Renewable Farming

A well-researched way to save cash on K this season: Foliar-apply as needed

If we said to you that “an extensive study of more than 2,100 yield response trials confirmed that soil-applied KCl (potassium chloride) fertilization is unlikely to increase crop yield,” would you consider us credible?

February 7, 2019 — And would you immediately click “close” on this website if we went on to say this: “Contrary to the inculcated perception of KCl as a qualitative commodity, more than 1,400 field trials predominately documented a detrimental effect of this fertilizer on the quality of major food, feed and fiber crops, with serious implications for soil productivity and human health.”

We’re not making this up. We’re citing three very astute scientists at the Department of Natural Resources and Environmental Sciences, University of Illinois. You can download their research paper here.

Their 25-page analysis appears in Renewable Agriculture and Food Systems. (That’s a research journal title that resonates well with us here at Renewable Farming LLC.) Note the report’s date: Accepted on June 5, 2013. If the International Potash Institute has contradicted this study, we missed the Institute’s report. 

We accept that potassium is vital for crop nutrition and human health. But the issue is, what’s the least expensive way to make the potassium available to crops? 

KCl prices hover around $215 per ton, and a common fall application range for corn is 100 to 200 pounds per acre. That’s a cost of $10 to $20 per acre plus application. Sounds cheap, but if the University of Illinois research is to be believed, is the KCl “insurance” worth it at $3.50 corn?

For years, potassium recovery from well-digested crop residue was considered the surest source of potassium for the next crop. Now, crop consultants like Bob Streit are challenging the formula-driven “NPK replacement” recommendations baked into most university and co-op fertility prescriptions. Along with Streit, we’re raising the concept that with careful tissue and sap analysis, you can meet the potassium needs in your growing crop with K in the right form and right time with foliar feeding. As always, we’d recommend WakeUP Summer tank-mixed with it. Our nearly 10 years of field trials indicate that if a foliar nutrient raises yields 5 bu. per acre, including five ounces of WakeUP Summer (a cost of $3 per acre or less) enhances performance of the nutrient by 80 percent, adding another 4 bushels. 

Working with AgriEnergy Resources, we tested this notion in 2013 on soybeans. We planted the beans on a newly rented 10 acres which had been in overgrazed pasture for years. Potassium deficiency showed up in the leaves early. We set up a foliar feeding experiment with a tote of K2SO4 from AgriEnergy on every other six rows across the field. Early response showed up clearly, as signaled by the photo below:

Beans sprayed with potassium sulfate every other six rows

The 2013 growing season was highly stressful in our region, and yields on these plots were not spectacular. At harvest, every foliar-fed strip outyielded every unsprayed strip. The strips which were not foliar fed had less foliage, heavy insect pressure (lots of buzzing midges and other critters) and 8 bu. less yield. 

You can read our entire field report and see more photos along with yield charts by downloading this 4-page PDF.

Cornstalk stover from a 200-bushel crop contains about 100 units of nitrogen, 50 units of  phosphorous (P2o5) and 200 units of potassium (K2o). Several field studies show that a biological residue-digesting program in the fall accelerates conversion of nutrients locked in stover into greater amounts of plant-available NPK for the following crop. By accelerating this conversion, there’s less competition during the early growing season for nutrients needed by microbes for residue breakdown. 

To recover potassium effectively, here are some biological buildup tools:

1. Cover crops — in diverse species and consistently.

2. Fall residue acceleration with one of the several excellent digesters. Our classic has always been AgriEnergy’s Residuce, sprayed as early as possible after harvest. Powerful new ones are coming on-stream now.  One is Biodyne USA’s Meltdown.

3. Crack open cornstalks so the microbes can get inside to munch the juicy pith. A cost-effective tool is the Devastator from Yetter Manufacturing. We’ve done a field study showing how that speeds stalk breakdown. Some growers rig a stalk shredder with a spray rig, and hire extra help to follow the combine with the residue digesting pass.

4. If you have in-furrow application capability, apply a mycorrhizal seed treatment like Myco Seed Treat from AgriEnergy or an in-furrow mycorrhizal blend such as Biodyne USA’s Environoc 401. Biodyne also has a microbe/fungal blend for spray application with premerge or early postmerge application.