Increasing the depth of soil disturbance increases yields of direct drilled wheat on the sandplain soils of Western Australia

Abstract

We evaluated on sandplain soils in the northern wheatbelt of Western Australia in 1990 and 1991 the effect on wheat yields (Triticum aestivum) of increasing the depth of soil disturbance (4-40 cm) while direct drilling. These sandplain soils are easily compacted and eroded by wind, but yields after direct drilling with tined implements are frequently poorer than yields after cultivation. Direct drilling with a tined seeder was compared with: (i) direct drilling with a modified seeder on which the front 3 rows of cultivating tines could be lowered relative to the rear 3 rows of seeding tines; and (ii) with direct drilling followed immediately by deep ripping. Progressively increasing the depth of disturbance reduced soil strength and generally increased grain yields of wheat. Effects on yield were more pronounced in the wetter year of 1991 on an experimental site that had not been previously ripped; responses of 32 kg/ha for each centimetre increase in depth of disturbance were recorded. The highest yields followed deep ripping (3429 kg/ha), and the lowest yields followed minimal soil disturbance using narrow (5 cm) seeding tines working to seeding depth only (2144 kg/ha). These results confirmed that it is possible to use a modified direct drilling technique (thus retaining the advantages of timely sowing after rainfall and lowered risk of wind erosion) and raise yields above those normally expected from direct drilling on these soils.