Soil pH Determines How Wheat and Microbes Compete for Nitrogen

For more than 100 years, nitrogen has been a major concern for farmers. It is among the essential nutrients required for crop growth.

When nitrogen is lacking, wheat stays pale and stunted. When supplied in suitable amounts, it thrives, grows vigorously and helps fill grain stores across the world.

Plants are not the only living things that require nitrogen. Soil also supports its own complex life. Billions of microbes live around plant roots, and they too depend on nitrogen.

Whenever fertilizer is applied to a field, an unseen race begins: will the crop or the microbes take up the nitrogen first? New research suggests that soil acidity can determine the outcome.

Soil acidity changes everything

Soil pH measures whether soil is acidic or alkaline. Although it may appear to be a minor figure in a laboratory report, pH strongly influences nutrient behaviour. In this case, it alters the contest for nitrogen between wheat and soil microbes.

Plants primarily take up nitrogen as ammonium and nitrate. Soil microbes are also able to absorb both of these forms.

In a controlled laboratory experiment, scientists cultivated wheat in two agricultural soils. One soil was acidic, while the other was calcareous, meaning it was more alkaline.

The team used nitrogen isotopes to follow the fertiliser nitrogen precisely over time. This allowed them to measure how much nitrogen was taken up by wheat plants and by soil microbes.

“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 from Sichuan Agricultural University.

“Understanding these interactions is essential for developing more efficient and sustainable fertilization strategies.”

Different soils and fertilizer strategies

Wheat responded differently in the two soil types. In calcareous soil, plants displayed a marked preference for nitrate during the first 24 hours after nitrogen application.

Over the same period in acidic soil, wheat showed no clear preference for either ammonium or nitrate. Overall, the crop took up nitrogen more effectively in calcareous soil than in acidic soil.

This contrast is connected to fundamental soil chemistry. Nitrification rates were higher in calcareous soil. Put simply, a greater amount of ammonium was converted into nitrate, which is the nitrogen form wheat generally favours.

Acidic soils, meanwhile, produced conditions that enabled microbes to retain nitrogen more strongly. As a result, soil type influenced which competitor gained the advantage.

Microbes grab nitrogen first

Immediately after fertiliser was added to the soil, microbes moved quickly. They initially dominated nitrogen uptake, responding rapidly and securing a substantial short-term lead.

That advantage was temporary, however. Within 48 hours, wheat had overtaken microbial nitrogen uptake in both soil types. Although microbes took the first share, the crop recovered more nitrogen over time.

Even so, the strength of this competition varied with pH. In acidic soil, microbial nitrogen assimilation remained significantly higher than it was in calcareous soil.

Under acidic conditions, microbes captured almost as much nitrogen as wheat. This points to more intense competition at lower pH levels.

In calcareous soil, by contrast, microbial competition was less pronounced. Wheat was better able to take control of nitrogen uptake.

Soil pH reduces fertilizer loss

Nitrogen fertilisers are vital for feeding billions of people, but they are frequently used inefficiently. Considerable amounts do not reach crops, instead entering waterways or escaping into the atmosphere as greenhouse gases.

If soil pH determines how much nitrogen crops can secure, managing pH is far more than a secondary consideration. It becomes a practical agricultural tool.

Liming and other methods of adjusting soil acidity could allow farmers to balance microbial activity with crop nitrogen uptake.

A better balance may reduce fertiliser waste. In turn, this could lower farmers’ costs and reduce pollution for everyone.

Ultimately, increasing wheat yields may rely as much on controlling acidity as on applying additional fertiliser. The underground competition is genuine, and pH now appears to help determine the winner.

The hidden timing of soil biology

The study also underlines an easily overlooked point: soil is not simply dirt. It is a dynamic system in which plant roots and microbes react swiftly to changes in nutrient availability.

Their approaches change according to soil chemistry and timing. A period of just 48 hours can alter who receives which nutrients.

By understanding this timing and chemistry, scientists and farmers gain fresh insight. They can use it to develop fertilisation practices that work alongside soil biology rather than against it.

The complete study was published in the journal Nitrogen Cycling.