Monitoring Sulfur And Other Lesser Crop Nutrients

Monitoring Sulfur And Other Lesser Crop Nutrients

If you are interested in enrolling your field in the On-Farm Network's crop nutrient testing program, here's what to do.

Most farmers try to keep up pretty well on applications of nitrogen (N), phosphate (P) and potash (K), but how's your sulfur supply these days? Do your fields and the crops that grow there lack sulfur? Corn and soybean producers working with the Iowa Soybean Association's On-Farm Network have been looking seriously at apparent sulfur deficiencies for several years now. "While we've seen more sulfur deficiency symptoms in the past couple of years, it might be because we are actually looking for them," says Tracy Blackmer, research director for the On-Farm Network.

Admittedly, corn in both of these strips shows some degree of sulfur deficiency. However, the corn on the left received fall anhydrous and that on the right was fertilized in the spring with an encapsulated slow-release urea. The theory is that dry weather affected nitrogen availability, which led, in turn, to a different rate of sulfur uptake by the crop. Question is: will this impact yield? We'll report back on that after harvest.

He adds, "We've seen visual symptoms of sulfur deficiency corrected in replicated strip trials where sulfur products were applied, but the average yield response over all trials with sulfur applications has been less than a bushel per acre."

In 22 strip trial tests with SuperCal SO4 on corn last year, the average yield response was about 0.2 bushel per acre improvement with this sulfur containing product being applied. An interesting finding of these studies was the range of yield response, from 8.8 bushels more corn per acre, in Bremer County, to a minus 8.0 bushels per acre in Delaware County. Check out the full list of these trials here. 

Best bean response to applying this product has been less than 3 bushels per acre

To date, the best response in soybeans with this product has been less than 3 bushels per acre, and the average response has been about minus 1.0 bushels per acre.

This Hardin County field was involved in testing the same two nitrogen fertilizer materials mentioned with the photo above. The strip in the center left received the spring N application, while the one on the right received fall anhydrous. Again, some corn in both showed some signs of sulfur deficiency, the symptoms were more visible in the spring-applied strips.

"We have a lot to learn about the interaction and balance of soil nutrients," notes Blackmer. "Two weeks ago, growers working with the On-Farm Network reported the appearance of sulfur deficiency symptoms in replicated strip trials testing nitrogen products. (See accompanying photos.) On-Farm Network personnel collected soil and leaf tissue samples from the different treatments. Lab analysis confirmed this week that the plants in strips that received a spring-applied nitrogen product were lower in sulfur than those in strips where fall anhydrous was applied. Both strips in the comparison received the same amount of nitrogen.

Consider enrolling your fields in micronutrient test to continue this project

To better understand the level of N, P, K, S, zinc and other minor and micro nutrients in Iowa soils, the On-Farm Network began a soil and plant tissue testing program last year to help establish a benchmark for comparing and monitoring soil nutrient levels into the future. More than 800 Iowa corn and soybean fields were enrolled in this program, dubbed the Nutrient Management Benchmarking Project, or Nutrient Benchmarking for short. Click here for summaries produced from the 2011 test results. Sulfur tests for corn and soybeans can be seen separately.

The On-Farm Network is now enrolling fields to continue this project. If you participated in the program last year, consider enrolling the same fields you enrolled before. As before, there is a fee to participate in this program. The cost will be $220 for an 80 acre field, with no discount for smaller fields and a surcharge of $1.70 per acre for each acre over 80 acres. "We'll again provide plant tissue and soil testing for two points within the field," says Blackmer. "If you'd like to test more than two points, the cost will be $16 for each additional soil sample and $18 for each additional plant tissue sample."

Some changes have been made in this field testing program this year

The On-Farm Network has made a few changes to the program. "Waiting on aerial imagery that we hoped would help you select points for sampling in fields created a bottleneck in sampling that led to a late return of many of the results," he explains. "While we're going to collect imagery on all fields enrolled this year, that imagery will not be used for picking points to pull soil and leaf tissue samples. It will arrive in time, though, to be used for collecting samples for stalk nitrate testing, and we'd encourage participants to enter all the cornfields enrolled in the Nutrient Benchmarking program in our Guided Stalk Sampling program as well."

You can click here for details of the 2012 Nutrient Benchmarking project. And send the project managers an email by clicking Email here if you'd like more information. Also, click here for the worksheet to help you organize your information before registering. Finally, to register fields in the program, go here.
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