44 



MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



Table 6. — Effect of soil temperature on soil 

 aggregation 



Soil temperature 1965 



1968 : 



1970 



Ambient 



45.5 ab 



36.7 b 



55.1 a 



32° C. 



39.8 b 



22.2 c 



42.0 b 



21° C. 



46.9 a 



35.2 b 



62.8 a 



10° C. 



50.0 a 



56.0 a 



64.8 a 



CV, percent 



17.0 



15.6 



5.8 



1 Orchardgrass grown for two seasons (average of ni- 

 trogen levels, shade and stubble height over two grow- 

 ing seasons). 



3 Values within each year with the same letter are 

 from the same statistical population at the 5-percent level 

 of significance. 



3 Average of Potomac and S-37 orchardgrass plus Cli- 

 max timothy grown for 3 years after 2 years of Potomac. 



* Average of creeping bentgrass grown at 10 fertility 

 treatments for 2 years. 



mixed and redistributed to that replication. 

 Therefore, values for 1965 and 1970 are the result 

 of two years of treatment while those for 1968 are 

 the accumulative effect from two studies (1964- 

 68). As expected, soil aggregation closely paral- 

 leled the pattern of root and crown growth. In 

 each experiment, the soil at 10° was significantly 

 higher in aggregation than at 32° with ambient 

 and 21° being intermediate. Percentage of soil 

 organic matter followed a similar pattern except 

 sample variation was higher. With increased 

 shade, there was a significant reduction in soil 

 aggregation and organic matter. 



Examples of mineral uptake by three forage 

 grasses as influenced by soil temperature are 

 presented in table 7. Percentage of total nitrogen 

 in the harvested forage was slightly lower at 10° 

 than at other temperatures which were similar. 

 However, the N0 3 — N was significantly reduced 

 at that temperature. Similar results are reported 

 elsewhere (34, 48, 76). Uptake of the nitrate 

 ion is greatly accelerated by large amounts of 

 available nitrate in the soil and by the presence 

 of cations, such as K (32, 40, 55). Schneider and 

 Clark (55) found significantly higher nitrate N 

 where K was applied alone or with Ca, Mg, or 

 both. Coupled with higher nitrate percentage in 

 the forage was a corresponding increase in K. 

 The reverse was true for P, Ca, and Mg. Thus, a 



cation balance system (40, 55) appears to be op- 

 erating and influenced by soil temperature. 



Soil analysis at the end of 1967 showed a 

 marked reduction in available K at cooler tem- 

 peratures (20.4, 52.6, 19.0, and 12.2 kg./ha. of 

 available K for ambient, 32°, 21° and 10°, respec- 

 tively). 3 The plots had been fertilized at the be- 

 ginning of the growing season with 74 and 195 

 kg./ha. of P and K, respectively. Nitrogen was 

 applied three times at a rate of 62 kg./ha. for a 

 total of 196 kg. Percentage of K in the forage was 

 lowest at 10° and highest at 32°, while the amount 

 available in the soil at the end of the season was 

 the reverse. This is understandable since almost 

 twice as much top growth was removed from the 

 10° as from the 32° plots, thus percentages need 

 to be considered in terms of yields. 



Further studies on the temperature-plant-nu- 

 trient-interrelationships are needed. Walker's re- 

 search (72) suggests growth ceilings with corn 

 may be tied in with soil temperature and Ca 

 transport. He also reported accumulations of 

 boron at high soil temperatures (71, 72). Experi- 

 ments are now underway in these temperature 

 plots to see if Walker's laboratory findings can 

 be duplicated in the field. 



Summary 



The equipment used in these studies made it 

 possible to modify soil temperatures in the field 

 to study plant-environment relationships. Al- 

 though field soil temperatures, were .not main- 

 tained at the exact prescribed level, it was pos- 

 sible to maintain relatively uniform temperature 

 differentials. Research to date suggests that such 

 facilities can provide a useful bridge in relating 

 growth-chamber data to field conditions. 



Soil temperatures had a dramatic effect on the 

 growth of grasses and legumes. Some of the more 

 marked responses were with tiller initiation, seed 

 head emergence, crown and root growth, forage 

 yields, mineral uptake, and stand persistence. 



Environmental conditions that encourage the 

 initiation of new tillers in cool-season grasses are 

 not necessarily the same as those that promote 

 greatest forage yields. 



3 Bandel, V. A., C. K. Stottlemyer, and C. E. Rivard. 

 Soil testing methods. University of Maryland Soil Testing 

 Laboratory, Agron. Mimeo 34. 1969. 



