Effect of fertilizing on establishment and early growth of tree plantations on Imperata cylindrica grasslands

Abstract

Effects of fertilizer combinations on early growth of fast-growing plantation tree species were tested in two separate experiments on Imperata cylindrica dominated grasslands in South Kalimantan, Indonesia. Effects of commercial NPK and locally made NPK mixtures on the growth of Acacia mangium, Gmelina arborea, Paraserianthes falcataria and Swietenia macrophylla were tested by applying the fertilizer one year after planting. In the second experiment the effects of N, P, K, and their combinations with trace elements on the growth of A. mangium, G. arborea and Eucalyptus deglupta were tested by applying the fertilizer in two doses, immediately after planting and one year after planting. Two years after planting different NPK-mixtures did not have significant effect on the growth of A. mangium or S. macrophylla. On the contrary, all the NPK treatments roughly doubled the basal area of P. falcataria. For G. arborea the fertilizing effect was somewhat similar, but not statistically significant at p < 0.05. In the second experiment significant differences in growth of A. mangium, G arborea and E. deglupta between sites and fertilizer treatments were detected. Responses were strongest in the treatments including phosphorous. Generally A. mangium had steady performance compared to G. arborea, P. falcataria or E. deglupta, which were more sensitive to fertilization treatments and site effects. Fertilization is important on forest plantations on grasslands as it clearly speeds up the early growth that is important for gaining site control over the grass. Phosphorous must be included in the fertilization treatments on grasslands. NPK-fertilization is recommended as a standard solution if detailed information on the site is not available. Studies are needed on the long term effects of fertilizers, rotation-length fertilization requirements and the economic profitability of fertilizing, as well as the interactions between tree species, fertilizers and soil.