Impact of different fertilizers on carbonate weathering in a typical karst area, Southwest China: a field column experiment

Abstract. Carbonate weathering, as a significant vector for the movement of carbon both between and within ecosystems, is strongly influenced by agricultural fertilization, since the addition of fertilizers tends to change the chemical characteristics of soil such as the pH. Different fertilizers may exert a different impact on carbonate weathering, but these discrepancies are as yet not well-known. In this study, a field column experiment was conducted to explore the response of carbonate weathering to the addition of different fertilizers. We compared 11 different treatments, including a control treatment, using three replicates per treatment. Carbonate weathering was assessed by measuring the weight loss of limestone and dolostone tablets buried at the bottom of soil-filled columns. The results show that the addition of urea, NH₄NO₃, NH₄HCO₃, NH₄Cl and (NH₄)₂CO₃ distinctly increased carbonate weathering, which was attributed to the nitrification of NH₄⁺. The addition of Ca₃(PO₄)₂, Ca–Mg–P and K₂CO₃ induced carbonate precipitation due to the common ion effect. The addition of (NH₄)₃PO₄ and NaNO₃ had a relatively small impact on carbonate weathering in comparison to those five NH₄-based fertilizers above. The results of NaNO₃ treatment raise a new question: the negligible impact of nitrate on carbonate weathering may result in an overestimation of the impact of N fertilizer on CO₂ consumption by carbonate weathering on the regional/global scale if the effects of NO₃ and NH₄ are not distinguished.