A new study reveals that soil acidity plays a critical role in determining how wheat competes with soil microorganisms for nitrogen, a nutrient essential for plant growth and global food production. The findings provide new insight into how farmers may optimize nitrogen use efficiency and improve crop productivity by considering soil chemical conditions.
Nitrogen is one of the most important nutrients limiting plant growth worldwide. Plants typically absorb nitrogen from the soil in two primary forms: ammonium and nitrate. However, plants are not the only organisms that rely on these nutrients. Soil microorganisms also compete for the same nitrogen sources, influencing how much nitrogen remains available for crops.
Researchers conducted a controlled laboratory experiment using wheat grown in two types of agricultural soil with contrasting pH levels: acidic soil and calcareous soil, which is more alkaline. By using nitrogen isotopes to track nutrient movement, the team was able to directly measure how wheat plants and soil microbes absorbed nitrogen over time.
“Our results show that soil pH fundamentally changes how wheat acquires nitrogen and how strongly microbes compete with plants for this vital nutrient,” said corresponding author Ting Lan. “Understanding these interactions is essential for developing more efficient and sustainable fertilization strategies.”
Uptake patterns
The study found that wheat displayed different nitrogen uptake patterns depending on soil type. In calcareous soil, wheat initially showed a strong preference for nitrate within the first 24 hours after nitrogen was applied. In acidic soil, however, wheat did not show a clear preference between ammonium and nitrate during the same period. Overall, wheat absorbed nitrogen more efficiently in calcareous soil compared with acidic soil.
The research also revealed dynamic competition between wheat and soil microbes. Microorganisms dominated nitrogen uptake immediately after fertilizer application, demonstrating a rapid response and strong short term advantage. However, within 48 hours, wheat surpassed microbial nitrogen uptake in both soil types. This suggests that while microbes quickly capture available nitrogen, crops may ultimately recover more nitrogen over time.
Acidic soil
Interestingly, microbial nitrogen assimilation remained significantly higher in acidic soil than in calcareous soil. In acidic soil, microbes captured nearly as much nitrogen as wheat, highlighting stronger competition between plants and microorganisms under lower pH conditions. In contrast, microbial competition was weaker in calcareous soil, allowing wheat to dominate nitrogen uptake more effectively.
The researchers attribute these differences to soil chemical processes that regulate nitrogen availability. Calcareous soil showed higher nitrification rates, meaning more ammonium was converted into nitrate, which wheat tends to favor. Acidic soils, on the other hand, supported conditions that enhanced microbial nitrogen retention.
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According to the study, these findings could have important agricultural implications. Improving soil pH management may help farmers balance microbial activity and crop nitrogen uptake, potentially reducing fertilizer loss and environmental pollution. Nitrogen fertilizers are often inefficiently used, with significant portions lost to the environment, contributing to water contamination and greenhouse gas emissions.
Complex and dynamic
The study also highlights the complex and dynamic nature of plant microbe interactions in agricultural soils. Nitrogen uptake strategies can shift rapidly depending on soil chemistry, microbial activity, and nutrient availability. Understanding these processes may help scientists develop improved crop management practices that enhance nutrient efficiency while maintaining soil health.
The research demonstrates that soil pH is a key regulator of nitrogen competition between crops and microbes and offers new insights into improving nutrient management in modern agriculture.
The full study is available in the journal Nitrogen Cycling.
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