Surface more important than depth

The loosening requirement for winter wheat is overestimated on clay soil, according to field trials investigating different cultivation depths. Shallow cultivation to around 10cm is enough and also saves diesel. A more important factor than depth in ploughless tillage is the smoothness of the soil surface and the ability of the seed drill to cope with harvest trash.

Ploughless tillage is mainly used to save time and money. The potential gains are generally larger with winter tillage than spring tillage. Winter wheat is well suited for a reduced tillage system, the greatest problem being spread of disease from harvest trash on the surface. With a cereal pre-crop, yield of winter wheat is lower in a ploughless system, but with peas or oilseed as the pre-crop the yield is generally the same for ploughed and ploughless tillage.

Balance at 15cm depth

In a ploughless system the topsoil becomes more compacted, since no soil loosening is carried out. This effect can be counteracted by cultivating to greater depth. However, this also increases the fuel consumption and the draught requirement. Trials on medium clay soil for eaxample show that shallow cultivation to 10cm depth gives substantial fuel savings, while deep cultivation to 20cm can result in higher fuel consumption than ploughing if more than one pass is needed. The balance point for cultivation work in two passes corresponding to the diesel consumption in ploughing lies at around 15cm.

Advantage of shallow tillage

Does deeper cultivation increase yield then? The table below shows relative yield for different cultivation depths in Swedish field trials 2006–2011. Mean yield of all crops was on average somewhat lower in ploughless plots than in the ploughed treatment (A). However the difference between deep (B) and shallow (C) cultivation was very small. The results were similar for most crops, including winter wheat – deeper cultivation did not increase yield. There was a certain tendency for greater cultivation depth to increase yield on lighter soils and to decrease yield on heavier soils. This is logical, since light soils generally have a higher loosening requirement.

Swift in field
Cultivator Swift 560

Overestimated loosening requirement

Therefore increasing cultivation depth seldom results in a yield increase, despite the higher mechanical resistance in the soil when it is not ploughed. The loosening requirement generally appears to be smaller than previously believed. However, there are still reasons to increase cultivation depth occasionally, for example to help control perennial weeds such as couchgrass and creeping thistle. It can also be necessary to increase cultivation depth in order to improve seedbed preparation and drilling in the spring if the combine harvester has left deep tracks behind.

Establishment decisive

The actual drilling operation can be a problem in ploughless tillage if large amounts of harvest trash are present. In such cases, the tillage depth must be adjusted to incorporate the trash into the soil. In the first instance, the tillage depth in ploughless tillage should be adjusted to give sufficient incorporation of harvest trash and a sufficiently smooth soil surface. Increasing the working depth of the cultivator to loosen the soil is seldom justified, particularly not on heavy soils.

No benefit of deep tillage

Tillage implement Rel. yield,
methods A-D
Rel. yield,
methods A-C
A. Plough 100 100
B. Cultivator, 10-20 cm 98,8 98,0
C. Cultivator, 5-10 cm 99,2 99,5
D. Disc cultivator, 5-10 cm 96,8 -
Number of trials years 55 93

Table: Relative yield (ploughing=100) produced by ploughless tillage to different depths, all trial years (2006-2011), various crops

The first column shows trials in which all forms of tillage (A-D) were included, and the second shows trials with different cultivator depths (methods A-C). Disc cultivator refers to a disc implement for shallow cultivation (3-7 cm) with a consolidating roller (Väderstad Carrier was used in these trials).

Text: Johan Arvidsson, SLU