Soil sampling is an essential tool in understanding the nutrient availability of soils, but unless the results are interpreted correctly, it could be a waste of money.

That is according to Simon Francis, technical and services manager for agronomy firm, ProCam.

He explains that not only is soil sampling required for farm assurance compliance purposes and to meet the statutory requirements of an increasing number of SFI schemes, but it is also time well invested in ensuring crops can perform to their full potential.

See also: How to make a comprehensive soil profile on-farm

However, unless soils are sampled and tested in a timely and accurate way, and the results interpreted appropriately by an experienced agronomist, it is unlikely the investment in soil sampling will generate a viable return.

Assessing the nutrient status

“Sampling prior to sowing any crop is key, as it provides an essential opportunity for growers to assess the nutrient status of soils and to make plans to redress any identified imbalances or deficiencies,” Simon explains.

He recommends each field should be tested at least every four-five years: “Generally, there’s no need to sample more frequently unless there’s a specific reason such as a change of cropping or land use.

“In extreme cases, for example where continuous high rainfall or an extended period of waterlogging has caused nutrient stores to be depleted due to leaching, increasing the frequency of testing could prove useful.

“Another example could be where a lack of organic matter prevents nutrients from being retained, thus causing leaching losses to be exacerbated.”

In addition, water logging also compromises root development, affecting a crop’s ability to access nutrients, so understanding what is available to the crop during the early stages of development is vital to maximise potential.

“Irrespective of the soil type, the very least growers should be doing is to test each field to build a basic picture of the farm’s P, potassium (K) and Mg indices as well as pH and organic matter: testing organic matter content can provide a good indicator of general soil health, from which it is possible to begin to understand the soils capacity to retain both moisture and nutrients,” Simon continues.

Macro- and micro-nutrients

Beyond this, the next step is to build a more comprehensive understanding of the macro- and micro-nutrients available to plants, so that a tailored nutrient programme can be drawn up proactively rather than reactively during the season, he advises.

ProCam says its SoilSense service takes soil testing to the next level by analysing not only the chemical composition of soil, but also the wider availability of micro- and macro-nutrients.

“The service also provides an in-depth picture of physical soil health and an advanced understanding of other key indices such as soil carbon, cation exchange capacity and structure,” says Simon.

ProCam says that armed with this level of detail, growers will not only remain compliant with the basic crop assurance requirements plus any additional information required by the various SFI schemes, but will also be able to work with their agronomist to develop a clear and detailed nutrient programme that ensures each crop in the rotation has access to the full complement of nutrients.

“For growers who want to take things even further, an analysis of the soil’s biological constituents including protozoa, mycorrhiza and saprophyte populations as well as positive and negative bacteria population dynamics can be assessed to give a full appreciation of the soil’s health,” Simon concludes.