Differential response of weed and crop species to potassium and sulphur fertilizers

Fertilization may affect the relative competitive ability of weeds and crops if the growth response to fertilizer differs among species. Greenhouse studies were conducted to evaluate the relative biomass yield response of 19 weed species and the crops canola (Brassica napus L.) and spring wheat (Triticum aestivum L.) to potassium (K) and sulphur (S) fertilization. Seven weed species showed a significant increase in biomass production at 6 wk with K fertilization, but biomass production of canola and wheat did not increase with K addition. Sulphur fertilizer increased the biomass production of canola, flixweed (Descurainia sophia L.) and wild mustard (Sinapis arvensis L.), three of the four Cruciferae species evaluated, as well as that of hairy nightshade (Solanum sarrachoides Sendtner), round-leaved mallow (Malva pusilla Sm.) and stork's-bill [Erodium cirutarium (L.) L'Her. Ex. Ait.]. Sulphur fertilizer did not increase the biomass production of spring wheat or of any grass weed species. The data from the greenhouse study support the concept that fertilization may shift the relative competition between a crop and the weed population if the weeds are more responsive than the crop to the type of fertilizer applied. However, this concept should be tested under field conditions.