IDENTIFICATION AND UTILIZATION OF MECHANISMS RESPONSIBLE FOR THE ADAPTATION OF CATTLE TO STRESSORS OF THE SUBTROPICS
Title: Growth and Quality of Perennial C3 Grasses in the Southern Great Plains
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 13, 2009
Publication Date: May 3, 2010
Citation: Coleman, S.W., Rao, S.C., Volesky, J.D., Phillips, B. 2010. Growth and Quality of Perennial C3 Grasses in the Southern Great Plains. Crop Science. 50: 1070-1078.
Interpretive Summary: Annually planted winter wheat is the major cool-season livestock forage resource in a large part of the southern Great Plains and is a good complement to warm-season (C4) perennial grasses. It has enjoyed popularity by producers because of the flexibility of combining grazing with a grain harvest. However, gaps in forage availability in both fall and spring exist in the system. If a grain harvest is desired, grazing livestock must be pulled at the first hollow-stem stage or grain yield will be reduced. We investigated eight entries of various species of perennial cool-season grasses to determine if they could partially replace or complement the use of wheat pasture. While introduced cool-season perennial grasses are not widely used in forage systems in the southern Great Plains, these data demonstrate they can establish and survive. Growth rate varied among entries and years, but in general the wheatgrass entries produced quite well. In general, they produce adequate high quality forage to support livestock grazing or for haying. However, their ability to produce sufficient forage in the fall for optimum grazing was seldom realized. Forage quality was generally adequate for growing animals (> 10% protein and 65% digestibility as determined by in vitro procedures). Comparison with wheat during two years indicated that if conditions are good for wheat forage growth, then neither the yield nor quality of perennials is as great as the wheat. During dry autumns however, perennials produced more forage that was as high in nutritive value as wheat.
Spring and fall gaps in forage production for systems utilizing winter wheat forage in the Southern Great Plains have led to an interest in additional resources such as C3 perennial grasses. We evaluated the potential of nine cool-season grass entries for forage production and quality through the fall and spring seasons over 4 yr in Oklahoma for growth rate and forage quality. Yield of DM, and percentage of CP, NDF, ADF, and IVOMD were regressed on days to determine daily changes. Following excellent growth in the spring of establishment year, yields in the fall were moderate and only exceeded that needed for optimum animal production in 1 of 3 yrs. Spring growth of ‘Fawn’ tall fescue, ‘Luna’ and ‘Manska’ intermediate wheatgrass and ‘Paiute’ orchardgrass all achieved the minimum amount of forage (1100 kg ha-1) by Feb 1 in all three years. All entries exceed the minimum with > 3000 kg ha-1) in the first 2 yrs. Quality (CP and IVOMD) declined with maturity, but most maintained high IVOMD (> 650 g kg-1) through March each year. In a sequentially staged harvesting regime, there were no differences in month of staging through March of each year, after which yield was significantly reduced. When fall moisture was adequate for wheat pasture, none of the perennial grasses yielded as high nor were as high in quality as wheat, but when moisture was limited, yields of wheatgrasses exceeded those of wheat. However, quality was always lower. Quality seldom exceeded minimum requirements for 1 kg steer gain d-1. Annually planted winter wheat is the major cool-season livestock forage resource in a large part of the southern Great Plains and is a good complement to warm-season (C4) perennial grasses. It has enjoyed popularity by producers because of the flexibility of combining grazing with a grain harvest. However, gaps in forage availability in both fall and spring exist in the system. If a grain harvest is desired, grazing livestock must be pulled at the first hollow-stem stage or grain yield will be reduced (Redmon et al., 1996). Cool-season (C3) perennial grasses common to the Northern Plains or western regions of the United States (Baron et al., 2000; Brummer and Moore, 2000; Volesky et al., 2008) may help fill the fall and spring forage gaps, but only recently have attempts been made to introduce them to the southern Great Plains (Redmon et al., 1997; Reuter and Horn, 2002; Zhao et al., 2008). While some C3 grasses are relatively productive, they are perceived to be inferior in both quantity (Malinkowski et al., 2005) and quality than wheat forage (Phillips et al., 2008). However, they may complement the wheat pasture system with high quality grazing earlier in both the fall and spring season, and provide adequate seasonal spring grazing to allow wheat to be harvested. Producers may still rely on wheat forage from mid-December through early February. Serious gaps exist in our knowledge on how many ha of C3 perennial grass pasture are needed to properly complement the traditional wheat pasture system.
Forage quality of grasses is generally lower than forbs, especially legumes, but C3 perennial grasses are usually higher in forage quality than warm-season grasses (Coleman et al., 2004). However, forage quality is generally more dependent on maturity at harvest than on the species or ecotype. While perennial C3 grasses have potential for high quality, the decline in quality with maturity may be an issue (Nelson and Moser, 1994). Hence, the objectives of these studies were to evaluate accumulated yield, growth rate and changes in forage nutritive value over fall and spring growing seasons.