Application of Natural and Calcined Oyster Shell Powders to Improve Latosol and Manage Nitrogen Leaching

Excessive N fertilizer application has aggravated soil acidification and loss of N. Although oyster shell powder (OSP) can improve acidic soil, few studies have investigated its ability to retain soil N. Here, the physicochemical properties of latosol after adding OSP and calcined OSP (COSP) and the dynamic leaching patterns of ammonium N (NH(4)(+)-N), nitrate N (NO(3)(−)-N), and Ca in seepage, were examined through indoor culture and intermittent soil column simulation experiments. Various types of N fertilizer were optimized through the application of 200 mg/kg of N, urea (N 200 mg/kg) was the control treatment (CK), and OSP and COSPs prepared at four calcination temperatures—500, 600, 700, and 800 °C—were added to the latosol for cultivation and leaching experiments. Under various N application conditions, the total leached N from the soil followed ammonium nitrate > ammonium chloride > urea. The OSP and COSPs had a urea adsorption rate of 81.09–91.29%, and the maximum reduction in cumulative soil inorganic N leached was 18.17%. The ability of COSPs to inhibit and control N leaching improved with increasing calcination temperature. Applying OSP and COSPs increased soil pH, soil organic matter, total N, NO(3)(−)-N, exchangeable Ca content, and cation exchange capacity. Although all soil enzyme activities related to N transformation decreased, the soil NH(4)(+)-N content remained unchanged. The strong adsorption capacities for NH(4)(+)-N by OSP and COSPs reduced the inorganic N leaching, mitigating the risk of groundwater contamination.