Ekanayaka, E. M. G. N.,Dissanayake, D. K. R. P. L.,Herath, H. M. S. K.Atapattu, A. J.2025-03-042022In Technological Transformation for Sustainable Development, 1st Annual Research Session Faculty of Technology ARSFOT-2022 (pp. 36). Eastern University of Sri Lanka.https://dl-cri.nsf.gov.lk/handle/1/4290Discarding large volumes of king coconut husks (KCH) is a major issue in the coconut water export sector. Even roadside sellers discard large amounts and there is no proper way to dispose them. Since king coconut is harvested at an early stage, the husk has no economic value due to less amount of fiber. KCH can be utilized in a sustainable manner by converting it into biochar and applying as a soil amendment. Biochar has a potential to minimize nitrogen (N) losses through leaching. A laboratory leaching column study was conducted to determine the impact of KCH biochar on N retention in sandy and clay soils when applied in the form of urea and ammonium sulphate (AS): application rate is 0.06 and 0.07 g cm-2 or 6 and 7 t ha-1, respectively. KCH biochar was prepared at 500 °C in a muffle furnace and amended topsoil of the columns at 0, 1, 2, and 3% (w/w) rates. KCH had 84% fixed C, 8% ash, 7% volatile matter, and 1% moisture content. Over a twomonths period, soil columns were leached with 200 mL of distilled water once a week, and the total N content of the leachates was analyzed. When AS was added to sandy and clay soils it depicted 49 - 62% N leached whereas urea, 34-49 % N leached in sandy and clay soils. This indicates that biochar application to sandy soils has a stronger effect on reducing leaching losses than in clay soils and soils with urea application showed lesser N leaching compared to AS. 2% biochar application rate with urea showed 34 - 42% N leaching in sandy and clay soil whereas 3% application rate showed 32 -58% N leaching in sandy soil and clay soil. Interestingly 2 and 3% application rates resulted the least amount of N drainage without a significant difference (P > 0.05) compared to the other two tested rates. In order to reduce N leaching in sandy soil, 2% KCH biochar with urea can be recommended as a soil amendment for field application.ensoils and plant nutritionfertilizerssandy loam soilsclay soilsnitrogen retentioncoocnut huskbiocharArticle