Weed Infestations in Wheat Cropping Systems as Affected by Crop Residues and Their Management Practices

Abstract

ABSTRACT Weed infestations in wheat crops as affected by different crop residues and their management practices were studied for three years in a field experiment in New Zealand. Treatments applied in the first year were four crop residues (white clover, perennial ryegrass, wheat or peas) each subjected to one of four management practices (burning, ploughing, rotary hoeing or mulching). These treatments were not repeated in subsequent years of the experiment. Half of the experiment received nitrogen fertilizer in the third year. Wheat was sown each year and its grain yield and total dry weight of weeds were determined. In the third year, species composition of weeds was also studied. Significant interactions were found in the first year between crop residues and management practices on weeds and wheat yield. After clover and wheat, dry weight of weeds was highest in the mulching treatment while ploughing reduced weed dry weight significantly. In the second year, dry weight of weeds was not significantly different between crop residues but was significantly higher under previous year's mulching treatment. Total dry weight of weeds was not affected by treatments in the third year but weed species were affected. The addition of nitrogen fertilizer increased the density of wild oat (Avena fatua L.) and dry weight of annual poa (Poa annua L.), field speedwell (Veronica arvensis L.) and some broadleaf weeds, but reduced the density of field speedwell, yarrow (Achillea millefolium L.) and browntop (Agrostis capillaris Sibth.) and dry weight of scentless chamomile (Matricaria inodora L.). Implications of these results in designing an integrated weed management strategy for wheat in low-input systems are highlighted.