"IF" they are Fertilizing with chicken manure thru the water, then either they have Liquid chicken manure from a Liquid pit or they are mixing dry chicken manure with a slurry of water and pumping this thru the irrigation system !
And this may Cause more water to be needed to keep the ground from drying out, because it may Create a lot of Heat and it takes water to cool down Heat so that the ground does not dry out !
It sounds like he is relying on his mgr of 30 years, so unless his mgr is willing to do something different then there may not be much anyone can help him with !
"IF" he is willing to make changes, I may be able to find out if there is anyone still working that area who could help him out ?
Smile Tis your choice.