Long-term application of chloride-containing fertilizers substantially suppresses soil nitrification, alters ammonia-oxidizing microbial communities, and reduces maize grain yield, according to findings from a 35-year field experiment conducted in Northeast China. The research, published in Frontiers in Microbiology, evaluated how decades of fertilizer-derived chloride inputs reshape inorganic nitrogen supply dynamics within a temperate agricultural brown-soil agroecosystem.
Chloride-containing fertilizers, frequently utilized as accompanying components alongside nitrogen fertilizers, are applied extensively across global soils for agricultural crop production. Despite their routine widespread adoption, the long-term ecological consequences of continuous chloride input on fundamental soil processes—specifically nitrification rates and the balance of plant-available inorganic nitrogen—have historically remained poorly understood by agronomists and soil microbiologists.
To assess these long-term agricultural dynamics, the researchers established experimental plots comparing chloride-free, low-chloride, and high-chloride fertilization regimes over a thirty-five-year period. Across all experimental treatments, total nitrogen, phosphorus, and potassium inputs were maintained at strictly equal levels to isolate the specific chemical and microbiological impacts of accompanying chloride additions under continuous field management.
Field measurements demonstrated that high-chloride treatments were consistently associated with lower soil pH levels. However, subsequent statistical path modeling revealed that the direct effect of chloride itself on soil pH was not statistically significant, indicating that ammonium-based fertilization serves as the primary direct driver of acidification in this agroecosystem, while combined applications of potassium chloride and chloride-containing nitrogen fertilizers exacerbate overall soil acidification.
Statistical evaluations using linear mixed models verified significant individual effects of both chloride addition and soil pH on the potential nitrification rate and the overall abundance of ammonia-oxidizing microorganisms. Based on these observed relationships, the investigators proposed two distinct pathways through which chloride suppresses soil nitrification: putative direct chemical inhibition exerted by chloride ions, and an indirect pathway driven by chloride-associated shifts in soil pH that subsequently suppress specialized nitrifying microbial populations.
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