Response by wheat, rape, and field peas to pre-sowing herbicides and deep tillage

Abstract

A field experiment near Yass, N.S.W., in 198 1 and 1982 compared several forms of deep tillage (loosening of the soil to depths from 15 to 60 cm, with little surface disturbance) following the application of various herbicides, on the growth and yield of wheat, rape, field peas and weeds. The deep tillage implements used were: Wallace Soil Reconditioning Unit, Domino Sub Tiller, and single tine ripper, cultivating to depths from 15 to 60 cm. The herbicides used were: glyphosate (Roundup at 1 L/ha), paraquat-diquat (Sprayseed at 2 L/ha) and paraquat-diquat (Sprayseed at 2 L/ha) plus dicamba (Banvel 200 at 0.4 Wha). A fallow treatment also was used in 1982. Crops, and weeds-which were a mixture of grass and broad-leaf species-responded more strongly to herbicide than to deep tillage treatments. At the rates used, paraquat-diquat plus dicamba controlled cereals more efficiently than did the other herbicides. The responses were generally increased growth of wheat and rape-field peas being much less responsive-and decreased growth of weeds. In 198 1, a year of average rainfall, herbicide (meaned over deep tillage treatments) increased wheat grain yield by 1.94 t/ha (1.8 1 v. 3.75 t/ha) and deep tillage (meaned over herbicide treatments) by 0.60 t/ha (2.81 v. 3.41 t/ha). In 1982, a year of below-average rainfall, fallow increased wheat grain yield by 1.67 t/ha (0.18 v. 1.85 t/ha), herbicide by 0.73 t/ha (0.18 v. 0.91 t/ha) and deep tillage by 0.36 t/ha (0.69 v. 1.05 t/ha). Covariance analyses indicated that, for all wheat crop parameters measured in 198 1, responses to both deep tillage and herbicide were strongly related to reduction in weed top growth, this effect being greater with the herbicide treatments than with the deep tillage treatments.