Written by Mike Hamilton, CCA & President of Turf Dietitian
Organic matter is the most essential of all soil components; organic matter is the most critical but, conversely, the most obstructive and misunderstood.
Organic matter provides a reservoir for nutrients, microorganisms, carbohydrates, organic compounds, and water. However, if the organic matter becomes too dense, it can exhaust oxygen supplies and shelter anaerobic organisms, making it challenging to manage moisture and maintain turf.
Acceptable levels and bulk density of organic matter in turf and farming are pretty different. Turfgrass managers are continually trying to prevent and remove organic matter accumulations. Ideal organic matter ranges in turf fall within 1% to 2%. In contrast, farmers are customarily trying to find ways to add and increase organic matter accumulations. Ideal organic matter ranges in agriculture are generally as high as 10%.
There are two explanations for these conflicting management philosophies.
- Most crops have deep fibrous root systems (12 to 24 inches), whereas turf tends to have shallow non-fibrous root systems. Roots fracture soil, which produces air pours that hold more oxygen. Roots also secrete carbohydrates and organic compounds to feed organisms. Oxygen-loving microorganisms generate life in soil: by exuding gums that coat soil particles and feed plants and other organisms. This process dramatically improves soil structure. In soils with an abundance of oxygen, where plant roots are deep, and microbial activity is high, it takes a much higher percentage of organic matter to sustain the life of that soil.
- Farm fields are plowed as deep as 18 inches 1 to 4 times yearly. On average, turf fields get aerified at 4 inches deep 1 to 4 times annually. The amount of oxygen and organic food for microbes added to farm soils yearly is substantially higher than turf.
Food and oxygen are the only factors limiting or enhancing microbial populations. After plowing a field, there is so much microbial activity in the soil due to the increase of oxygen and food that the microbes consume organic matter faster than can be replaced. In turf (especially greens), we remove a vast amount of microbial food and only replace small amounts of oxygen at a shallow depth. Therefore, with turf management, organic matter builds up faster than many managers remove.
An acre of soil measured to a depth of 6 inches weighs approximately 2,000,000 pounds, which means that 1 percent of organic matter in the soil would weigh about 20,000 pounds per acre. Remember that it takes at least 10 pounds of organic material to decompose to 1 pound of organic matter, so it takes at least 200,000 pounds (100 tons) of organic material applied or returned to the soil to add 1 percent stable organic matter under favorable conditions.
Good management of organic matter includes not only adding enough to build a good reservoir of crop nutrients and good soil structure but also monitoring what you are doing and not adding too much.
Excessive organic matter in the root zone’s upper 1 to 4 inches can lead to rapid turf decline during stressful environmental periods. Heavy organic matter hinders a Superintendent’s ability to control moisture levels in the root zone. When a Superintendent loses the ability to wet and dry greens properly, any environmental stress, such as extreme temperature, excess precipitation, pest intrusions, or limited sunlight, amplifies the potential of turf decline. Excessive organic matter also results in low soil oxygen, shallow rooting, high soil moisture content, decreased percolation, and increased disease or pest activity.
The optimum range for growing healthy turf is 0.8% to 1.5% organic matter. The life expectancy of a green increases significantly if the organic matter gets maintained within the optimum range. If organic matter accumulates more than the optimum range, the potential for turf decline will dramatically increase each year, especially during periods of environmental stress.
Expecting cultural practices to be the same yearly is short-sighted and a receipt for long-term disaster. Hundreds of factors affect the rate at which a plant produces organic matter. Therefore, soil structure will deteriorate if a Superintendent is not allowed to adjust cultural practices to compensate for higher yields.
The reality: If a Superintendent loses ground for two or three seasons, the chance of them ever catching up is unlikely.
The reluctance to allow a Superintendent to implement effective cultural programs is understandable but ill-advised. Golfers hate aerated greens because putting surfaces can be impaired for a few weeks. General Managers, Golf Pros, and Club Managers hate aerated greens because of the loss of revenue and a barrage of golfers’ complaints. I guess a club has to determine whether it’s more acceptable to spend large sums of money and be closed for an entire summer every 10 to 15 years, or is it more tolerable to inconvenience customers more frequently and accept short-term revenue loss.
The most crucial factor in managing organic matter is oxygen.
Oxygen encourages and enhances root growth, but more importantly, it sustains and enhances the aerobic populations of microbes. The one component that all healthy soils have in common is large healthy populations of diverse species of microorganisms.
Many beneficial microbial species’ sole purpose in life is to decompose and mine the organic matter produced by plants. In healthy soils, plants and microbes have an interdependent relationship. Plants excrete waste through a metabolic process called respiration. This waste product feeds aerobic microbes. Microbes then mineralize the waste, returning life-sustaining nutrients, sugars, organic acids, and plant growth hormones to the plant for consumption. In the process, aerobic bacteria also secrete what is called microbial gums. Microbial gums attach to soil particles, separating them and flocculation the soil.
