Root architecture affects nitrate leaching from bentgrass turf

Understanding the determinants of nitrate leaching should improve nitrogen uptake efficiency and reduce ground water contamination. This column lysimeter study examined the effect of root architecture on NO3 leaching from two genotypes of creeping bentgrass (Agrostis palustris Huds.) differing in rooting characteristics. Ammonium nitrate was applied (50 kg N ha(-1)) and the columns were irrigated dth 1, 2 or 3 em day(-1) (Exp. 1) or irrigation was delayed 1, 3 or 5 d (Exp. 2). In Exp. 1, leachate NO3 concentrations and total N leached from the shallow-rooted (SR) genotype were approximately twice those from the deep-rooted (DR) genotype. An average of 38 and 18% of the applied N leached from the SR and DR genotypes, respectively. Cumulative leaching losses increased with irrigation depth. In Exp. 2, NO3 leaching was reduced 90% or more by increasing the time period for immobilization from 1 to 5 d. Recovery of applied N-15 in the tissue averaged 87% after 2 mo. Absorption of NO3 and NH4 was measured in nutrient solution culture. The SR genotype had significantly higher uptake rates than DR for both forms of N, expressed on a root weight basis. Collectively these data indicate that a deep-rooted turfgrass absorbs N more efficiently than a shallow-rooted turf, reducing the concentration and total amount of NO3 leached. The effect is apparently not due to differences in N uptake, but rather to rooting patterns. Environmental conditions and management practices that affect roofing depth and density may thus affect N nutrition and NO3 leaching.