214 



MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



Table 11. — Average seasonal' 1 wind velocity (km./hr.) at dif- 

 ferent heights above the ground surface under grazed and 

 ungrazed treatments 



Treatment 



Wind velocity (km./hr.) at heights above ground 



15 cm. 



30 cm. 



90 cm. 



130 cm. 



145 cm. 



Grazed 

 Ungrazed 



2.1 

 0.6 



3.9 

 2.4 



7.9 

 7.1 



8.4 



1 Wind measured from June 6-Sept. 30, 117 days. 



2.4 km./hr. during September. On the ungrazed 

 site, the average wind velocity in June at the 15 

 cm. height was 1.1 km./hr. It decreased to 0.3 

 km./hr. For the season, wind velocity at 15 cm. 

 on the grazed site was 3i/o time that on the un- 

 grazed site. 



Soil Moisture 



Soil moisture samples were taken at approxi- 

 mate weekly intervals throughout the season from 

 May 25 to October 5. Four samples were taken on 

 each site to a depth of 120 cm. with a 1-inch 

 sampling tube. Soil moisture was determined 

 gravimetrically, expressed as percent, and then 

 converted to cm. of water in the profile by 10-cm. 

 segments. 



The precipitation pattern in the 1970 season 

 was not entirely favorable. A total of 14.58 cm. 

 of rain in May combined with moisture already 

 in the soil resulted in 20 to 25 cm. of moisture in 

 the soil to a depth of 120 cm. on May 27. when 

 the first soil moisture sample was taken. In June 

 8.00 cm. of rain were measured, in Julv 11.33, in 



August 0.99, and in September 4.06 cm. After 

 the May rainy period, the principal rains which 

 occurred were : June 2 — 26.16 mm. ; June 13 — 19.81 

 mm.; July 14 — 22.86 mm.; July 23 — 18.54 mm.; 

 and July 29 — 46.48 mm. The soil moisture pattern 

 reflects the general precipitation pattern to a con- 

 siderable extent. 



There was somewhat more moisture in the soil 

 under the ungrazed treatment than under the 

 grazed treatment from the beginning of the study 

 period until about the middle of August (table 

 13). Soil moisture conditions appeared to be es- 

 sentially similar under both treatments for the 

 balance of the season. Pressure plate determina- 

 tions at 15 atmospheres indicated that soil mois- 

 ture would become unavailable in the upper 50 

 cm. of soil on both sites at approximately the 

 same moisture level — 1.46 cm. on the grazed site 

 and 4.36 cm. on the ungrazed site. Thus, soil 

 water in the upper 50 cm. of soil became unavail- 

 able for plant use under both the grazed and un- 

 grazed treatments on or before July 6, and re- 

 mained so until sometime between July 20 and 

 Julv 28, after which soil moisture in this laver 



Table 12. — Average wind velocity (km./hr.) by month at 15 

 cm. above ground surface on the grazed and ungrazed sites, 

 1970 season 



Treatment 



Average 



wind velocity 



by 



months — km./hr. 





June 



July 





Aug. Sept. 



Grazed 

 Ungrazed 



2.7 

 1.1 



1.9 

 0.5 





1.6 2.4 

 0.3 0.6 



