Changes in soil chemical properties in agroforestry system at USU Arboretum Kwala Bekala

Abstract

One of the opportunities for utilization and optimization of the Arboretum land is by intensive cultivation of crops commodities to fulfil the needs of food, vegetables and other commodities. This study aims to analyse changes in soil nutrient status in four types of forest trees combined with agroforestry using soybean. Soil survey was carried out in area of USU Arboretum Kwala Bekala by soil sampling and then analyzed in the laboratory. Composite soil samples were taken from Jabon tree stands, (Anthocephalus cadamba Miq.), Gmelina (Gmelina arborea Roxb.), Rubber (Hevea brasiliensis.), and Mindi (Melia azedarach L.) at a depth of 0-30 cm. This sampling was carried out twice, namely before planting and after harvesting of soybeans. The results of soil analysis were assessed based on the criteria of Soil Research Center. Parameters observed for soil sample were N total (Kjeldahl method), phosphate (Bray method), C organic (Walkey and Black), Potassium and Sodium (Flame photometer), Calcium and Magnesium (AAS). The data obtained were analysed using a paired t test at the level of α 0.05. Almost all of the values of soil chemical properties gradually increased, and significant differences in those chemical properties were found between two condition, before and after the growing of soybean in four type stand of woods. Generally, Agroforestry system in four main stands (Rubber, Gmelina, Mindi and Jabon) with soybean for period 1-year can improve soil chemical fertility through increasing pH, C organic, N total, P available, Potassium, Na and Ca.