Evaluation of Liquid-Applied Nitrogen Fertilizers on Kentucky Bluegrass Turf

Solution and suspension N sources have been developed as substitutes for urea in spray solutions used by lawn-care professionals. A field study was conducted to evaluate the response of Kentucky bluegrass (Poa pratensis L.) growing on a Catlin silt loam (Typic Argiudoll), to applications of the new solution and suspension N sources, alone or combined with urea, by comparison to turf response from application of the traditional fertilizer materials ammonium nitrate (AN), Nitroform (ureaform), sulfur-coated urea (SCU), ammonium sulfate (AS), granular urea, spray-applied urea (US), and urea-ammonium nitrate (UAN) solution. Also, urea and AS treated with dicyandiamide (DCD) were compared to the untreated sources. Fertilization rate was 195 kg N ha–1 yr–1 split into four applications except SCU which was applied twice. Turfgrass color and clipping production were monitored along with thatch accumulation and soil pH. In a second field experiment, foliar burn potentials of the new N sources were evaluated by comparison to burn potentials from US, UAN, and a liquid 12-1.8-3.3 fertilizer. Turf response to Formolene (solution N source) paralleled that due to US. Turf treated with US received higher color ratings than did that treated with Nitroform or FLUF (suspension N source) during the early growing season but this trend was reversed by late summer. Turf fertilized with FLUF resembled turf fertilized with Nitroform but was inferior to turf fertilized with SCU. There was no benefit from the inclusion of DCD with either AS or urea. Soil pH after 2 yr ranged from 5.3 to 6.4 and was lowest with AS treatment; thatch depth ranged from 7.0 to 19.3 mm and was greatest with AS treatment. Formolene and FLUF caused less foliar injury than did US, UAN, or the 12-1.8-3.3 fertilizer. Results from the two experiments indicated that the major advantage of using Formolene or FLUF was the reduced potential for foliar fertilizer burn