Effect of biochar application rate on macronutrient retention and leaching in two coconut growing soils

Abstract

Low nutrient reserves and poor soil fertility management in coconut cultivation have limited coconut productivity. Biochar is one of the best solutions to improve soil nutrient reserves and fertility over time. This study explored the best rate of biochar application in coconut-growing soils to reduce leaching losses and macronutrient enrichment. Two major coconut-growing soil series; Madampe (Sandy) and Andigama (Sandy loam) were used in the experiment. <italic>Gliricidia</italic> wood biochar (BC) pyrolyzed at 700 °C was used to amend the 0-15 cm topsoil in PVC columns at the rates of 0% BC, 1% BC, 2% BC and 3% BC (w/w) with recommended doses of inorganic fertilizer. Columns were arranged in Completely Random Design (CRD) with three replicates and leached two weeks intervals over five months. Our findings revealed two distinct scenarios for sandy and sandy loam soils. Considering the retention of macronutrients in sandy loam soil treated with 2% and 3% biochar, the order of retention was P &gt; K &gt; Mg &gt; Ca. However, soil N was not altered substantially (<italic>P</italic> &gt; 0.05) with the amount of biochar amendment. Similarly, in sandy soil, 3% BC treatment demonstrated the sequence P &gt; Mg &gt; N = Ca, although soil K was not differed significantly (<italic>P</italic> &gt; 0.05) with biochar amendment rate. Albeit a once-in-lifetime application of 3% biochar could be recommended on coconut-growing sandy soils, application of this rate would be unprofitable. Thus, the 2% rate will be more appropriate for both sandy and sandy loam soils. These application rates must be validated through long-term field experiments under major coconut-growing soils.