Time to Use Late Spring Soil Nitrate Test for Corn

Soil samples should be collected when corn is 6 to 12 inches tall, and sent to a lab for testing to help you make better nitrogen decisions.

It's getting close to the time to collect soil samples for the late spring soil nitrate test. Soil samples should be collected to a one-foot depth with a soil probe when the corn is 6 to 12 inches tall, says Brian Lang, Iowa State University Extension field agronomist at Decorah in northeast Iowa.

It is best to use a systematic method of soil sampling called "sets-of-eight" rather than a random method to collect the samples, says Lang. Pull the first of eight cores in the corn row, the next core you should pull is one-eighth of the distance between rows, the next one you pull should be one-fourth of the distance between rows, etc. until you have worked your way across the rows.

ISU information sheet shows proper way to sample

Do this at least twice for a total of 16 cores (two sets-of-eight) or better yet three times for three sets-of-eight. This way you avoid over or under representing areas that have bands of nitrogen - such as anhydrous bands, manure bands, starter fertilizer, etc. The soils samples should be sent to a lab immediately after sampling. Results can help to fine-tune nitrogen management or adjust manure management plans.

For more details see the publication "Nitrogen Fertilizer Recommendations for Corn in Iowa" at www.extension.iastate.edu/Publications/PM1714.pdf

Many soil testing labs conduct the late spring soil nitrate test.  ISU's information sheet for Late Spring Soil Nitrate Samples is available at www.agron.iastate.edu/soiltesting/howto(fieldcrops).htm

Diagnosing anhydrous ammonia burn on corn roots

The northwest corner of Iowa has consistently missed rainfall this spring, says Joel DeJong, ISU Extension field agronomist at LeMars. The area is about 5 inches below normal so far this spring. Last week he started noticing lawns beginning to go dormant. "Although our subsoil moisture reserve has barely been tapped at this time, the surface soil is really getting dry," he reported on June 3.

In most fields it hasn't been a problem because the corn and bean roots are reaching down to get moisture. But there have been some bean fields where seeds were sitting in dry soil last week. Also, some cornfields were struggling to get the nodal root system established and were showing signs of stress. Fields that struggle to get those roots established often start looking uneven because the nodal roots need to get established to feed the plant at this four-collar stage when it is starting to grow more rapidly.

In addition to dry soils where roots are trying to grow, causes of stress also include soil compaction, insect injury, herbicide injury and anhydrous ammonia injury to roots from spring application. He recommends you dig and examine roots from each field to determine what the cause is in each situation. He also observes that an inch of rain would prompt most of these issues to go away - as the rain would help the roots grow though the problem.

How to avoid anhydrous burn on corn roots

DeJong has seen some fields with anhydrous burn on corn roots this year. He isn't surprised. "We had little rain in this area of northwest Iowa since the ammonia was applied in many fields this spring," he says. "Both the dry soil and an application that is too shallow are factors that increase the risk of root injury. In one field I looked at, the depth of the anhydrous application was about 5 inches deep. That's a little shallow for a spring application, in my opinion."ISU Extension soil fertility specialist John Sawyer has written an article about nitrogen burn injury to corn roots. It's on his Web site, along with some descriptive photos. Sawyer discusses why damage can occur, how it occurs and makes some management suggestions to help farmers avoid this corn injury. Go to www.agronext.iastate.edu/soilfertility.

Sawyer's summary: "Anhydrous ammonia and urea are good N fertilizer sources. With proper management, and help from Mother Nature, most fields do not experience crop injury issues from use of these materials. However, sometimes problems arise due to a variety of reasons. Potential for crop injury can be greatly reduced by not matching corn rows with ammonia tracks and urea bands. Having enough soil separation between the N band and the corn row is the key. So, applying at an angle, having good injection depth, and good soil conditions at application, or use of RTK GPS (real-time kinematic GPS) to place bands away from future corn rows is what you want to do to avoid this injury."

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