The interaction of nutrients and tillage methods on wheat and weed development

Abstract

This study evaluated the relative performance of spring wheat under direct drill in comparison with more conventional tillage methods, under a wide range of nutrition treatments and in the presence of an aggressive weed component, Phalaris aguatica (syn. tuberosa). Four tillages were applied: conventional fallow; direct drilled plus pre-emergence grazing; direct drilled plus the pre-sowing herbicide glyphosate; and reduced tillage. There were five levels of phosphorus and two of nitrogen, and a post-emergent herbicide 2,4-D was applied to half of the plots. Growth of crop and weeds was measured at six stages of development, together with final yields. Nitrogen and phosphorus uptake and concentration were measured throughout development. Plant nutrients were not released as efficiently with direct drilling as cultivation. Crop plants in direct drilled were not only deficient in nitrogen but also in phosphorus during early development, whereas cultivation ensured that high nutrient levels were attained in fallow plots. Direct drilled plots did not appear to recover completely from this initial deficiency unless fertilized and freed from weed competition. When weeds were controlled, yields of direct drilled plots were comparable with yields of fallow at higher levels of phosphorus and nitrogen, because at these high nutrient levels yields in fallow were suppressed. However, weed competition and/or poorer nutrition lowered direct drill yields. It was concluded that direct drilling requires a new approach, sensitive to the changed agronomic conditions that it engenders. Competition with weeds may be avoided by choosing a vigorous cultivar, avoiding dominant weed species and using herbicides strategically and economically. A high plane of nutrition proniotes the success of direct drilling.