Tillage and growth of a wheat crop in a loamy sand

Abstract

In the fourth consecutive year of a long-term tillage trial in a loamy sand in Western Australia above- and below-ground growth of a wheat crop (cv. Gamenya) was monitored. The grain yield was nearly 20% greater in the crop sown after ploughing than in those crops sown by direct drilling. A similar trend had been noted in each preceding year. Cumulative water use was 15 and 9 mm less with zero and minimum tillage than with ploughing. The ploughed treatment had lower soil strengths, not only in the seedbed but also to 50 cm in the subsoil, until 8 weeks after seeding. These lower soil strengths coincided with more-rapid wetting of the subsoil under ploughing, and faster root extension rates. Dry matter production was significantly greater in the ploughed crop from the initial sampling date, and direct-drilled crops were not able to compensate in the later part of the season, despite using slightly more water during that period. The slower wetting of the profile under direct drilling was a persistent feature over several seasons in this soil type. It was considered responsible for the increased soil strength and slower root extension rates. The implications of direct-drilled sandy soils for crop productivity, and drainage control of recharge soils in saline catchments, are discussed.