Foliar Nitrogen Uptake Efficiency of Creeping Bentgrass as Influenced by Spray Volume, Adjuvants, Tank-mixing, and Fertilizer Formulation.

Nitrogen is often foliarly applied to highly managed turfgrass swards but methods to enhance N-uptake efficiency are not well characterized. This study was conducted to determine the factors that control N-uptake efficiency by the foliage of creeping bentgrass [(Agrostis stolonifera L.)] with a goal of maximizing foliar N uptake. The effects of spray volume, adjuvants, tank-mixing, and fertilizer formulation were investigated using 15N labeled urea or ammonium sulfate at Urbana, IL on a Drummer silt loam (fine-silty, mixed, mesic Typic Endoaquoll). Nitrogen uptake was monitored by sampling foliage over a 24-hour period for total Kjeldahl nitrogen (TKN) and 15N enrichment by mass spectroscopy. Ammonium sulfate was taken up as effectively as urea, but caused unacceptable turf injury during warm (>20 C) weather. Most nitrogen applied to the foliage in ammonium form was absorbed by the plant within 4-6 hours. Uptake efficiency was greatly reduced during periods of hot (>30C) weather. Also, there was daily flux of nitrogen in the leaves of turf, indicating there may be rapid transport of the nutrient throughout the plant during the day.