The Effects of Herbicide on Nutrient Uptake

Types of Herbicides

• Farms use two main types of herbicides: selective and nonselective. Selective herbicides target and kill certain weeds without seriously harming the desired crop. Nonselective herbicides kill all plants they come in contact with. Even selective herbicides are apt to damage crops or turf when applied at the incorrect time, under certain environmental conditions or in excessive dosages. Herbicides may improve or decrease nutrient uptake of plants, depending on the type of chemical, environmental conditions and plant species involved.

Decreased Nutrient Uptake

• Glyphosate, one of the most widely used herbicides in the world, has been frequently observed to reduce uptake of iron, zinc and manganese in many plants, including sunflowers and soybeans. This effect was even observed in soybeans with a designed resistance to glyphosate. Some herbicides diminish root growth in such a way that their presence impedes a plant's ability to absorb certain nutrients.

  An Oxford study found that the herbicide chlorsulfuron affects the growth of fine roots in wheat and barley plants and diminishes their ability to absorb zinc, copper and manganese. As an immobile nutrient, zinc depends on large root surface area for uptake. Mobile nutrients such as calcium and magnesium are not as seriously diminished because they do not require the same uptake mechanism. Wheat grown in soil with low zinc levels are especially susceptible to this problem with chlorsulfuron.

Increased Nutrient Uptake

• Certain herbicides improve a plant's ability to absorb nutrients but may damage the plant's growth abilities. In a study published in the journal "Communications in Agricultural and Applied Biological Sciences," the application of metribuzin, metobromuron and chlomazon herbicides improved phosphorous and potassium uptake among various potato varieties but diminished shoot weight. Nitrogen uptake improved in some potatoes treated with metribuzin herbicide but decreased tuber weight in the study. The results indicate that while nutrient levels were higher in treated potatoes, total weight was lower. Plants treated with these herbicides may have difficulty using nutrients for growth.

Improving Nutrient Uptake

• Proper application and ideal environmental conditions are necessary for successful herbicide use. When using glyphosate, select crops that are efficient in nutrient uptake, and ensure adequate levels of nutrients by amending with manganese, copper and zinc following application. Herbicidal effects are complicated in plants and are not well understood in humans. For these reasons, growers can benefit from other methods of weed control that do not involve chemicals, such as mulching and manual removal.