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Fluid Journal : Fluid Journal 1993-1995
1 Fluid Journal Fall 1994 FFF Exclusive "Zinc is the most widespread micronutrient "Zinc is the most widespread micronutrient "Zinc is the most widespre ad micronutrient "Zinc is the most widespre ad micronutrient "Zinc is the most widespre ad micronutrient deficiency in the Corn Belt." deficiency in the Corn Belt." deficiency in the Corn Belt." deficiency in the Corn Belt." deficiency in the Corn Belt." An interview with Dr. John Mortvedt of Colorado State University. FJ: You were with TVA for a long time weren't you? Yes, for almost 31 years. FJ: What were your responsibilities? I conducted research and development mainly on micronutrients and other fertilizers. Another part of my job was determining the fate of metals in sewage sludges and phosphate fertilizers after application to the soil. I was also involved with studies on nitrogen and phosphorus fertilizers, as well as working with the TVA field staff. FJ: Did you do much of your research in greenhouses? Yes. In addition to field research, many of my published papers are concerned with greenhouse research. We worked with university extension and research people to obtain in-field results where fertilizers are used. FJ: What were some of your findings on sewage sludges? We know there's a potential for heavy metal buildup when high rates of sewage sludges are used. I think you'll find the current regulations that went into effect in February of '94 pretty well reflect this. It amounts to having some limits on heavy metals in the sludge that would allow a gradual buildup in the soil. The object is to see that N and P in these sludge are applied on a sound agronomic basis. I think the regulations should stand the test of time. After all, they're based on over 25 years of research. FJ: A lot of sludge have high levels of salts. What happens to the salts? Where there is low rainfall, you may have a problem. There salts won't be washed out of the root zone. So we have another limiting factor for the application of these materials. FJ: For a grower interested in making sure he doesn't have a micronutrient deficiency, how reliable are current micronutrient soils tests? I'm confident of the tests. Various test have been calibrated for certain types of soils in different regions of the country. The important thing is to send a soil sample to a regional lab to assure the correct procedure is used for that region. How you sample is particularly important for micronutrients, because you need to get a representative sample of the field in question. After you've obtained the sample, you've got to be very careful that you don't contaminate the sample with other micronutrients that are also at very low levels in the soil. For example, you shouldn't use any type of brass or galvanized container for storing soil samples for zinc analyses. The sample should be placed in a plastic container. Stainless steel probes also should be used to avoid contamination. Following correct procedures, I think, will produce reliable results. FJ: Where do you sample? Most of the time in the root zone which is generally four to eight inches deep. Once you take deep samples, and include those with shallow samples, you're going to end up with a lower value because the level of available micronutrient decreases quite quickly below the root zone. FJ: What depth are we talking for sampling? It depends on fertilizer placement. If we take a representative sample, then it should be in the root zone. But if you're not tilling, the levels are going to again decrease because the previously applied micronutrients won't be down towards the bottom of that 12-inch zone. FJ: What if you're not tilling at all? I don't know if anyone has really studied whether, after five or ten years of reduced tillage, we'll see
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