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Debunking the Hype: A Deep Dive into Sap Analysis vs. Leaf Tissue Analysis for Accurate Plant Nutritional Assessment

Is sap analysis a better alternative to traditional leaf tissue analysis for determining plant nutritional status?

Two years of comparisons between sap and leaf analysis, hundreds of samples over multiple production cycles and an accumulation of a huge pool of data, yielded this conclusion from Deerpoint Group: there are no statistical differences between the two types of analysis for nutrient status. Sap analysis results may not deliver a real time diagnosis of plant health and nutrient status, and may lack vital micronutrient ranges.

This painstaking internal research conducted by Deerpoint Group was not done to discredit other laboratory work, but to point out to growers of California specialty crops the reality that they might want to look closely at sap analysis claims and understand what this testing method can and cannot do within the context of their own operations.

While sap analysis has been widely promoted as a new tool to assist with fertilizer use efficiency and ensure crop quality and yield, the scientific research to back up the claims just isn’t there, said Jeff Carr, DPG Director of Grower Relations.

A key point to understand is that sap analysis reveals what the plant has absorbed , but not metabolized, while dry tissue or leaf analysis shows what the plant has metabolized.

Before being drawn in by claims of saving money on fertilizer, growers should be aware of the different methods and plants used in sap analysis testing. Tomato plants were the most widely tested with sap analysis, mainly looking at nitrogen and nitrate levels. There are few long term studies using sap from permanent crops. Many studies were conducted under controlled greenhouse conditions. While sap analysis is not new in agriculture, the lack of established optimal nutrient levels means the sap analysis laboratories can only offer comparisons to other samples.

Deerpoint’s multiple year study of sap analysis determined the average range of the analyzed nutrients were 2.3 times larger in the sap than in the tissue. This shows, Carr said, that nutrients found in sap samples and the methods of analyzing them have a much greater variability than leaf tissue analysis. He also pointed out that many of the laboratories doing sap analysis are located on the east coast or in Europe. In addition to the lack of standard methods for sap extraction and collection, environmental factors including light, temperature and water status can add to variability and misleading test results. Independent studies on sap analysis invariably yield this conclusion: ‘more studies needed.”

Trends in nutrient status of permanent crops including almond trees tracked over time were more evident in the leaf tissue analysis than in the sap analysis. Without good history of an orchard’s nutritional status, a sap analysis report may only be a guess. The claim that nutrients are not translocated to the leaves is also suspect.

Leaf tissue analysis is done during the growing season to determine nutrient levels in a plant at the time of sampling. The leaf analysis can show undetected nutrient deficiencies as well as confirm visual symptoms of deficiencies.

Plant tissue analysis shows the nutrient status of plants at the time of sampling. This, in turn, shows whether soil nutrient supplies are adequate. In addition, plant tissue analysis will detect unseen deficiencies and may confirm visual symptoms of deficiencies. Toxic levels of nutrients also may be detected.

The analysis can show if the key macro nutrients- nitrogen, phosphorous and potassium are at optimal levels for plant growth and yield. Nitrogen provides the growth necessary for production and energy to pull up nutrients. Phosphorous is needed for metabolic activity and potassium is critical for reproductive activity and crop yield. Micro nutrients also play an important role in plant health.

The state-of-the-art laboratory at DPG is fully capable of providing both leaf tissue analysis as well as sap analysis, but variables involved in sap analysis and lack of definitive research on sap analysis in California specialty crops has led to the conclusion that analysis of sap squeezed from the leaf did not show any significant difference in the data than leaf tissue analysis. Short of calling sap analysis a ‘gimmick’ or a cool sounding testing technique, DPG laboratory results provided no clear reasons why leaf tissue analysis should be traded for sap analysis.

Another way to look at ensuring adequate nutrition for trees and vines is to re-examine the value of the “4Rs” – a longtime almond industry guideline for efficient fertilization. Right source, right rate, right place and right time provides a foundation for fertilization of permanent crops. Deerpoint is a strong proponent of this fertilization strategy because it not only promotes efficient use of expensive inputs, but results are clear with leaf tissue analysis.

Growers should also be aware that the practice of ‘slug feeding’ nutrients is not compatible with use of sap analysis to determine plant nutrient status.

“Slug feeding” fertilizers, particularly nitrogen, was not considered a problem when costs were low, but as growers are looking at lower cost strategies for feeding trees, they need to re-visit the 4Rs of Fertilization. The right source, right rate, right time and right place” should be the plan for crop fertilization with a goal of maintaining plant health and yields while using only the amounts necessary. Using nitrogen applications as an example, Deerpoint research has shown that smaller doses over the growing season allows for more efficient uptake. Following this strategy not only improves efficiency in nutrient use, growers can save on fertilizer costs by reducing inputs – an important consideration when fertilizer prices are high.