Paper No. 4 



PLANT ENVIRONMENT STUDIES WITH CONTROLLED SOIL 

 TEMPERATURE FIELD PLOTS 1 



By A. Morris Decker 2 



Abstract 



The effects of soil temperature on plant growth 

 and development of forage species were investi- 

 gated. Use of equipment and facilities to modify 

 soil temperature in the field is described and dis- 

 cussed. Tiller initiation, leaf growth, crown de- 

 velopment, root growth, plant reserves, mineral 

 uptake, and plant persistence were all markedly 

 affected by variations in soil temperature. The 

 use of this facility serves as a bridge between field 

 studies with no environmental control and the 

 growth chamber where climatic factors are rigid- 

 ly controlled but are unlike the natural field 

 environment. 



Additional key words: Plant climate, soil tem- 

 perature, forage, mineral nutrition, tillering, per- 

 sistence 



Introduction And Literature Review 



Soil temperature affects plant growth directly 

 and indirectly through chemical, physical, and 

 biological activities. In the field, specific effects 

 of soil temperature are difficult to determine be- 

 cause of wide soil differences and because of the 

 close relationship of soil to air temperature which 

 directly affects plants. 



Seed germination and early growth are inti- 

 mately related to soil temperature but, as plants 

 grow, aerial environments play a greater role. 

 Sosebee and Herbel (56) reported reduced sur- 

 vival of 11 of 14 range species at high soil tem- 

 peratures even when soil moisture was main- 

 tained at field capacity. According to Daubenmiro 



1 Contribution No. 4443. Scientific Article A1689 of the 

 Maryland Agricultural Experiment Station. Department 

 nf Agronomy. College Park, Md. 



'Professor of Agronomy, University of Maryland, Col- 

 lege Park. 



34 



(19), root temperatures closely approach those of 

 the immediate environment. Thus, the root system 

 of a single plant in the field may be subjected to 

 wide ranges in temperature. 



Morphology of plants can be modified by soil 

 temperatures. Dickson (25) found subcrown in- 

 ternode elongation of wheat and relative growth 

 rate of the coleoptile was slower than the culm 

 growing point as soil temperatures increased. The 

 initiation and growth of new roots in cool-season 

 grasses is highest in spring and fall when soil 

 temperatui'es are cool and least in midsummer 

 when they are high (10, 11, 28, 63, 64-). Saper and 

 Mitchell (54) found that high temperature along 

 with reduced light intensity decreased nodal roots 

 of ryegrass. 



Tillering of cool-season species decreases with 

 high temperatures. Taylor and Templeton (66) 

 reported maximum tillering of orchardgrass in 

 spring and fall with a marked drop during sum- 

 mer. Mitchell (46) found increased tillering of 

 ryegrass at lower temperatures, but at equal leaf- 

 appearance age differences were not significant. 

 Similarly, in smooth bromegrass (24, 49) and tall 

 fescue (53, 68) low temperatures favor tiller pro- 

 duction. Others reported that plant age, light 

 conditions, and so forth, maj 7 , at times, play 

 a greater role than temperature (6, 41, 44)- Opti- 

 mum temperature for tillering differs with geno- 

 type (47, 75). Hiesey (29) concluded, after study- 

 ing 33 clones of Poa, that field behavior of un- 

 known clones could be predicted from growth 

 chamber response. 



Tiller development was shown by Robson (53) 

 to be closely associated with leaf and leaf axil 

 bud development. Both leaf initiation and elonga- 

 tion are affected by temperature (38, 62, 67) . Tre- 

 harne and others (70) found that fully expanded 

 leaves maintained high apparent photosynthesis 

 (PR) for 15 to 20 days but declined rapidly 



