Nitrate uptake and nitrogen use efficiency by Kentucky bluegrass cultivars

Efficient utilization of fertilizer-nitrogen (N) by turfgrasses is probably related to N uptake efficiency of roots and metabolic efficiency of absorbed N in roots and shoots. This study evaluated Kentucky bluegrass (Poa pratensis L.) cultivars for potential differences in nitrate uptake rate (NUR), temporal variation in NUR, and the relationship between NUR and N use efficiency (NUE), defined as grams dry matter per gram N. Six cultivars were propagated from tillers of seeded plants, grown in silica sand, mowed weekly, and watered daily with a complete nutrient solution containing 1.O mM nitrate. A nutrient depletion method from an initial nitrate concentration of 0.5 mM was used to determine NUR of 5-month-old plants. NUR (μmol·h-1 per plant) of the six cultivars ranked as follows: \u27Blacksburg\u27 \u3e \u27Conni\u27 \u3e \u27Dawn\u27 \u3e \u27Eclipse\u27 = \u27Barzan\u27 \u3e \u27Gnome\u27. When NUR was based on root weight, \u27Conni\u27 ranked highest; when NUR was based on root length, surface, or volume, \u27Eclipse\u27 ranked highest. Averaged across cultivars, NUR on the second day was greater than NUR for the first day of nitrate exposure. Temporal variation was greatest in \u27Blacksburg\u27, while none was noted in \u27Conni\u27 or \u27Eclipse\u27. Cultivar differences in NUE were significant in fibrous roots, rhizomes, and leaf sheaths, but not in leaf blades and thatch. Total nitrate uptake was positively related to total N recovered and total plant dry matter, but NUR based on root weight was negatively correlated with NUE of the whole plant