accuracy, measurements of the soil surface layer, to a depth of 

 about 1 foot, require a different calibration than the measure- 

 ments at greater depth below the soil surface. Determination of 

 a suitable calibration is under study by the department and other 

 agencies at this time. It is believed at the present that the er^ 

 ror of measuring the losses of water from the soil surface is not 

 large, considering the total water use from the entire profile, 

 in the case of deeper rooted crops. 



Inherent variabilities, such as found in physical measure 

 ments of any natural phenomenon, occur in soil moisture depletion 

 measurements. Generally, although affecting any given measurement, 

 such variations tend to be compensating and, over a period of time, 

 such as a year, tend to cancel out. 



Two neutron scattering devices were acquired in 1958^ 

 shortly after this equipment became commercially available. The 

 neutron equipment was used for determination of soil moisture in 

 all field plots since early spring of 1959. The same criteria 

 used for selection of gravimetric sampling plots were followed in 

 establishing the plots sampled with the neutron probe. 



Effort was made to keep the crop in the plot area gen- 

 erally typical of the normal conditions of the entire field. Light 

 weight, portable sampling platforms with working areas of 15 to 30 

 square feet were fabricated in 1959 to carry the neutron scattering 

 equipment. These also served as portable working platforms. They 

 have been particularly advantageous in facilitating the field work 

 and in avoiding trampling and injury to the alfalfa and grass crops 



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