Dry Weight Production and Nitrogen Efficiency Traits in Kentucky Bluegrass Cultivars in Nutrient Solution and Soil

Because of the importance of such factors as appearance and vigor in turf management, genetic selection of Kentucky bluegrass (Poa pratensis L.) is often conducted at high levels of N application. This process can mask potential differences between genotypes in N efficiency, especially under low N levels. The case is also made that because soil is the medium in which plant selections ultimately must perform, cultivar screening for N efficiency in solution culture should relate to results in soil. This study was conducted to evaluate N-utilization efficiency (NUE – mg plant dry matter mg-1 plant N) in six bluegrass cultivars at low (0.2, 0.7 mM NO3-N) and high (3.5 mM NO3-N) levels of N supply in nutrient solution culture (nutriculture) and soil. With high N supply, total plant N accumulation and N-root uptake efficiency (NRE-mg plant N g-1 root dry matter) increased in each cultivar, while NUE and shoot efficiency ratio (SER–mg shoot dry matter mg-1 shoot N) decreased, with the magnitude and relative response dependent on genotype and medium. As a group, as well as individually, cultivars Asset, Dawn, and Trenton were higher yielding, more responsive to increasing solution N concentration, and more efficient (NUE) at low levels of N supply than cultivars Limousine, Barzan, or Midnight. Under low N supply, NUE in nutriculture ranged from 26.2 (g plant dry weight mg-1 N) in Limousine to 40.1 in Asset, and in soil from 63.6 in Midnight to 77.4 in Asset. Differences in NUE among cultivars were more associated with shoot efficiency than with root absorption efficiency. Despite noticeably higher NUE in soil than in nutriculture, and significant effects of N fertility, genotypic differences in the various N efficiency traits in solution culture were also apparent in soil. The results suggest that NUE in Kentucky bluegrass can be enhanced by cultivar selection under low-N conditions. While the similarities of the actual N conditions between nutriculture and soil remain in question, it appears that solution culture can be used as an effective surrogate for characterizing NUE in divergent types of bluegrass cultivars