Finger-harrowing of durum wheat under different tillage systems

The effect of finger-harrowing (FH) on weed control and yield of durum wheat (Triticum durum Desf) grown under conventional tillage (CT) or no-tillage (NT) was studied in 1995-96. Mechanical weeding-eight combinations between four tine adjustments and two treatment intensities (one or two passes)-was compared with post-emergence herbicide spraying and an unweeded control. Tine working depth was higher in CT than in NT due to lower soil dry bulk density, and increased with the theoretical aggressiveness of tine adjustments, but its correlation with short- and long-term effects on crop and weeds overall was poor, suggesting that tine adjustment was not a major factor involved. In 1995, durum wheat grain yield in FH was very low, because of high weed development in both tillage systems. In 1996, lower weed pressure resulted in FH grain yield, on average 3982 kg ha(-1) for CT and 2809 kg ha(-1) for NT, comparable with that obtained with herbicides. Durum wheat grain yield and weed biomass were much more affected by tillage system than by tine adjustment or harrowing intensity, and seemed mostly dependent on the lower crop competitive ability in NT, caused by reduced emergence, higher weed abundance and presence of aggressive weed species, Ammi majus in 1995 and Lolium multiflorum in 1996. Dependence of FH effect upon soil and weed conditions encountered seasonally in the two tillage systems suggests that, in low-input durum wheat, mechanical methods alone would not always guarantee adequate weed control and grain yield.