PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



107 



month from May to November, but all plots 

 grazed in August and September yielded more 

 than those not grazed in either of these 2 months. 



McGowan (21) conducted studies on methods 

 of keeping ryegrass in new pastures and of re- 

 storing it to old pastures in which it had been 

 replaced by barley grass and silver grass. The 

 studies showed that grazing at low and seem- 

 ingly impracticable stocking rates was the only 

 way of maintaining ryegrass in a new pasture. 

 Inflorescences and seeds of ryegrass and soft 

 brome are eaten by livestock, whereas those of 

 barley grass and silver grass are not. Harvester 

 ants collect ryegrass seeds but not barley seeds 

 and are more active in heavily than in lightly 

 grazed pastures. The larger quantity of seed 

 available for regeneration in autumn and the 

 deeper cover of plant litter on lightly grazed 

 plots are considered to be responsible, at least 

 in part, for better regeneration of ryegrass at low 

 stocking rates. 



Annual grass pastures that are late cut for hay 

 in early November are generally silver grass 

 dominant in the following year unless resown 

 with ryegrass (21). Seeds of silver grass mature 

 earlier than those of ryegrass or barley grass and 

 may have fallen by time of hay cutting in No- 

 vember. The awned seeds of silver grass establish 

 well on ground bared by hay cutting. Plots that 

 were cut in mid-October for silage when silver 

 grass was heading had twice as many ryegrass 

 seedlings and only 5 percent as many silver grass 

 seedlings in the following year as those cut for 

 hay. Silver grass, unlike the later maturing bar- 

 ley grass, did not produce further tillers after 

 cutting in October. 



McGowan concluded that the only way of re- 

 storing "Wimmera ryegrass to old pastures other 

 than by ploughing, sowing to crops and later re- 

 sowing, was to sod-seed with ryegrass seed in 

 autumn after cutting for hay the previous year. 

 Shier (39) claims that autumn cultivation every 

 3 years will sustain ryegrass in pastures in the 

 Southwest. 



Smith (4-1, 1$) studied the balance between 

 grass and clover in annual pastures and proved, 

 experimentally, the commonly held view that an 

 early break in the season — that is, autumn rain — 

 results in clover dominance, whereas a late break 

 favors grass dominance. He found that the most 



pronounced dominance of clover followed an 

 early break in absence of moisture stress, and 

 that the greatest grass dominance resulted from 

 a late break and subsequent moisture stress espe- 

 cially in the presence of high nitrogen. A factor 

 in grass dominance following a late break is the 

 relatively slow growth rate of clover at low tem- 

 peratures. 



The negative relationship between barley grass 

 and clover yields is a possible explanation of the 

 seemingly anomalous results of Myers and Squires 

 (29) who found that deferment of grazing for 20 

 days, and to a lesser extent for 40 days, followed 

 by continuous heavy grazing for the rest of the 

 season virtually eliminated barley grass from a 

 barley grass-clover pasture. The early break of 

 growing season, induced experimentally in mid- 

 February by irrigation, favored clover; and from 

 the spring yields of dry matter, 2106, 3508, and 

 2700 kg./ha. for the 10-, 20-, and 40-day defer- 

 ment, respectively, it would appear that some pro- 

 tection from grazing was also advantageous to 

 clover. Shading of barley grass stem bases by 

 the early growing clover presumably inhibited 

 basal bud formation and. consequently, the re- 

 placement of primary tillers removed by grazing. 

 For example, Puckeridge (31) suggested that 

 tiller production ceases at high plant densities 

 because of low light intensities below the her- 

 baceous canopy. At low densities, however, tiller- 

 ing is limited apparently by nitrogen rather than 

 by tiller bud numbers. Aspinall (6) showed that 

 tillers do not elongate at low light intensities and 

 postulated that tiller buds and developing seeds 

 compete for nutrients. At low light intensities, 

 carbohydrate levels would be low and in such 

 circumstances it may be inferred from Williams 

 (1(8) that amounts channelled to tiller buds 

 would be small. 



Shoot apices are elevated earlier and floral 

 initiation is more rapid at high densities. It has 

 already been suggested that late defoliations may 

 not stimulate tillering because by then most of 

 the nutrients would have been channelled to in- 

 florescences subsequently removed by cutting. This 

 is a possible explanation of the different effects 

 of defoliation on seed production observed by 

 Rossiter (34) on subterranean clover and those by 

 Loch and Humphreys (20) on Townsville stylo. 

 Earlier defoliation of the more erect tropical 



