Don’t guess it, soil test it...

Colman Wardein Consultancy

Although poor performing turf can indicate underlying soil problems, one cannot identify soil pH and nutrient problems by sight. Soil analysis is needed to determine if these factors are limiting grass rooting and nutrient uptake. If so, fertiliser is then recommended to rectify these nutrient levels.
Here are some guidelines for proper soil testing.

Take a proper sample

A sample that adequately represents the soil area of interest is key. Soil pH and nutrient levels can be extremely variable naturally due to non uniform applications of fertiliser and water. I have heard of pH variance between 6.0 and 8.5 within a single golf fairway due to differences in soil type. So, a lot of samples across the entire site is required. If there are specific problem areas there needs to be a composite sample taken because, a sample taken from a full fairway, would lead to a confusing and improper reflection of the problem area.

Sampling Techniques

Take fifteen to twenty soil cores randomly from throughout each sampling area using a 0.5" to 1.0" soil probe. Samples for pH and nutrients should be taken 6" to 8" deep prior to turf establishment, but only 3" to 4" deep thereafter. Remove the thatch and turf layer and thoroughly mix the soil cores in a clean plastic bucket. Fill a soil sampling kit box to the top with the sample and discard the excess.

Annual soil sampling is recommended for native soils but more frequent sampling may be prudent on sand based rootzones. Soil pH and nutrients levels can change rapidly on greens and tees, particularly when recently constructed. Seasonal variation in soil pH occurs so standardising the time of sampling is a benefit to tracking the changes from year to year. Soil samples do not need to be dry before posting to the laboratory, but excessively wet samples should be air dried to moist conditions prior to shipping.

Fertiliser recommendations from Soil analysis

Most soil testing laboratories make fertiliser recommendations for the major nutrients, phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg), and these recommendations are based on the "sufficient levels" approach. This philosophy acknowledges that, as the soil test level of the nutrient increases, the chance of getting a response to adding that nutrient decreases and the magnitude of the response, if it occurs, is diminished.

At a low soil test nutrient level a response to adding the nutrient is expected most of the time and the response should be relatively large. Adding the nutrient to soil with a medium level of the nutrient should garner a growth response about half the time, but the enhancement will be less than at low soil test levels.

Maintaining soil test levels in the upper part of the medium category or the lower part of the high category is a safe and efficient way to manage P, K, Ca and Mg. Building high soil test levels of P and K will be difficult in sand based rootzones, especially when recently constructed, because the ability to retain these nutrients is very limited.

Soil testing procedures can identify insufficient soil supplies of manganese (Mn) and copper (Cu), as well as excessive levels of Cu. Soil pH has such a dramatic effect on Mn availability that it must be used in combination with the soil test Mn level to make a fertiliser recommendation. For example, at a soil pH of 7.0 soil test Mn must exceed 9ppm to be sufficient . However, at a pH of 6.0 only 4ppm is needed. Copper deficiencies in turfgrass are rare, only occurring in organic soils.

What is the Scotts soil analysis service?

The Kit

The Scotts professional soil analysis kit contains all the components for having six separate soil samples analysed. The samples can be posted free of charge to the research laboratory for analysis. These laboratories are independently operated using state of the art technology.

The Results

The samples are analysed individually for the following:

• pH status of sample
• Phosphorus Concentration
• Potassium Concentration
• Magnesium Concentration

It should be noted that high levels of Phosphorus are usually present in the soil but are mostly tightly bound to the soil, resulting in little free phosphorus being available. The phophorus in each soil sample is analysed by specialist assays that measure only the available phosphorus, and is therefore a true measure of the concentration available to the plant.

The computer will then assess all results against the criteria the customer provides on the record card and prints out the yearly requirements for Nitrogen, Phosphorus and Potassium in Kilogrammes per hectare.

To obtain a soil analysis kit, contact your local Scotts area manager and we will be delighted to talk you through any of your questions and guide you through the process.

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