Retention of macronutrients in a sandy soil amended with vermiculite under Tanzanian field conditions

The study assessed the ability of vermiculite to enhance the retention of extractable nitrogen (N), phosphorus (P), and potassium (K) in arable Tanzanian soils. Raw and expanded vermiculites pre-heated at 600 oC were mixed with a sandy soil in varying amounts. Inorganic fertilizers N, P and K were added to the soil-vermiculite mixes and buried at 0-15 and 15-30 cm depth in litter bags for three months during the rainy season. After that period, extractable N, P and K retained in the mixes were determined. The result showed that less than 10% of the applied N was retained whereas for K it was 26-48%. Phosphorus was highly retained and in part fertilized from vermiculite over the control. The maximum extractable fertilizer P retained in soil amended with expanded vermiculite was 78%, whereas in soil with raw vermiculite it was 141%, suggesting that vermiculite also retains soil P mineralized over the course of the experiment. More retention of N, P and K occurred at 15-30 cm than at 0-15 cm and increased with the amount of vermiculite mixed with the soil. Thus, use of vermiculite enhances soil productivity by retaining extractable essential macronutrients which could be used for crop production