Ameliorating soil acidity with calcium carbonate and calcium hydroxide: effects on carbon, nitrogen, and phosphorus dynamics

Calcium carbonate (CaCO 3 ) is frequently used to ameliorate soil acidity in agricultural soils. An alternative is calcium hydroxide (Ca(OH) 2 ), which is more soluble than CaCO 3 . However, the associated change in soil parameters remains unclear. We aimed to evaluate the different responses of available nitrogen (N) and phosphorus (P), microbial biomass carbon (C), N, and P (MBC, MBN, and MBP), and dissolved organic C and N (DOC and DON) to CaCO 3 and Ca(OH) 2 . We amended an acidic soil (pH of 5.6) with CaCO 3 or Ca(OH) 2 at 5 different loadings of hydroxide (OH − , 0.025, 0.05, 0.1, 0.25, and 0.75 mmol g −1 ) in a 30-day incubation experiment. Both Ca(OH) 2 and CaCO 3 rapidly increased soil pH, but soil pH increased to 10 with the highest loading rate of Ca(OH) 2 , while soil pH levelled off at 7.5 with an OH − loading of 0.25 mmol g −1 as CaCO 3 . Higher ammonium and lower nitrate concentration with high OH − loading of Ca(OH) 2 (>0.25 mmol g −1 ) suggests that nitrification was constrained under basic soil conditions, while adding CaCO 3 showed the opposite results. Ca(OH) 2 addition increased DOC and DON, along with MBC and MBN, suggesting that desorption of organic matter stimulated microbial growth. High OH − loading with CaCO 3 reduced available P due to high P-fixation more than Ca(OH) 2 . Our study shows that while both Ca(OH) 2 and CaCO 3 can be used to ameliorate soil acidity, Ca(OH) 2 may be able to reduce nitrification and thus N loss at high OH − loading and enhance available P more than CaCO 3 .