Effects of site preparation and soil amendment on the early growth performance of Acacia auriculiformis A. Cunn. ex Benth planted in Alimodian clayloam soil

Site preparation had a highly significant effect on the total nitrogen (N) and calcium (Ca) content, a significant effect on soil pH, phosphorus (P), magnesium (Mg) and cation exchange capacity (CEC) but no significant effect on the potassium (K) content of Alimodian clayloam soil. An increase in soil acidity from strongly acid to very strongly acid condition was observed in the intensely prepared chemically-treated (HT) and burned (CBu) plots while N was significantly increased relative to the least prepared plots. Total N, Ca content and CEC of the CBu plots were significantly reduced to 50%, 30% and 1% respectively compared to the control. A higher percentage survival was observed in the control plots while the lack of protective vegetation against exposure to direct sunlight, high air and soil temperature resulted to greater seedling mortalities in the chemically-treated burned and clear-brushed plots. Soil amendment had a highly significant effect on seedling diameter and height growth in the nursery and in combination with site preparation, similar effects were observed in the field. The application of tablet organic fertilizer (TOF) or inoculation with vesicular-arbuscular mycorrhizal fungi enriched with inorganic NPK fertilizer (VNPK) improved height and diameter growth outperforming those treated purely with NPK fertilizer or VAM and those without any soil amendment. Growth responses to the independent effects of treatments however showed that the method of site preparation had a more meaningful effect than soil amendment attributed to the long-term effects of site preparation on the soil properties of Alimodian clayloam that were observed significant up to the third year of growth. Interaction effects were best expressed in the treatment combinations of TOF and VNPK and most pronounced when combined with either chemical treatment or controlled burning. Growth responses translated into wood yield in terms of gross volume and biomass after three years, were observed affected more significantly by site preparation than by soil amendment with the HT plots yielding the greatest height and diameter growth.