I would guess it should last a real long time. I think as long as it still looks like SBM it's going to be good. I would recommend you do your best to keep the material dry and if it smells good (or simply not bad) then it is not decaying and is plenty good to throw on the lawn.

50 lbs will cover 2,500 sq.ft. of lawn and the normal rate of 20#/1000. Most people use up all they buy to avoid storage issues. In a tightly closed plastic container, it should keep for 90 days or so. The concern is that it may get bugs in it, and it may attract rodents. Bill Hill

Use it on your lawn and also around all your inside and outside plants.

Yeah the problem is my total lawn front and back is only about 1700 sq ft so it's a little overkill. I could use half and store half which is probably what I'll have to do as none of the feed stores I call can get it in less than a 50lb bag.

Since my bermudagrass likes to be fed every 4 wks, when I go to the feed store, I buy two 50lb bags, use one the day I bring it home & just leave the other in the garage for the 4 wks & then use it. I've never had any bug problems etc....I don't know why you couldn't just use half the bag, then roll up the end real good & leave it in a dry place to use later. As long as later isn't sometime next year! :)

Oh, and the normal rate most folks use soybean meal is approx 14lbs/1000 sqft, at 47% protein it's an approx 7-1-2 and so for your 1700sqft, half the bag is about perfect! :)
Dan

In San Antonio I would have 50% bugs in it by weight in the spring.