Now Let's Get Sappy! What is sap sampling and how can you use it to make better agronomic decisions?
A sap analysis measures the active liquids in the vascular tissues, the xylem, and the phloem. It provides real-time assessment of the nutrients available in the plant. Sap is extracted through linear pressure, without compromising the integrity of the leaf. By using methods that do not include mastication heat, acids, or solvents, we get a clear view of what is active in the plant at the time of sampling. Tink of a sap analysis like a blood test. Sap will provide a snapshot of nutrients that are currently available in the plant. Tis data can provide information such as nutrient excesses and deficiencies in crops. Tis allows you to see problems and symptoms long before they become visible in the field.
In a normal sap sample, they pull old leaves and new leaves from the plant, and they are analyzed. By doing this you are able to see nutrient mobility—something that a sap sample can provide versus a tissue test. Nutrient mobility is how we can detect excesses and deficiencies in the plant. For example, nitrogen being highly mobile in the phloem will start to show deficiencies in the old leaves if the plant has been without nitrogen for extended periods of time. Old leaves will start to turn yellow due to lack of chlorophyll synthesis.
In a sap analysis, you can see the nitrogen deficiencies long before the leaves turn yellow. In the new leaf tissue samples, you will see higher amounts of N versus the old leaf tissue samples, meaning the plant is remobilizing N from the old leaves to the new leaves to continue supporting the new growth of the plant when there isn’t enough N available to support both. In an excessive N situation, you will see the N higher in the old leaves than in the new.
Now as you all know and are probably asking, how do you sample old tissue from sod if we are constantly mowing? Tat's a great question and one that I had as well. So what we came up with and are currently implementing is pulling the sap sample and sending it in together with a rapid soil test. Tese two tests can put a pretty good map together of what’s happening. Te rapid soil test data shows us what is in the “tank” and available for the plant to uptake and the sap data shows what the plant has taken up.
What Sap Sampling Does for Us When we started sap sampling our eyes were opened to the things that were and were not working in our agronomic plan. In the first year of using sap samples, we were able to cut our fertilizer costs by $125,000. Being able to see what the plant needs and not just guessing was a game changer.
Over time and with some basic education on the process and results, I stopped relying on our field men because I could now see and understand the results myself. We only apply what the plant is asking for and needs. On our farm, we pull sap samples every two weeks—giving us time to apply something if needed and then giving the plant time to react. Two examples of our sap sampling analysis, one from May 12, 2024, and one from June 19, 2024, are on pages 24 and 25.
Learning Experiences Have we had some learning experiences with sap sampling? Absolutely. But those experiences have always taught us something. For example, just this year we would sample, and for about four consecutive samplings, we hardly saw any change. We would apply and apply with little or no results.
I started to get somewhat frustrated until I reached out to Rocky Mountain Ag’s Jared Cook, who is the sap analysis wizard. As we talked and looked over the results he started to ask a few questions, and I realized I was probably overwatering. It was right in the middle of July and when I would probe the soil it seemed fine. But Jared explained to me that all that plant was doing was sucking up water and the nutrients were diluted, and that I wouldn’t see the plant start to take up nutrients and fully react until a dry down.
In a drier situation, the plant can actually use the nutrients that are there and available. (And to be clear, the $125,000 savings from the previous year were probably spent on this eight-week oversight.)
Our Goal Our goal with sap analysis is to better our product with fewer inputs. It is changing the way we operate, and we believe that by customizing our applications for each field we will see improved plant health and increased savings. What more could you want?
Spencer Mendenhall is manager of Raft River Sod in Raft River, Idaho. They grow over 1,000 acres of various types of sod and move about 600 acres annually. Before the sod farm, he was a golf course superintendent but traded in the Club Car for a John Deere five years ago—and he loves it. When farming allows free time, Spencer enjoys it with his wife and four children riding their horses, wake surfing in the Snake River, snow skiing, golfing, and camping.
spencer@raftriversod.com
All graphics and charts courtesy of Spencer Mendenhall. TPI Turf News November/December 2024 23
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