Soil moisture does more than help crops grow. It also shapes the invisible microbial reactions that determine whether nitrogen fertilizer is efficiently converted in soil or temporarily builds up as reactive nitrogen compounds. A new study published in Environmental and Biogeochemical Processes reveals how changing soil water levels can disrupt the balance between two key steps of nitrification, a central process in the soil nitrogen cycle.
“Nitrogen cycling in soil depends on a delicate microbial partnership,” said corresponding author Shurong Liu of Sun Yat-sen University . “Our results show that when soil moisture and nitrogen availability change together, this partnership can become unbalanced, leading to nitrite accumulation under certain conditions.”
Nitrification is usually a two-step microbial process. First, ammonia-oxidizing microorganisms convert ammonia into nitrite. Then, nitrite-oxidizing bacteria convert nitrite into nitrate, a form of nitrogen that plants can use but that can also leach into waterways. Under stable conditions, the two steps are closely linked, so nitrite usually does not accumulate. However, nitrite is a reactive intermediate that can contribute to environmental problems when its production and consumption become mismatched.
To understand how moisture affects this microbial handoff, the research team incubated agricultural soils under four water-holding capacity levels: 40%, 60%, 90%, and 120% , representing relatively dry, moderate, wet, and waterlogged conditions. The soils also received three levels of ammonium nitrogen: 50, 100, and 200 mg NH4+-N per kg soil .
The results showed that under low nitrogen input, soil moisture had little effect on ammonia oxidation. But when ammonium levels were higher, the picture changed. Moderate moisture levels of 60% to 90% water-holding capacity strongly enhanced ammonia oxidation , especially by ammonia-oxidizing bacteria. In these treatments, ammonia was rapidly converted into nitrite.
The problem was that nitrite oxidation did not always keep pace. The study found that nitrite accumulation was most pronounced under high nitrogen input and moderate moisture , where fast ammonia oxidation by bacteria outpaced the capacity of Nitrobacter, a key nitrite-oxidizing bacterial group. This imbalance created a temporary bottleneck in the nitrogen cycle.
“Our findings suggest that nitrite buildup is not simply caused by more nitrogen or more water alone,” Liu said. “It emerges when ammonia oxidizers accelerate faster than nitrite oxidizers can respond.”
The study also revealed important differences among microbial groups. Ammonia-oxidizing bacteria were most active under high nitrogen and moderate moisture , while ammonia-oxidizing archaea responded less consistently. Among nitrite oxidizers, Nitrobacter was more sensitive to saturated conditions , whereas Nitrospira showed broader tolerance across moisture extremes .
When soils became waterlogged at 120% water-holding capacity , nitrification was suppressed because oxygen diffusion was limited. Under these saturated conditions, nitrite and nitrate accumulation remained low, likely because oxygen-poor conditions shifted nitrogen processing toward denitrification, a pathway that can consume nitrate and nitrite and may contribute to gaseous nitrogen losses.
These findings have practical implications for agriculture and environmental management. Fertilizer use, irrigation, rainfall, and waterlogging events all influence the moisture and nitrogen conditions that govern microbial nitrogen transformations. By showing how moisture and ammonium availability jointly regulate the balance between ammonia and nitrite oxidation, the study provides a clearer picture of when soils may become prone to inefficient nitrogen cycling or reactive nitrogen buildup.
The research highlights the need to consider soil water status when managing nitrogen fertilizer , especially as extreme rainfall and drought cycles become more common. Better understanding these microbial thresholds could help improve nitrogen use efficiency, reduce nitrogen losses, and support more sustainable farming systems.
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Journal reference: Li Z, Ma J, Chen M, Kuang W, Cai G, et al. 2026. Soil moisture-driven changes in the balance of ammonia and nitrite oxidation. Environmental and Biogeochemical Processes 2: e010 doi: 10.48130/ebp-0026-0005
https://www.maxapress.com/article/doi/10.48130/ebp-0026-0005
About the Journal:
Environmental and Biogeochemical Processes (e-ISSN 3070-1708) is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment.
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Environmental and Biogeochemical Processes
Experimental study
Soil moisture-driven changes in the balance of ammonia and nitrite oxidation
29-Apr-2026