CROP QUALITY & UTILIZATION Nitrogen Fertilization of Buffalograss

spp.) showed that forage DM intake was positively correlated with N fertilization rate. Fertilization may also Because native, shortgrass prairies are not typically fertilized and increase forage preference by livestock. Cook and Jeffotherwise extensively managed, little information is available on their response to nitrogen (N) fertilization. An experiment was conducted eries (1963) showed that cattle grazed previously fertilin 1997 and 1998 to study the effects of N fertilization on forage yield ized areas substantially more than unfertilized areas. and quality, forage height, and subsequent nitrate accumulation in the Similarly, Hooper et al. (1969) showed that it was feasisoil of a rangeland site consisting primarily of buffalograss [Buchloë ble to manage for more uniform distribution of forage dactyloides (Nutt.) Engelm.]. The N treatments were 0, 34, 68, 102, utilization and increased profitability by fertilizing pasand 136 kg ha21 arranged in a Latin square design. An increase (P , ture and range. 0.05) in forage dry matter (DM) yield was obtained with 34 kg ha21 Because native shortgrass prairies are typically not N. Greater (P , 0.05) forage yields were achieved with an additional fertilized and otherwise extensively managed, little in102 kg ha21 N (total 136 kg ha21 N). Forage yields averaged 2540 kg formation is available on their response to N fertilizaha21 in 1997 and 2340 kg ha21 in 1998. Nitrogen fertilization increased tion. Thus, the objectives were to study the effect of N crude protein (CP) of buffalograss forage. Each unit of 34 kg ha21 N linearly increased CP up to approximately122 g kg21 of DM forage. fertilization on forage yield and quality, forage height, Weather conditions influenced in vitro digestible dry matter and nitrate accumulation in the soil of a rangeland site (IVDDM). As long as moisture conditions were favorable for forage consisting primarily of buffalograss. growth, IVDDM increased linearly with N fertilization rate. In 1997, IVDDM ranged from 565 g kg21 for the control to 658 g kg21 for the MATERIALS AND METHODS 102 kg ha21 N application rate. In 1998, IVDDM declined linearly (P , 0.05) with N fertilization rate. In vitro digestible dry matter This study was conducted at the Oklahoma Panhandle Research and Extension Center, Goodwell, OK, (368359 N, averaged 539 g kg21 for the control to 482 g kg21 for the 136 kg ha21 N application rate. Nitrogen fertilization of buffalograss dominated 1018379 W, elevation 992 m) on a Richfield clay loam soil (Fine, smectitic, mesic Aridic Argiustolls). Plots were established on semiarid rangeland can enhance forage production and quality. Nitrate accumulation in the soil was insignificant over the study period. a native, rangeland site consisting primarily of buffalograss (.90% cover). The experiment consisted of four N fertility treatments, 34, 68, 102, and 136 kg ha2 N (urea, 46-0-0) and a check (0 kg ha2 N). Twenty-five plots (3.3 by 7.5 m) were A of fertilization trials have been conarranged in a Latin square design. Prior to fertilization the ducted on native and reseeded rangeland sites in first year, two soil samples were taken from every plot to the Great Plains (Huffine and Elder, 1960; Launchprovide a baseline for nitrate accumulation. Soil was sampled baugh, 1962; Burzlaff et al., 1968; Warnes and Newell, at the 0to 15and the 15to 60-cm depths. Soil samples were 1969; Rehm et al., 1972; Pettit and Deering, 1974; Samtested for nitrate content at the Oklahoma State University uel et al., 1980; Gillen et al., 1987; Berg, 1990; Hart et Soils Laboratory, Stillwater, OK. Plots were fertilized on 24 June 1997 and on 30 June 1998. Plots were harvested on 26 al., 1995; Gillen and Berg, 1998); however, midand tall Aug. 1997 and on 1 Sept. 1998. After harvest each year, soil grass species dominated in these studies and results were samples were collected and tested as outlined previously. mixed among experiments. Increases in forage DM proAt harvest each year forage height was measured on each duction have been achieved with as little as 34 kg ha21 plot. The forage DM yield of each plot was determined by N and greater than 100 kg ha21 N (Burzlaff et al., 1968; harvesting a 0.5by 7.5-m area to a stubble height of 5 cm Lorenz and Rogler, 1972). Increases have also been through the center of each plot. The harvested material was reported for crude protein concentration in forages ferweighed fresh, a 250to 300-g subsample collected and dried, tilized with nitrogen (Houston and van der Sluijs, 1975). and DM determined. The total DM of each plot was calculated Several known benefits can be attributed to fertilizaby multiplying the DM content of the oven-dried sample by tion. Forage availability and forage DM intake by livethe harvested green weight of the plot and converted to kg ha2. Oven-dried samples were ground to pass a 1-mm screen stock increase with increasing N fertilization rate. Burin preparation for analysis of CP concentration and IVDDM. ton et al. (1956) with bermudagrass [Cynodon dactylon Crude protein concentration was determined by procedures (L.) Pers.] and Cook (1965) with wheatgrass (Agropyron outlined by AOAC (1990). In vitro digestible dry matter was determined with the ANKOM system (ANKOM Technology Corp., Fairport, NY). C.M. Taliaferro, Oklahoma State Univ., Dep. of Plant and Soil Sciences, Stillwater, OK 74078; T.L. Springer, USDA-Agric. Res. Serv., Data for forage height, DM production, CP concentration, Southern Plains Range Res. Stn., 2000 18th Street, Woodward, OK and IVDDM were analyzed as a Latin square design analysis 73801. Contribution of the Oklahoma Agric. Exp. Stn. Received 13 March 2000. *Corresponding author ([email protected]). Abbreviations: CP, crude protein; DM, dry matter; IVDDM, in vitro digestible dry matter; N, nitrogen. Published in Crop Sci. 41:139–142 (2001).