PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



117 



tectorum (7). These studies show that the compe- 

 tition for soil moisture by cheatgrass growing 

 with Agropyron spp. is intense. 



Herbicides have been used to manipulate plant 

 competition during the seedling stage. Kay and 

 McKell (2£) used preemergence herbicides to con- 

 trol competing annual range species, and favor 

 the establishment of Trifolium hirtum and Phal- 

 aris tuberosa L. var. stenoptera (Hack.) Hitch. 

 Before weather conditions became favorable 

 for seeding, an experimental area was burned 

 to remove old litter and concentrate seeds at the 

 soil surface. Subsequently, preemergence herbi- 

 cides were applied to the surface. Two months 

 later, after favorable moisture conditions oc- 

 curred, the experimental plots were seeded with 

 the introduced species. Competition from an- 

 nual weeds was sufficiently controlled to allow 

 successful stand establishment of the introduced 

 species. Chemical treatments which were most 

 effective included atrazine. simazine, and EPTC 

 at rates from 2 to 4 pounds per acre. Subsequent 

 refinements of the original techniques have re- 

 sulted in considerable success. Kay 2 applies a 12- 

 inch band of paraquat, then seeds introduced 

 species below it. The seeds are protected by the 

 soil from the effect of the chemical, which de- 

 stroys the young annual grasses and forbs on 

 the surface. 



Root Growth 



Rapid root growth is fundamental to establish- 

 ment and development in annual rangeland com- 

 munities, particularly when moisture stress is a 

 constant threat during the period of plant estab- 

 lishment. Species may acquire a competitive ad- 

 vantage under stress conditions by (a) a faster 

 rate of root growth, or (b) the ability to remain 

 active in both root and top growth for a longer 

 period. This extra growth is most important at a 

 time when competing plants are inactive, or at 

 the end of the growing period. Harris and Wil- 

 son (10) reported that rapidly elongating B. tec- 

 torum and T. asperum roots penetrated the soil 

 .ahead of Agropyron spicatum (Pursh) Scribn. 

 & Smith, because they were able to continue root 

 growth at low temperatures. Field studies indi- 

 cated that B. tectorum roots grew well at temper- 



Personal communication, 1971. 



atures as low as 3° C, while A. spicatum roots 

 grew very slowly at temperatures below 8° to 10°. 

 Therefore, B. tectorum seedlings are able to gain 

 a competitive advantage over seedlings of A. 

 spicatum by rapidly elongating their roots during 

 winter months and using moisture through a 

 large portion of the soil profile. 



Any management practices which influence root 

 growth are extremely important as tools in ma- 

 nipulating the annual plant forage resource. Fer- 

 tilization has been shown to increase the overall 

 abundance of roots in the areas normally occu- 

 pied by roots of annual range species, although 

 rooting depth was not changed much (39). 



Grazing management also has a significant ef- 

 fect on root growth. Numerous studies (19, 20) 

 have shown that intense grazing decreases root 

 growth. In general, plants which are grazed ex- 

 cessively will have a much shallower root system 

 than will plants which are grazed conservatively 

 or not at all (31). This favors greater root de- 

 velopment and greater seed production of less 

 palatable species, and of late-growing weedy spe- 

 cies, such as tarweed and other noxious annual 

 forbs. 



Grazing management may also be used as a 

 means of balancing competition during the es- 

 tablishment phase of annual and perennial seeded 

 species. Love (32) recommends a moderate 

 amount of grazing during the early spring period, 

 when plant competition is extreme. If competi- 

 tion is not reduced, growth of seeded species is 

 retarded. 



Top Growth 



In the developing annual seedling, expansion 

 of leaf blades proceeds at a rapid pace. With 

 the development of tillers upon tillers, the in- 

 crease in diameter of the grass plant can be rap- 

 id; this increase may begin in the late fall and 

 proceed into the early spring period of growth. 

 Under extremely crowded conditions, tillers do 

 not form, and only single stemmed grass plants 

 result. Competition with other species is critical 

 to the development and survival of annual range 

 species at this point. With sufficient space, most 

 species begin to expand the diameter of the 

 plant. Under very dense crowding, little if any 

 expansion takes place, and grasses continue to 

 grow with a single upright rolled leaf sheath 



