Effects of sunflower residues and tillage on winter wheat

Abstract

Wheat ( Triticum aestivum L.) and sunflower ( Helianthus annuus L.) offer oppurtunities for double-cropping but little is known about possible effects of sunflower residues on wheat in a cropping sequence. In this study, we have investigated effects of sunflower extracts and residues on wheat germination, growth and yield. Wheat germination in a soilless medium was not affected by aqueous extracts of sunflower residues; however, stem and leaf extracts (1:10 dilution) of dried sunflower tissues did inhibit dry-weight gain of 5-day-old wheat seedlings by 20–40%. In greenhouse studies, ground leaves or forage-chopped shoots, when surface-applied, promoted wheat growth. Wheat tissue had significantly greater N in wheat grown with ground leaf residues. Forty-day-old wheat grown in pots with incorporated, chopped sunflower residues had only one-third the dry weight of plants with the same amount of residue on the soil surface. Chopped sunflower residues equivalent to 6.9 Mg/ha suppressed weed numbers by 50% if incorporated, and ground leaf material surface-applied at 15 Mg/ha reduced weed populations by approximately 75% when compared to residue-free treatments. In a split-plot study, wheat was grown following sunflower or fallow. The plot splits were managed as either no-till (residues on surface) or conventionally tilled (residues incorporated). Wheat grain yields were higher in the no-till treatments (5.2 Mg/ha) than in the conventionally tilled treatments (4.9 Mg/ha). Residue applications rates did not affect grain yields. Overall, the results suggest that sunflower residues can inhibit early wheat and weed growth and that incorporation of residues may reduce grain yields, but no-till production of wheat following sunflower appears viable.