and compaction of the soils. Three types of portable sampling 

 platforms used at Fall River Mills and Bakersfield are shovm in 

 Figure 3. 



To provide neutron probe access into the soil, thin- 

 walled aluminum tubes 20 feet in length with removable l8-inch 

 extensions at the top were permanently installed flush with the 

 soil surface. Stoppers were placed in the tube at the surface 

 and immediately below the extension to exclude foreign material 

 from the tubes. In this way, the tubes did not extend above the 

 ground to Interfere with tillage and crop cultural operations. 

 When tillage operations damaged the upper extensions, they were 

 simply and easily replaced. The access tube design is shown in 

 Figure 4. 



Plttvllle Neutron Probe Moisture Depletion Measurements . 

 The Plttvllle site is located at an elevation of about 3^340 feet, 

 in the northeastern intermountaln region, at a latitude of 4l de- 

 grees. Selection of the neutron measurement site was preceded by 

 four years of gravimetric sampling in the Fall River Valley and 

 other mountain valleys in the northeastern area. The Plttvllle 

 1 S site was sampled using the gravimetric technique in 1956, 1937 i 

 and 1958. This prior experience indicated that the Plttvllle al- 

 falfa field possessed the desirable combination of soil and irri.- 

 gatlon conditions for a moisture depletion plot. Topographically, 

 the site is gently sloping with small swales. There is a small 

 ridge 6OO feet north of the plot site, which is about 100 feet 

 higher than the plot. The land at the plot site slopes 3 percent 



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