"Oz" wrote in message
...
Danielle Davis writes

How many years can you plant the same crop in the same spot before all
the nutrients are gone from the soil.

That depends on whether you replace them or not.

There is a trial set up by rothamsted in the 19C and still running where
no fertilisers have been applied and the field is/was sown to wheat.

At least that is what is claimed. Unfortunately rothamstead do not
publicly supply this data unless you have a contract with them, and then
claim copyright anyway.

A highly deplorable situation for what claims to be a scientific
establishment, at one time government owned.

The answer, by the way, appears to depend on soiltype and the amount of
nutrients coming in via rainfall and soil breakdown.

On this farm, when we came in the 1970's, soil index levels were very
low indeed and yields by our predecessors were close to 2.5T/Ha when
adjacent farms were obtaining twice this. However our predecessors did
apply limited amounts of fertiliser.

OSU has a plot of wheat that has received manure only for about 80 years and
it averages 14 or 15 bushels an acre or 1/3 normal yields. Fifteen to twenty
bushels is about what we expect from wheat with no fertilzer on a long term
basis. There are still people doing that. They put in just enough the cows
don't starve in the winter and have a job in town that they don't do to well
at either.

I know one farm that was in cotton for 70 years and it made about 1/2
average yields not from loss fertility but form nematodes and disease. One
rotation of alfalfa put it back as a top producing farm. It was sandy farm
that was sub irrigated. That is it was only 6 to 10 feet to water and
cotton and alfalfa could tap this moisture. Not high enough to be a problem
but height enough to assure a nice crop if you could get it up.

Gordon