Was told to be careful using Humus/Manure

[tulsanurse1]

I purchased a bad of humus & manure to use in my container vegetable garden. I was in a feed store yesterday talking gardening and mentioned that I had purchased this, and the gentleman said to only place a small amount (about 2") in the bottom of the container because mixing it in could cause an quick influx of nitrogen in my soil, that would be too high and could damage my plants. Is there any truth to this?