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Zinc cannot be ignored as an important nutrient for corn production on some soils in Minnesota. When the results of a soil test indicate a need for this nutrient, it can be either broadcast or applied in a band at planting. There are economic advantages to the banded application. As more corn growers look to placing fertilizer close to the seed, there are questions about the effect of fluid zinc fertilizers placed close to the seed when zinc is needed for optimum yield.

In order to get some answers to these questions, a study was conducted at two locations during the 2005 growing season. Soils with two contrasting textures were used. For the trial in Dakota County, irrigated corn was grown where the texture was a loamy fine sand. The soil at the Renville County site had a silty clay loam texture.

For these trials, three fluid sources of zinc (Nulex, TraFix, Origin) were mixed with 10-34-0 at rates to supply either 0.1 or 0.5 lb. Zn per acre. The 10-34-0 was applied at a rate of 5.0 gallons per acre. The 10-34-0 was used without zinc for the control treatment. The 10-34-0 with the zinc fertilizer was placed either with the seed or on top of the seed. When placed on top of the seed, there was about 1/2 to 3/4 inch of soil between the seed and the fertilizer.

Stand counts were taken about three weeks after corn emergence in order to measure the effect of treatment on germination. Then, grain yields were measured in October.

The soil test for zinc at the Dakota and Renville County sites was 1.5 ppm and 2.6 ppm respectively. These values are considered to be high with no response to zinc fertilization expected. Therefore, any measured difference in yield would be a consequence of differences in emergence and/or early growth.

The impact of treatment on corn emergence is summarized in Tables 1 and 2. Emergence is reported as a percent of the control which was 29,403 plants per acre and 33,977 plants per acre for the Dakota and Renville County sites respectively.

Considering the site with the loamy fine sand texture, emergence was only affected by the rate of zinc applied. When averaged over source and placement, emergence was 99.9% and 95.1% of the control when the rate of applied zinc was 0.1 and 0.5 lb. zinc per acre respectively. This is a small difference in emergence. Neither placement nor source of zinc used had a measurable effect on emergence at this site.

When the texture was a silty clay loam (Renville site), emergence was not significantly affected by zinc source, placement and rate of zinc applied. So, there appears to be less of a risk for damage to emergence with fine textured compared to very sandy soils.

Considering the soil with the loamy fine sand texture, yields were affected by the source of zinc used (Table 3). When averaged over both placement and rate, yield was 183.2, 169.9, and 161.9 bu. per acre when the zinc source was Nulex, Origin, and TraFix respectively. The explanation for the yield difference associated with the three sources is not apparent from the data collected in this study.

Compared to the control, the use of zinc regardless of source, placement, and rate of application did not increase corn yields. The yield reduction was affected by source. However, the data collected do not provide an explanation for this reduction. The soil test for zinc at this site was 1.5 ppm. With this high value, a response to zinc fertilizer would not be expected. None was measured.

Corn yield at the Renville County site was not affected by the application of zinc regardless of rate, source, and placement (Table 4). The soil test for zinc was 2.6 ppm. A response to zinc fertilization was not expected. None was measured.

The results of this study provide an answer to some questions. There are fluid sources of zinc that can be mixed with 10-34-0 and not have any negative effect on emergence and yield if the soil is not sandy. Different conclusions were reached for the sandy site. The high rate of zinc reduced emergence. In addition, there was a reduction in the yield when the zinc was applied as TraFix and Origin.

The texture of the soil is very important. There is a higher risk for damage to emergence when soils are sandy. If the results of a soil test show that zinc is needed for these soils, a buffer of one inch of soil between seed and fertilizer is suggested.

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