The agronomic benefits of analysing soils
NRM
Agriculture
Many of the agronomic benefits of measuring soil texture and available nutrient content are taken for granted as we have been testing soils for many years. From time to time, it is useful to reflect on the significant advantages gained for crop production. Today, the need to improve nutrient use efficiency and optimise both yield and quality is even more important, so there is no better time to reassess the benefits of soil analysis. A fantastic way of doing this is by testing soils for both macro (potassium, phosphorus and magnesium) and micronutrients—and not just pH. These are referred to as broad spectrum results.
The advantages of broad spectrum results
Broad spectrum results, especially when viewed in the context of the soil texture, the proportion of sand, and the silt and clay content of a particular field, help to provide a more complete picture. A deficiency of just one micronutrient can impact crop performance and undermine investment in applied macronutrients such as nitrogen.
Consider the impact of the lack of boron in root crops, causing heart rot, browning of cauliflowers, cracking of apple skins, and the disintegration of the soft parts of fruit. Brassicas, especially when rooting is restricted, can suffer from split stems, reducing yield and crop quality. These deficiency symptoms are most likely in coarse and sandy soils, and so knowing the texture of each field will enable deficiency risks to be anticipated.
The availability of a micronutrient is strongly influenced by soil pH: some are more available in acidic conditions, such as manganese, and others in alkali conditions like magnesium. This means that routine pH monitoring is critical to improving nutrient uptake and overall nutrient use efficiency. Due to micronutrients being required in very small quantities, anticipating deficiencies, and taking action to improve availability of nutrients and maintain optimal yields, is extremely cost effective. Targeted broad spectrum analysis is the first step in managing and improving productivity.
The link between soil health and nutrient availability
High clay content soils may hold substantial quantities of phosphate, but how much is available to plants? To optimise access to phosphate, the roots of all crops need to proliferate freely, which is only possible in well-structured, healthy soil. In soils with high levels of microbial activity, there will also be the opportunity for phosphate solubilising bacteria to increase the crop-available phosphate pool. So, maintaining soils at the optimal pH for the crop with good organic matter levels and adequate aeration will provide the ideal conditions for a healthy soil.
A healthier soil will support high levels of microbial activity that enhances nutrient release and crop uptake, building system resilience to maintain higher yields. Soil organic matter content is critical to a functioning soil system and should be monitored frequently to determine the impact of any management change.
Rothamsted trial results undertaken over many years have shown that adding fresh phosphorus to compensate for low soil indices has limited effect on optimal yield for the crop grown in the year of application. A system of replacing the nutrients removed by the crop and maintaining target indices (index 2 for cereals) provides the best opportunity to consistently produce higher yields. Providing the ideal conditions for inherent soil phosphorus to be solubilised, especially in heavier soils, as well as high microbial activity, is essential. A healthy functioning soil can reduce fertiliser costs, but soil supplies must be monitored to ensure nutrient availability is maintained.
How NRM can help
Soils at or above target index for both phosphate and potash will support good yields. However, indices will slowly decline if no fresh P or K is replaced. The rate of decline is very dependent on soil type and the quantities of nutrients removed by the crop, but eventually soil levels will need to be replaced before yield is compromised. Regular monitoring is key to avoiding a crash in soil indices. Balancing nutrient applications with soil reserves must begin with a good knowledge of all the available nutrients in each field. Contact NRM or your agronomist to arrange for your samples to be analysed.
NRM has also recently published its annual soil summary and interactive soil map for 2020-2021, allowing farmers and their advisors to understand current nutrients status across the UK. The published data, consolidated from thousands of soil samples across the UK since 1995, also enables growers to benchmark against other farms with up-to-date data, and to consider how to improve soil health to optimise crop production. Visit our website to see how you stack up.
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