Row spacing and nitrogen : Effect on alfalfa-bermudagrass quality components

Interseeding legumes into grass sods increases herbage quality. Interseeding alfalfa (Medicago sativa L.) into bermudagrass [Cynodon dactylon (L.) Pers.] has given yields comparable to grass fertilized with high rates of N. Our objective was to compare forage quality attributes of N-fertilized bermudagrass with alfalfa-bermudagrass mixtures. N rates of 0, 112, 224, and 448 kg ha-~ were applied to bermudagrass monoculture and to alfalfa interseeded into bermudagrass at 20-, 40-, and 60-cm row spacings. Experiments were conducted on a Cecil sandy clay loam (clayey, kaolinitic, thermic Typic Kanhapludult) and a Norfolk sandy loam (fine-loamy, siliceous, thermic Typic Kandiudult) site. Hand-harvested herbage samples were separated into botanical components. Crude protein, acid-detergent fiber and neutral-detergent fiber were measured using a combination of wet-lab and near infrared reflectance spectroscopy (NIRS) procedures. Nitrogen increased the crude protein in bermudagrass monoculture by 11 to 61 g kg-~. The crude protein response of bermudagrass in mixtures to N was slight to nonsignificant. Increasing row spacing of alfalfa reduced grass crude protein by 9 to 23 g kg-~ and had no effect on alfalfa crude protein. Fiber fractions decreased slightly in grass with added N, but fiber in alfalfa was not influenced by any treatment. Yield of crude protein increased with N, particularly in bermudagrass monoculture, but interseeding alfalfa without N produced crude protein yields that usually exceeded those of bermudagrass monocuiture at the 448 kg ha-~ N rate. Interseeded alfalfa, even at wide row spacings, appears to produce enough biological N to replace 448 kg fertilizer N ha- ~ or more in the production of herbage protein in bermudagrass. B ERMUDAGRASS forms a dependable perennial base for many pasture and hay production enterprises in the southeastern USA. There are many well-adapted ecotypes of common bermudagrass (BG), as well improved hybrid varieties. All of these cultivars share the common trait of relatively low forage quality for grasses of tropical origin (Moore and Mott, 1973), especially under mid- to late-summer weather conditions (Akin, 1989). The forage quality deficit derives from high fiber concentration (Mertens et al., 1987) and relatively low crude protein concentration in the absence of high rates of fertilizer N. Alfalfa and other legumes exhibit lower concentrations of fiber fractions and higher protein and digestible energy than grasses (Sheaffer et al., 1990), and have been used to increase forage quality and animal performance on grass-based pastures (Burns and Standaert, 1985). Alfalfa can be established and will persist when interseeded in BG sods (Brown and Byrd, 1990; and Stringer et al., 1994). Yields of interseeded mixtures were equivalent to BG monoculture fertilized with 200 kg ha-1 or more of N. The growing season was lengthened by earlier growth initiation in spring and more active growth in autumn. Bermudagrass persistence Dep. of Agronomy and Soils, P.O. Box 340359, Clemson, SC 29634-0359. Contribution of the South Carolina Agric. Exp. Stn. Journal no. 4127. Received 25 Sept. 1995. *Corresponding author (Email: bstrngr@ clemson.edu).