Historically, spoon-feeding fertilizer programs have necessitated the use of liquid fertilizers, as granular materials commonly contain high nitrogen concentrations, which make it difficult to achieve acceptable levels of uniformity applied at low rates. With the advent of new production methods and formulations, however, granular materials have been created that could potentially be utilized in a spoon-feeding regimen. This experiment was performed to determine the feasibility of using granular materials in a spoon-feeding fertilizer program.

The trial was initiated on the ‘Penncross’ creeping bentgrass (Agrostis palustris Huds) USGA green at the Iowa State University Research Station. A randomized complete block design with three replications was utilized to organize the study. Each individual block consisted of ten 5x5 ft treatment plots containing nine fertilizer treatments and an untreated control. The nine products utilized in the study included three Lesco Novex fertilizers with analyses 18-2-18, 19-2-19 and 32-0-0, a 10-2-10 Sustäne and Nutralene experimental material, a 12-2-12 Sustäne and Novex experimental material, a 17-3-17 PPSCU Lesco granular fertilizer, a 19-3-19 Scotts Contec fertilizer, a 14-14-14 UHS material and a liquid fertilizer composed of urea and potassium sulfate (46-0-0 and 0-0-50, respectively). All of the fertilizers were applied at a rate of 0.25-lb of N/1000 ft² every ten days. In addition, potassium was applied at a rate of 0.25-lb/1000 ft² in the liquid fertilizer treatment. 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 material/1000 ft². The first fertilizer treatment applications were made on May 22 with subsequent applications made at ten-day intervals.

Weekly, visual turf evaluations of color and uniformity were made on a scale from 1 to 9, with 9=best, 6=lowest acceptable and 1=worst. In addition, tissue samples were taken from each treatment plot every 30 days and analyzed for total nitrogen content. The Iowa State University Horticulture Plant Nutrition Laboratory used the Kjeldahl method to determine the total nitrogen content.

Weekly color ratings indicated that, while all three of the Novex materials and the Sustäne and Novex 12-2-12 experimental fertilizer produced high color ratings, the liquid fertilizer consistently resulted in the best color ratings (Table 1). The UHS 14-14-14 fertilizer and the untreated control resulted in the lowest color ratings and the Sustäne and Nutralene 10-2-10, Lesco PPSCU 29-0-0 and Scotts Contec 19-3-19 produced intermediate ratings.

The liquid fertilizer also consistently produced the highest uniformity ratings (Table 2). On the other end of the spectrum, was the UHS 14-14-14 fertilizer. UHS 14-14-14 treatment plots oftentimes exhibited several small green spots of over-stimulated turf, a sign of poor nitrogen distribution characteristics. Only the untreated control received lower uniformity ratings then the UHS 14-14-14 fertilizer. The remaining seven fertilizer materials achieved uniformity ratings that were intermediate between the liquid and UHS 14-14-14 fertilizer treatments. It is acknowledged that the UHS 14-14-14 is not designed for, nor is it recommended by the manufacturer for spoon-feeding. This fertilizer was included in the study only as an example of the poor nitrogen response characteristics resulting when a fertilizer with a large particle size is applied at low rates and in no way is indicative of the quality of UHS products.

Little significant data can be interpreted from the tissue sample total nitrogen content, other than that treatment plots receiving fertilizer application generally resulted in a higher concentration of total nitrogen in tissue samples than the untreated control (Table 3).

Of all of the fertilizer treatments, the liquid material resulted in the highest ratings, both in color and uniformity. Other fertilizer materials, such as the three Novex materials, both of the Sustäne materials and the 19-3-19 Scotts Contec materials, however, also produced high color and uniformity ratings. The greatest difference between the liquid fertilizer treatment and these materials was a slight reduction in uniformity. These materials produced similar color ratings, but did not result in as high a level of uniformity throughout their plots. The UHS 14-14-14 was not designed, nor intended, for use in a spoon-feeding program and did not perform as well as the other products. When applied in larger quantities the UHS 14-14-14 fertilizer produces turf of high quality. The three Novex materials and the Sustäne and Novex 12-2-12 materials resulted in plots of excellent quality, similar in color to the liquid and with only a slight reduction in the uniformity. The Sustäne and Nutralene 10-2-10, LESCO PPSCU 29-0-0 and Scotts Contec 19-3-19 produced plots of intermediate quality. While superior to the UHS 14-14-14 and untreated control treatments, they seemed to lag slightly behind the liquid, Novex and Sustäne and Novex treatments, never quite achieving the same level of visual quality.

Table 1. Color¹ of ‘Penncross’ creeping bentgrass treated with the following fertilizers.