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

Abstract

Calcium carbonate (CaCO3) is frequently used to ameliorate soil acidity in agricultural soils. An alternative is calcium hydroxide (Ca(OH)2), which is more soluble than CaCO3. 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 CaCO3 and Ca(OH)2. We amended an acidic soil (pH of 5.6) with CaCO3 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 CaCO3 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 CaCO3. 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 CaCO3 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 CaCO3 reduced available P due to high P-fixation more than Ca(OH)2. Our study shows that while both Ca(OH)2 and CaCO3 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 CaCO3.