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The seasonal change ol dry matter (DM) yield, estimated in vivo dry matter digestibility (DMD), and crude protein content of the vegetative and floral tillers of ‘Rosana’ western wheatgrass (Agropyron smithii) and ‘Lodorm’green needlegrass (Stipa viridula) was determined on forage harvested April through October on 10 dates during 1973 and on 11 dates during 1974. Vegetative tillers on both grasses were comparable in seasonal DM yield, DMD, and crude protein for both years. Flora tillers of western wheatgrass produced only 20% as much forage as did floral tillers of green needlegrass; however, they contained on the average 2 and 4 percentage units more crude protein and DMD, respectively, than floral tillers of green needlegrass. On an average, floral tillers contained 4 and 8 percentage units fess crude protein and DMD, respectively, than companion vegetative tillers. When floral tillers are harvested before DMD decreases below 5090, they are most valuable for maintenance of mature animals. Preventing development of floral tillers would increase DMD but decrease DM yield. Range managers, planning their grazing management for native rangeland in the northern Great Plains, should consider more than dry matter (DM) yield and forage quality of whole plants. They should also consider DM yield and quality of floral and vegetative tillers. Their ratio can be manipulated by management (Lawrence 1973, Hyder and Sneva 1963, Field and Whitford 1980). Damage or removal of floral primordia prevents floral tiller development and the tiller remains vegetative. Lawrence (1973) showed that cutting Russian wildrye (Elymus junceus) during late May or early June prevented floral tiller development. Hyder and Sneva (1963) proposed heavy livestock grazing of crested wheatgrass (Agropyron desertorum) when the shoots were in the boot stage to remove flora primordia. Application of growth regulators can also change the ratio of floral to vegetative tillers (Field and Whitford 1980). Timing of management practices to prevent floral tiller development will depend on time of floral primordia initiation. Some species such as western wheatgrass (Agropyron smithii), prairie junegrass (Koeleria cristata), Russian wildrye, and other temperate-origin grasses initiate floral primordia in the fall (Lawrence and Ashford 1964, Johnston and MacDonald 1967, and Hodgson 1966). However, those species that require vernalization for floral induction initiate the floral primordia in the spring (Evans 1964). Preventing development of floral tillers could reduce forage yield, yet increase forage quality if the tillers remained culmless. Knowledge is needed of seasonal DM yield and quality of both vegetative and floral tillers of major forage species before management systems are formulated that will prevent development of floral tillers. The author is range scientist, USDA, Agricultural Research Service, Northern Plains Soil and Water Res. Center, P.O. Box 110!2, Sidney, Mont. 59270. This study is a contribution from USDA, Agricultural Research Service, in coopcration with Montana Agr. Exp. Sta., Sidney, Mont. Journal Series No. 1295. Manuscript received June I, 1982. 402 The in vitro digestibility of whole plants of western wheatgrass or green needlegrass (Stipa viridula) have been studied (Bezeau and Johnston 1962, Kamstra 1973, Lawrence 1978, White and Wight 1981). Still needed is information on the seasonal change of DM yield and DMD of vegetative and floral tillers of western wheatgrass and green needlegrass. The objective of this study was to determine the seasonal change of DM yield, DMD, and crude protein content of vegetative and floral tillers of western wheatgrass and green needlegrass. Materials and Methods The study was conducted on a Shambo soil (fine-silty, mixed Typic Haploborolls) 7 km southeast of Sidney, Mont., at an elevation of 610 m. Average annual precipitation at this site is 345 mm, with 21% received from October through March, 44% from April through June, and 35% from July through September. Precipitation from October 1972 through March 1973, April through June, and July through September 1973 was 73, 134, and 129% of normal, respectively. Precipitation from October 1973 through March 1974, April through June, and July through September 1974 was 103, 104, and 8 1% of normal, respectively. January and July long-term mean temperatures are -13 and 2O“C, respectively, and the average frost-free is 125 days. The study was conducted during 1973 and 1974 on adjacent fields of ‘Rosana’ western wheatgrass and ‘Lodorm’ green needlegrass seeded during early September 1971. The land had been summer-fallowed during 1970 and 1971. Both species were seeded at 30 live seeds per meter of row with a double disc drill with openers spaced 18 cm apart. Clipping plots were arranged in a randomized, complete-block design with 4 replications (each 6 by 20 m) per grass species. Forage was harvested from different 0.36-m by 4-m clipping plots with a 0.4-m border between plots in the western half of each replication on 10 dates during 1973 and from the eastern half on I I dates during 1974. Plants were sampled on a biweekly interval from April through July and then monthly through October. At each sampling date, plants on a previously unharvested plot were clipped 5 cm above ground and separated into vegetative and floral tillers. Plant material was dried at 700 C and ground to pass through a l-mm screen before analyses. A modified Tilley and Terry (1963) two-stage method was used to determine in vitro DMD as previously described by White et al. (198 1). To overcome random week-to-week variation, standard forage with a known high, medium, and low in vitro DMD were included in each run and their deviations from a long-term average were used to correct all values. The resulting in vitro DMD values were converted to estimated in vivo DMD by using a regression equation previously reported by White and Wight (1981): Estimated in vivo DMD = 10.78 -I0.767 (in vitro DMD); R = 0.87 This equation was previously determined as the regression of in JOURNAL OF RANGE MANAGEMENT 38(3). May 1983 vivo DMD of 8 forages, fed to sheep, upon the in vitro DMD of A two-way analysis of variance was performed on DM yield, these same forage samples determined by the above procedure. DMD, and crude protein of vegetative and floral tillers of each Nitrogen was determined with an auto analyzer (Schuman et al. species in each year. All differences discussed in this paper are 1973) after forage samples had been wet digested on a block significant (o-CO.05) unless otherwise stated. Linear regression digestor. Nitrogen concentration was multiplied by 6.25 to estianalysis was used on DMD and crude protein data for the period May-July, when values were declining linearly, to determine the mate crude protein. average decrease per day.

Seasonal Changes in Yield, Digestibility, and Crude Protein of Vegetative and Floral Tillers of Two Grasses