Tennessee Turfgrass - October / November 2007

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Making Turfgrass Fertilizers Work – and Pay – for You (Part 2 of 3) By Tom Samples, Ph.D., a n d John Soroch a n , Ph.D., The University of Tennessee , a n d Bra d Jakubowski, The University of Nebraska

the first part of our three-part series on turfgrass nutrition (published in the August/September 2007 issue of Tennessee Turfgrass), we introduced plant and turfgrass nutrition; we briefly described the mobility of these nutrients in soils; and we provided tables to describe the appearance of turfgrass under various macronutrient and micronutrient deficiencies.


following formulas are useful when converting lbs. of phosphate (P2O5) to lbs. of phosphorus (P) and lbs. of potash (K2O) to lbs. of potassium (K). To convert the amount in lbs. of P2O5 to the amount in lbs. of P, P = P2O5 x 0.44. To convert the amount in lbs. of K2O to the amount in lbs. of K, K2O x 0.83 = K. So, in addition to 10 lbs. of N, a 50-lb. bag of fertilizer with a 20-5-15 analysis contains 0.5 x 5 x 0.44 = 1.1 lbs. of P; and 0.5 x 15 x 0.83 = 6.2 lbs. of K.

In this issue of Tennessee Turfgrass, we take a closer look at the 16 essential plant elements as they might appear on product labels. We describe how macro- and micronutrients function in turfgrasses and the consequences of too little or unavailable plant nutrients, and we outline the common commercial sources of plant nutrients.

Primary macronutrients

Nutrients on the fertilizer label Fertilizers applied to turfgrasses often contain all three primary macronutrients (nitrogen, phosphorus and potassium), and they may contain one or more secondary macronutrients and micronutrients. Information regarding the nutrient content of a fertilizer is printed on the product label. For example, fertilizer with a 20-5-15 analysis contains 20% nitrogen (N), 5% phosphate (P2O5) and 15% potash (K2O) by weight. A 50-lb. bag of 20-5-15 contains 0.5 x 20 = 10 pounds of N; 0.5 x 5 = 2.5 pounds of P2O5; and 0.5 x 15 = 7.5 pounds of K2O. Since the fertilizer label reports percent P2O5 and percent K2O (by weight) rather than percent elemental P and K, the 16



Nitrogen (N) Some N sources are very soluble in water and are released to turfgrasses within hours after being applied. Others (controlled-release sources) are formulated to dissolve or release very slowly into the solution surrounding turfgrass roots. Nitrogen sources may be inorganic (containing no carbon) or organic (containing carbon), synthetically produced or natural, and coated or non-coated (Table 1). Ammonium nitrate, ammonium sulfate, calcium nitrate and potassium nitrate are examples of inorganic N sources. Each is very soluble in water and may absorb moisture from the air during storage. Aerial shoots of turfgrasses may be severely injured (e.g., foliar burn) if too much of an inorganic N source is applied. Examples of natural organic N sources include dried, activated sewage sludge (Photo 1), animal by-products (e.g., manure and feather, leather and blood meal) and plant

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