Contrastive nutrient leaching from two differently textured paddy soils as influenced by biochar addition

Purpose The aims of the current study were to (1) examine the interactive effects of biochar addition and differently textured soils (clayey and sandy soils) on nutrient leaching and (2) identify potential mechanisms related to the leaching. Materials and methods A repacked soil column experiment was set up to test the effects of five biochar rates added to clayey and sandy soils grown with rice (Oryza sativa L. ssp. japonica) for 3 months. Four leaching events were conducted to measure concentrations of ten elements in the leachate, including calcium (Ca), sodium (Na), potassium (K), magnesium (Mg), aluminum (Al), iron (Fe), manganese (Mn), ammonium nitrogen (NH4+), nitrate nitrogen (NO3-), and phosphorus (P). Results and discussion On the sandy soil, biochar addition linearly and significantly reduced Ca concentration (by 38%), but increased Na (by 92%), K(by 292%), and P (by 411%) concentrations in the leachate, compared to the non-biochar-added soil. In contrast, on the clayey soil, biochar addition showed no obvious effect on the leaching of these elements. Biochar addition significantly reduced leaching of Al, Fe, Mn, and NH4-, but increased leaching of Mg. Mechanisms related to the reduced leaching of NH4-, Ca, Al, Fe, and Mn could be involved in the liming effect and increased nutrient holding capacity by biochar addition, and those responsible for increased leaching of Na, K, and P could be involved in co-addition of these elements with the added biochar. Conclusions Biochar addition had contrastive effects on nutrient leaching, which was more profound on sandy soil than on clayey soil grown with rice crop.