Establishment of seeded zoysiagrass in a perennial ryegrass sward: effects of soil-surface irradiance and temperature

Abstract

Conversion from perennial ryegrass (Lolium perenne L.) to zoysiagrass (Zoysia japonica Steud.) in the transition zone of the USA may reduce irrigation and fungicide requirements. However, environmental conditions under perennial ryegrass canopies may inhibit establishment of seeded zoysiagrass. Our objectives were to quantify solar irradiance and temperatures at the soil surface and determine their effects on establishment of ‘Zenith’ zoysiagrass seeded into existing perennial ryegrass canopies. A 31-day shade study was conducted during 2002 near Manhattan, Kansas, USA. Zoysiagrass was seeded into bare-soil plots, each covered with shade cloth that blocked 40%, 65%, or 85% of solar irradiance. Additionally, two separate experiments were conducted in 1999-2000 (Study I) and 2002 (Study II) in which perennial ryegrass canopies were maintained at: 1) 1.4 cm (untreated); 2) 0.6 cm (scalped); or 3) treated with glyphosate (N-phosphonomethyl glycine [glyphosate-treated]). Irradiance below the canopy was modeled in both experiments and seedbed temperatures were measured with thermocouples in Study II. In the shade study, zoysiagrass seedling emergence and growth decreased as shade increased in bare-soil plots (r = -0.59 to 0.69). In perennial ryegrass, scalped and untreated turf shaded the seedbed surfaces by 36% and 72%, respectively, and soil temperatures averaged 1.1oC cooler compared to glyphosate-treated turf. In scalped and glyphosate-treated plots, zoysiagrass seedling emergence was 90% greater the first year and coverage 59% greater the second year compared to untreated perennial ryegrass. Higher light penetration and seedbed temperatures during the initial 5 to 7 weeks after seeding contributed to higher zoysiagrass establishment in scalped and glyphosate-treated plots.