Im down in South East Texas, hurricane IKE deposited a nice 6ft of salt water across one of my fields that stayed put for about 3 weeks....2 months later I did my soil sample to determine if it was even feasible to plant a rye crop that year. The return from the place told me that I needed 300lbs Nitrogen and 2.6 tons Lime/Acre...I thought about it for about 2 seconds, and said naa....not worth it. I stuck out 2 bags of rye in November to just see what happened....never rained anyways.
Bout the end of February we got our first winter rain, and wouldn't you know it, that Rye popped up anyways. I never grazed it, just mowed it under after it went to seed. But 4-5 tons seems excessive...I cant imagine a field being in much worse shape than mine, and I was nowhere near what your planning on doing. And my N was almost off the charts on the low side.