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MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



optile. After a few days these leaves broke over 

 at the chlorotic band. Many workers have ob- 

 served young tree seedlings that have been heat 

 girdled at the soil surface. It is reasonable to 

 assume that grass seedlings may be subject to 

 similar injury. 



The loss of seedlings following frost heaving 

 of soil is well recognized in regions where slow 

 freezing and thawing occurs at seasons of high 

 soil moisture on heavy, fine-textured soils with 

 poor drainage. Fall seedlings in the foothills of 

 California often are severely heaved before 

 spring. We know more about the conditions which 

 produce soil heaving than we do about the action 

 of heaving on the plants themselves. Too often 

 the effects of heaving are noted at some consider- 

 able time following the stress. Portz {27) re- 

 ported that the more prostrate varieties of alfalfa 

 heaved less than an upright variety under over- 

 wintering field conditions in Illinois. He sug- 

 gested that morphological and anatomical factors 

 probably influence varietal differences, but these 

 were not studied. Biswell and others {2) noted 

 that taproots reaching depths of 0.9 to 1.2 meters 

 in 1-year-old brush seedlings were broken by 

 heaving at 10 to 15 centimeters below the soil 

 surface. Reseeded legumes were more subject to 

 heaving than reseeded grasses, and smilo {Oryz- 

 opsis miliacea (L.) Beuth and Hook ex Aschen. 

 and Schweinf.) with finely branched roots was 

 heaved more than hardinggrass {Phalaris tuber- 

 osa L.) with coarser roots. 



Perhaps the most detailed measurements of 

 frost heaving injury to specific plants is reported 

 by Kinbacher {14-) who studied hardinggrass. 

 perennial ryegrass {Lolium perenne L.) and two 

 winter wheats. By using a method to produce 

 heaving in the laboratory {15), he was able to 

 observe seedlings at definite times after known 

 soil and plant movement. With this technique, 

 stem and leaf breakage proved more frequent 

 and lethal than root breakage. After heaving, 

 plants were permitted to recover under favorable 

 growth conditions in the greenhouse. Kinbacher 

 found in this favorable recovery environment 

 that if the break occurred below the soil surface 

 but above the shoot apex, most plants failed to 

 recover since subsequent leaf growth was unable 



to emerge above the soil. If the break was in 

 the roots and adventitious roots grew quickly, the 

 plants survived. Generally perennial ryegrass 

 seedlings were less injured than hardinggrass, but 

 no explanation was given for this difference. 



Ice cover of vegetation has been studied with 

 regard to the overwintering of perennial forage 

 plants. Injury under ice sheets has been attributed 

 by various workers to accumulated carbon dioxide 

 or other respiratory products, or to reduced oxy- 

 gen. However, hardened plants appear able to 

 survive for several weeks under ice. Beard {!) 

 working with turf of Kentucky bluegrass and 

 bentgrass {Agrostis palmtris Huds.) reported 

 that although both species tolerated a 5-cm. ice 

 cover, or a 2.5-cm. ice cover over a 5-cm. snow 

 layer for 51 days without reduction in survival, 

 compacted slush covered with 5-cm. of ice 

 for 6 days greatly reduced the survival of the 

 bluegrass, with only 5 percent of the rhizones or 

 stolons recovering. He . suggested that the com- 

 paction reduced air pockets in the sod, and recom- 

 mended the control of trampling during slushy 

 conditions. Were range species to react like the 

 bluegrass, one might well consider the effect of 

 animal treading on low herbaceous cover during 

 alternate thawing and freezing when ice sheets 

 may form. 



Grasses are particularly sensitive to tempera- 

 ture stress at the flowering stage. Recognition of 

 the meager temperature tolerance of the staminate 

 parts of the flower has led plant breeders to em- 

 ploy heat or cold to emasculate grass florets. 

 Emasculation by frost occurs in nature and has 

 been studied particularly in cereals where con- 

 siderable economic losses may be encountered. 

 Suneson {33) reported that Ramona wheat yields 

 at Davis, Calif., were reduced from 30 to 60 

 percent in 3 out of 12 successive years. Minimum 

 night temperatures ranging from freezing down 

 to —2° C. can produce this injury when occur- 

 ring at precise stages of floral development. The 

 pistillate organs remained receptive to pollen 

 after the anthers of the same floret were ren- 

 dered sterile as indicated by successful cross pol- 

 lination. No doubt both frost and heat emascu- 

 lation of range grasses occurs under natural con- 

 ditions. 



