The value of soil analysis
Your club might occasionally have a green soil analysis done. Some clubs insist on doing this annually, others only when prompted by a supplier or when a particular problem occurs on the green. If you’ve had greens soil analysis done or are considering one as a means of informing your greenkeeping regime, this
guide will help you to better understand the results (writes John Quinn).
Greens soil analysis reports come in many shapes and sizes. Some include a comprehensive breakdown of all key nutrients, some only the ones deemed most important by the instigator of the test. A routine greens soil analysis report will usually measure the soil pH and in some cases might even point out some of the basic physical characteristics of the soil such as sand content. Regardless of the detail of the report, there are some key factors that are essential for you to know, if the report is really going to help you in your maintenance of your green.
Chemical analysis: This type of analysis is intended to give you a snapshot of the current chemical condition of your green’s soil and can include a plethora of information, some of which can be very confusing. Let’s have a look at the main headings you’re likely to find in your greens soil analysis report.
pH: The pH scale runs from 0 to 14 (very acid to very alkaline) and 7 is said to be neutral or neither acid or alkaline. Our fine perennial grasses like the soil to be somewhere between 5.5 and 6.5, slightly acid. The H in pH stands for hydrogen, so the pH section of your greens soil analysis is all about hydrogen; in fact a measure of the number of exchangeable hydrogen ions in the soil. An atom of any element has an equal number of protons and electrons. An ion is simply an atom with an imbalance of these, usually due to losing or gaining electrons. This imbalance gives
the ion an electrical charge which can be negative or positive in polarity. Acidic soil contains more hydrogen ions (H+) than neutral or alkaline soil. Positively charged ions like H+ are referred to as cations (positively charged ions), whilst negatively charge ones are called anions.
Cation Exchange Capacity: Cation Exchange Capacity (CEC) measures the number of negatively charged sites there are in the soil for positive cations to bind to. This helps to hold nutrition in the soil and prevents nutrients from leaching out through the drains. These positive cations include calcium (Ca), potassium (K), magnesium (Mg), sodium (Na), and of course hydrogen (H). A higher CEC means more nutrients that can be held within the root zone without the risk of leaching out through the drains.
The exchange of cations takes place only in the clay and humus components of the soil, so very sandy soils often exhibit a very low CEC reading.
Electrical Conductivity: The electrical conductivity of the soil solution is an indirect measurement of the salt content of the soil solution. As salinity increases plants become less able to extract water efficiently from the soil, which exacerbates any water stress conditions that may already exist. High electrical conductivity is caused by high levels of mineral salts in the soil solution, either as a result of using too much high salt mineral fertiliser, or anaerobic, poorly aerated soil or a mix of both.
Base Saturation of Cations: A thorough greens soil analysis report will include details of the base saturation of your soil. If the base saturation is right, then CEC (in the presence of sufficient clay and humus) and pH are usually about right too. It’s not a guarantee, but I have also found that in greens where the base saturation graph looks good, then the underlying soil texture is often quite close to the ideal Sandy Loam texture also.
Organic Matter: Soil organic matter or humus is made from of the decaying remains of plants, microbes and animals, usually dead and dying roots and shoots of grass plants in our case. Preferably, comprising around 5 or 6% of the root zone, humus plays an essential role in supporting the microbial activity needed for nutrient retention and recycling, disease suppression and perennial grass growth. Physically, it provides good soil structure, enhanced root growth and promotes the water holding capacity of the soil.
Nutrients: In your greens soil analysis report, you will see some or all of the common plant nutrients mentioned. They are split into three groups; the primary nutrients, secondary nutrients and trace elements.
Primary Nutrients (N:P:K): Nitrogen (N): We all know that nitrogen is a very important plant nutrient and the most recognised requirement when we think of fertilisers. So, it might seem confusing that it doesn’t even warrant a mention in your soil analysis report…what’s that all about? The most readily available form of nitrogen in the soil is nitrate (NO3-) and that minus sign tells us why it isn’t measured in the greens soil analysis. As an anion (negatively charged ion) it isn’t attracted to the soil colloid and in fact is actively repelled due to the clay and humus particles responsible for cation exchange being negatively charged too. This means that nitrate is readily leached from the soil and partly explains why traditionally we have needed to add nitrogen more frequently and in higher volume. Healthy root zones with an active soil food web can produce up to 50Kg nitrogen per hectare per year by converting the proteins and carbohydrates in root exudates to ammonium.
Phosphorous (P): Phosphorous is critical in most plant metabolic and enzymatic processes essential for growth. Phosphate is needed for seed development and root growth. Potassium (K): Potassium activates the enzymes used in protein, sugar, and starch synthesis. Potassium is vital to many plant processes. The correct amount of plant potassium improves drought tolerance, cold hardiness and disease resistance.
Calcium (Ca): Calcium should be the largest available nutrient for healthy grass growth, strong cell walls, nutrient availability and the correct pH. Plant available calcium is often deficient in sandy root zones especially if excess phosphate has been applied. Magnesium (Mg): Magnesium is important for photosynthesis because it forms the central atom of chlorophyll. It is an activator for many critical enzymes, essential for carbon fixation and metabolism.
Sodium (Na): Sodium in small quantities is a plant nutrient that aids metabolism, carbon fixation and synthesis of chlorophyll. However, in excess it reduces water uptake and limits enzyme production.
Sulphur (S): Sulphur is an essential turf grass nutrient. It has a role in many enzymes and is involved in carbon fixation, photosynthesis and plant defence. Low sulphur levels produce chlorosis of younger leaves. Sulphur is only taken up by the plant as sulphate SO42-, but microbial activity is necessary for the conversion.
Iron (Fe): Iron is taken into the plant in Fe2+ and Fe3+ forms. Iron is used in
protein functions, as a catalyst and for respiration and photosynthesis. It is also used in plant defence because it binds tightly to proteins rendering them inaccessible to pathogens. Iron deficiencies result in chlorosis of young leaves.
Boron: Boron plays an important role in the development and growth of new plant cells and chemical and physical plant defence.
Zinc (Zn): Zinc assists chlorophyll production and carbon fixation.
Manganese (Mn): Manganese is important for the production of chlorophyll, photosynthesis, enzyme functioning and the plant defence mechanisms.
Copper (Cu): Copper plays a part in enzymatic processes and is important in use of nitrogen within the plant.
The Value of a Greens Soil Analysis
Traditionally, the greens soil analysis report has been something to glance at once a year and then file away, which is good to some degree, because it is a very useful reference tool for monitoring trends in your green over the long term.
If you routinely get a greens soil analysis done, but you aren’t seeing improvements in the sward composition, disease resistance or playing performance of your green, maybe it’s time to dig a little deeper and really start to understand what your greens soil analysis report is telling you.
Questions and comments welcome
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