Trash distribution and cultivation depth in minimal tillage and direct establishment systems for winter wheat

Abstract

A replicated experiment was conducted at four sites over two seasons to examine the effect of stubble raking and varying degrees of straw incorporation on the subsequent establishment and yield of winter wheat.

In each year two sites followed oilseed rape and two followed winter wheat. Different stubble heights and degrees of loose stubble were achieved by topping the harvested stubble. The loose trash was raked using a zig-zag or comb harrow. Soil was cultivated using a set of heavy discs once to a 7 cm depth or twice to a depth of 12 cm, or seed was direct-drilled with no prior cultivation. This resulted in a range of straw:soil mixtures.

Cultivation treatments (including raking) resulted in varying degrees of straw incorporation, assessed as straw on the seedbed surface. Subsequent establishment of the cereal crop was affected by the degree of cultivation. The poorest establishment was associated with the greatest amount of loose surface trash - achieved by trimming the stubble, not raking to distribute the trash evenly and sowing with a disc drill, which did no additional cultivation. The results were confounded to some extent by the deeper disc cultivation resulting in a loss of soil moisture which caused poorer establishment. Reduced yields observed in two of the eight trials were associated with the poorest establishment.

Raking loose trash should only be necessary if the stubble is short, resulting in a higher level of loose surface trash, or if trash is poorly distributed and the following crop is to be direct-drilled with a drill which does no soil mixing in its own right. In other situations, particularly where chopped straw is well spread behind the combine and some straw:soil mixing is achieved through subsequent cultivation, trash re-distribution will be unnecessary.