Row Spacing and Nitrogen: Effect on Alfalfa-Bermudagrass Quality Components
- William C. Stringer ,
- Benjamin C. Morton and
- Bruce W. Pinkerton
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−1 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−1. 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−1 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−1 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.
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