NDSU Crop and Pest Report

ISSUE 2   May 13, 2004


This winter and spring, growers have evidently either been soil testing more fields than usual or at least they are paying attention to them more. Since 1996 when the last healthy spike in crop prices occurred, the big phosphate fertilizer question I received was about how low could they go. Now that checking accounts are a little better, I havenít heard this asked. However, they have asked why the recommendations from some labs are much higher than others. Most soil test labs will provide similar soil test results as any other using the same soil test procedures, especially if they send away check samples to an unbiased outside source and use blank and check samples as standards during their testing day. However, the big difference is the recommendations that come out of the lab in the reports.

Recommendations completely sanctioned and backed by University researchers and extension people in this three-state area of South Dakota, North Dakota and Minnesota appear in the NDSU extension circular SF_882 (revised 2003), Fertilizer Tables and Equations, and similar publications in the other two states. These recommendations are our best suggestions for rates that growers should apply for sustained high yields. They are not law, just strong suggestions. Some leeway is implied by the term "recommendationí. Unlike a pesticide label, there is no law restricting the recommendation of a commercial salesman or applicator regarding their rate or recommendation of rate to a grower. There is an understanding that the person working with the grower one-on-one will take into account factors such as field history, grower economic status, tenure status on the field, and personal long-term goals before a decision on fertilizer rate is finally made. But why is there such a gulf sometimes between the University fertilizer recommendation and the recommendation on a soil test report?

The difference usually is not in the nitrogen recommendation. The difference is usually with phosphate, potassium and sometimes micronutrient recommendations. The states in this region adhere to a sufficiency nutrient approach. This means that rates are recommended based on soil test and the rates of fertilizer needed to maximize yield in the year of application. Rates increase as soil test decreases. At lower rates, especially below medium levels, the extra fertilizer recommended not only helps with increasing yield, but also helps to increase soil test levels over time.

The alternate philosophy comes from the central corn belt, where life is beautiful for corn and soybean plants most of the time and crop failures due to environment are few and far between (see:Great Plains- tornados, flood, drought, low humidity, frost, snow, sleet, hail, wind, heat, flash-flood). In this philosophy, the response of crops to a single application is not considered as highly as the goal of either maintaining soil test by replacing what the crop removed, or applying enough fertilizer to both replace the removed nutrients plus add enough to build soil test levels to some optimum level over time.

The sufficiency approach has been compared to the buildup-maintenance approach in long-term studies in both Nebraska and Minnesota. Over the length of the experiment, the corn fertilized under the sufficiency approach performed the same as the corn under the buildup-maintenance approach at far less cost (summary available on request).

I believe that growers should have more informed input into their fertilizer recommendations. They should be handed a sheet that says that this is what the University recommends for rates that optimize yield this year, and these are the suggestions from the lab if you are interested in building up soil tests to this level over this many years on this farm. With this information, the grower can put together his own situation and decide on a more profitable course of action. I know in my own fertilizer selling experiences in my prior life, cash rental farms and farms operated by people who would retire in a few years were treated much differently from those farmed by people with many years ahead of them and farms that would stay in the family for awhile. They still raised good crops.

Growers should be given the same options here as well.



No fertilizer should be applied in the row with dry beans. Lucky people have been able to get by some years with a little 10-34-0 in the furrow, but this is not a good plan. Most dry bean growers have wisely set the planter up for a 2 by 2 band of fertilizer, liquid or dry. Most newer planters are set up for liquid due to the high price of dry banded equipment. For dry beans, liquids are especially a good option. About 1 qt/acre of zinc chelate or an ammoniated zinc product in the 2 by 2 band should take care of most zinc problems that year. For long-term dry bean growers, application of 5 to 10 lb/acre zinc as zinc sulfate will take care of zinc needs in the future due to the increase in soil test levels that will result. If soil test zinc is higher than 1 ppm, no additional zinc should be required. In dry 2 by 2 starter bands, 1 to 3 lb/acre zinc as zinc sulfate could be supplied, but some years it might not be as helpful due to granule distribution, as in others. In dry soil areas, zinc sulfate broadcast or banded might not be as available as in wetter years and a foliar treatment might be necessary. If the young beans start to appear bronzed or stunted, a foliar zinc treatment usually helps. One to two quarts/acre of zinc chelate would help correct the problem. The best answer is to address the zinc soil test level sometime during the rotation using appropriate rates of zinc sulfate or an equivalent rate of water-soluble dry zinc product.

Dave Franzen
NDSU Extension Soil Specialist

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