Ask an Agronomist: Agronomy Q&A

March 12, 2011 12:34 PM

Have a row spacing, crop rotation, tillage or pest question? Through Farm Journal’s Ask an Agronomist blog, you can find answers. A team of Farm Journal agronomists weigh in with their independent experience and from the field insight to provide expert responses. Here are a few questions and answers from the blog:

Q: Why should I care about lime quality? I’ve always thought one source is as good as any other.

A: The foundation of a systems approach to growing corn is soil pH. The keys to lime applications are quality and fineness. You do need to look at the purity of rock and how much neutralizing value the lime has, which requires lab analysis. The neutralizing value comes from the calcium carbonate, and the lab will compare the limestone sample to a product with 100% neutralizing value. Properties of limestone range in neutralizing power. In comparing one quarry over another, there can be a $3 to $4 per ton difference in quality. Another part of the lime equation is that you need to pay attention to the fineness of the lime. The more fine the grind, the more neutralizing power is available due to more surface area. You also have to weigh the spreadability of the lime and have your equipment calibrated for the fineness of the product.

Q: What can I do to control corn rootworms besides plant Bt seed? 

A: T-banded soil-applied insecticides are still a good option for controlling corn rootworms in corn.

Q: How much sulfur should I apply to corn on corn? What is the best way to broadcast it; can I put it in with my preplant 28% or Harness?

A: A 200 bu. per acre corn crop has a sulfur uptake of about 30 lb. per acre and an actual removal rate of around 15 lb. per acre. In recent years, there has been a greater yield response to applying sulfur for corn production. Soil fertility specialists believe the sulfur response is increasing because of the reduction of the atmospheric deposition of sulfur (cleaner air, less pollution) because fertilizer sources are cleaner (less incidental sulfur) and because farmers are making fewer manure applications.

Broadcast applications of sulfur are common. There are several sources of dry fertilizer products that contain sulfur: ammonium sulfate (AMS 21-0-0-24S), K-Mag or Sul-Po-Mag (0-0-22-11 Mg-22S), elemental sulfur, some MicroEssentials products and others. Liquid sources of sulfur can also be used. Liquid AMS (8-0-0-9S) contains 9 lb. of sulfur for every 10 gal. applied. Liquid ammonium thiosulfate (ATS 12-0-0-26S) contains nearly 29 lb. of sulfur for every 10 gal. applied. Application rates are often15 lb. to 30 lb. of sulfur per acre.

Select a product that best fits your fertility program needs. Refer to the herbicide’s label for compatibility issues before adding a liquid sulfur product to your weed-control program.

Visit the Ask an Agronomist blog or e-mail your questions directly to

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