Retention behavior of phosphate in sandy regosol

Abstract

The Sandy regosols are found along the coastline of Sri Lanka. These soils receive heavy organic as well as inorganic fertilizers, in excess to the proposed guidelines. Continuous applications of phosphate(P) in excess of plant requirements results in the upper soil layers becoming enriched, and eventually saturated, with P. Large amounts of P could then be leached into deeper soil profiles and even into ground water, or P could be transported in surface runoff. A laboratory leaching experiment was conducted to understand the adsorption- desorption behavior of phosphate in sandy regosol for different types of fertilizers. . For this study six treatments and three replicates were tested. These treatments were; cow dung (T1), poultry manure (T2), Triple super phosphate (T3), vegetable mixture (T4) tuber and onion mixture (T5) and control (T6) fertilizers applied at the rate of proposed guideline of Department of Agriculture, Sri Lanka . Columns were leached with water at an application rate of 21.82 cm/ day for up to 9 to 10 days. Phosphate in leachate and soil was measured using spectrophotometer. In the study P leached in the order of T3> T1 > T2 > T5> T4>control. Triple super phosphate (T3) leached the highest amount of phosphate (48.45 mg kg-1). P retained is in the order of T1> T2 > T6 > T3> T4>control.