40 



MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



Table 2. — Dry matter yields per plot from three forage grasses grown 

 at four soil temperatures 



Soil 







Dry matter yield per 



plot 1 



temperature 



Species 



1966 



1967 



1968 







100 g. 



100 g. 



100 g. 



Ambient 



Potomac 



6.56 cd 



10.04 ab 



8.62 be 





S-37 



6.54 cd 



9.76 abc 



7.39 ef 





Climax 



4.70 ef 



8.31 e 



7.09 f 





Av. 



5.93 C 



9.38 AB 



7.70 B 



32° C. 



Potomac 



4.82 e 



6.82 f 



7.16 ef 





S-37 



4.51 f 



5.99 f 



5.62 g 





Climax 



2.52 g 



4.17 g 



3.86 h 





Av. 



3.83 D 



5.66 C 



5.55 C 



21° C. 



Potomac 



7.01 be 



8.97 cde 



8.45 bed 





S-37 



6.65 c 



8.61 de 



7.43 def 





Climax 



5.96 d 



8.76 de 



7.23 ef 





Av. 



6.61 B 



8.77 B 



7.70 B 



10° C. 



Potomac 



7.61 ab 



10.45 a 



9.68 a 





S-37 



7.68 a 



9.82 abc 



9.30 ab 





Climax 



6.56 cd 



9.28 bed 



8.16 cde 





Av. 



7.28 A 



9.86 A 



9.05 A 



Average : 



Potomac 



6.50 X 



9.07 X 



8.48 X 





S-37 



6.25 X 



8.54 Y 



7.44 Y 





Climax 



4.78 Y 



7.63 Z 



6.58 Z 



CV, percent 





17.1 



5.8 



21.3 



1 Values within each column with the same letter are from the same statistical 

 population at 5-percent level of significance. Capital letters are used for main effects. 



Hesketh (26) found that high altitude maize 

 races had a lower net photosynthetic rate at high 

 vs. low soil temperatures. 



Tillering patterns of the three entries were 

 similar in the first two experiments. Although 

 data were taken at each harvest over a 3-year 

 period, only three dates for 1966 are presented 

 since they are representative (table 3). In the 

 spring of each year, differences between varieties 

 were small, and as the season progressed, num- 

 bers declined for each entry. These reductions 

 occurred after only one month of increased soil 

 temperature. At the end of the summer, orchard- 

 grass had greater tiller numbers than timothy 

 with S-37 having the most. Species differences 

 were small at 10°, but by mid-August, Climax at 



32° had significantly fewer tillers than either 

 orchardgrass. As air temperatures dropped in 

 September, new tillers were initiated on all spe- 

 cies at all temperatures, but total numbers re- 

 mained low at 32°. This is similar to the pattern 

 reported by Taylor and Templeton (66) where 

 plants tillered profusely during autumn and early 

 spring, then declined rapidly in May and June, 

 with greatly reduced tillering during midsummer. 

 Tiller numbers for the ambient and 21° plots 

 were similar just as the temperature profiles were 

 similar (figs. 3 and 4). Many have reported in- 

 creased tillering with lower temperature regimes 

 (2,6,12, 20, 24, 6U 62, 66). 



In ambient and 32°C. plots, tiller initiation and 

 development slowed considerably during mid- 



