Fertilizer Source and Rate to Reduce Summer Chlorosis of Kentucky Bluegrass.

Kentucky bluegrass managed in semiarid to arid regions develops severe chlorosis during hot summer months.  The cause of chlorosis is unknown, but no pests have been associated with these symptoms.  Yellowing may be associated with a nutrient imbalance, especially when urea-based fertilizers are applied.  The objective of the study was to determine the effectiveness of Anuvia Plant Nutrient’s new product, a 16-0-2-17S-3Fe multi-nutrient fertilizer containing 16% organics alone, combined with urea, or urea alone on chlorosis and overall quality of Kentucky bluegrass.  Initial applications were made on 31 March at 49 or 88 kg ha^-1 with some follow up applications on 11 May 2015 at 49 kg ha^-1.  Every two weeks turf quality, chlorosis, digital image analysis, NDVI, and clipping yield were obtained.  Monthly tissue samples were obtained monthly for nutrient analysis.  Soil samples were obtained at 10 cm depth to determine soil chemical properties and quantify microbial population dynamics.  Few statistical differences were observed due to variations among blocks.  As temperatures warmed into the summer months, chlorosis was more pronounced.  The follow-up treatments exhibited less chlorosis than untreated and urea only treatments following the second application.  Those same treatments had improved quality, green color, and cover compared to other treatments and the controls through 22 July.  There may be a correlation with foliar manganese levels and the presence of chlorosis.  Soil microbial community composition was altered by the treatments with higher fungi:bacteria ratios and greater arbuscular mycorrhizal fungi in the combined urea/Anuvia treatments regardless of proportions or N rate compared to urea alone or untreated. In contrast, the control had greater relative abundance of bacterial groups compared to the other treatments.  This trial will hopefully be repeated next year to confirm the results obtained from this year’s trial and verify the potential for nutrient toxicities or microbial population dynamics.