I am considering havin the farm gps grid mapped with intention for using them for variable P and K rates. My main concern is that all the farms p and k is applied as manures in the form of Farmyard manures and bio solids and green wastes, and as we use contractors to spread all the manures who don't have access to gps systems it means the maps will only be used to show high and low areas. This will obviously give us a clearer view to using the manures in a better way, and remove a substantial amount of guess work from my current fertiliser plans. The majority of companies offer the 4 year service at £20/Ha but my main worry will be whether we justify it on 100 hectares of land. Or will it be the start of spending further money on compatable gps systems to get the most benefit.

I've recently had a similar discussion with my agronomist about all the arable. I don't use contractors for anything, and like to think I know all the good and bad spots around the farm from soil workability and crop health. No P or K has been applied for over ten years, just manures, and indices are all 3 and above.

In my situation we decided I was better off doing a very thorough soil sampling myself, picking particular spots of interest and single samples for larger uniform areas. Dung spreading isn't an exact science, despite what some contractors and spreader manufacturers would have you believe, and I felt the grid mapping would be overkill for what basically boils down to a policy of 'lump the muck heavy onto the poor bits' when a field come round for application in the rrotation.

bovril:

I felt the grid mapping would be overkill for what basically boils down to a policy of 'lump the muck heavy onto the poor bits' when a field come round for application in the rotation.

Well, as a smallholder rather than a large area farmer, I know exactly where the poor bits on my fields are, and can chuck muck on them with some accuracy. It's obviously more difficult remembering the dodgy bits on a bigger farm, but my neighbour used to stun me with the accuracy of his knowledge over 1000 acres, and I don't doubt that many others could do the same thing.