Soil Testing: What’s The Point, And How Often Should I Do It?

Soil testing is increasingly recognised as an essential practice on farms, but is this trend motivated by best practices or merely compliance with various schemes? Ideally, soil analysis should be viewed as a best practice because it offers important financial benefits for all farmland soils.

Farmers often identify underperforming fields or tired leys that need reseeding. The typical first response is to plan for ploughing. However, before taking drastic measures, it’s crucial to examine the soil structure by digging inspection holes to check for compaction. This should be complemented with a broad-spectrum soil analysis to identify underlying issues.

Historically, soil analysis has been simplified with a narrow focus on just four metrics: pH, phosphorus (P), potassium (K), and magnesium (Mg). This approach primarily served the purpose of selling fertilizers rather than truly improving soil health. While phosphorus and potassium are essential macronutrients, focusing solely on them neglects the role of over a dozen other nutrients vital for soil, plant, and animal health. To optimize your soil’s potential, conduct a comprehensive soil analysis that measures all the cations, including calcium, magnesium, potassium, and sodium, along with cation exchange capacity (CEC). Include pH, phosphorus, sulphur, and several micronutrients in this suite. Assessing soil organic matter (OM) can provide further insights into soil health.

Soil structure is fundamental to biological health, relying heavily on its chemical and physical makeup. Creating an aerobic environment where beneficial soil biology can thrive is paramount. This is why it's imperative to measure the balance of these four key cations; an imbalance—especially between calcium and magnesium—can significantly influence soil structure and nutrient release.

It’s a common misconception that achieving the target pH means that all nutrients are in balance. In reality, pH can be heavily influenced by magnesium, potassium, or sodium, which could mask deficiencies in calcium. The ideal levels should see calcium at 65-70% of the base saturation and magnesium at 10-15%. Without a thorough analysis and knowledge of CEC, understanding the base saturation and the overall chemical structure of the soil remains elusive.

Calcium should be regarded as the king of soil nutrients. It plays a critical role in enhancing soil structure by creating air spaces for drainage and root penetration. Maintaining optimal calcium levels also facilitates the release of a range of other nutrients from the soil. Soil analysis is valuable not only for identifying deficiencies but also for recognising excesses that can lead to antagonisms between nutrients, potentially impacting plant and animal health. In cases where large volumes of slurry and manure are regularly applied, soil tests often reveal elevated levels of phosphorus and potassium, especially in grazing and continuous maize systems.

Other nutrients like magnesium, copper, and zinc may also reach excessive levels due to high mineralization from livestock. These imbalances can lead to reduced availability of copper and zinc, while excess potassium can hinder magnesium absorption, lowering chlorophyll production and ultimately reducing yield.

Understanding soil organic matter is another useful aspect of soil analysis, with an ideal level around 5%. Organic matter has a nutrient-holding capacity three times that of clay, serving as an excellent nutrient reservoir. However, high levels—greater than 10%—can indicate an anaerobic condition, where organic matter is not being broken down effectively, leading to nutrient lock-ups and undesirable releases of other nutrients.

Broad-spectrum soil analysis is an indispensable tool for modern farming. When combined with organic manure, forage minerals, and leaf tissue analyses, significant gains can be made in the performance of soils, plants, and livestock.

While any soil analysis is better than none, investing in quality analysis and effective interpretation of your soil results really pays off. It would be advised to test every 4 or 5 years, or before any major crop or land usage changes. This will help you identify your farm's greatest limiting factor, whether it’s a deficiency or an excess.

Remember, when you receive your soil test results, use them—don’t file them away! Understanding and applying these insights can lead to substantial improvements in soil health and farm productivity.

For more guidance on managing your soil and maximising its potential, visit our Soil Health Hub, which features articles, case studies and testimonials as well as giving you the opportunity to upload your own soil results for a detailed analysis of what you need to be doing to improve it.

Please contact us, or reach out to Jonny McKinney at 07841 341305, if you have any questions.