BRANDON, Man. – A soil and plant analyst from North Dakota has a simple message for farmers who want better bean yields.
“Don’t skimp on the zinc,” Ed Lloyd told a recent meeting of the Manitoba Pulse Growers’ Association.
“I do not think we should try to grow dry beans unless we have adequate availability of zinc in the soil, or else you plan to make adequate applications of foliar zinc so that the plant doesn’t suffer,” said Lloyd, president of Agvise Laboratories in Northwood, N.D.
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Lloyd explained beans need at least one part per million zinc in the soil to grow properly. About half the fields his company tests have inadequate levels of zinc for the crop.
Fields can also have variable levels of zinc. “That’s why often times when you drive across a field in your combine … there’s a difference in the amount of beans coming into the combine.”
Slower to mature
Lloyd told the farmers about research done in Idaho showing beans take five days longer to mature when there’s less than 20 ppm zinc in the leaves, and 30 days longer when there’s less than 12 ppm.
“I think in our northern latitude area … we have to be aware of this,” Lloyd said. “The one thing we can’t have is a delay in our maturity because when we get into the short days of September, it takes a long time for those beans to mature.”
Factors affecting zinc levels:
- Acidity: Soil with 7.5 pH or higher needs more zinc.
- Phosphorus: High levels of phosphorus will tie up the zinc in the soil so plants cannot use it as well.
- Soil temperature: Cold soils prevent plants from absorbing zinc, stunting the crop.
- Clay content: Zinc will stick to clay particles.
nOrganic matter: It stores zinc, making it available to plants.
Nitrogen may also affect zinc performance. Lloyd said higher nitrogen levels increase yield, but beans will take longer to mature. He said more research needs to be done into whether nitrogen-fixing bacteria would help strike a balance between higher yields and shorter maturity times.
Lloyd recommended farmers broadcast and incorporate eight pounds of zinc sulfate for soils with low zinc and phosphate levels but high pH levels. He noted zinc is expensive, but this type of application will take care of the problem for a few years.
For soils with low zinc levels but high phosphate and pH levels, he gave farmers a few options. At planting, apply zinc chelate or zinc sulfate five centimetres below and beside the seed. Before the plant reaches the third tri-foliate stage, “rescue” it by applying zinc chelate.
Lloyd said farmers should determine their yield goal before buying zinc.
“If you only want to raise 800 pounds of beans, don’t worry about it. If you’re going to go for 2,200 pounds of beans, you’re going to have to have more consideration for the availability of zinc.”
