The effects of temperature, time and cycles of drying and rewetting on the extractability of zinc added to a calcareous soil

The effects of temperature, time and cycles of drying and rewetting on the extractability of Zn added to a calcareous soil were studied by three successive extractions with DTPA. The concentrations of DTPA-extractable Zn increased linearly with the concentration of added Zn. The proportion of added Zn in the DTPA-extractable fraction decreased with increasing incubation time and with increasing temperature. The proportion of added Zn not extracted by three extractions of DTPA was found to be a function of the square root of equivalent time adjusted to 22 degrees C. There were similar effects of temperature to time on the extractability in DTPA of Zn added to soil, The apparent diffusion rate coefficients (E(a)) were from 10(-10) to 10(-11) sec(-1) and were increased by increasing temperature. The diffusion activation energy (E(a)) was estimated to be 55 kJ mol(-1). The times (y) required for the extractability of added Zn in DTPA to decrease by 90% were estimated to be about 43 y at 4 degrees C, 10 y at 22 degrees C and 3 y at 40 degrees C. It was suggested that the processes which lead to the decreases in the extractability of Zn added to soil are controlled by the diffusion of sorbed Zn(OH)(+) in soil, probably through micropores. Drying and rewetting appeared to enhance this process.