Daily Light Integral Requirements for Zoysiagrass and Bermudagrass Cultivars: Fertility, Mowing Height, and Growth Regulator Interactions

Abstract

Growing quality turf in shade is a significant management concern for many turf managers. Proper turfgrass selection for shaded environments can be challenging due to difficulty in quantifying necessary light levels particular to each unique environment. Rather than responding to a number of hours of sunlight or percent shade level, plants ultimately respond to the cumulative daily total number of photons (mols m^-2 d^-1) received within the photosynthetically active wavelengths (400-700 nm), termed ‘daily light integral’ (DLI). Most prior works investigating turfgrass DLI requirements have been with bermudagrass putting greens and shorter-term greenhouse studies. Furthermore, little to no research has examined Nitrogen (N) rate and trinexapac-ethyl (TE) interactions on the shade tolerance of ‘Tifway’ bermudagrass under golf or athletic turf situations.

A field study was conducted over multiple seasons under replicated treatments offering 0 to 90% reductions in photosynthetic photon flux (PPF) and investigating effects of mowing heights and monthly TE (0.2 kg ai ha^-1) application during summer months. Our results demonstrated that zoysiagrass cultivars achieved superior turf quality, maintained higher levels of green cover and NDVI, higher shear strength measurements, and had overall lower DLI requirements than bermudagrass cultivars under moderate to heavily (50-90% shade) shaded conditions. Monthly TE application and increased mowing heights simulating golf course rough also improved turf quality and performance of all cultivars under low-light conditions. Seasonal differences in DLI were also noted across cultivars, with highest DLI requirements observed in summer and reduced DLI occurring in spring and fall seasons.

A greenhouse study was then conducted under Full Sun, 30%, and 50% shade levels to evaluate effects of N and TE on Tifway bermudagrass performance over a 12-week period. Results demonstrated that TE (0.1 kg ai ha^-1 per 14 days) application combined with low N rate (9.96 kg N ha^-1 per 14 days) benefited shaded Tifway bermudagrass in terms of both turf quality and percent green cover. Also, high N rate (24.4 kg N ha^-1 per 14 days) with TE application contributed to improved turf quality relative to high N rate without TE application. The high N rate also contributed to greater clipping yields under both full sun and shade environments. These data offer insight to turf managers for improving turfgrass cultivar selection and cultural management for shaded conditions.