Optimizing crop nutrition is a key component of maximizing yield and efficiency, and sap testing is proving to be a game-changer in this space. At the recent Hiawatha Irrigation Clinic , Mike Evans, co-owner of Integrated Ag Solutions, shared his insights into sap analysis, its advantages over traditional tissue testing, and how growers can use this data to make informed agronomic decisions.
Understanding Sap Testing vs. Tissue Testing
Sap testing provides a more detailed and real-time look at plant nutrition than traditional tissue testing. Evans explained that while tissue testing involves whole-plant ash analysis, sap testing extracts the xylem fluid directly from the leaf, offering a snapshot of nutrient mobility within the plant.
“The xylem is like a railway,” Evans noted. “It takes water and minerals from the root through the plant. The phloem, on the other hand, moves sugars and proteins back down to the roots or dominant seed.” By analyzing plant sap, growers can assess how well nutrients are moving and where deficiencies may be occurring.
Unlike tissue testing, which only samples new growth, plant sap analysis examines both old and new growth, revealing how nutrients are flowing through the plant. Evans emphasized, “Tissue sampling gives us a look at new growth, but sap sampling tells the full story by comparing old and new growth together.”
Key Learnings from Plant Sap Analysis
Evans detailed the importance of distinguishing between mobile and immobile nutrients. “When we see deficiencies in new growth, it’s often due to immobile nutrients like calcium, boron, and zinc,” he explained. “Deficiencies in older growth typically point to mobile nutrients such as nitrogen, phosphorus, and potassium.”
One major finding from their data set was the critical role of potassium. “By side-dressing potassium at V6 to V8, we’ve seen an increase of 9 to 15 bushels per acre,” Evans said. Their data showed that as soil potassium levels declined, the plant began mobilizing potassium from older leaves, reinforcing the need for in-season applications.
Phosphorus was another limiting factor. “We initially thought phosphorus wasn’t an issue based on tissue tests, but sap analysis and rapid soil testing revealed otherwise,” Evans shared. This led them to shift phosphorus applications to later in the season, targeting reproductive stages when demand spikes.
The Nitrogen Story: Conversion and Efficiency
One of the standout advantages of plant sap testing is its ability to measure nitrogen conversion efficiency in the current crop conditions. “With sap testing, we can see total nitrogen, ammonia, and nitrate levels separately,” Evans explained. “If plant conversion efficiency drops below 95%, we know there’s a dysfunction in the plant.”
He highlighted how excessive nitrate accumulation leads to weaker plant structures and increased disease susceptibility. “Nitrate causes extreme growth, enlarging plant cells and making them more vulnerable to pathogens. When we have balanced calcium, boron, and potassium, those cells tighten up and resist disease pressure.”
To address nitrogen inefficiencies in a corn plant, Evans recommends applying micronutrients and carbon sources. “Applying soluble carbon with iron can drive ammonium out of the plant within six days,” he said. Similarly, copper applications can help eliminate excess nitrate, improving plant health and resilience.
The Role of Micronutrients and Carbon Sources
Micronutrient deficiencies in a corn plant were another key focus, with Mike Evans highlighting the widespread shortage of zinc, boron, iron, and copper. “Zinc is the regulator for phosphorus—it controls how fast phosphorus enters the plant,” he noted. Without sufficient zinc, phosphorus uptake becomes inefficient, limiting yield potential.
To address these issues, Evans advocates for a two-pronged approach: incorporating micronutrients into base-rate corn fertility programs and making targeted in-season applications. “We can’t apply enough liquid micros in one shot to sustain the plant,” he said. “Instead, we need to allocate those dollars across multiple passes to maintain a steady supply.”
Carbon sources like humic and fulvic acids also play a critical role. “Fulvic acids can carry 10 times their weight in nutrients, helping with absorption,” Evans explained. Enzyme-processed carbon sources, such as their ‘Backbone’ product, further enhance nutrient availability and plant performance.
Moving Forward: Practical Steps for Farmers
Evans encouraged growers to start small and focus on their biggest pain points. “Find two or three major nutrient issues in your fields and address those first,” he advised. He also stressed the importance of in field data collection, using plant sap testing alongside soil tests to refine fertility programs.
“For those using irrigation, integrating sap-driven fertility management with water applications can be a game-changer,” he added. “The first year is about discovery—tweaking blends and learning what works best.”
Final Thoughts
In season plant Sap testing provides growers with unprecedented insights into plant health, allowing for more precise nutrient management and improved crop performance. By leveraging this data, farmers can optimize fertility programs, reduce inefficiencies, and ultimately increase yields. As Evans put it, “When a plant is nutritionally balanced, it can better tolerate stress, fight disease, and maximize production.”
For those looking to refine their approach to crop nutrition, plant sap testing is a tool worth considering. With continued advancements and field data, corn growers can push their operations to the next level, making informed decisions backed by real-time plant insights.
