EFFECT OF APPLICATION OF DIFFERENT LEVELS OF UREA AND AMMONIUM SULPHATE AT DIFFERERNT PROPORTIONS ON SOIL pH, SOIL PHOSPHORUS AND MICRO-NUTRIENTS AVALABILITYIN TEA SOIL

Abstract

Soil samples were collected at a depth of 0-15 cm and 15-30 cm from experimental plots of a long term field trial carried out at the Tea Research Institute of Sri Lanka, Talawakelle to investigate the performance of ammonium sulfate (SA) and urea at two rates (240 and 360 kg N ha' 1 yr'1) in five combinations of SA and urea (urea : SA = 100:0, 75:25, 50:50, 25:75 and 0:100). The samples were analyzed for soil pH, Borax extractable phosphorus, DTP A extractable Mn, Cu, Fe and Zn. The results indicate that the soil pH (water and 0.01 M CaCfe) decreased linearly with the proportional increase of ammonium sulfate in the SA/Urea combination at both (0-15 and 15-30 cm) depths. There is a decreasing trend of soil phosphorus with the decrease in soil pH at both depths at both N levels. However these changes are not statistically significant. DTP A extractable Iron availability was linearly increased as soil pH (water and 0.01 M CaCb) decreased at both (0-15 and 15-30 cm) depths at both N levels (240 and 360 kg N). Further zinc, copper and manganese concentration also linearly increased (not statistically significant) as soil pH (water, 0.01 M CaCfe) decreased, at (0-15 and 15-30 cm) depths at both levels of N (240 N and 360 N).