Nitrate Leaching from Two Kentucky Bluegrass Cultivars as Affected by Nitrate Uptake Capacity and Subsurface Soil Compaction

There are a number of strategies to minimize NO3- leaching from turfgrass, including planting turfgrass cultivars with higher NO3- absorption abilities. This column lysimeter study was conducted to examine NO3- leaching from two Kentucky bluegrass (Poa pratensis L.) cultivars differing in NO3- uptake capacity. Subsurface soil compaction was included as a second factor. Tillers of Julia and Midnight Kentucky bluegrass, previously identified as having high and low NO3- uptake capacity, respectively, were grown in column lysimeters. Each column was filled with Wagram loamy sand with or without a subsurface compaction layer 8.5 cm below the surface. The two cultivars were established and then treated to impose moderate N deficiency. Potassium nitrate was applied in solution at 49 kg N ha(-1) followed by daily heavy irrigation. Leachate was collected and analyzed for NO3- N. Cumulative N leaching loss of applied N ranged from 2.6 to 19% and 2.8 to 21% for Julia and Midnight, respectively. In two out of three trials, both cultivars absorbed NO3- very efficiently in noncompacted soil, with only trace amounts of NO3- leaching. While NO3- N loss averaged 4.7% of applied N in noncompacted soil across all trials, subsurface soil compaction increased that to 8.9%. Results indicated that despite being identified as more efficient for NO3- uptake, NO3- leaching from Julia was generally similar to that from Midnight. Soil conditions and differences in root morphology and/or architecture may played a more important role than root uptake capacity in determining NO3- leaching from these Kentucky bluegrass genotypes.