SOIL AMELIORATION EFFECTS ON NUTRIENT AVAILABILITY AND PRODUCTIVITY OF GROUNDNUT ON ACID SANDY SOILS OF ZIMBABWE

The effects of four calcium-containing materials on soil pH, nutrient availability and productivity of groundnut (Arachis hypogaea) on acid soils were studied in field experiments conducted at the Horticulture Research Centre and the Makoholi Experiment Station in Zimbabwe. The materials were calcitic limestone, dolomitic limestone, gypsum and single super phosphate. Application of dolomitic or calcitic limestone significantly increased soil pH and exchangeable calcium and magnesium levels, whereas gypsum and single super phosphate did not. Application of 4000 kg ha−1 calcitic limestone increased calcium levels by up to 125% at the Horticulture Research Centre and 872% at Makoholi Experiment Station, while dolomitic limestone increased magnesium levels by 183% and 473% at the Horticulture Research Centre and Makoholi Experiment Station respectively. Combining gypsum and single super phosphate with 2000 kg ha−1 calcitic or dolomitic limestone did not affect soil pH differently than the limes alone. Furthermore, gypsum and single super phosphate applications on their own had no effect on pH, calcium and magnesium levels. The phosphorus, potassium and nitrogen levels were not significantly affected by the calcium-containing materials. Application of either dolomitic or calcitic limestone significantly improved productivity of groundnut, with 4000 kg ha−1 calcitic limestone producing the largest increases in kernel yields at both sites. Yield responses to gypsum were not significantly different from the control treatment. Despite the notable changes in soil chemical properties observed at both sites, deficiencies of nitrogen, phosphorus, potassium, calcium and magnesium, coupled with low pH per se, remained the primary reasons for poor growth on the acid sandy soils at both sites.