38 



^MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



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FIRST DAY OF WEEK ( MONTH-DAY ) 



Figure 3. — Example of mean weekly temperature 8 cm. 

 below the soil surface under an orchardgrass sod 

 (1965). 



to S-37 in maturity but more temperature sensi- 

 tive) were added to 1966-68 studies. Light, nitro- 

 gen, and stubble height differentials were elim- 

 inated. 



In 1968, red clover plants (Trifolium pratense 

 L.) from a Maryland strain selected for longevity 

 (MD. Syn-1) and from 'Dollard' were started in 

 the greenhouse from seed. Uniform plants were 

 placed in plastic pots and clipped three times 

 before being moved to the field. Plants were 

 placed systematically in solid timothy sward and 

 harvested each time the latter was cut. The next 

 spring similar red clover plants and clonal pro- 

 pagules from a single Climax timothy plant were 

 placed on 18-cm. centers in bare soil in contrast 

 to the timothy sward used in 1968. Each species 

 was placed in a separate section of each tempera- 



ture plot. Thus, competition was minimal and 

 between plants of the same species. All plants 

 were harvested on the same date. At the end 

 of each season surviving plants were removed and 

 crown root development determined. 



Results And Discussion 



The effects of soil temperature, light intensity, 

 nitrogen fertilization, and stubble height at har- 

 vest upon total forage yields and tiller produc- 

 tion of Potomac orchardgrass are presented in 

 table 1. Since there were few significant inter- 

 actions, and effects were generally additive, only 

 main-effect means are shown. Lowest yields were 

 obtained at high soil temperature, low light, 

 low N fertilization, and high stubble. Tiller pro- 

 duction was greatest at the coolest soil tempera- 

 ture, full sun. low nitrogen, and high stubble. 

 Although tiller production at 10° C. was signifi- 

 cantly higher than at all other temperatures, 

 dry matter yields were similar for all except 32°. 

 Similar results have been reported by others (33, 

 46, 58, 66). 



Table 1. — Effects of soil temperature, shading, 

 nitrogen level, and stubble height on forage 

 yields and tiller production of Potomac or- 

 chardgrass 





Dry matter 



per plot 





Main effects 



1964 



1965 



Tillers per 





(100 g.) 



(100 g.) 



0.05m. 2 , 1964 



Soil temperature : 









Ambient 



2.81 a 



6.19 a 



130 b 



32° C. 



2.25 b 



4.51 b 



120 b 



21° C. 



2.88 a 



5.77 a 



139 b 



10° c. 



2.76 a 



5.62 a 



204 a 



Shaded 



2.53 h 



4.21 h 



128 h 



Full sun 



2.82 g 



7.21 g 



169 g 



High N (84 kg./ha.) 



3.02 r 



6.31 r 



128 s 



Low N (28 kg./ha.) 



2.33 s 



5.11 s 



169 r 



High stubble (8.9 cm.) 



2.37 y 



4.95 y 



169 x 



Low stubble (3.8 cm.) 



2.98 x 



6.46 x 



128 y 



CV, percent 



39.7 



9.1 



18.5 



1 Values within each year and each main effect, fol- 

 lowed by the same letter, are from the same statistical 

 population at the 5-percent level of significance. 



