Competitive effects of Nuttall\u27s and weeping Alkaligrass in Kentucky bluegrass

Mechanisms of interspecific and intraspecific competition and survival between the agronomic species Kentucky bluegrass (Poa pratensis L. \u27Midnight\u27), with the native grass Nuttall\u27s alkaligrass (Puccinellia nuttalliana (Schult.) Hitchc.) and the introduced grass weeping alkaligrass (Puccinellia distans (Jacq.) Parl) were assessed over a two year period. A matrix of competitive regimes was created consisting of 4 monoculture densities and 16 mixtures of all possible pair-wise combinations. Response surfaces and substitution analysis of the three species were generated within the matrix to study competition dynamics between the species. Plants were grown under natural conditions, on a pH neutral (6.9) silt loam site, with no added irrigation or fertilizer. In general, in year 1, weeping alkaligrass was more competitive than Nuttall\u27s alkaligrass and both species were far more competitive than Kentucky bluegrass. Both weeping and Nuttall\u27s alkaligrass exhibited low survival (40% and 60%, respectively) following harvesting. There was also a shift in competitive effects in Year 2, such that weeping alkaligrass was equally competitive with Kentucky bluegrass, and both were far more competitive than Nuttall\u27s alkaligrass. Even though weeping alkaligrass had very low survival rates its affect on Kentucky bluegrass into year 2 was equal to that of year 1. Thus, the legacy effect of weeping alkaligrass will likely have long-term implications to a rotation of Kentucky bluegrass plants, even if removed in the first year. However, the notion of a legacy effect of competition should not be limited to an agricultural setting. It is highly likely that similar interactions are exhibited across plant communities and that long term competition studies are required to adequately address this issue. © 2009 by the Northwest Scientific Association. All rights reserved