This subject is attracting a great deal of scrutiny in the press now and rightly so as many soils have been found to have become depleted in organic matter. More specifically those in arable rotations where animal manures, green manures and grassland have not been included often have become low in humus and consequently have become less healthy than they should be. Managing land to correct these deficiencies is now often referred to as ‘regenerative farming’.
Optima Excel assesses several hundred soil cores each year and carries out analysis to assess the biological, physical and chemical health of each.
A biological measure assesses the bacterial activity of soil microbes usually testing for the volume of carbon dioxide being released from a sample. This method is used because most desirable bacteria are aerobes and the more active, they are the more carbon dioxide they release. However, where soils are low in organic matter, compacted, waterlogged or starved of oxygen their activity is impaired. A good indicator of soil health is earthworm activity although assessing this is not as straightforward as it might seem, as there are several species of earthworm that are active at different depths in the soil profile.
A chemical analysis involves measuring the levels of available crop nutrients although may on occasions also include testing for potentially toxic ones. All soil analysis tests should include pH and available levels of phosphate, potash and magnesium. Other tests might include those for organic matter, calcium, sulphur and nitrogen although these results are to be regarded with a degree of caution as they can vary quite quickly within a short period of time. More commonly an estimate of soil nitrogen supply can be made using the ‘SNS’ system described in RB209.
It is also possible to assess the ‘Cation Exchange Capacity’ (CEC) of the soil as this is critical to learning how well major nutrients are retained. Soil sampling is best done in the spring or autumn when soils are damp and plants and temperatures over 8C. Avoid sampling in frosty, drought or waterlogged conditions.
A physical analysis of soil involves not only the dissemination of soil particle sizes into coarse sand, find sand, silt and clay but also and assessment of compaction and evidence of ‘panning’ caused by machinery and livestock. One of the most basic tests is to try putting a spade or fork in the ground when the soil is moist. If it won’t go in using natural bodyweight then there may well be a problem.
All three of the above assessments can be key to managing healthy soils and where crop rotations have become polarised into limited groups much as only oilseed rape and cereals or where certain cultivation methods have been used to excess all three examinations should be made.
Most importantly, obtain advice from a FACTS qualified adviser as he or she is obliged to keep up to date with the latest research and advice on all aspects of soil health and crop nutrient management.
Table 1 illustrates the results of the soil tests made by Optima Excel over the past three years on a wide range of farms and soils growing a wide range of crops. The results are indicative of the need to ascertain the nutrient supply for each crop; what suits one crop will not suit another!
Table 1:
Number of samples taken: 1016.
Proportion of soils with pH below optimum for crop type: 62%
Proportion of soils with level of ‘P’ below Index 2: 61%
Proportion of soils with level of ‘K’ below Index 2: 46%
Proportion of soils with level of ‘Mg’ below Index 2: 16%
The advisory service at Optima Excel considers all aspects of soil health when considering how best to manage physical, biological and chemical treatments thereby avoiding ‘inadvertent’ or misplaced practices.
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