You want to apply 50 lbs N per acre and 10 lb P2O5 per acre to a 123 acre potato

Question

You want to apply 50 lbs N per acre and 10 lb P2O5 per acre to a 123 acre potato field. You will be using fertigation. The center pivot irrigation system you are working at can cover all 123 acres in 5 hours if it is running at 100%. Show all calculations for full credit!!!

What forms of fertilizer will you use?

Solution 32 has 3.55 lb N/gal

10-34-00 has 1.16 lb N/gal and 3.95 lb P2O5 / gal

At what speed will you need to set your injection pump if you are running the pivot at 100%?

Why might you not want to run the pivot at 100%?

Explanation / Answer

Since your field is 123 acres you need 123 x 50 ibs N = 6150 lbs N.

Amount of P205 needed will be 123 x 10 lbs P =1230 lbs

Solution 10 - 34 - 00 has 3.95 lbs P205 / gallon, so you need 1230/3.95 = 311. 39 gallons.

This 311.39 gallons will also supply 311.39 x 1.16 lbs N = 361.21lbs N

Total N required is 6150 lbs, so the balance N has to come from solution 32.

Total N required is 6150 lbs and already available from solution 10 - 34 - 00 is 361.21 lbs. Balance is 5788.79

So the balance N comes from 5788.79 / 3.55 = 1630.64 gallons of sol 32.

So fertilizer used will be a mixture of 311.39 Gallons of 10 - 34 - 00 and 1630.64 Gallons of sol 32.

Speed of the injection pump with pivot running at 100% D = s x t,

Convert 123 acres into sq Km = 0.498 sq Km. time is 5 hrs. Speed = D / t = 0.7 x 0.7 / 5 = 0.098 = 0.1 Km /hr.

We cannot run the pivot at 100 % at such low speed .

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