In autumn or very early in the year, soil samples are usually taken, and various play areas are sampled. This is a very important procedure to identify and assess problems and an important tool for determining the nutritional requirements for the following season.
The soil sample is usually preceded by a regular inspection of the playing surface and rootzone with a visual assessment of the turf quality. Unfortunately, our ability to visually recognise nutrient deficiencies is very limited. It may be possible to diagnose a nitrogen deficiency and an insufficiency of phosphorus with the naked eye, especially in spring.
Other parameters such as the stress level of the grasses, the density of the sward, or the quality of the soil profile can be evaluated by experienced turf managers and provide us with vital information for the ongoing planning of maintenance.
In this picture from a football pitch, the obvious break between the turf sod and the turf base layer can be seen, with the resulting conclusions about the requirements for mechanical maintenance.
The best time to take a soil sample is autumn, October, November or spring, perhaps February. However, the time of the sampling should consistently be the same every year to ensure better comparability of the results. Winter precipitation changes the content of nutrients in the soil that are at risk of leaching, such as potassium and nitrogen.
The part of the rhizosphere where roots are growing is sampled, on most golf greens 10-12 cm, sometimes even more.
Using a suitable soil core sampler, you now walk diagonally across the turf and take samples at 15-20 sampling points and send these 300-500 g of topsoil in suitable packaging to the laboratory as quickly as possible.
Alternatively, you can send in a core taken with the cup cutter, but preferably take 15-20 small samples to get a clearer picture of the complete green.
Every greenkeeper should study the basic parameters of a soil analysis from time to time to be able to evaluate them independently and develop independent maintenance strategies.
The pH measures the negative logarithm of the H+ ions. The pH indicates how acidic or alkaline the soil is. Turf grows very well in a wide pH range of 5.5-8. Most nutrients are available around pH 6. The pH of the soil is often determined by the installed turf rootzone mix, the topdressing material, and the irrigation water used.
An important parameter in soil analysis is the cation exchange capacity (CEC). It is a measure of the potential of the soil to store nutrients. Soils with a CEC of 1 are very sandy and have a high leaching potential.
Turf rootzones with a CEC of around 6 can store nutrients better and buffer nutrient fluctuations. In comparison, good agricultural arable soils have significantly higher CEC values due to their higher clay and silt content, which explains why they are difficult to compare with sports turf.
The percent base saturation helps to see if the nutrients in the soil are available in the right ratios.
The soil organic matter (SOM) should also be closely monitored, and its development observed over several years.
The organic matter is determined by the loss on ignition. The soil sample is dried, weighed, then incinerated at a very high temperature to burn off all organic matter and carbon, and then weighed again.
A value of 1% SOM would be a turf base layer with poor nutrient storage and low biological activity. Values above 3% SOM indicate potential problems such as thatch and would indicate mechanical countermeasures such as aerification, graden or scarifying.
Further information on determining and managing organic matter can be found in this article.
We are often faced with a major problem when it comes to the most important parameters in soil analysis. What is the optimum value for phosphorus, potassium, magnesium, calcium, sulphur, zinc, manganese, copper, iron and boron?
Soil analyses from different laboratories cannot be compared 1:1. Different analysis methods result in differences in the level of the nutrient values. However, all laboratories will tell you, at least on request, which analysis methods were used for the various nutrients.
The most significant difference in terms of analytical methods exists for phosphorus. What is the best method to determine phosphorus levels in the soil?
NRM uses the Olsen P as this is the method that is used in the DEFRA Fertiliser recommendation manual used in the UK.
The most commonly used tests for Phosphorus are the Mehlich-3 soil test, the Bray-1 and the Olsen P tests. All soil tests just try to measure the plant available fractions of a nutrient in the soil. The nutrients in the soil solution and the nutrients easily extractable and in this way available to the plant. The total amount of nutrients in the soil is much higher but unreachable for the plant even over a long period of time.
The Olsen P procedure contains sodium bicarbonate and was specifically developed for calcareous soils.
You are very much dependent on the interpretation of the various laboratories, which categorise values as: Deficient, Too Low, Good or Too High.
With a little research, you could also compare the recommendations with other sources for such guidelines, for example, the SLAN (Sufficiency Level of Available Nutrient) and the MLSN (Minimum Levels for Sustainable Nutrition) guidelines. Newer recommendations usually recommend lower nutrient levels in the soil.
MLSN guidelines from comparative soil analyses indicate the minimum values for healthy plant growth. Some providers of soil analyses can also draw on a large database of soil analyses and compare them. Experience gained from observing the course over the last few years should also be considered when determining requirements.
TourTurf® sends soil samples to NRM, part of Cawood the UK’s biggest independent provider of analysis. TourTurf®'s nutrient target values are derived from Minimum Level for Sustainable Nutrition (MLSN), Sufficiency Level of Available Nutrient (SLAN) and UK's AHDB recommendations. The analytical methods used are as described in DEFRA Reference Book 427.
In most cases, fertiliser should only be applied when there is a nutrient deficit. This aspect is becoming increasingly important, especially considering the ever more stringent requirements for environmental protection and sustainability.
Plants have an outstanding potential to make nutrients available in the soil. Especially through processes in the area directly around the root hairs, the rhizosphere. The root can grow in the direction of the nutrients, actively absorb nutrients while consuming energy, and acidify the rhizosphere by releasing root exudates or chelating compounds to make nutrients more readily available and absorb them effectively.
However, the recommended minimum values should not be undercut, as otherwise the plants will become deficient and physiological processes in the plant will no longer be able to function at their optimum.
Soil analyses are essential to determine nutrient requirements. The time it takes to take soil samples and analyse the results carefully is time well spent. Regular analyses are an important tool in turf management and will help to prepare the plants well for any stress.