Spring 2010 worm counts comparing a ploughed field with direct drilling

April 23, 2010

Two fields were compared, Hornfield – ploughed and power harrowed, sown to winter wheat, and Cobb Hill – direct drilled to OSR.  Both fields have reddish brown slightly stony silty clay loam soils with coarse prismatic or blocky subsoils.

Worm counts were carried out using the Visual Soil Assessment method (Landcare Research, 2000).  Numbers of worms in a 20cm3 soil sample were counted over a 5 minute period.  Penetrometer readings were taken to assess soil compaction at each sample site and a visual note of soil structure in each soil sample was made.  Five sample sites were tested in each field.

The results below include the penetrometer readings taken in Cobb Hill in October 2009 for comparison.

Average penetrometer readings (MPa)

at depth:



April 2010

(Ploughed and power harrowed. Planted with winter wheat)

Cobb Hill

April 2010

(Direct drilled to OSR)

Cobb Hill

October 2009

(Direct drilled to OSR)

5 0.5 1.4 1.4
10 0.6 1.7 2.1
15 0.7 1.7 2.7
20 1.0 1.8 2.8
25 1.4 1.9 3.0
30 1.7 2.3
35 2.1 2.6
40 2.4 2.7
45 2.6 3.0
Average number of worms in 20cm3 soil

(range 2 – 20)


(range 29 – 43)

per m3 equivalent 315 860


Topsoil structure in Hornfield was coarsley granular but rather wet and easily smeared.  The subsoil became increasingly compacted with depth but had a good blocky structure.  Numbers of worms in each sample were variable, the worms were rather small in size and were found in the upper 20cm of the soil profile.

The soil on Cobb Hill was compacted, especially below 10 cm depth.  The majority of the worms found were in the top 10cm of the soil profile where the soil structure was good, coarse granular.  Below 10 cm depth the soil formed a typical argillic clay enriched B-horizon, generally having a coarse prismatic or blocky structure but with horizontal plates in parts.

General analysis / comment:

There is a clear difference in worm numbers between the two fields, with much higher numbers of worms in the direct drilled field.  This is probably because of the previous year’s crop debris (organic matter) available in Cobb Hill (direct drilled) for the worms to feed on.  Organic matter from the previous year’s crop debris has been ploughed in in Hornfield.  Cultivations carried out in Hornfield will also have disturbed the worm ecosystem, reducing numbers.

Soil structure in the two fields reflects management.  Hornfield (ploughed and harrowed) has a much looser soil structure compared with Cobb Hill (direct drilled) with little compaction until below 30cm depth.  Previous examination of Cobb Hill had already identified the soil compaction in this field, and the apparent easing of the compaction between the October and April readings will be because of the increase in moisture content in the soil after the winter (which allows easier penetration of the penetrometer) and not a reduction in the soil density.

The higher worm population in Cobb Hill will be responsible for the good soil structure in the upper 10cm of the soil profile and their activities will be increasing organic matter content so increasing the moisture and nutrient retaining capacity of the topsoil.  However the compaction lower down the soil profile will be reducing the potential of the crop roots to exploit the full depth of the soil profile.  A point for debate is whether the increased worm population in Cobb Hill and the improvement they will make to the topsoil makes up for the compaction and reduced root exploitation lower down in the soil profile.

Dr. Nancy Oakes conducting a worm count


One Response to “Spring 2010 worm counts comparing a ploughed field with direct drilling”

  1. oli on April 24th, 2010 4:34 am


    Interesting to see these results… i am surprised to see such a difference in worm numbers, this i think bodes well for the future, and i am equally surprised at the lack of difference in the penetrometer readings… sure the ploughed field has lower readings (as one would expect) in the top 15cm of soil (i’m guessing this is approximate ploughing depth) but the change in six months of the meter readings for Cobb Hill are significant… will be interesting to see the penetrometer readings at harvest time, i think you will be surprised at how close they are to the ploughed field… and this is just one year of not till… it should get better (at least that is what they tell us)

    nb. Spring has arrived on the Canadian Prairies… on in the field yet, but hope to be planting by May 1st… soil temperature is slowly warming up, but not up to my preferred 10C yet. I’m still in the process of fitting the liquid fertilizer kit to the drill, but should be done that in the next few days. I seem to be doing a lot of welding to the machine this year… i hope my modifications are strong enough.

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