Nitrogen is an important agronomic input for bermudagrass production in the southern USA. Fertilizers that can efficiently provide N to grass pastures and hay meadows are an important issue because of increasing costs and environmental problems associated with N losses. This experiment was designed to determine the effectiveness of various N sources on ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] production and N uptake efficiency. Nitrogen was applied at 0, 45, 90, and 135 kg ha−1 harvest−1 as urea–ammonium nitrate (UAN), urea, ammonium nitrate (AN) and ammonium sulfate (AS) on Gallime (Glossic Paleudalf) and Lilbert (Plinthic Paleudult) soils. Mixtures of S with UAN and of Ca and B with urea were also evaluated. Bermudagrass was periodically harvested and subsampled for total N analysis. At termination of the study soil samples were collected for pH and extractable NO3–N analyses. Bermudagrass yield responses to N sources were significant only in the Gallime soil. In this soil, AN and AS increased yields and resulted in greater N uptake compared to urea and UAN. Lilbert soil showed no effect of N sources on dry matter (DM) production. There was a yield response to N rates and maximum bermudagrass production was generally achieved at the 90 kg ha−1 N rate regrowth−1. Fertilizer efficiency declined as the N rate was increased. Soil acidity increased in response to N application, particularly for the AS treatments. Selection of N sources and rates should be carefully planned to avoid detrimental effects on soil acidity and, consequently, fertilizer efficiency.

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.

Information about dinitrogen (N2) fixation and transfer is needed to determine potential benefits from growing binary mixtures of alfalfa (Medicago sativa L.) and hybrid bermudagrass [Cynodon dactylon (L.) Pers.] on Coastal Plain soils of the USA. Our objectives were to quantify N2 fixed by alfalfa and transferred to bermudagrass. ‘Alfagraze’ alfalfa was grown at row spacings (RS) of 23, 46, 69, and 91 cm in a mixed stand with ‘Coastal’ bermudagrass on a Darco loamy fine sand (loamy siliceous, semiactive thermic Grossarenic Paleudult). The mixed stand was fertilized with 0, 28, 56, 84, and 112 kg N ha−1 applied for each bermudagrass regrowth. Isotope dilution was used to estimate N2 fixation and subsequent transfer to bermudagrass in the zero‐applied N plots. Wider alfalfa RS significantly increased bermudagrass yields. Higher N rate (NR) significantly improved bermudagrass yield during cool temperature and drought stress periods in 1994 and 1996. Narrower RS and higher NR significantly increased alfalfa production. Legume N derived from the atmosphere ranged from 42 to 91% and the fixed N yield ranged from 80 to 222 kg N ha−1 yr−1. Bermudagrass N derived from atmospheric N2 fixation ranged from 1.0 to 77%, and the transfer N yield (TNY) was ≤18 kg N ha−1 yr−1. Results varied depending on harvest date, year, treatment, and grass yield. Alfalfa RS had little effect on TNY. The low bermudagrass yield and subsequent TNY in this binary forage production system suggest that monoculture alfalfa may be the best approach for managing alfalfa on Coastal Plain soils.

Alfalfa (Medicago sativa L.) is rarely grown on the Coastal Plain of southern United States. Production problems include infertile acid soils, inadequate pest control, and high humidity with frequent rainfall events that preclude adequate alfalfa hay drying conditions in spring. Research to overcome soil fertility problems included evaluation of nitrogen (N) rates over alfalfa row spacings and limestone and boron rates in split plot studies; phosphorus (P) rates using a randomized complete block design on eight soil series; and potassium (K), magnesium (Mg), and sulfur (S) rates and zinc (Zn), copper (Cu), and molybdenum (Mo) rates in central composite, rotatable design studies. Field-scale demonstrations were conducted to verify data from small plot research. Results indicate little need for N fertilization of alfalfa on Coastal Plain soils except possibly under cool or dry surface soil conditions. Increasing the between-row planting distance from 23 to 69 cm lowered alfalfa dry matter yield by 2.1 Mg ha 21 the seedling year. Alfalfa yielded 11 Mg ha 21 at all row spacings in the drought-affected third year. Dry matter yield was maximized at 49 -73 kg applied P ha 21 on soils testing below 19 mg P kg 21 by the NH 4 OAc-EDTA extraction method. The alfalfa stand was lost after one season on plots not fertilized with K. Applied Mg, S, Zn, Mo, and Cu had no significant effect on alfalfa yield. Dry matter increased .5 Mg ha 21 as pH was increased from 6.0 to 7.5. Boron applied at 3.4 kg ha 21 increased alfalfa yields 3.9 Mg ha 21 . With improved methods for site selection and adequate fertility, sustainable economic production of alfalfa is possible with rain-fed conditions on selected, limed Coastal Plain soils.

Slow reactivity of coarse-grade ag-lime surface applied on soils established to perennial grasses led us to study the effectiveness of finer-ground limestone. Legume production and soil pH were used to evaluate treatments in a glasshouse experiment that included soil-incorporated and surface-applied limestone at increasing rates and effective calcium carbonate equivalence (ECCE) percentages that can be converted to kilograms of effective liming material (ELM) Mg 21 . Excessive rates of limestone and the highest ECCE percentage materials decreased clover yield when applied and left on the soil surface. Comparison of ECCE 62% limestone with ECCE 100% limestone verified the initially greater efficiency of the finer lime for forage production. Four to seven years after application, annual ryegrass yields were similar for the ECCE 62% and 100% limestone materials. Seven years after the final 2935