ISSUE 12   July 30, 2008


If Hamlet farmed today and the soil test recommended phosphate, no doubt he would ask that question. I took a break from my nitrogen calibration work last weekend to pour over reams of papers and data from NDSU, Canadian and corn-belt studies on various crops. NDSU work, along with that of the USDA in Culbertson, MT and Mandan, are quite extensive in wheat. Taking those calibration equations developed by Halvorson, Grant Jackson and Black, I inserted today’s costs of phosphate of about $1/lb P2O5, and $8 wheat into them. The following graph illustrates that building P at this time is not a wise decision.

Phosphate graph

Unless the P test is less than 7 ppm, the economics do not support building P test levels even when wheat is $8/bu with P costs of $1/lb. If MAP costs drop to $600 (P cost about 50 cents/lb P2O5), then building low P tests to about 10 ppm makes "cents" again.

I also reviewed the ND and Canadian literature on broadcast vs banded P for wheat, and clearly there is at least a 2-1 advantage in efficiency, with banded having the distinct edge. If you request University recommendations from your lab du jour this fall, you will be presented with a recommendation for P based on broadcast rates. With P costs at current levels, my recommendation is to band, either with seed, or near seed, and reduce these rates by one-half.

For corn, there is also an efficiency to banding, but probably not one-half. The biggest mistake a grower may make is not requesting University recommendations. Differences between "industry" and "University" recommendations for corn can be huge, with little difference in resulting yield when using either one. Remember, we live in North Dakota, not the central corn-belt. Reducing these rates by one-third would be wise with current cost/price structure. Banding for corn will require either a strip-till-style system of about 2 inches below the projected seed zone, or a 2X2 band planter set-up.

For soybeans, broadcast P with rates not cut appears profitable for $10 or higher soybeans and low P levels. Once P test hits about 10 ppm, there is no profitable response to P in soybeans.

Dave Franzen
NDSU Extension Soil Specialist

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