Sounds like you'll need a balanced grade then. That's 0-12-12 in these parts but may be a higher concentration your way?
Had it two years ago won't have it again.
Grass seeds seem particularly good at picking out spreading inaccuracies. Had 200 acres done by contractor and was very disappointed with the spread .Probably wrong and unlucky but now sooner pay more and use a granular product through my spreader that' been tested with the product over trays. Plus you can use VR.
I have been looking at their 0-18-18? Need plenty to get it going. Just old neglected ground that I can no longer afford to do things the way they have been for many years
Do not apply any more P and K to anything if you intend to 'dispose' of all that FYM first!
These bulk products only work if you are doing an area/rate that amounts up to a full load or two otherwise you are better off bagged.
If the old man is still reluctant with your capers just do a small area this spring and say 'told you so'.
The risk with chicken muck is up to you. I had a customer who used it and spread it on grassland, when he was harrowing it in in the spring he found 1 part of one wing and he made an effort to look. Had no issues even though he made silage from some of it.
If you are going to plough it down pronto I would use it simply because it works so well.
There is no need to mix it with anything, you spread it fairly gently, it is rocket fuel.
Other guys I know take slurry from a neighbouring dairy or pig farm. I did not do the sums but the saving must have gone some way toward making it worthwhile buying their own tanker.
So would be better with the chicken muck over the cow? I am going to go for the litter whatever the end result as it's rare stuff round here to be offered. We've enough 'wildlife' that would possible pick anything dead up round here...
Most folk round here keep a hold of their slurry but it would be good if I could get a hold of some that is for sure.
I am going to incorporate no matter what comes, so spray off, subsoil, muck and plough. Then chuck some N on and stand back on this reseed ground.