N2O emissions and product ratios of nitrification and denitrification are altered by K fertilizer in acidic agricultural soils
2020
Li, Zhiguo | Xia, Shujie | Zhang, Runhua | Zhang, Runqin | Chen, Fang | Liu, Yi
Potassium (K) fertilizer plays an important role in increasing crop yield, quality, and nitrogen use efficiency. However, little is known about its environmental impacts, such as its effects on emissions of the greenhouse gas nitrous oxide (N₂O). A nitrogen-15 (¹⁵N) tracer laboratory experiment was therefore performed in an acidic agricultural soil in the suburbs of Wuhan, central China, to determine the effects of K fertilizer on N₂O emissions and nitrification/denitrification product ratios under N fertilization. During 15-d incubation periods with a fixed initial N concentration (80 mg kg⁻¹), K application increased average N₂O emission rates significantly (1.6–10.8-fold) compared to the control treatment. N₂O emissions derived from nitrification and denitrification both increased in K-treated soil, and denitrification contributed more to the increase; its contribution ratio rose from 32% without K fertilizer to 53% with 300 mg kg⁻¹ of K applied. The increase in N₂O emissions under K fertilization is probably due to an increase in the activity of denitrifying microorganisms and acid-resistant nitrifying microorganisms caused by higher K⁺ concentrations and lower soil pH. Combined treatment with potassium chloride (KCl) and N fertilizer produced lower N₂O emissions than combined treatment with potassium sulfate (K₂SO₄) and N fertilizer during 15-d incubation periods. Our results imply that there are significant interaction effects between N fertilizers and K fertilizers on N₂O emissions. In particular, combining N fertilizers with fertilizers that reduce soil acidity or contain Cl or K ions may significantly affect agricultural N₂O emissions.
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