Nitrogen Fertilizer Efficiency in Bermudagrass Production

Abstract

AbstractEfficient N applications are necessary to maximize bermudagrass (Cynodon dactylon L.) dry matter yield and N uptake in forage. Significant losses of NH3 from surface applications of urea and NH4‐N fertilizers by volatilization have been reported. Field experiments were conducted over a three‐year period under a wide range of climatic and soil conditions in Oklahoma to determine the efficiency of N applications for dry matter production and N uptake in bermudagrass forage. Four locations were selected in 1978 and one each in 1979 and 1980, representing four typical soil types for bermudagrass production with a pH range of 4.7 to 6.9. Anhydrous ammonia (AA) and ammonia passed through a Cold‐Flo adapter (ACF) were injected into bermudagrass sod and urea‐ammonium‐nitrate (UAN), urea, and (NH4)2SO4 (AS) were broadcast. Rates of N were 0, 112, 224, and 448 kg·ha−1 initially as well as 224, 336, and 448 kg·ha−1 in split applications. An additional experiment was established in 1980 to evaluate the effect of S on yield and N uptake. Rates of S were 0 and 64 kg · ha−1 and sources were elemental S, CaSO4 · 2H20, MgSO4, and AS. There were two harvests at each location in 1978, three in 1979, and two in 1980.Yield and N uptake from AA and ACF applications were not significantly different, but generally were lower than with broadcast UAN, urea, and AS. Yield and N uptake generally were lower from urea than UAN and AS. Relative efficiency of N sources obtained from averaging across N response experiments were in the order of AS > UAN > urea > AA > ACF. Split application of N in 1978 and 1980 did not increase yield, but in 1979 an increase in yield was obtained with more even rainfall distribution during the growing season. Sulfur fertilization decreased N:S ratios in forage, but did not increase yield or N uptake or improve N efficiency. Potential losses of NH3 by volatilization from broadcast urea, UAN, and AS in these experiments were considered minimal.