136500 and 22000 d/m ovar a productive life of 10 years. The fotal removal over a 12 yaar period should then lie between 192500 an 356000 d/m. On the basis of these figures, the annual removal pf radiostrontium from the sail by what wa have termed an average cow would lie between 16000 and 30000 d/m. Available figures for the region in question indicate the tot strontium in the soil to be of the order of 3'x 106 d/m/Acre. assume that the anmal produce from 5 acres of land will supp nutrient needs of this cow, the store of radiostrontium from wht she will draw is of the order of 1.5 x 107 d/m. The ratio of moved annually by an average dairy cow would give a first esti rate of depletion. Thus 1.5 x 107 = (2) (2x 104) = 2.5 x 102 It is likely that this value of 250 years, which might be calléd the mean life, is of the order of 1.5 times the "half life". Thus] 170 years might be said to be an estimate of the lower limit of thé "half life" in the depletion of the stores of radiostrontium in the s@il of this region by dairy cows. Case II = Cows [To Not Lives on Pastures If land having a store radiostrontium that might be specified 3 x 106 d/m/Acre should be cropped continuously to cowpeas har fs as hay in_which the radiostrontium content might be specified fs 1.09 x 10? d/m/1000 lbs., the depletion "half time” may be esthi as follows: a maan life time may be defined as the ratio of the strontium in soil to the amount removed psariy in a orep of which the yield commnily ranges from 1 to 3 tons per acre. 1.5 x 10° $ 2.18 x 10° = 6.86 1.5 x 10° 6 ofe and 6.55 x 10? = 2.29 yield estimates of mean life for 5r89-90 in soil cropped as specified from which one might risk the statement that the depletion end0 life" under the specified cropping system and yields would be of th 0 rder of 1.5 to 4.5 years.