Influence of Nitrogen Forms of Fertilizer on Tall Fescue Salinity Tolerance.

Tall fescue (Festuca arundinacea Schbeb) is moderately tolerant to salinity.  Its application as a low maintenance species has recently been extended from the transition zone into cold climate zone where winter snow cover persists.  The use of ice-melting salts in this region raised a special demand for salinity tolerance.  The objective of this study was to investigate the effect of nitrogen (N) sources on turf quality of tall fescue under salinity stress.  Seven tall fescue cultivars ‘Wolfpack’, ‘Wolfpack II’, ‘Tarheel’, ‘Tarheel II’, ‘Jaguar 3’, ‘Jaguar 4G’, ‘Arid 3’ were seeded in August 2010 at a rate of 850 kg ha^-1 at the agricultural research station in Fargo, ND.  The fertilization treatments were conducted in 2011 and 2012 with N forms from 15.5-0-0 -26.5% CaO (14.4% N from NO₃-N; 1.1% N from NH₄-N) (Haifa Chemicls Ltd, Altamonte Springs, Florida), 19-0-19-8.31% S (N from Urea) (Spring Valley, Jackson, WI), 21-0-0-24% S (N from NH₄-N) (Spring Valley, Jackson, WI), 21-0-11-3.74%S (2.9% N from Urea; 0.17% N from NH₄-N; 8.28% water-insolulble-N; 9.65% slow release water soluable-N) (Spring Valley, Jackson, WI), 22-0-4-24%S (N from nutrisphere-stabilized urea) (Spring Valley, Jackson, WI), and 5-2-0 (Milorganite, Milwaukee, WI).  Nitrogen was applied at N rate of 50 kg ha^-1 monthly from May to September with K balanced using K₂SO₄ and S balanced using granular sulfur (Montana Sulphur & Chemicals Co. Billings, MT).  Ice-melting salts (NaCl:CaCl₂ in 1:1) were applied at an annual rate of 100 kg ha^-1 in equal amount monthly from May to September in 2011 and 2012. The grass was mowed at 6.5 cm.  The experiment was in a split-split plot design repeated three times, and with the cultivar as main plot factor, ice-melter as sub-plot factor and N source as sub-bub-plot.  Nitrogen source resulted in significant differences in turf quality, which also was confirmed by dark green color index (DGCI) using image analysis, and by NDVI data.  Nutrisphere-stabilized urea consistantly provided best turf quality compared to other N sources followed by sulfur-coated urea.  There was no interaction between N form and salinity treatment, indicating that same effect of N forms on turf quality are expected regardless of salinity stress levels.  There was a significant difference among cultivars in turf quality, greenness and NDVI, and the ranking was not affected by salt treatment.  ‘Wolfpack II’ showed the best turf quality during the two-year study.