236 POWELL AND BOX Foundation. M. S. Thesis. A & M MCINTYRE, G. A. 1952. A method for preference values of South Texas College of Texas. 88 p. unbiased selective sampling, using woody species for deer and cattle. LI, J. C. R. 1957. Introduction to ranked sets. Austral. J. Agr. Res. J. Range Manage. 19: 212-214. statistical inference. Edwards 3: 385-390. SNEDECOR, G. W. 1956. Statistical Brothers, Inc., Ann Arbor, Michi- POWELL, J., AND T. w. Box. 1966. methods. 5th Ed. The Iowa State gan. 568 p. Brush management influences Univ. Press, Ames, Iowa. 534 p. Bud Activity in the Stem, Crown, and or low water supply prevent growth. Rest is the type of dor- Rhizome Tissue of Switchgrassl mancy referred to when external conditions are favorable, but G. S. HEIDEMANN AND G. E. VAN RIPER= growth is limited by unfavor- Graduate Assistant and Associate Professor, Depar.t- able internal conditions. ment of Agronomy, University of Nebraska, Lincoln. Dormancy has been demon- strated primarily in buds and Highlight in the summer may severely seeds of horticultural crops. Co- Bud activity appears fo be cyclic weaken the switchgrass plant ville (1920) found that dormancy in nafure in the switchgrass plant. and induce the invasion of Certain vegetative buds are dormant commonly occurred among trees weedy species. while others are active during the and shrubs of cold climatic re- growing season. This study suggests Axillary buds located on the fhaf swifchgrass should be grazed gions. rhizomes, crown, and stem por- prior fo floral initiation so ihaf maxi- Evans and Ely (1935) studied mum forage production can be ob- tions of the plant are important the rhizomes of several species tained from acfivaied sfem buds. meristematic areas for vegeta- of grasses and found that both tive reproduction in switchgrass. Switchgrass, Panicum virga- below and above-ground shoots The initiation and development turn (L.), is a perennial, native, develop, to a limited extent, at of these buds determine not only warm-season grass of North all times when weather condi- thickness of stand, but also the America. The warm-season tions were favorable for growth. revegetative potential of the growth habit of switchgrass is Laude (1953) reported that a grass under grazing conditions. advantageous for use in pasture number of perennial grasses in Preliminary investigations at rotation systems. It can be California become dormant dur- Lincoln, Nebraska have shown grazed during the hot summer ing the summer even though that these buds display a sea- months when most cool-season supplied with adequate water. sonal variation in activity. Al- grasses are dormant or semi- He associated summer dormancy though several other perennial dormant. However, early and with high temperature and a grasses also display dormancy medium maturing switchgrass long photoperiod. during the growing season, little decreases rapidly in nutritive In a study of quackgrass rhi- work has been done to charac- value and palatability with ma- zomes (Agropyron repens (L.) terize the nature of this dor- turation. On the other hand, Beauv.), Johnson (1962) found a mancy. when switchgrass is grazed so rest period in April and May The purpose of this study was that the growing point is re- which he described as “late- to determine the seasonal activ- moved before emergence from spring dormancy” rather than ity of buds located on the rhi- the boot, regrowth may be initi- the more common “summer dor- zome, crown, and stem portions ated from the uppermost 2 or 3 mancy.” This conclusion was of the switchgrass plant. axillary buds. Vegetative re- reached because prevailing growth in mid-summer provides Liierafure Review weather conditions before and palatable forage for cattle, and In a review by Samish (1954) during the period were relatively they continue to gain satisfac- the term “dormancy” is defined cool and moist and favorable for torily. Heavy grazing too early as the temporary suspension of quackgrass growth. visible growth; which he further The apical bud of nutgrass 1 Published with the approval of the breaks down into two main (Cyperus rotundus (L.)) has been Director as paper No. 1948, Journal “quiescence” and “rest .” reported to prevent growth of Series, Nebraska Agricultural Ex- types, Quiescence is the type of dor- other buds on the same tubers periment Station. mancy exhibited by the plant (Loustalot et al., 1954). This phe- 2 Now Manager, Department of Agronomy, Engineering Research, when unfavorable external con- nomenon is commonly referred Deere & Company, Moline, Illinois. ditions such as high temperature to as apical dominance. Another SWITCHGRASS BUD ACTIVITY example of apical dominance is Table 1. Elongation and dry weight of rhizome, crown, and stem buds of swifchgrass grown in ihe dark af 28 C for 14 days during 1962.1 that found in the potato tuber. -_ When the intact potato tuber Rhizome Crown buds Stem buds becomes active after a rest pe- Sampling Dry Dry DYY riod, one or more apical buds dates Lengths Weight Length” Weight Length2 Weight cm elongate, but the lateral buds 1962 cm mg cm mg mg usually fail to grow. If, however, 3-10 5.32 - 9.94 - 0.55 - lateral buds and apical buds are 3-22 3.66 - 11.14 - 0.13 - 5.25 98 11.69 325 0.74 cut out and grown separately, 4-5 31 5.39 95 12.26 310 0.42 5 both start growing at the same 4-19 5-3 4.39 64 7.34 115 0.60 13 time (Michener, 1942). 5-17 2.65 28 0 0 2.32 100 It is believed that the dor- 5-31 3.30 45 1.07 6 2.18 35 mancy of buds in woody plants, 6-14 0.61 7 3.78 32 2.16 21 tubers, and herbaceous perenni- 6-28 2.07 32 5.30 75 2.93 31 als have similar fundamental 7-12 2.68 48 6.72 101 2.90 44 processes (Samish, 1954). There- 7-26 4.13 66 7.69 157 4.29 95 fore, since there are few basic 8-9 1.72 34 10.60 304 1.84 40 differences between the buds of 8-23 0.32 6 9.87 240 1.63 38 1.99 34 9.34 342 0.50 12 an underground stem and the 9-6 1.81 38 6.85 244 0.23 5 buds of its above-ground coun- 9-20 10-4 3.30 64 7.16 243 0.75 23 terpart, findings of any of these lo-18 3.87 70 6.46 170 0.76 16 various forms may well be re- 11-15 1.98 37 5.17 214 0.28 9 lated to the others. 1 Implanted in agar and each bud value based on 25 sections for each Materials and Methods sampling date. The experimental area (3200 fts) 2 An average of the longest elongated bud of several which occurred on was located on the Agronomy farm each rhizome or stem-crown section. at Lincoln, Nebraska. Nebraska-28 switchgrass was seeded in April, 1959. A uniform stand was ready for Table 2. Elongation and dry weight of rhizome, crown, and stem buds of swifchgrass grown in the dark ai 28 C for 14 days during 1963.1 sampling in the spring of 1962. The ~__ ~_ ~____ -___ soil was a well-drained Sharpsburg Rhizome buds Crown buds Stem buds silty clay loam which was fertilized Sampling Dry Dry =Y annually with 55 lb/acre of elemental dates Lengths Weight Lengths Weight Length2 Weight N as NH4NOs. The pH of the soil 1963 cm mg cm mg cm mg was 6.0. Seventy-one lb/acre of ele- 3-12 4.67 96 mental P were applied as 42% con- 10.72 312 1.62 24 3-26 5.42 87 10.17 centrated superphosphate on Febru- 214 1.96 28 4-9 4.82 93 8.53 190 1.63 ary 20, 1962. 30 4-23 4.26 63 0 Axillary bud activity of rhizome, 0 1.78 37 5-7 2.42 34 0 1.19 30 crown, and stem was determined by 0 5-21 1.61 16 0 0 2.47 57 using an in vitro method similar to 6-4 2.09 27 1.84 15 0.30 10 that described by Johnson (1961). 6-18 1.48 24 7.96 122 0.42 3 Plant tissue was obtained bi-weekly 7-2 1.56 31 6.39 99 3.53 48 by digging up 2 to 3 ft2 of sod to a 7-16 1.30 20 9.41 220 5.76 152 depth of three to four inches (Tables 7-30 1.85 29 10.54 247 2.58 57 1 and 2). Plants obtained from the 8-13 0.89 20 9.45 258 3.82 83 field were washed free of soil with 8-27 0.82 13 8.65 273 4.00 84 cold tap water. The plants were kept 9-10 0.83 16 11.18 449 2.06 65 moist during the trip to the labora- 9-24 2.49 51 5.04 241 0 0 tory by first wrapping them in a __ -- _- moistened burlap sack, and then 1 Implanted in agar and each bud value based on 25 sections for each placing the entire bundle in a plas- sampling date. tic bag. In the laboratory, the plant 2 An average of the longest elongated bud which occurred on each rhizome material was placed in a refrigera- or stem-crown section. tor at 5 C and removed as needed during processing.