Agronomic and Economic Performance of Maize-Soybean Intercrop under Rhizobia and Soil Amendments in Western Kenya

Low crop responses to N and P fertilizer application among small holder farms are common phenomena in degraded acidic soils of western Kenya. An on-farm trial was established in Shianda sub-location in Mumias District, Western Kenya during two seasons in 2011 to determine the effect of inoculation (Bradyrhizobium japonicum), lime (CaCO3) and inorganic P (Single Super Phosphate) on soil chemical properties and yield components of soybean (Glycine max L.) and maize (Zea mays L.). The experiment was a 23 factorial with 4 replicates laid out in a randomized complete block design giving a total of 32 plots. Experimental treatments were Lime (0 and 2.5 tons lime ha-1), P fertilizer (0 and 30 kg P ha-1) and Inoculation (soybean inoculation and no inoculation). Lime application at 2.5 t ha-1 led to a significant increase in soil pH from 4.85 to 5.58 (P=.05) after two cropping seasons. Increase in soil available P was in the order of lime > P > inoculation (9.35>6.50>5.10 mgkg-1). A combination of Lime + P + inoculation recorded the highest maize (4490 kgha-1, 3470 kgha-1) and soybean (970 kgha-1, 830 kgha-1) grain yields during the long rain (1st) and short rain (2nd) seasons respectively. Sole P treatment gave higher average number of nodules per plant and average plant biomass, (7.7 and 21.8 g) respectively than both sole inoculation (4.3 and 19.2 g) and sole lime treatments (2.3 and 16.8 g) during the 1st cropping season. On average, across the treatments during the two seasons benefit-cost analysis indicated that the lime + P + inoculation treatment gave the highest net benefit (Ksh. 107,518.60) with a benefit-cost ratio of 1.7. These results indicate that a combination of lime + P + inoculation offers a better option for increasing maize and soybean grain yields in the degraded soils of western Kenya.