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NOVEMBER-DECEMBER 2001 9
Zinc Application Methods Band or starter applications of zinc are best. The primary methods of applying zinc (Zn) fertilizer to beans are broadcast, banding, and foliar sprays. Each method has advantages and disadvantages. A Zn fertilizer can be blended into other fertilizers being broadcast. While this is rapid and convenient, broadcasting zinc has not produced consistent responses, even on low-testing soils. Many Colorado soils have high Zn-fixing capacity. In other words, much of the zinc applied reacts with other soil minerals and becomes unavailable to plants. Availability is reduced further if soil conditions, such as compaction, restrict root growth. Banding concentrates Zn in the root zone, improves the probability of root contact, and reduces fixation. Greater efficiency of band applications means that lower rates can be used to get the same crop response. Broadcast applications usually call for 5-10 lbs Zn/acre while 1-5 lbs Zn/acre is adequate for banded application. Research studies comparing band and broadcast applications of Zn have demonstrated more consistent responses to banding than to broadcasting. In some cases, banding has produced crop responses even on high-Zn soils. Foliar applications are usually used to correct an unanticipated deficiency that occurs during the growing season. A water-soluble fertilizer such as a Zn chelate or Zn sulfate is dissolved in water and applied at about 0.5 to 1.0 lbs Zn/acre in enough water to wet foliage, about 20-30 gal of solution per acre. Repeated applications are often necessary to maintain healthy plants when soils are deficient in available Zn. A discussion of Zn application on dry beans should include the use of starter fertilizers. Starter fertilizers have been shown to improve early growth and development of many crops. In Colorado, dry beans are often planted into cold, high-pH, low organic matter soils. Compaction is often present. Under these conditions, early plant growth and development are slow and many nutrients, especially Zn, are less available. Yield potential of beans is established during early vegetative
growth. Flower cells are being formed at this time. Stress during this
formative period reduces the number of flower cells that are formed and
thereby reduces yield potential. By applying Zn in a starter fertilizer,
early vegetative growth is increased, the photosynthetic factory is greater,
and yield potential increases. While starters are not commonly used on beans, Wyoming research has demonstrated significant profit opportunities with the use of starters. As little as 1 lb Zn/acre in a starter containing N and P was effective in producing an additional 130 lbs bean yield/acre, hastening maturity by two days, and increasing profit by more than $20/acre over a starter containing only N and P. This response was observed on soils with very high soil Zn. Be aware that starters should not be placed in direct contact with bean seed. Beans are very sensitive to salts, and stand loss will result from seed-placed fertilizer. Band or starter application of Zn on beans in Colorado is highly recommended if soil pH is high, N and/or P supply is high, soil compaction is present, or yield potential is high. The advantages outweigh the inconvenience. |
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