Morupule fly ash as amendments in agricultural soil in Central Botswana

Abstract

The potential of Morupule fly ash as a soil amendment was evaluated using spinach and rape vegetables planted successively in Palapye soils added with 0 fly ash (FA), 5% FA, 10% FA, and 15% FA (w/w) in combination with four nutrient sources as no fertilizer (-NF), compost (+COMP) at 20 tones ha −1 , inorganic NPK (+NPK) and a combination of 1 2 NPK and 1 2 compost (+NPK+COMP). Spinach was grown first for 40 days followed by rape as a second crop planted on the same pots and treatments after harvesting spinach. The application of FA increased the pH, EC, and the total concentration of As, Cu, and Pb of soil while compost increased the total Zn. The available concentration of Cr, Cu, Mn, Ni, and Pb were significantly reduced by FA. FA increased the yield of spinach and rape, especially in 10FA+NPK+COMP. The heavy metal concentration in the shoots of spinach and rape were below the maximum acceptable limits (MAL) for vegetables in 10FA+NPK and 10FA+NPK+COMP treatments. Overall, an application rate of 10% FA combined with compost and fertilization gave the highest yield and safe level of As, Cr, Cu, Mn, Ni, Pb, and Zn in the edible shoots. • First report on using Morupule fly ash as an amendment in agricultural soils in Botswana. • A combined with compost and inorganic fertilizer improved the growth and yield of spinach and rape grown successively. • Fly ash amendments reduced the available concentration of Cr, Cu, Mn, Ni, and Pb in soil. • Fly ash at 10% application combined with compost and inorganic fertilizer produced spinach and rape safe for human consumption.