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FORAGE & GRAZINGLANDS

Ecogeographic Factors Affecting Inflorescence Emergence of Cool-Season Forage Grasses

^a Dep. of Crop and Soil Science, Pennsylvania State Univ., University Park, PA 16802
^b Agronomy Dep., Univ. of Wisconsin, Madison, WI 53706
^c Univ. of Wisconsin Lancaster Experiment Station, Lancaster, WI 53813
^d Univ. of Wisconsin Spooner Agricultural Research Station, Spooner, WI 54801
^e Upper Peninsula Experiment Station, Chatham, MI 49816
^f Dep. of Crop and Soil Science, Michigan State Univ., East Lansing, MI 48824
^g Univ. of Kentucky, Princeton, KY 42445
^h Crops and Livestock Research Centre, Charlottetown, PEI C1A 4N6, Canada
ⁱ Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN 55108

^* Corresponding author (mhh2{at}psu.edu).

The ability to predict when a cool-season forage grass cultivar will begin inflorescence emergence under different ecogeographical conditions would allow plant breeders, agronomists, and grass-seed marketers to better position that cultivar into a forage production system. Our objective was to determine the ecogeographical factors (longitude, latitude, elevation, day of year when average daily temperature exceeds 0°C for five consecutive days [DOY at 0°C], cumulative growing degree-day [GDD], photoperiod, and cumulative photosynthetic active radiation [PAR]) that have the greatest effect on grass maturation in the spring. Inflorescence emergence was monitored in established cultivars of festulolium (x Festulolium spp.), orchardgrass (Dactylis glomerata L.), ryegrass (Lolium perenne L. and Lolium multiflorum Lam.), tall fescue (Festuca arundinacea Schreb.), and timothy (Phleum pratense L.) at eight locations in North America during the spring of 2004 and 2005. As latitude increased, the day of year when grasses reached 1% inflorescence emergence (DOY) also increased, while cumulative GDD and PAR decreased. Latitude, cumulative PAR, and DOY at 0°C were more closely correlated (r² 0.67) to the onset of inflorescence emergence than the other variables. Latitude combined with the inverse transformation of PAR provided the best prediction of when these grasses would initiate inflorescence emergence (validation R² for all species 0.83).

Abbreviations: DOY, day of year • DOY at 0°C, day of year that the average daily temperature exceeded 0°C for five consecutive days • DSWRF, downward shortwave radiation flux • GDD, growing degree-day • InPAR, inverse of photosynthetic active radiation • Lat, latitude • NARR, North American Regional Reanalysis • PAR, photosynthetic active radiation • PP, photoperiod • RMSE, root mean square error • SURFRAD, surface radiation