Unlike corruption it is very straight forward to figure this out just by looking =P I suppose for a new player this would be actually pretty helpful, but just chop off the last three numbers and that is your decay. If the last three numbers were 500+ then add one to the number you have for decay. =P
-> Troops, Jets and Turrets eat 0.001 bushels per turn (up from 0.00042)
-> Tanks eat 0.003 a turn (up from 0.0012)
-> Spies eat 0.005 a turn (up from 0.00180)
-> Pop eats 0.030 a turn (up from 0.02756)