Use of Different Sawdust Biochar as Soil Amendments to Improve Allelochemical-laden Soils Caused by Bamboo in the Landscape

Abstract

This study was conducted to find out the ameliorative effect of biochar in allelochemical-laden soils to improve upon soil physicochemical properties. The study was conducted at the Department of Horticulture, KNUST-Ghana. Some trees in the landscape suppress the growth of any other plant species beneath them. This is reported to be caused by the presence of allelochemicals which are released into the soil by the plants, a mechanism known as allelopathy. Soil amendment is therefore needed to curb the effects of these allelochemicals and make nutrients in the soil available to other plant species that may be planted beneath the allelopathic trees. Biochar, a pyrolised biomass, is a fine-grained, highly-porous charcoal substance that is used as a soil amendment. Biochar produced from three different types of sawdust (Tectona grandis, Celtis mildbraedii, and Entandrophragma cylindricum) and absolute control were the treatments used. Randomized Complete Block Design (RCBD) layout with four (4) treatments and three (3) replicates were employed in the study. The treatments were applied to the soil at a depth of 3 inches at a ratio of 1:1. Data collected included; allelochemicals in the tree and in the soil, rate of growth of grass, percentage coverage of grass, soil water-holding capacity, soil pH and soil nutrient analysis.The study was carried out beneath a bamboo stand–a tree species suspected to be allelopathic. Stenotaphrum secundatum (St. Augustine’s grass) was used for the study because it prefers shaded growing environmental conditions. Data collected over a period of twelve weeks included presence of allelochemicals in the soil and in the tree species, soil physicochemical analysis, rate of growth, and percentage coverage of grass. The results of the initial phytochemical screening revealed that the following allelochemicals were present in the leaves and roots of the bamboo: alkaloids, tannins, glycosides, saponins, flavonoids and triterpenoids.There were no significant differences for total N and soil Potassium. The results of the study also indicated that the bamboo species is allelopathic. Biochar was able to nullify the effects of the allelochemicals and hence allowed the grass to grow well.