Roy M. Sachs rmsachs@ucdavis.edu
Mon, 20 Oct 2003 10:40:37 PDT
I use slow-release fertilizer, 25% N, 4% K and 4% P at a rate that 
will supply approximately 50 lbs N/acre (= 50 Kg/ha).  I'm not sure 
that our clay soils ever become deficient in potassium or phosphorous 
so I buy the richest slow-release source of nitrogen (which just 
happens to be 25/4/4).

Per 1000 sq.ft. (ca 100 sq.m) to get 50 lbs N from the slow release 
granules, I apply 4.6 lbs (ca 2.1 kg) annually, 2.3 lbs in the spring 
and 2.3 lbs in the fall.

Slow release is easiest for me with varied irrigation rates and 
sometimes very heavy rainfall, but I have used ammonium sulfate (21% 
N) successfully. The ammonium form of N tends to exchange with other 
cations on the clay and compost that I use.

I have calculations on a worksheet if anyone's interested.

Davis, California; Sacramento Valley, very hot dry summers , mild 
spring and fall; irrigation required (usually) from April through 

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