22 



Journal of Agricultural Research 



Vol. xni, No. I 



should closely approach the maximum capillary field capacity. The 

 higher average ratio found, 1.98 ±0.14, is due in part to the fact that 

 the soils are heavier and therefore undergo greater change in structure 

 when disturbed. The probable error of the ratio for a single observa- 

 tion is ±0.24. 



Table IX. — Comparison of the maximum capillary capacities of disturbed soils as deter- 

 mined in the laboratory with the maximum quantities of water contained after irrigation 

 by the surface foot of the soils in place 



Degree of 



irrigation. 



Heavy 



Name and location of tract. 



Medium 



Wigno, Los Molinos 



Griffes, Woodland 



Bundy , Los Molinos 



Hofhenke, Los Molinos 



Hughson, Woodland 



Huartson, Gridley 



O'Hair, Orland 



Geer, Los Molinos 



University Farm, Davis 



Average 



Guile, Woodland 



Jackson- Woodward, Woodland 

 Beck, Woodland 



Average 



Maxi- 

 mum in 

 labora- 

 tory 

 (inches 

 per foot 

 of soil). 



4. 00 

 4.90 

 6.28 

 5.02 

 5.61 



5-93 

 5.88 

 4-83 

 6.52 



5-44 



7.64 

 6.97 

 6.8=; 



7-15 



Maxi- 

 mum 

 after irri- 

 gation 

 (inches 

 per foot 

 of soil). 



2.62 



2.58 



3-5° 

 3-27 

 2.87 

 2. 92 

 3- 14 

 3- 67 

 ?,■ 10 



3-07 



4. 00 

 4.04 

 2.97 



3- 67 



Ratio, 

 labora- 

 tory to 

 field ca- 

 pacity. 



1-53 



1. 90 

 1.79 

 1-54 

 1-95 

 2.03 

 1.87 

 1.32 



2. 10 



Pore 

 space of 

 soils in 



place 

 (inches 

 per foot 

 of soil;. 



1.78 

 :0.o6 



I. 91 

 I. 72 

 2.30 



7. 10 

 6.66 

 6.31 

 6. 32 

 6.66 



6.43 



5-78 

 6. 42 

 6. 18 



±0. 14 



6. I' 



Ratio, 

 labora- 

 tory ca- 

 pacity 

 to pore 

 space. 



Per cent. 

 56.4 



73-5 

 99-5 

 79-5 

 84.2 



96 

 76 



103 



85-4 



132. 

 108. 



117. o 



In Table X comparisons are made between the maximum quantities 

 contained after irrigation by the first- and second-foot sections of soil 

 and their m.oisture equivalents (3) . Examination of the ratio of the mois- 

 ture equivalent to the maximum quantity of water held after irrigation 

 indicates the former to be slightly larger than the latter. The averages 

 of this ratio, i.i3±o.o2 and i.i2±o.o2, for the first- and second-foot 

 sections, respectively, of the heavily irrigated soils show remarkable 

 agreement.^ The increase in the average ratio of the second group 

 from 1. 20 ±0.06 to 1. 38 ±0.02 is due to the fact that the heavier soils 

 of the second group were not so fully wetted in the second foot. Like- 

 wise, the average ratio 1.48 ±0.05 for the third group is high because of 



' The ratio of the moisture equivalent to the moisture content, one week after irrigation, of various soils 

 of Montana and Idaho has been determined by Prof. S. T. Harding, of the University of California, while 

 connected with irrigation investigations of the United States Department of Agriculture. The moisture 

 equivalents of the soils on which Mr. Harding worked varied from 14.9 to 29.3. His results show an average 

 ratio of 1. 1 7 in the surface foot of soil, of 1.16 in the upper 2 feet, and of 1.08 in the upper s feet. Considering 

 the wide range of soils studied and the many variations in other conditions, these ratios agree very well 

 with the ones above presented. 



