Renewable Farming

Sap analysis has paid off for farmers served by this crop consultant

John Kempf of the firm Advancing Eco Agriculture presented several reports on experience with crop sap testing at an online webinar July 14. After two full seasons of experience with sap testing, and fieldwork with it so far this year, the firm’s fertility recommendations to farmers have changed drastically. And their farmer clients are clearing more profit from higher yields and quality.

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Here’s a summary of our notes as we listened to the webinar. For a replay of the 90-minute session, visit the website of Crop Health Labs.

One of major change in their recommendations to tomato growers was that sap analysis showed adequate potassium levels, which was sharply different from results of tissue tests. Kemp said his firm had been “selling trailer loads of potassium sulfate” based on tissue tests,” but sap testing revealed it wasn’t necessary. “So we stopped applying that form of potassium,” he said.

Also, sap testing revealed that the crop showed no response to manganese sulfate. Previously, tissue testing had indicated that the crop rose in manganese levels after manganese sulfate applications. Apparently, the tissue test was measuring non-mobile manganese on the leaf, not what was actually involved in metabolism. So Kempf changed the manganese source to a chelated form, and the sap test showed a positive response.

Deficiencies of manganese also vanished. In severely deficient manganese cases, the leaf veins are lighter in color than the main areas of the leaf. Extreme cases show up as “yellow flash,” such as those following glyphosate spraying.

“As Mn levels rose, K levels smoothed out,” said Kempf. “The sap tests showed that manganese in the plant system tended to regulate potassium levels toward just the level which the plant needed.”

Using chelated manganese as the “moderator” of potassium led to another benefit: “When we stopped applying potassium, then calcium levels rose.  Calcium and potassium have an antagonistic relationship: High potassium inhibits calcium.”

And in turn, the payoff arrived for the tomato growers:  “As we increased calcium content, tomato quality went up.”

The stepped-up applications of chelated manganese also resulted in lower rates of diseases such as verticillium wilt.

“Applications of K in fertigation dropped by 65%.   We had sold potassium by the trailer load before sap tests, but that dropped a lot. That’s okay by us, as our growers made more money, and their confidence in recommendations rose. They could see the evidence in how sap testing correlated with yield and quality. Sap analysis gave farmers confidence in us.  Farmers realized we wouldn’t recommend products just to sell them.  Their engagement with nutrition management went up.”

Advancing EcoAgriculture works with a wide range of growers, including cherry growers. 

Main objectives of the cherry grower are fruit firmness, size and sweetness. In the past, the typical approach was to use high potassium applications to get large fruit. And to apply zinc aggressively to get large leaf size in the cherry tree.

However, sap analysis of cherry trees showed low calcium, already high potassium, very high zinc, and low levels of other trace elements such as Mn, Cu, Fe, Co, and B.

Kempf told webinar participants, “On 90% of the crops we work with, sap testing showed us that deficiencies are not the most common problem. Excess applications of some elements are usually the problem. We learned that high zinc applications inhibited other elements. In cherries, we eliminated zinc, added all other traces, and cut all potassium applications before fruit fill.”

The result: Higher levels of calcium occurred from blossom to cell expansion, a critical time for healthy fruit.

Kempf explained: “From the moment of pollination, there’s a 14-day period of rapid cell division in the embryo which becomes fruit. Then the embryo switches to cell expansion, and no new cells are formed. Cell numbers are limited by any early deficiency,  and the deficiency is usually calcium.”

In cherries, as with tomatoes, when manganese levels were adequate at this crucial stage of fruit cell division, manganese becomes the ‘regulator’ for potassium.

“Making sap tests every 14 days, we can chart the nutritional needs of the plant,” Kempf explained. “When we changed our fertility formulation as indicated by the sap testing, cherry tree leaf size remained the same, fruit size rose, firmness rose, and we had more disease resistance.”

He adds, “Sap analysis data corresponds closely with field observations. Sap analysis correlates with disease susceptibility. We are able to make pro-active decisions about nutrient management.

“Typically, farmers must react to problems like disease or deficiencies. Sap analysis gives us a tool to be proactive, taking actions on fertility before problems occur. 

Plants do everything they can to maintain ideal nutritional levels in new growth. Sap testing examines and compares older leaves and new leaves. Deficiencies show up in the old leaves first. They are being cannibalized.

Kempf says, “We look at the ratios of mobile elements between old and new leaves. If new leaves are greater than 10% higher in nutrient levels than the old leaves, there’s a potential deficiency just ahead.”

Kempf noted toward the close of his presentation that if farmers refuse to use sap analysis, advising them on fertility is often “an exercise in frustration.”

On July 16, AgriEnergy Resources posted a GroundWork newsletter announcing that AgriEnergy is encouraging use of sap testing.  Check out AgriEnergy’s GroundWork series for their report on sap testing.