Effect of biochar on nutrient retention and nectarine tree performance: A three‐year field trial

Abstract

We performed a series of experiments in controlled conditions to assess the potential of hardwood‐derived biochar either as a source or as a removing additive of macronutrients [nitrate‐nitrogen (NO 3‐N), ammonium‐N (NH 4‐N), potassium (K), phosphorus (P), and magnesium (Mg)] in solution. In addition, a 3‐year field trial was carried out in a commercial nectarine orchard to evaluate the effect of increasing soil‐applied biochar rates on tree nutritional status, yield, fruit quality, soil pH, soil NO 3‐N, and NH 4‐N concentration and soil water content. In controlled conditions, the concentrations of K, P, Mg, and NH 4‐N in solution were significantly increased and positively correlated with biochar rates. Biochar was ineffective in removing NO 3‐N, K, P, and Mg from enriched solutions, while at the rate of 40 g L−1 biochar removed almost 52% of the initial NH 4‐N concentration. In a mature, irrigated, fertilized, commercial nectarine orchard (Big Top/GF677) on a sandy‐loam soil in the Italian Po Valley, soil‐applied biochar at the rates of 5, 15, and 30 t ha−1 were effective in reducing the leached amount of NH 4‐N in the top 0.25 m soil layer over 13 months, as estimated by ion exchange resin lysimeters. Nevertheless, independent of the rate, biochar did not affect soil pH, soil N mineral availability, soil moisture, tree nutritional status, yield, and fruit quality. We conclude that, unless an evident constraint is identified, in non‐limiting conditions (e.g., water availability and soil fertility), potential benefits from biochar application in commercial orchards are hidden or negligible.