Approaches for Improving Crop Competitiveness Through the Manipulation of Fertilization Strategies

Weeds are often more competitive with crops at higher soil nutrient levels. This can result in increased de- pendency on herbicides and tiliage to maintain adequate weed control. A number of studies have shown weeds accu- mulate higher concentrations of nitrogen, phosphorus, po- tassium, calcium, and magnesium than crops, thus depleting soil nutrient levels more quickly and reducing crop yield. Understanding basic mechanisms and timing of nutrient uptake in weeds and crops can lead to fertilization strategies which will enhance the competitive ability of crops while reducing interference from weeds. Such strategies can in- clude deep band application of fertilizers to the crop row, as opposed to broadcast applications. Banding techniques also reduce the potential for nitrate contamination of surface or groundwater. The addition of nitrification inhibitors or in- creasing the proportion of nitrogen as ammonium or urea in fertilizer mixtures can restrict growth of ammonium- or urea-sensitive weeds. The timing of fertilizer applications can take advantage of maximal rates of nutrient uptake into crop roots at specific developmental stages. In addition, nutrient use efficiency can be enhanced by choosing appropriate crop cultivars, maintaining effective weed control practices, or altering row spacing or seeding rate to increase accumulation of nitrogen, phosphorus, and potassium in crops. Additional index words. Banding, competition, ecophysiology, fertilizers, nitrogen, nutrient uptake.

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