Soil testing has value for farmers

By Roger Don Gribble, commentary

July 05, 2008 10:56 pm

— Growing wheat profitably involves many things, not the least of which is managing fertilizer inputs to the greatest return on your investment.
This one aspect of wheat production requires several considerations and usually involves both short-term and long-term assessments. Short cutting fertilizer inputs one year may improve that year’s profit/loss margin, but it may require increased fertilizer and results in reduced profits the next year, even if yields were normal. It is important to have both an economically and environmentally sound rationale for your fertilizer practices.
Sometimes the type and rates of fertilizer used are a result of doing it the way it has always been done. In this case, producers see that a traditional program has resulted in satisfactory yields and there is no need to change that practice. The fallacy in this approach is it fails to systematically account for unused nitrogen following years of below-normal yields and a buildup of phosphorus over time.
In a more scientific approach, producers sometimes fertilize to restore what they expect the crop removed during grazing and harvest of grain the year before. Producers feel they are sustaining soil fertility at current levels.
Using a soil test that has been calibrated for this part of Oklahoma avoids the pitfalls of trying to add what was removed or of fertilizing according to some standard practice.
A couple of years ago, a national magazine published an article on soil testing that showed a large variation in fertilizer recommendations among labs across the United States that tested the same soil for Pennsylvania. Because the soil test values and the fertilizer recommendations were so different among the 50 labs involved, the article concluded soil testing was of questionable value.
If you took a single tractor to 50 farmers and had them check the oil in that tractor using a dip stick from one of their own tractors, what would you expect? Farmers who owned the same tractor would get a very accurate reading, while those with different tractors would get a wide range of readings. This article called attention to the importance of using a local lab that will have procedures and calibrations that apply to your soils, crops and growing conditions.
Today’s wheat producer is finding soil testing can be a valuable tool of technology for improving profitability. As we prepare for soil fertility needs for the 2009 harvest wheat crop, applying too much or too little fertilizer will be costly. As 18-46-0 approaches the $1,100 per ton range, there would be little need in over-applying phosphorus. The only way of knowing what the correct phosphorus fertility needs of our wheat soils would be the use of soil testing.
Your Oklahoma Cooperative Extension Service ag educator can help you with obtaining a good soil test and directions to labs in our area that can supply recommendations for your wheat crop. They also can assist in analyzing your recommendations for a sound fertilizer program for your wheat crop.

Gribble is Oklahoma Cooperative Extension Service northwest area agronomist.

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