Renewable Farming

More farmers learning how to foliar feed with sap testing diagnostics

We pulled some sap testing samples on soybeans late this season, and now have a better understanding how how sap testing can help you gain more effectiveness and efficiency with foliar nutrition.

A main benefit of sap testing versus conventional tissue testing: It’s an early indicator of potential nutrient deficiencies — or excesses —  in the growing crop. That includes primary and secondary nutrients.

Virtually all of the high-yield contest winners foliar-feed their crops through the season to maintain the pace of growth and to fend off late diseases.

(One of our growers who foliar-fed soybeans this year called from the combine today, saying, “I’ve never seen the combine monitor register 90-bushel beans… until right now!  It’s bumping up to 96 bushels in some spots.”) He insisted that we don’t tattle on him.  “It’s not me that caused that yield; we have to give the credit to the Creator.”

Sample of sap analysis form

The soybeans we sap tested on our place this summer won’t approach 90 bushels. But they’ll do much better than in previous seasons. The image nearby is a small version of a full sap test report. We suggest that you download these PDF reports and either open them on the screen, or print them out for comparison side by side.

Report one: Soybeans with no potassium deficiencies.

Report two: Soybeans which show potassium deficiencies. 


The purpose of showing you these reports is to simply get a bit more exposure to sap testing here in the United States. It’s much more widely used in the EU, and particularly in the Netherlands, where NovaCropControl has its laboratory. 

What’s especially revealing during the early to mid growing season is emerging differences in sap nutrient content showing up between new leaves and old leaves. The light green bar shows the reading in new leaves, which of course you sample separately. I pull a fresh trifoliate leaf from a given soybean plant, and then take an old trifoliate leaf from low on the same plant. If the plant is becoming deficient in any nutrient, it will scavenge the needed elements from old leaves — just as corn will cannibalize lower leaves late in the season, to fill kernels. 

In this case, one of our chronic problems on a rented farm is low potassium. That showed up clearly when we sampled from test strips showing definite potassium deficiency in late September. The deficient leaves tested only 1030 parts per million (old leaves) to 1170 parts per million (new leaves).  The plot which hadn’t shown visible symptoms was still in the lower third of the full range, showing 1620 ppm (old leaves) to 1810 ppm (new leaves).

NovaCropControl has detailed “optimum” ranges well-established throughout Europe, particularly on high-value greenhouse crops. The U.S. standards will be assembled over the next two to three years.  By the 2016 season, Crop Health Labs of Beltville, OH. should have its own licensed sap testing facility up and running. That will speed up analysis a few days. You could overnight samples to Ohio and have results back within 48 hours – possibly sooner.

Iowa farmer Mike Holst has encouraged farmers to use sap testing, and made arrangements this year to buy a large number of tests at a discounted rate to save Midwest growers money.  We used his service, called Top Growers, for this year’s testing. If you’re interested, see Renewable Farming’s contact information, send us an e-mail and we’ll help you connect with Mike.

Published Oct. 1, 2015 by Jerry Carlson