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ISSUE 2   May 11, 2000


    Although I have not been out everyday with my GPS backpack receiver, I was out last week one day after the military scrambling was lifted. In the past, my readings jumped around a little. For example, a reading of latitude of 46o 40' 30.85 would be 0.10 on bad days and 0.03 on good days. The day after the scrambling was lifted, there was no movement at all when I stopped to record. I did not think that lifting the scramble would make that much difference, but it certainly seems that it did. Do you still need differential? Yes, but your readings will now be much more reproducible and if you lose differential,
your readings will still be very close to true. A communication from a fertilizer company that does GPS directed work in the central part of North Dakota presented a field read without differential before scrambling was lifted and afterwards. The before map contained overlapping tracks and irregular boundaries. After unscrambling, the tracks were regular, straight and true. I was amazed. Hopefully the signal will remain this way in the future. It is a great benefit.



    Now that growers are in the last half of their planting season, certain plans call for top dressing seeded crops on purpose or for rescue. Also, for crops that are yet to be seeded, such as soybeans or sunflowers in the north or west where it is still too early to seed, but planting is caught up, regular fertilizer treatments could be applied in some cases days before incorporation.

    Urea has the highest potential for volatility of ammonia through the activity of soil enzymes. This time of year, significant rainfall ( inch is usually enough) needs to fall within two days or the urea should be incorporated. A product called Agrotain can be impregnated unto urea, and when coated it extends the non-volatility to about 10days without need of incorporation. Agrotain is not useful for other nitrogen containing products.

    Ammonium sulfate has lower volatility of the ammonium part of the fertilizer compared to urea, but still has some volatility especially in high carbonate containing soils. However, ammonium sulfate is usually applied at much lower N rates than urea because it is used to provide sulfur mostly and not so much for N. If the amount of N applied is large, however, it should be incorporated within five days. The sulfur portion of ammonium sulfate is stable and will not volatilize.

    Ammonium nitrate is not volatile and is used heavily in winter wheat areas which must be top dressed and where incorporation is not an option. The nitrogen in MAP and DAP are slightly volatile, especially in high calcareous soils, but less than ammonium sulfate. The phosphorus component of MAP and DAP are not volatile.

    Micronutrients, zinc, copper, are not volatile, but in order for the plants to use them, they should be incorporated into the soil. Copper sulfate, however, was used in a no-till site and incorporated only in the seeding slit and yet produced a significant yield increase at a North Dakota site in 1998.

    For any top dress application to be effective, rain must eventually occur. Even when crops are emerged, little is taken into the leaves, except for the micronutrients and protein enhancement of small grains through foliar feeding of N.

Dr. Dave Franzen
NDSU Extension Soil Specialist

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