at all sites followed the order 60 > 30 > 0 kg P ha-1. There was no significant effect of P rate on maize yields at Bugeng‟i and Ebusakami in the LR season. The available P was also not significantly related to maize yields at these sites in the LR. This lack of response to P is attributed mainly to the lower than average rainfall and therefore water became a more limiting factor than P for maize growth. This is in contrast to the SR season at Bugeng‟i when with adequate rainfall, significant effects of crop arrangement were observed with the mean yields for conventional and Mbili arrangements being statistically similar, but significantly higher than those of maize planted in the same hole with beans. Significant effects of P rates were also observed at the same site with maize yields increasing with P rate. The available P was significantly related to both LAI and maize yields at Bugeng‟i in the wetter SR and not the drier LR season. The highest beans yields were obtained in the sole bean crops mainly because of their higher plant population compared to the intercrops. The bean yields of the other crop arrangements did not generally differ significantly. The total LERs were >1 at all sites and therefore showed yield advantage of intercropping maize and beans, irrespective of crop arrangement, over sole crops apart from the Bugeng‟i site in the LR. Rainfall was very low in the LR at this site and therefore sole crops performed better under the water stress than the intercrops. Therefore intercropping should only be recommended in areas with adequate rainfall. Financial returns were low because of high input costs and low output prices and none of the treatments therefore met the threshold BCR > 2 suggesting that none of them is likely to be adopted by farmers under conditions similar to those of this study.