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ISSUE 1   May 3, 2001

 

FERTILIZER WITH THE SEED

The most popular spring question is "How much fertilizer can be placed with the seed? This question has been answered in a series of NDSU circulars since 1995. The current spring wheat, canola and soybean circulars all contain language or tables to guide a grower through the process of determining a rate to use. These circulars are also on-line at

http://www.ext.nodak.edu/extpubs/soilfert.htm

Because of the number of new soybean growers this spring, this question will come up even more frequently. It is important to realize that for many broadleaf crops, with the exception of sugarbeets, canola and potatoes, responses to banded P is not high, especially if soil P levels are medium or higher. Research on field peas and lentils during the past several years have failed to show a good response to P even at low soil P levels. Some Canadian publications have stopped recommending P on flax due to lack of response. Old NDSU P application data on sunflowers is not very supportive of using P fertilizer on medium or higher testing soils.

It is important to understand the two principles of P management in order to distribute P well in a rotation- Short Term P management and Long Term P management.

Short-Term P management means the use of concentrated starter P applications or broadcast P application meant to give a yield response that one year. This is important in small grain, corn, canola, sugarbeet and potato production. All of these crops respond well to concentrated band applications of P. In fact, based on one year of data at Crookston last year, many sugarbeet growers will be applying 3 gallons of 10-34-0 with the seed of sugarbeets and will probably achieve similar yields as growers applying 200 lb/a of 18-46-0 broadcast. Why? Because the first increment of P that is applied is the increment that gives the greatest response to P.

So why in the world would NDSU not recommend 3 gallon of 10-34-0 for everything instead of the 20-50 lb actual phosphate recommended in the tables? Because of the often overlooked second principle- Long-Term P management.

Long-Term-P management is the understanding that some healthy level of P needs to be bathing the plant roots to make the Short-Term P management ultimately be most effective. Forgetting that soil test levels need to be at medium or higher levels and preventing soil P levels from back-sliding to low or very low levels maintains yield. Failure to maintain levels could result in unseen yield reductions of 15-25%. Levels that would not be noticed by growers, since they have no access to a "check plot" on their farms.

High priced P fertilizer marketers make their money by convincing farmers to try the Short-Term approach only. They understand that low rates of 10 lb phosphate are going to look good in comparison in a banded approach to 20-40 lb phosphate compared to DAP or MAP. However, they do not tell the growers that their soil tests will fall over time and that their yields will suffer in a few years. It is easy for growers to forget Long-Term P management.

Dave Franzen
NDSU Extension Soils Specialist


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