This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A new study led by Dr. Shikma Zaarur of the Hebrew University of Jerusalem, in collaboration with Dr.
Ran Erel of the Agricultural Research Organization–Volcani Institute, reveals that agricultural soils may contain a substantial unaccounted-for reservoir of potassium, an essential nutrient for plant growth, that is largely overlooked by conventional soil testing methods. The findings could pave the way for more precise fertilizer recommendations, potentially reducing unnecessary fertilizer use while supporting sustainable agricultural production. Published in the journal Plant and Soil, the research challenges a long-standing assumption in agricultural management: that the potassium measured by standard soil tests accurately reflects the amount available to crops.
Potassium is one of the three major nutrients required for plant growth, alongside nitrogen and phosphorus. Farmers routinely apply potassium fertilizers to maintain crop productivity, with recommendations commonly based on measuring the soil's readily available, or "exchangeable," potassium. However, the new study demonstrates that this conventional approach may significantly underestimate the soil's natural capacity to supply this essential nutrient.
The research team conducted a 13-month greenhouse experiment using three agricultural soils characteristic of Israel's Mediterranean environment: clay-rich soil from the coastal plain, loess soil from the western Negev and red sandy soil from the Rehovot area. The researchers grew alfalfa, a crop with particularly high potassium requirements, and harvested it 16 times under intensive growing conditions. By carefully tracking potassium uptake and changes in soil chemistry, they discovered that plants absorbed between two and nearly four times more potassium than could be explained by conventional measurements of readily available potassium and natural inputs.
The researchers found that 50% to 74% of the potassium taken up by plants grown without additional potassium fertilizer originated from non-exchangeable soil reserves—potassium bound within minerals that have long been recognized as potential nutrient sources, but whose release was generally assumed to occur too slowly to contribute significantly within agricultural growing cycles. "Our findings show that soil is not simply a passive reservoir of nutrients, but a dynamic system that continuously responds to plant demand," said Zaarur. "As plants take up potassium, minerals in the soil can release additional supplies much faster than previously assumed.
Understanding this natural process could help us develop more accurate fertilization strategies, reducing unnecessary inputs without compromising crop productivity." The study also revealed important differences between soil types. Clay-rich soil showed little improvement in overall plant biomass following potassium fertilization, suggesting that its natural mineral reserves were largely able to sustain crop growth during the experiment. In contrast, potassium fertilization increased biomass by approximately 13.5% in the potassium-poor red sandy soil.
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