4^4 University of California Publications in Agricultural Sciences [Vol.3 



The ideal way to collect a representative sample of soil for laboratory studies 

 is to make a number of borings scattered about the field or fields, so that the sam- 

 ple Avill approximate an average. But in the case of collecting the samples for this 

 study it was considered best not to attempt such a procedure, for the reason that 

 it was desired to have the samples for the greenhouse work and for the physical, 

 chemical, and bacteriological studies, come from the same lot of soil. The collec- 

 tion of such a large amount of soil, about 250 pounds in all, from a number of 

 places about the selected field would be very tedious. Hence as nearly a typical 

 place as possible was selected, close to a wagon road, in order that the samples 

 could be transported readily. Care was used that the location be far enough out 

 into the field to allow the sample to be representative of the conditions in the field. 



The subsequent procedure was as follows: The selected spot was cleared of 

 grass or other surface material or accumulation that did not belong to the soil. 

 A hole was dug, usually one foot deep (the depth depending entirely upon the 

 nature of the surface soil and any noticeable changes toward the subsoil), and 

 big enough to give sufficient soil to make up the greenhouse sample of from 225 

 to 250 pounds. The soil was shoveled directly into tight sugar or grain sacks, no 

 attempt being made to mix the sample at this time. Some sacks of the soil would 

 contain more of the surface material, and others more of the lower portion, but a 

 later thorough mixing and screening at the greenhouse gave a uniform sample. 

 After the large sample was collected, the hole was usually dug two feet deeper, 

 giving a hole three feet deep. One side of this hole was made perpendicular, and 

 from this side the small samples were collected. The A, B, and C horizons were 

 marked off on this wall, and the samples collected by digging down a uniform 

 section of the designated portion, using a geologic pick and catching the loosened 

 material on a shovel. About ten pounds of soil were so collected, and placed in 

 clean, sterile canvas sample sacks. Care was used not to contaminate the samples, 

 so that the bacterial flora might remain nearly unaltered. It seemed imprac- 

 ticable to attempt to collect the laboratory sample under absolute sterile condi- 

 tions, especially since some of the deeper (B and C) samples were obtained by 

 means of the soil auger. When the auger was used to collect the samples from 

 greater depths the boring was done from the bottom of the hole made in collect- 

 ing the larger sample. The size of the laboratory sample required the boring of 

 five or six holes with the usual 1.5 inch soil auger. The laboratory sample of the 

 first foot, or the A sample, was always collected from the side of the large hole. 

 Notes regarding the sample, field condition, the place of collection, together with 

 photographs and marked maps are given in appendix B. 



As described above, the soils were collected in separate portions from the sur- 

 face to the 12 inch, from the 12 to 24 inch depth, and from the 24 to 36 inch 

 depths where there were no abrupt or marked changes in the color, texture, or the 

 like, as in the Hanford fine sandy loam. But since in some cases, as most fre- 

 quently in the San Joaquin sandy loam, the samples do not represent the first, 

 second, or third foot depths, as the case might be, the term, horizon, has been 

 used. Horizon A indicates the surface sample, horizon B the second sample, and 

 horizon C the third sample. 



Laboratory Preparation of Samples 



The large samples were stored in the greenhouse until ready for use. The lab- 

 oratory samples were allowed to remain in the sacks until air dry, when they were 

 passed through a 2 mm. screen. This was a difficult matter, with the heavy soils, 

 as well as with the heavy subsoils of the San Joaquin sandy loam. Cautious use 



