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Geochemical Journal
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Impact of fertilization with irrigation on carbonate weathering in an agricultural soil in Northern China: A column experiment

Song Chao, Liu Changli, Han Guilin
Geochemical Journal, Vol. 51, No. 2, P. 143-155, 2017

ABSTRACT

Fertilization and irrigation (FI) are exerting an important impact on the fluxes of carbon, both between and within ecosystems in an agricultural area. However, the impacts of urea, diammonium phosphate ((NH4)2HPO4) and animal manure, as the most common fertilizers in Northern China, and irrigation on carbonate weathering in soil are still relatively unknown due to the complicated biogeochemical process of these added fertilizers. In this study, four soil columns with different treatments (control (CK), fresh cow manure (FM) urea (NF) and diammonium phosphate (PF)), were established to explore the influence of fertilization and irrigation on carbonate weathering in an agricultural area in Northern China. The pH, K+, Ca2+, Na+, Mg2+, NH4+, NO3, NO2, free CO2, HCO3, Cl, SO42–, COD and HPO42– in leachates from the soil columns were analyzed. The results showed that Ca2+ and NO3, HCO3, SO42– were the dominant cations and anions (>25% in meq%) in the leachate from the CK and FM columns, respectively, while Ca2+ and NO3 were the dominant cations and anions in NF and PF treatments, respectively. The addition of fresh cow manure had no distinct effect on the hydro-chemical characteristics in the soil solution, and the weathering rate of carbonate, whereas an increase in the weathering rate of carbonate, CO2 concentration, Ca2+, Mg2+ and NO3 was observed after the addition of urea and (NH4)2HPO4, which was mainly attributed to the release of protons from the nitrification reaction. The co-precipitation of phosphate ions with calcium carbonate had a blockage effect on the leaching of phosphate, but has no apparent effect on the weathering rate of carbonate when (NH4)2HPO4 was added to the carbonate-enriched soil column. The widespread application of urea and (NH4)2HPO4 along with irrigation in the agricultural area of Northern China increases the rate of carbonate weathering and soil CO2 emission. The enhanced Ca2+, Mg2+ and DIC (free CO2 + HCO3 + CO32–) due to the addition of urea and (NH4)2HPO4 as well as irrigation should not be disregarded when evaluating CO2 consumption by mineral weathering in the agricultural area.

KEYWORDS

fertilization and irrigation, carbonate weathering, agricultural area, fertilizer, CO2 consumption

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