Response of Overseeded Alfalfa and Bermudagrass to Alfalfa Row Spacing and Nitrogen Rate

Abstract

Alfalfa (Medicago sativa L.) is a rare forage crop on Coastal Plain soils. Acid soils, wet conditions, and the prevalence of perennial, warm‐season grasses limit alfalfa production. Development of grazing‐tolerant varieties raised interest in growing alfalfa on the Coastal Plain. This three‐year dryland field study was conducted to evaluate coincident production of ‘Alfagraze’ alfalfa and ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] as a sustainable forage system. Limestone (effective calcium carbonate equivalence ECCE 72%) at a rate of 6.1 t ha−1 was incorporated by roto‐tilling 15 cm deep in an established sod of Coastal bermudagrass on a Darco loamy fine sand (loamy, siliceous, thermic Grossarenic Paleudults) in late winter 1990, with an additional 3 t ha−1 surface‐applied in June 1991. Alfalfa was seeded in October 1990 at 23, 46, 69, and 92 cm between rows in main plots of a split‐plot design. Nitrogen rates from 0 to 112 kg ha−1 in increments of 28 kg ha−1 were applied to subplots for every bermudagrass regrowth cycle. Other plant nutrients (including P, K, Mg, S, B, Zn, and Cu) were applied at rates considered adequate for alfalfa on a low‐fertility soil. Yield of alfalfa at the 23‐cm row spacing in 1991 was 8.8 t ha−1 and declined to 6.7 t ha−1 at 69cmtrue(P=0.05true), while yield of bermudagrass increased from 3.2 to 5.7 t ha−1, respectively, at these row spacings. In 1992, alfalfa yield increased an additional 2.2 t ha−1 at each row spacing, with a compensating decline in bermudagrass production. Alfalfa yielded 11 t ha−1 at all row spacings in 1993, despite a midseason drought, while bermudagrass yield was <450 kg ha−1. Row spacing had no effect on total forage production in any year. Higher N rates increased bermudagrass yield the first two years. Applied N increased alfalfa yield at certain harvests, but had no effect on total annual production. Crude protein in alfalfa declined or remained similar as row spacing was widened. Soil pH was lowered by increasing N rates and by narrower alfalfa row spacings. Results indicate that alfalfa competes well with Coastal bermudagrass, even in drought conditions.

Sustainable Alfalfa Production on Coastal Plain Soils of the United States

“…In the humid eastern United States, fertilizer recommendations based on soil test results indicate the need for K application (11), particularly in low buffer capacity, acid sandy soils testing low to medium in plant-available K. Coarse-textured soils sometimes are better suppliers of K for plant growth than would be expected based on exchangeable K concentrations (12). Splitting 372 kg K ha 21 at rates of onehalf each in fall or spring, or one-fourth for each cutting, starting in early spring, did not increase the 3-yr average yields of alfalfa on a loam soil at a yield level of 17 Mg ha 21 (13). Calcitic and dolomitic limestones are the principal sources of Ca, and dolomitic limestone supplies Mg when applied to acid soils.…”

“…Increasing N rates split applied for each bermudagrass growth period significantly increased bermudagrass dry matter at yield levels that declined annually but had little effect on total annual yield of alfalfa dry matter production on a Darco loamy fine sand (21). Applied N significantly increased alfalfa dry matter production at specific harvests.…”

“…Deep, coarse-texture soils low in organic matter have the greatest supplemental S requirement for crop production. An application of 28 kg S ha 21 was optimum for alfalfa growth on responsive sites (14). Inorganic soil S is mobile and susceptible to leaching.…”

“…Phosphorus application at seeding is an accepted practice in the United States and Canada, particularly on soils testing low in P. However, rates of 45 kg P ha 21 applied at planting resulted in decreased seedling growth measured after 10 weeks in both low and high testing soils (9). Smith and Powell (10) concluded that 57 kg ha 21 Bray P1-P was an adequate soil level for yields of 7-8 Mg ha 21 . In the humid eastern United States, fertilizer recommendations based on soil test results indicate the need for K application (11), particularly in low buffer capacity, acid sandy soils testing low to medium in plant-available K. Coarse-textured soils sometimes are better suppliers of K for plant growth than would be expected based on exchangeable K concentrations (12).…”

Allelopathic Effects of Cereal Rye on Weed Suppression and Forage Yield in Alfalfa

“…Most of these growers were attracted to alfalfa because they have seen enormous improvement in the quality of their hay, and they were able to save on the application of nitrogen fertilizer. Studies evaluating the sustainability of production of alfalfa interseeded in bermudagrass showed that alfalfa competes well with bermudagrass, even in drought conditions [11]. Another part of the forage system in the region is cereal rye that is grown for late fall and early winter grazing when bermudagrass goes dormant.…”