108 



MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



legume to allow access of light and induction of 

 branching and flowering at lower nodes may pos- 

 sibly prevent losses in seed production from graz- 

 ing prior to flowering, but experiments are needed 

 to verify this. 



The failure of bulrush millet to develop axil- 

 lary tillers, following removal of shoot apices 

 by cutting or grazing, may be due also to low 

 light intensities at stem bases and to competing 

 demands of large and rapidly growing stems for 

 nutrients. Here, again, the possibility of altering 

 the morphology of the plant by grazing appears 

 worthy of study. 



From the few data available at present, it 

 appears that the stages of morphological develop- 

 ment in which annuals can be utilized most effec- 

 tively may differ for tropical and temperate spe- 

 cies. Grazing after floral initiation and during 

 stem elongation stimulated seed production in 

 temperate but not in tropical species. Grazing at 

 this stage also increased dry matter production 

 in barley grass but, again, not in the tropical 

 bulrush millet. 



According to Smith (4-1, 1$) the most impor- 

 tant single factor in winter productivity of an- 

 nual pastures is plant density, thus emphasizing 

 the importance of seed setting, seed survival and 

 germination on composition and productivity. 

 Donald (15, 16, 17) showed that yields of dry 

 matter per unit area of both clover and ryegrass 

 increased steeply to a maximum and remained 

 constant, despite further increases in plant den- 

 sity. However, the number of seeds per unit area 

 reached a maximum and then declined with fur- 

 ther increases in density. The highest numbers 

 of seeds per plant were attained at the lowest 

 density, but the individual seed weights and num- 

 bers of seeds per inflorescence were greatest at 

 higher densities. Donald (17) explains these re- 

 sults on the basis of intraplant competition — at 

 the lowest density there would be no competition 

 during the early stages of growth, and flower 

 primordia would develop in large numbers. Con- 

 sequently, at flowering and seed setting, inflo- 

 rescences would be numerous, and competition 

 among them would reduce seed production per 

 inflorescence and size of seeds. At higher densi- 

 ties, interplant competition would be operative 

 at floral initiation and would reduce the number 



of inflorescences and, thus, subsequent competi- 

 tion among them. 



The developmental morphology of the tem- 

 perate annual pasture species for which data are 

 available appears to be similar, and the principal 

 problem in the management of annual pastures 

 appears to be control of species composition. 



Grazing from the beginning of the growing 

 season, with high stocking rates during the period 

 of stem elongation to promote seed production, 

 would seem to be the most appropriate manage- 

 ment system for self-regenerating temperate 

 grasses and legumes. Adverse effects of high 

 stocking rates are discussed by Sharkey and 

 others (37) and by Rossiter (36). Beneficial ef- 

 fects are discussed by Davidson and Donald (llf) 

 and by Smith (4.1, 44)- 



Deferment of grazing in the early part of the 

 season, mowing when grasses are in head, or 

 both, appears to promote legume dominance. In 

 the early part of the season, grasses are favored 

 by grazing and by high levels of nitrogen and 

 phosphorus (28, 35. 45, 50). It seems that where 

 animal production depends on annuals, an effec- 

 tive system of husbandry would be to have grass 

 and legume dominant pastures and to manage 

 them to achieve changes in dominance every few 

 years. 



There seems little scope for management in 

 arid areas, other than for the preservation of the 

 perennials of the community and the mainte- 

 nance of soil conditions suitable for the reestab- 

 lishment of annuals. 



Literature Cited 



(1) AlTKEN, T. 



1955. FLOWEB INITIATION IN PASTURE LEGUMES. I. 

 FACTORS AFFECTING FLOWER INITIATION IN TRI- 



folium subterraneum l. Austral. J. Agr. Res. 

 6: 212-244. 



(2) 



(3) 



1955. flower initiation in pasture legumes. II. 

 geographical implications of cold tempera- 

 ture requirements of trtfolium subterrane- 

 um l. Austral. J. Agr. Res. 6: 245-257. 



1955. FLOWER INITIATION IN PASTURE LEGUMES. III. 

 FLOWER INITIATION IN MEDICAGO TRIBULOIDES 

 DESV. AND OTHER ANNUAL MEDICS. Austral. J. 



Agr. Res. 6: 259-264. 



(4) 



1962. SHOOT APEX ACCESSIBILITY AND PASTURE MAN- 

 AGEMENT. J. Austral. Inst. Agr. Sci. 28: 50-52. 



