Impacts of precipitation on leaching behavior of plant nutrients in agricultural soils of the tropics

This study evaluates the leaching behavior in terms of leaching pattern and losses of plant nutrients including potassium, magnesium and calcium caused by heavy annual precipitation in different agricultural soils in the tropics of Thailand. Leaching experiments were conducted in the laboratory in which unpolluted water with pH 7.0 was applied to the soil columns. The calculated volume of annual precipitation was applied in three phases representing rainy seasons, each phase having a period of 15 days. Soil leachate samples were collected on regular basis in plastic bottles placed under the columns and analyzed for the target nutrient cations i.e. K⁺, Ca²⁺ and Mg²⁺ by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). Results showed that precipitation caused very high concentrations of C²⁺ and Mg²⁺ in the leachate samples reaching 71.9 and 16.0 mg/l, respectively from slightly acidic soil (Pak Chong). Very small concentrations of K⁺ were found in leachate samples from all the soils. Leaching losses of bivalent nutrient cations were higher than that of the monovalent nutrient cations from all the soils. Precipitation induced more leaching losses of nutrient cations in clayey soils than in sandy soil. Almost same leaching losses of K⁺ were found in all soils ranging from 0.82 to 1.52 mg/kg soil. Quite high leaching losses of Ca²⁺ were found in clayey soils ranging from 94.09 to 150.45 mg/kg soil. However, maximum leaching of magnesium occurred in clayey soil with acidic nature i.e. 25.82 mg/kg of soil. This study found that soil texture, soil reaction (pH) and original nutrient status are important factors affecting the leaching behavior of nutrient cations (K⁺, Ca²⁺ and Mg²⁺) in the tropical soils.