Impacts of nitrogen fertilizer type and application rate on soil acidification rate under a wheat-maize double cropping system

• Published in: Journal of environmental management 2020-09, Vol.270, p.110888, Article 110888
• Main Authors: Hao, Tianxiang, Zhu, Qichao, Zeng, Mufan, Shen, Jianbo, Shi, Xiaojun, Liu, Xuejun, Zhang, Fusuo, de Vries, Wim
• Format: Article
• Language: English
• Subjects: Agriculture; Ammonium chloride; China; Cropland; Fertilizers; Hydrogen-Ion Concentration; Nitrogen; Soil; Soil acidification; Soil pH; Triticum; Urea; Zea mays
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2020.110888

Nitrogen (N) fertilizer-induced soil acidification in Chinese croplands is well-known, but insight in the impacts of different N fertilizer management approaches (fertilizer type and rate) on soil acidification rates is very limited. Here, we conducted a field experiment on a moderate acid soil to quantify soil acidification rates in response to N fertilization by different fertilizer types and N rates through monitoring the fate of elements (mainly nutrients) related to H+ production and consumption. Two N fertilizer types (urea and NH4Cl) and three N rates (control, optimized and conventional, 0/120/240 kg N ha−1 for wheat, 0/160/320 kg N ha−1 for maize) were included. Nitrogen addition led to an average H+ production of 4.0, 8.7, 11.4, 29.7 and 52.6 keq ha−1 yr−1, respectively, for the control, optimized urea, conventional urea, optimized NH4Cl and conventional NH4Cl plots. This was accompanied with a decline in soil base saturation of 1–10% and in soil pH of 0.1–0.7 units in the topsoil (0–20 cm). Removal of base cations by crop harvesting and N transformations contributed ~70% and ~20% to the H+ production in the urea treated plots, being ~20% and ~75% in the NH4Cl treated plots, respectively. The large NH4+ input via fertilization in the NH4Cl treated plots strongly enhanced the H+ production induced by N transformations. The low contribution of N transformations to the H+ production in the urea treated plots was due to the limited NO3− leaching, induced by the high N losses to air caused by denitrification. Increased N addition by urea, however, strongly increased H+ production by enhanced plant uptake of base cations, mainly due to a large potassium uptake in straw. Our results highlight the important role of optimizing fertilizer form and N rate as well as straw return to the field in alleviating soil acidification. •Soil acidification rates in response to N fertilizer management were quantified.•N transformation processes dominated soil acidification by NH4+ based fertilizer.•Base cation uptake by crop was the main contributor to soil acidification by urea.•Straw return is an effective method to mitigate soil acidification in case of urea.