PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



39 



1.5 M i 



30.5CM 



DEGREES 



CENTIGRADE 



Figure 4. — Examples of mean weekly temperature profiles for early spring and midsummer, along with diurnal vari- 

 ations, under an orehardgrass sod (1965). 



The maturit}^ of Potomac orehardgrass in this 

 first experiment was shifted as much as 2 weeks 

 by combinations of soil temperature, light inten- 

 sity, and nitrogen fertilization. For this and 

 other reasons S-37, a late-maturing orehardgrass, 

 and Climax timothy were added to the next ex- 

 periment (table 2). 



In 1966, Potomac at 32° C. started heading 

 April 20. Within 7 days, heads appeared on Po- 

 tomac at 21° and S-37 at 32°. By May 26, all 

 Potomac plants at 32°, 90 percent at 21° and 85 

 to 90 percent at ambient had flowered, but at 10° 

 plants were still in the late joint to early head 

 stages. S-37 at 32° was similar to Potomac at 

 21°. A few heads were emerging from Climax 

 sheaths at 32°, but at cooler soil temperatures 

 this species was either in the early joint or vege- 

 tative growth stages. This response was repeated 

 each spring and is similar to reports of others 

 (44, 62, 67). Ridley and Laude (52) reported 



temperatures near the stolon apex of white clover 

 to have a greater influence on flowering than tem- 

 peratures in the vinicity of expanded leaves. 

 Likewise, temperatures in the crown area of 

 grasses in this study had a major effect on tiller, 

 crown, and root growth. 



Forage yields from the second study were 

 highest for Potomac followed by S-37 and then 

 Climax but these differences were not always 

 significant (table 2). Climax produced 86 per- 

 cent as much forage as Potomac when grown at 

 10° but only 56 percent as much when grown at 

 32°. The pattern was similar between Potomac 

 and S-37, but differences were smaller. Varieties 

 originating in cooler regions were less tolerant 

 of high soil temperatures, and timothy was more 

 sensitive than orehardgrass. This resembles find- 

 ings of Watschke and others (74.), where blue- 

 grasses originating in warmer regions were better 

 adapted to high soil temperatures. Duncan and 



