Submitted to: International Grasslands Congress
Publication Type: Proceedings
Publication Acceptance Date: 6/4/2005
Publication Date: 7/15/2005
Citation: Coleman, S.W., Breman, J., Blount, A.S., Quesenberry, K.H. 2005. Tissue damage and nutritive value of warm-season grasses following a freeze. XX International Grasslands Congress: Offered Papers. p.451. Interpretive Summary: Bahiagrass is the predominant forage for livestock feed in the subtropics of the U.S.A. While it grows rapidly and produces abundant forage during the growing season, it is often lacking in quality or the ability to support animal growth and milk production, especially after frost. The residue after frost is particularly disliked by grazing animals and therefore bahiagrass is considered a poor candidate for stockpiling. Some previous research in Florida has shown that some selections of bahiagrass are more tolerant to below-freezing temperatures. We tracked the forage yield and quality after freezing of bahiagrasses both tolerant and intolerant to freezes and compared them to some native grasses common to the mid- and south-western U.S.A. Single plant yields for three bahiagrass varieties averaged 18 g/plant while that for switchgrass was 222 g/plant. Big bluestem and Indiangrass were intermediate. The leaf content of bahiagrasses was over 80% of their dry matter whereas that for native grasses was ~22%. Native grasses and Argentine bahiagrass were totally killed by a freeze whereas Tifton 9 was only partially damaged. Pensacola was intermediate. Crude protein declined in all types except Tifton 9 bahiagrass where it remained above 8% for 28 days after the freeze. Fiber increased with time with all but Tifton 9, but especially with switchgrass and Argentine bahiagrass. These data suggest that Tifton 9 bahiagrass should be suitable for stockpiled winter forage in the subtropics.
Technical Abstract: Bahiagrass (Paspalum notatum Flugge) is a major forage for livestock in the subtropics of the U.S.A. However, it is subject to freeze damage with minimal winter regrowth, and is generally considered a poor grass for stockpiling due to poor quality of the residue. Bahiagrass genotypes have been found showing a range of leaf freezing tolerance in the in the field (-30 C). Other C4 grasses have been reported to have genotype-specific tolerances to below-freezing temperatures ranging from -3 to -100 C . This research was begun to try to understand the processes that take place following freeze injury to bahiagrass. Three grasses native to the Midwest, big bluestem (Andropogon gerardii Vitman cv Alamo), Indiangrass (Sorghastrum nutans (L.) Nash cv Lometa), and switchgrass (Panicum virgatum L. cv Kaw) and commonly used for stockpiling were used for comparison. Plots were fertilized twice, staged on 1 July 2003 to 6.08 cm for bahiagrass and 15.24 cm for native grasses, and allowed to grow thereafter to stockpile dry matter until a killing frost would occur. Harvests included a pre-freeze event baseline (16 Nov 2003), freeze event -3.3C (30 Nov 2003) followed by harvest at 3, 7, 14, and 28 d post-freeze. Leaf tissue cold tolerance (LTCT) was rated after 28 d using the USDA G.R.I.N. scale (1= no damage or 100% green leaf, 9= total top growth damaged or 0% green leaf). Crude protein (CP) and neutral detergent fiber (NDF) were determined on all samples using NIRS calibrated with 20% of the samples. Switchgrass had the highest yield and bahiagrass had the highest leaf percent. Leaf yield was more similar, but switchgrass produced more than twice as much leaf of any other cultivar. Tifton 9 showed the most resistance to freeze damage whereas the native grass cultivars and Argentine bahiagrass were completely damaged. Crude protein of native grasses and Argentine declined dramatically following the freeze. Tifton 9 increased slightly in CP concentration and remained above 8%. At this level, Tifton 9 would provide maintenance protein for dry beef cows during the winter. Pensacola would be marginal. Neutral detergent fiber increased following the freeze for all grasses except Tifton 9, but more dramatically for switchgrass and Argentine. Midwest native species can accumulate tremendous amounts of dry forage in the subtropical U.S.A. for stockpiling but requires protein supplement. While bahiagrass has the reputation of being very poor in quality after a freeze, this study suggests at least one variety (Tifton 9) maintains quality quite well following a freeze and may not require additional supplement for non-lactating cows.