Soil condition is the most important factor in timing. It should be moist, friable and warm, thus providing the best environment for biological indicators such as earthworms. Typically, this is in autumn before soils get cold or in spring as soils start to warm again. Having a growing or recently senesced crop present will help to assess rooting. Avoid dry, frozen or fully-saturated soils, as this can lead to poor or false diagnosis and worm activity will be low.
You can take a local benchmark of how a healthy soil should look and smell from undisturbed areas at the field edge. Field assessment should start on well-performing areas away from headlands and heavily trafficked areas, then move to areas of concern where crops may be performing poorly to give a contrast. Drones or simpler tools such as Google Earth can help identify crop differences from above.
Dig enough holes to give a good representative sample of the whole field (typically 4-5), particularly on variable soil types.
For a visual evaluation of soil structure (VESS) to assess structural issues and earthworm abundance, holes about a spade’s width and depth will suffice (roughly 20x20x20 cm). Detailed guidance in the form of a do-it-yourself VESS chart can be found here.
Earthworms are a useful indicator of soil health to inform management actions. Five pits should be dug in a ‘W’ pattern across a field, contents hand-sorted, and results recorded. Note the total number of worms and record the presence of surface, topsoil and/or deep burrowing worms. Also check for deep-burrower earthworm signs including surface middens and large, pen-width vertical burrows in and around each soil pit. Guidance is available in Rothamsted Research’s free #30minworms survey booklet and online earthworm identification quiz.
ADAS’s Yield Enhancement Network (YEN) considers that an 11 t/ha wheat crop requires about 330 mm of water between April and July when average rainfall is only 200 mm. Most soils hold between 140-200 mm per 1 m of depth, so good crops need to be well-rooted down to at least 1m to access adequate moisture, even in an average year.
Dig a 1-1.4 m pit in March/April to assess subsoil condition in good and bad areas to inform subsoil management. Look for vertical cracking, deep worm holes and rooting depth.
A good wheat crop should have some roots to 1 m by this time and many roots by early June. The pit should be wide enough to allow comfortable assessment of the soil profile.
A similar visual examination of subsoil structure can be made using the SUBVESS technique, along similar lines to the one for the topsoil.
Recording location and assessment data, and taking photos, are essential for improving soil health, allowing future assessments to be planned and progress related to changes in management practices tracked over time.
There are several services and ‘big data’ initiatives that can help with this. Agronomy groups and consultancy firms such as Hutchinsons and SAC Consulting in Scotland offer comprehensive soil health assessments for farmers.
6 common signs of poor soil health are outlined below:
Below, we’ve listed 7 tips for ensuring a healthy soil structure:
Thanks to the following experts who helped compile this article:
This article is taken from Bayer’s Crop Focus magazine - Spring 2019. If you’d like to subscribe to the magazine click here.
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