Performance of multipurpose trees in coconut based agroforestry systems and their influence on soil physico-chemical and biological properties

Abstract

An experiment was conducted to study the effects of intercropping of three fast growing MPTs viz. Casuarina equisetifolia, Ailanthus triphysa and Leucaena leucocephala in coconut plantations, on soil physico-chemical and biological properties; the field experiment was laid out at the Instructional farm, Kerala Agricultural University, Vellanikkara. The influence of three water harvesting structures viz. simple pits, contour trench and ring trench, which were established in the seedling phase were also compared. The experiment was laid out during 1993 in one year old coconut plantation spaced at 7 x 7m .The MPTs were planted between rows of coconut at a spacing of 2.33 m. The experiment was laid out in Randomised Block Design (RBD), with three replications.

The result showed that casuarina recorded maximum height (28.02 m) and girth (GBH of 71.76 cm) and biomass accumulation among different MPTs studied. Ailanthus intercropped systems intercepted about 93 percent available sunlight and control plots (coconut alone) intercepted the least with around 57 percent due to their stand leaf area index of 3.21 and 1.52 respectively. It was observed that MPTs had an adverse effect on the productivity of coconut during later stages of the cropping system.

MPTs had tremendously increased the water holding capacity and infiltration rate of the soil. Ailanthus interplanted plots showed better water holding capacity and improved the infiltration capacity of the soil. Resorting to agroforestry practices considerably increased the organic carbon content of the soil. Casuarina interplanted plots showed higher available N, P and K and the surface layer had more concentration of available nutrients. As the soil depth increases the available nutrient concentration was found to decrease.

Microbial population viz., bacteria, fungi and actinomycetes were also found to increase due to the influence of MPTs intercropped in coconut plantations. The microbial population viz. bacteria, fungi and actinomycetes was found more in coconut intercropped with casuarina plots. Fungi and bacterial population were found more in the 30-45 cm soil layer but actinomycetes was found more in the surface layers. The percentage of VAM infection on the roots was also seen more in casuarina intercropped in coconut garden.