How to achieve a clean bill of health for your soil

Thursday 15.10.2020 , News

Soil health is a key driver of grass production and sub-optimal levels of specific nutrients in the soil will not only limit the production of grass but will determine how cost-effectively that grass can be produced.

Paying attention to soil health by interpreting a recent soil analysis will allow farmers to determine the exact requirement for nutrients in their grassland, which will feed into an effective and efficient fertiliser plan for next spring.

A fertile soil will contain all the major nutrients for basic plant nutrition:

  • Nitrogen (N) – No soil test available
  • Phosphorus (P)
  • Potassium (K)

As well as other secondary nutrients needed in smaller quantities:

  • Calcium (Ca)
  • Magnesium (Mg)
  • Sulphur (S)

Trace elements:

  • Iron (Fe)
  • Manganese (Mn)
  • Zinc (Zn)
  • Copper (Cu)
  • Boron (B)
  • Molybdenum (Mo)

When soil sampling, P and K are the most common nutrients tested for along with soil pH. The most limiting nutrients for plant production are N, P and K. Secondary nutrients can be tested for, but must be specified when submitting soil samples. Generally, there is no need to test secondary nutrients unless you have been advised of a specific problem.

When to sample your soil

While both spring and autumn are noted as the best time of year to take a close look at your soil health, by carrying out soil testing now, you are better prepared come next spring. It is recommended that soil testing is carried out every 2 to 3 years, and at the same time each year but avoid sampling when soils are extremely wet or dry and the advice is to wait 3-6 months after the last application of P, K or slurry to generate an accurate result.

There are 3 elements that contribute to a healthy soil status.

  1. Biological – this refers to living organisms in the soil, including bacteria, fungi, nematodes, earthworms etc. These help to break down litter and cycle nutrients through the soil. Earthworms help create a healthy soil structure by eating decomposing plant material and creating channels through which air and water can permeate.
  2. Physical – this refers to the physical structure of the soil, including particle size and compaction, ability to store water and allow drainage. Good physical structure will enable rain infiltration; reducing runoff and soil erosion while supporting good soil aeration. Good physical structure will also support the root development of plants.
  3. Chemical – this relates to the pH and nutrients in the soil. Organic Matter (OM) is a store of nutrients including N and P which can be made available to the soil through mineralisation. Each percent of OM in soil represents about 1000 kgs of organic nitrogen in addition to other nutrients.

Managing soil health webinar

Considering that a large proportion of soils in Ireland are in poor health status, particularly from a soil pH perspective, the whole area of soil health should be pushed to the top of the farm checklist.

We recently held a webinar on soil health, soil fertility and how to soil sample properly. This webinar can now be watched on YouTube using the link below.

There are also a number of changes coming in 2021, one of which may push a lot of farmers into derogation. Those farms will need a derogation plan with up-to-date soil sample results. Those that go over the 170 organic N per Ha limit and not go into a derogation will be bound by the same regulations as being in a derogation.