Correction to GLOBE
Soil Water Content Calculations

The current definition/formula for soil water content in all Phase I GLOBE material is in error (3/96). Soil water content should be defined as the water weight divided by the dry sample weight and is often multiplied by 100. The incorrect formula was given as water weight divided by wet sample weight. Soil scientists normallize by the dry sample weight because this is more reproducible than the ever changing wet sample weight.

Please recalculate and resubmit any soil moisture data that you have entered on the GLOBE data server using this procedure.

Soil Water Content should be determined by the following formula:

Example: 
     Wet weight = 105 g
     Dry weight = 90 g
     Can weight = 35 g

a) Subtract dry weight from wet weight 

     Wet weight                               105.0 grams
     Dry weight                            -   90.0 grams
                                           --------------
     Water weight                              15.0 grams

b) Subtract can weight from dry weight 

     Dry weight                                90.0 grams
     Can weight                              - 35.0 grams
                                           --------------
     Dry Sample weight                         55.0 grams
 
c) Divide water weight by sample weight: 15.0 / 55.0  = 0.273
 
                                                .273
     Multiply by 100                          x  100
                                           --------------
     Soil Water Content                          27.3

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Last updated: 7/4/96
Comments? globe@hwr.arizona.edu