ISSUE 1 May 15, 2008
SO NOW WHAT?
Although many gritted their teeth and felt a churning in their gut when they did it, those growers that prepaid for N and P last fall made a good decision. Those that did not are now faced with N prices about double those of fall, and P prices at least triple the fall price. Feedback from the field so far has indicated that in the east and in areas with decent subsoil moisture, N and P rates for small grains and corn are similar to those in the past. In the drier areas (and itís as dry as I have seen it in parts of the west and north since coming to NDSU in 1994) N and P rates have been reduced, and often the N application has been delayed to see if anything will come up.
As we now enter soybean, sunflower and other warm-season crop planting, a review of N and P rates with an economic slant is appropriate. Our work with wheat and corn so far has shown that N rate should be modified somewhat due to N price and crop price. In reviewing our sunflower response data, it appears that even with a doubling in sunflower price within the last year, the increase in N costs would suggest that reducing the total available N rate by at least 10% on most soils, and perhaps 20% on higher organic matter fields (greater than 3% OM) would be justified. With $1,200/ton 11-52-0, the return on P is greatly reduced from what it has been in past years.
A good yield increase in sunflower on a low testing soil is seldom more than 20%. That means that in a ton crop, a 400 lb/acre increase might be realized on a low testing soil. The return from that increase at 25 cent flowers would be about $100/acre. Our chart rates for P show a recommendation of 40 lb/acre P2O5, or about 80 lb/a 11-52-0. The cost of that application would be $48/acre plus application, which is still profitable. As the soil test P increases, the likelihood of a profitable response decreases. In past years, it would still be profitable to apply P at medium soil test levels. However, an increase of 100 lb/acre flowers ($25/acre) that one would see on a medium-testing soil from P application would not profitably support the P application (20 lb P2O5, or $24/acre + application) on a medium-testing soil. Basically, in our warmer season broadleaf crops, medium-P-testing soils do not support the profitability to apply P at current prices.
ALTERNATIVES TO 10-34-0
Due to the general scarcity of P fertilizers this year, 10-34-0 is generally unavailable in the area. Alternatives to 10-34-0 are the various normally high-priced in comparison, but maybe not this year, slate of specialty liquid fertilizers, such as 9-18-9, made from white phosphoric acid. When using these products, pay close attention to the maximum rate recommended to be used with the seed. Most of these products contain urea, so they are generally more harmful to the seed at higher rates than what you may be used to. Do not push the rate beyond label recommendations.
APPLICATION OF AMMONIA TO DRY SOILS
Many soils in our drier areas are the consistency of ash. However, even these soils contain a thin water film around soil particles. I would still consider application of anhydrous on these soils, however, the ammonia will move more initially in these soils laterally and vertically than normal. Application down to 6 inches would be my best recommendation. Shallow applications (3 inches or more shallow) will lose at least 10% of product soon after application. Application using larger hoses/tubes (Ĺ inch instead of 3/8) may reduce the ammonia expansion initially. Make sure that there is at least 3 inch lateral distance between seed and ammonia application point. If the only ammonia application method alternative is shallow application, considering the lost efficiency, perhaps urea application would be a better choice in these soils if it is applied beneath the soil surface.
NDSU Extension Soil Specialist