Optimizing Boron Nutrition in Peanut (Arachis hypogaea L.): Effects of Soil and Foliar Applications on Yield, Seed Quality, and Mineral Composition

In the sun-drenched fields of the Mediterranean, where summer heat bakes the earth and winter rains arrive late, farmers grow a crop that is as much a source of protein as it is of oil: the peanut. This legume is a marvel of agricultural engineering, sending its flowers above ground but burying its developing pods beneath the soil to mature. For this underground growth to succeed, the plant relies on a delicate balance of nutrients, much like a human body needs a specific mix of vitamins to function. Among these essential elements is boron, a trace mineral that acts as a structural glue for plant cells and a vital signal for reproduction. Without enough boron, a peanut plant may flower but fail to fill its pods, leaving farmers with empty shells and hollow hearts inside the seeds. However, boron is a fickle partner; too little starves the crop, but too much can poison it. The challenge for growers is finding that narrow, perfect window where the soil provides just enough of this nutrient to support a bountiful harvest without tipping the balance into toxicity.

Researchers in southern Turkey set out to solve this puzzle for peanut farmers working in similar dry, alkaline soils. They wanted to know the best way to deliver boron to the crop: should it be mixed into the soil before planting to feed the roots over time, or sprayed directly onto the leaves during the critical flowering stage to give the plant a quick boost? To find the answer, they planted a specific variety of peanut known as Ayşehanım across a large field in the Adana region. They divided the land into plots and applied different amounts of boron to the soil, ranging from none at all to very high doses. In a separate set of treatments, they sprayed some of these same plants with a liquid boron solution during their reproductive phase, while others received no spray. Over two growing seasons, they carefully tracked how many pods formed, how heavy the seeds were, and how much oil and protein they contained, while also analyzing the chemical makeup of the plant leaves to see how the nutrients moved through the system.

The results painted a clear picture of what works best for these conditions. The researchers found that adding boron to the soil made a significant difference, but only up to a point. When they applied a moderate amount, specifically between two and four kilograms per hectare, the peanut plants produced their best yields. These moderate doses increased the total weight of the harvest, improved the number of healthy pods, and boosted the amount of oil and protein the plants could generate. The plants grown with this moderate soil treatment were robust and productive. However, when the researchers applied the highest dose of boron, eight kilograms per hectare, the yield did not continue to climb. In fact, the plants with the most boron in their tissues did not produce the most peanuts. This confirmed that simply flooding the soil with more of the nutrient does not help; once the plant has enough, extra boron becomes useless or even counterproductive, failing to translate into more food.

While the soil application was the primary driver of success, the leaf sprays played a supporting role. The plants that received the foliar spray showed some improvements, particularly in the quality of their protein and a few other specific traits. Yet, this method was not as consistent or powerful as feeding the roots through the soil. The spray acted more like a helpful supplement during the busy flowering season rather than a complete solution. The study showed that relying on the spray alone, without adequate boron in the soil, would not be enough to maximize the harvest. The most successful approach was a combination where the soil provided a steady, moderate foundation of nutrients, and the spray offered a targeted boost when the plant was most vulnerable.

The analysis of the plant tissues revealed another important lesson about balance. The plants that produced the most peanuts did not necessarily have the highest concentration of boron inside their leaves. Instead, they had a more balanced mix of minerals, including copper, magnesium, and zinc. The highest-yielding plants were those that managed to keep their internal chemistry in harmony. When the soil was overloaded with boron, the plants absorbed it, but this did not lead to better growth; it simply meant the plant was holding onto an excess that it could not use. This suggests that the goal of farming should not be to pack the plant with as much of a single nutrient as possible, but to create an environment where all the necessary elements work together smoothly.

For farmers in this region, the takeaway is practical and precise. To get the best harvest from peanuts grown in slightly alkaline, dry soils, the most effective strategy is to apply a moderate amount of boron to the soil before planting. This amount, roughly two to four kilograms per hectare, provides the sweet spot where the crop thrives. Adding more than this is a waste of resources and offers no extra benefit. A spray on the leaves can be used as a helpful addition during the flowering stage to fine-tune the plant's performance, but it cannot replace the foundation built by the soil. By focusing on this balanced approach, growers can ensure their peanuts fill out fully, producing high-quality seeds rich in oil and protein, while avoiding the risks of over-fertilization.