Effect of soil incorporated leaf prunings on soil productivity in alley and sole cropping systems using leucaena leucocephala (lam) de wit and calliandra calothyrsus meissn

Abstract

Crop yields on small-scale farms in the central Kenya highlands continue to decrease due to declining soil fertility, resulting from continous cropping without adequate replenishment of nutrients through addition of fertilizers and/or manure. A study was therefore conducted to investigate the feasibility of using leaf prunings of Calliandra calothyrsus Meissn and Leucaena leucocephala (Lam.) de Wit for soil fertility and productivity improvement. Alley and sole cropping systems were studied. The experiment was located at KARl's Regional Research Centre's Agroforestry site in Embu District of Kenya. The experimental design was a randomised block with ten treatments. Results of three seasons, namely, 1993 long rainy season (1993 LR), 1993/94 short rainy season (1993/94 SR) and 1994 long rainy season (1994 LR) are reported. Generally, the sole cropped treatments had consistently higher maize grain yields than alley cropped treatments in all seasons. This was attributed to competition between the trees and the crops for growth resources in alley-cropped treatments. Generally, also, the fertilizer treatments, performed better in terms of maize and bean grain yields than the leaf incorporated and the alley cropping treatments. During 1994 LR, the fertilizer treatments gave significantly (p=O.05) higher maize grain yield than all the other treatments. This was ascribed to the readily available nutrients from fertilizer. Infiltration rate and total nitrogen increased in treatments with leaf prunings incorporation and with tree hedges. Calcium decreased across the seasons in all treatments but generally less in the treatments where prunings were added. Addition of prunings, however, did not cause significant changes in soil pH, phosphorus, potassium, sodium, magnesium, manganese, organic carbon levels, and bulk density among treatments in all seasons. This was attributed mainly to low biomass production by the hedgerows, therefore, low input of nutrients coupled, with removal of nutrients through crop harvests. Insensitivity of conventional soil analysis methods to detect small changes was cited as another reason. Feasibility of using leaf prunings for soil improvement in an alley cropping system was found to be limited due to low biomass production and possibly competition between the tree hedges. More research on below ground interactions would be useful to provide a better understanding for improving the system. In sole cropping system, incorporation of leaf prunings as source of plant nutrients seem feasible but with fertilizer supplementation. Opportunities of using Calliandra calothyrsus, and other promising fodder legumes for soil erosion control and fodder production, and the possibilities of improving soil fertility through recycling of nutrients by manure should be explored.