What if agricultural soils could provide far more nutrients than scientists and farmers previously believed? A new study reveals that up to 74% of the potassium absorbed by crops can come from mineral reserves that conventional soil tests largely overlook. The discovery challenges traditional fertilizer recommendations and could open the door to more accurate and sustainable farming practices that reduce unnecessary fertilizer use while protecting crop productivity and health.
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 un-accounted 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 scientific 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.
Soil mineral reserves: From geological to agricultural timescales
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.
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