Lookout here comes me thinking again!
This says carbohydrates constitutes about 10% of soil organic matter.
This says carbohydrates carbs are a significant component of the organic matter of all soils, commonly accounting for 5-20% of soil organic matter.
So does it matter how much sugar you can put into the soil vs how much organic matter there is in the soil?
A 1'x1'x6" deep square foot of soil is 0.5 cubic feet of soil and should weigh about 40 lbs or 18,144 grams.
If the average soil contains 5% organic matter and 10% of that is carbohydrates, that is about 90 grams of carbohydrates per square foot of soil 6 inches deep. 18,144 x 0.05 x 0.10 = 90.72 g.
Still not sure what the optimum amount for microbial growth but at least the following gives some ideal about how much of these would be in the soil if you are comparing carbohydrate content.
Granulated sugar is 100% carbs.
90 g of carbohydrates is 90 g of granulated white sugar or about 7.5 tablespoons per square foot of dirt.
Molasses is 92% carbs.
90 g of carbohydrates is 98 g of molasses or about 5.6 tablespoons per square foot of dirt.