The proliferation in the use of sand-based greens presents a unique maintenance problem to a growing number of turfgrass managers. The low nutrient holding capacity inherent with sand-based systems makes it difficult to provide adequate nutrition to turf while minimizing fertilizer leaching and runoff. Frequent applications of liquid fertilizers at low rates have become the standard means by which to supply nutrients to sand-based greens. This "spoon-feeding" approach affords great versatility in a fertility program — allowing turfgrass managers to rectify nutrient deficiencies quickly while providing just enough nutrition to promote healthy, but not excessive, turf growth. Historically, "spoon-feeding" has required the use of liquid fertilizers, as granular materials contain high nitrogen concentrations that, when applied at low rates, would result in irregular green dots over stimulated turf. The objective of this study was to screen the efficacy of the new Lesco Matrix granular fertilizers — an improved methylene urea technology - as a dry "spoon-feeding" fertilizer material. Matrix fertilizers can be produced in low nitrogen concentration formulations with other nutrients incorporated into the fertilizer, such as iron and magnesium. These traits make Matrix fertilizers a useful product for use as a sand-based green fertilizer material.

The trial was arranged on the ‘Penncross’ creeping bentgrass USGA green at the Iowa State University Research Station and organized as a randomized complete block design with three replications. Each individual block consisted of five 5x5 ft treatment plots. The five fertilizers utilized in the study included granular Lesco Matrix fertilizers with analyses of 5-0-28, 12-0-22 and 17-3-18, a standard 17-3-17 Lesco granular fertilizer and a liquid fertilizer composed of urea and potassium sulfate (46-0-0 and 0-0-50, respectively).

Application timing and rate differed between the fertilizer treatments. The three Matrix fertilizers and the liquid fertilizer treatments were applied at a rate of 0.25 lbs of N/1000 ft² every ten days — a "spoon-feeding" fertilization program. The solid 17-3-17 standard Lesco fertilizer was applied at a rate of 0.75 lbs N/1000 ft² every 30 days. All treatments received a total of 0.75 lbs of N/1000 ft² over a period of 30 days. The initial fertilizer application was made on June 17 and the last on September 15. Table 1 lists all fertilizer application dates of the study. Granular fertilizers were applied to each individual 5x5 ft plot by hand, and in two different directions, to ensure uniform coverage. The liquid fertilizer applications were made using a CO₂ powered backpack sprayer calibrated to deliver 3.0 gallons of solution/1000 ft².

Table 1. Application dates¹ of fertilizer treatments.

Turf evaluations of color and uniformity were made on a weekly basis and ranked on a scale of 1 to 9 with 9=best, 5=lowest acceptable and 1=worst. Table 2 lists the weekly color evaluations for each treatment. Uniformity assessments can be found in Table 3. Statistically significant differences in color occurred on July 1, July 14, July 21, July 28, August 4, August 11, August 18, August 25, September 1, September 9, September 15, and September 23. In general, the 5-0-28 Matrix fertilizer produced the best color, until the beginning of August. At this point, the 5-0-28 and 12-0-22 Matrix fertilizers became indistinguishable from one another — and superior in color to all other fertilizer treatments. The standard solid 17-3-17 and liquid fertilizer’s color fluctuated greatly over the course of the study, but were of higher quality than the 17-3-18 Matrix fertilizer. The 17-3-18 Matrix fertilizer produced the lowest color rating at all data collection dates except August 11.

² Comprised of urea (46-0-0) and potassium sulfate (0-0-50)

NA - means between treatments are not statistically significant per Fischer’s LSD test.

Statistically significant differences in uniformity occurred on July 21, July 28, August 11, August 18, and September 1. Note Table 3. The 5-0-28 Matrix fertilizer resulted in excellent uniformity throughout the study and, once again, became virtually indistinguishable from the 12-0-22 matrix fertilizer treatments after July 28. As expected, the liquid fertilizer treatment demonstrated high levels of uniformity, especially after July 14 - although not to as high of a degree as the 5-0-28 and 12-0-22 Matrix fertilizer treatments. The Lesco standard solid fertilizer also produced excellent uniformity. The 17-3-18 Matrix fertilizer, however, did not result in an even nitrogen response — especially early in the study. Areas of the treated plots were often irregular in color and appearance and were of lesser quality than the other treatments. The high nitrogen concentration of the fertilizer and the low application rate most likely resulted in non-uniform distribution of the nitrogen over the treated plot.

Table 3. Uniformity¹ of ‘Penncross’ creeping bentgrass treated with the following fertilizers.

² Comprised of urea (46-0-0) and potassium sulfate (0-0-50)

NA- means between treatments are not statistically significant per Fischer’s LSD test.

At the conclusion of the study, September 23, tissue samples were taken from each treatment plot and analyzed for total nitrogen content. The Iowa State University Horticulture Plant Nutrition Laboratory performed the tests using the TKN for plant digests method. The results are listed in Table 4. Notice that all the solid fertilizer treatments have total nitrogen contents higher than the liquid fertilizer treatment. Mowing results in tissue loss from the grass plant - and the main source of nitrogen for liquid fertilized turf. While turf grown in the solid fertilizer treatment plots can take up more nitrogen from the rootzone, no nitrogen will be made available to the turf grown in the liquid fertilizer plots until subsequent applications of foliar sprays are made.

Table 4. Total Nitrogen Content¹ of tissue collected from each treatment

² Comprised of urea (46-0-0) and potassium sulfate (0-0-50)

The 5-0-28 and 12-0-22 Matrix fertilizers clearly have potential for use in dry "spoon-feeding" fertilizer programs. The color and uniformity ratings achieved by these treatments met or exceeded the results produced by the liquid fertilizer — the current fertilizer standard in a "spoon-feeding" program. The ability to incorporate other nutrients such as iron or magnesium into a low nitrogen fertilizer would allow for great flexibility in a sand-based green fertility program. Custom formulations of the granular Matrix fertilizers could be created to meet the needs of high maintenance turf at all stages of growth and development, making these fertilizers valuable assets in a fertilizer regimen.