Hidden Soil Nutrients Could Mean Lower Fertilizer Bills for Farmers, Study Finds

Jerusalem, 9 November, 2026 (TPS-IL) — Farmers may be spending money on fertilizer their fields don’t actually need. Israeli researchers have found that crops can draw substantial amounts of potassium from natural soil reserves that conventional tests largely overlook, potentially opening the door to lower fertilizer costs and more precise agricultural practices.

The findings could eventually help farmers reduce fertilizer costs and avoid unnecessary applications while maintaining crop productivity. In an interview with The Press Service of Israel, the researchers discussed the implications for farmers, explained why conventional soil tests may need to be rethought and cautioned against cutting fertilizer use too aggressively.

The study, led by Dr. Shikma Zaarur of the Hebrew University of Jerusalem found that soil minerals supplied between 50% and 74% of the potassium absorbed by plants grown without additional potassium fertilizer. The finding challenges a longstanding assumption that these mineral reserves release nutrients too slowly to make a significant contribution during a crop’s growing season.

Potassium is one of three essential nutrients for plant growth, alongside nitrogen and phosphorus. Farmers routinely apply potassium fertilizers to maintain crop productivity, with recommendations generally based on measurements of the nutrient readily available in the soil.

But conventional tests largely overlook potassium bound inside soil minerals. Although scientists have long recognized these reserves as a potential nutrient source, their contribution was generally considered too slow to matter significantly during agricultural growing cycles.

The new findings suggest that as plants absorb readily available potassium, minerals replenish the supply much faster than previously assumed.

A Hidden Source of Plant Nutrition

To investigate, the research team, which included Dr. Ran Erel of the Agricultural Research Organization’s Volcani Research Center and researchers from the Geological Survey of Israel and Ben-Gurion University of the Negev, conducted a 13-month greenhouse experiment.

The researchers grew alfalfa, a crop with particularly high potassium requirements, in three types of agricultural soil characteristic of Israel: clay-rich soil from the coastal plain, loess soil from the western Negev and red sandy soil from the Rehovot area. They harvested the plants 16 times under intensive growing conditions while monitoring potassium uptake and changes in soil chemistry.

The plants absorbed between two and nearly four times more potassium than could be explained by conventional measurements of readily available potassium and natural inputs. Between 50% and 74% of the potassium absorbed by plants that received no additional potassium fertilizer came from the overlooked mineral reserves.

The researchers said the scale of the contribution was greater than they had anticipated, although earlier studies had provided clues that plants could access potassium beyond what standard tests measure.

“We expected the soils to supply more potassium than the standard test predicted,” Zaarur and Erel told TPS-IL. “But I did not expect the contribution from soil minerals to be as large as it was.”

They said the research also demonstrated how quickly mineral weathering — the natural process through which minerals release nutrients — can accelerate in response to sustained crop demand. The team used geochemical tracers to identify the mineral reserves supplying the additional potassium.

The researchers also found that different soils responded differently to fertilizer. Adding potassium produced little improvement in overall plant growth in the clay-rich soil, suggesting its natural reserves could meet much of the crop’s needs during the experiment. In contrast, fertilizer increased plant biomass by approximately 13.5% in the potassium-poor red sandy soil.

Precision Fertilizing

The findings could lead to more sophisticated soil tests that measure not only how much potassium is immediately available to plants, but also how much can be released naturally from soil minerals during a growing season. Such tests could help agricultural advisers tailor fertilizer recommendations to individual fields rather than relying primarily on conventional measurements.

The researchers said the findings could have international relevance because alkaline, calcium-rich soils similar to those studied are common throughout the Mediterranean and Middle East, as well as parts of North America and Europe.

“We think, and hope, that these findings could benefit many farmers in many countries,” they told TPS-IL.

However, they warned against interpreting the study as a reason to abandon potassium fertilization. Every harvest removes potassium from the soil, and relying too heavily on natural reserves could eventually undermine long-term fertility.

“Continually removing more K than is replaced could eventually deplete soil fertility and potentially affect other soil properties as well,” they said.

The researchers are now interested in developing more accurate and affordable soil tests, but emphasized that the findings must first be examined under field conditions and across different crops and soil types. They hope to make progress toward practical testing methods in the coming years.

The study was published in the peer-reviewed journal Plant and Soil.