Calcium and phosphorus interact to reduce mid-growing season net nitrogen mineralization potential in organic horizons in a northern hardwood forest

► Calcium addition reduced net N mineralization in the Oa horizon, by increasing N immobilization. ► Phosphorus availability interacted with Ca to reduce net N mineralization in Oe and Oa horizons. ► Soil acidification may be increasing net N mineralization in forests of the northeastern USA. ► These effects are likely sensitive to soil P and proportions of Oe and Oa in the forest floor.