HELPFUL HINTS HELPFUL HINTS
HELPFUL HINTS
FROM THE LAWN INSTITUTE FROM THE LAWN INSTITUTE
FROM THE LAWN INSTITUTE PHOSPHOROUS AND TURFGRASS HEALTH
Phosphorous is one of the many inorganic elements that plants require for growth. Tese elements are often referred to as essential elements and are classified as macronutrients or micronutrients, depending on their relative concentration inside of plant cells. Phosphorous, along with nitrogen and potassium, constitute the three macronutrients required by plants and each has various roles and forms in plants and soils. Phosphorous plays a vital biochemical role in many internal plant processes including photosynthesis, respiration, building of plant membranes, key enzymes, and much more. Like other essential elements, phosphorous is readily absorbed by plant roots when present in soil solution where it is then incorporated into many organic compounds, each with a specific function.
Fertilizer materials that contain significant levels of phosphorous often include monoammonium phosphate, diammonium phosphate, superphosphate, and triple superphosphate. Tese products are mined from rock phosphate ores and can contain between 20 percent and 50 percent phosphorous. Tey also can be blended with other fertilizer materials to produce ratios with lower levels of phosphorous such as 16-4-8, for example. When looking at fertilizer labels, phosphorous is represented by the second number in the ratio and in many turfgrass fertilizers will often be lower than nitrogen.
Phosphorous amounts are typically low in fertilizer ratios for two reasons. First, plants need a much smaller amount of phosphorous than they do nitrogen so there is no need to supply equal amounts. For instance, there is at least seven times the amount of nitrogen in plant dry matter as there is phosphorous. Second, phosphorous does not leach readily from soils like nitrogen, so its residual after application lasts much longer, meaning that re-application as often isn’t necessary.
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TPI Turf News March/April 2019 9
However, there are instances when turfgrasses and other plants will benefit from phosphorous application. While phosphate ions are readily absorbed by turfgrass roots, they also are readily bound by inorganic iron and aluminum cations to form insoluble compounds, especially in low pH soils. So, even though there may be adequate phosphorous in the soil, it is present in tightly-held forms that cannot be accessed by plant roots. Phosphorous also is often thought of as a “starter” fertilizer where ratios such as 18-24-12 are commonly found in garden centers and agricultural supplies stores. As a result, it is common for starter-type fertilizers to be applied at planting so when new roots first begin to penetrate the soil, phosphorous and other nutrients are readily available for uptake. Also, because phosphorous is immobile, it will likely remain in place until germination and/or root penetration.
Symptoms of phosphorous deficiency include stunted growth in young plants, dark green coloration in leaves, necrotic spots, and a purple coloration resulting from excess anthocyanin production. However, the best way to determine whether or not a lawn or other turfgrass site will benefit from phosphorous is through a soil test or plant tissue test. As with all nutrients, phosphorous applications should be made with calibrated equipment to ensure precise application to turfgrass areas only. It also is important to sweep or blow any excess fertilizer from hardscapes and not to apply this or other nutrients prior to excessive rainfall. Accurate and timely application of this essential element can no doubt improve turfgrass health and lead to hardy, well-rooted, stress-tolerant lawns for everyone to enjoy.
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