Food security

How do nutrients in leaves inform farming practices?

Last fall, I spent hours washing leaves as I would wash my hands – first, I dunked them in soapy water and wiped off any residues. Then I rinsed the leaves with distilled water until there were no more hints of soapiness. I spread them on brown paper to dry, and eventually sent them to a lab for nutrient analysis.

I was working on a research project involving grapevine nutrition. Specifically, I was investigating which vine parts are most reliable for tissue nutrient analysis. Tissue nutrient analysis can help farmers decide if their plants are hungry – that is, whether the plants are getting their nutritional needs met. There are many benefits of tissue nutrient analysis, such as:

  • Deciding what kinds and how much fertilizer to add
  • Troubleshooting and diagnosing plants that are not growing ideally
  • Being able to correct nutrient deficiencies relatively quickly
vineyard with hand holding bouquet of leaves to be used for nutrient analysis
Collecting leaves from a vineyard. Both the stems and leaves will be analyzed for nutrients. Researchers are working to determine if analysis from the stems or leaves is better (or the same), in managing vineyards. Credit: Jaclyn Fiola

Plants obtain most of their nutrition from the soil. A leaf tissue test shows how much of those nutrients the plant can retrieve. When a tissue nutrient analysis indicates that the plants are low in a certain nutrient like magnesium, the farmer knows to supplement the plants’ magnesium. By diligently sampling every year, they can monitor how the plants and that field are doing over time. If some of their plants look different – weird colors on their leaves or stunted growth – they can sample those and compare them to healthier-looking plants to hopefully diagnose the issue.

Through the years, researchers and Cooperative Extension personnel have pinpointed and calibrated ideal nutrient levels for different plants. To compare their plants’ nutrient levels to those ideal nutrient levels, farmers must follow specific sampling procedures related to the time of year and the type of plant tissue (such as a particular leaf, group of leaves, or portion of the plant).

For instance, after corn plants produce silks and tassels, farmers collect the leaves opposite an ear of corn. They collect leaves from many different plants just in case one of those plants is abnormal. If there is any soil or residue on the leaves that could distort the results, the farmer washes the leaves. Then, they dry the leaves and submit them to a lab for analysis.

grapes hanging on a vine and large leaf
Measuring the amount of nutrients in leaves has been found to be a good indication of both the quantity and quality of the fruit. And the quality of the fruit affects the quality of the wine! Credit: Jaclyn Fiola

The results of the tissue nutrient analysis will show a comparison of each nutrient in the analyzed corn leaves with relation to ideal nutrient levels. The report usually shows ratings of low, sufficient, or high. If a nutrient is low, farmers can fertilize appropriately. Taking this step will likely improve plant health, yield, fruit quality, or some combination of those. One example is phosphorus deficiency. It can cause lower yields and stunted growth.

Alternatively, if the tissue nutrient analysis reveals a nutrient is at a sufficient or high level, the farmer knows not to add any more. Applying too much fertilizer is expensive and wasteful and can have detrimental effects on plant health and on the environment.

I work in vineyard research. For grapevines, different countries have different recommendations for tissue nutrient analysis. In the U.S., most recommendations are to collect and analyze petioles (the bit that connects the leaf to the stem) when the vines are flowering. In Europe they typically use leaves instead. That’s part of the reason for our research – we want to learn if leaves or petioles are better suited for nutrient analysis here in the Mid-Atlantic United States. Vineyard nutrient management is challenging because nutrients (deficiencies and excesses) can affect both the quantity and quality of the fruit. And the quality of the fruit affects the quality of the wine!

two rows of grape plants in vineyard with paper bag used to collect leaves and stems for nutrient analysis
Leaves and stems are collected, washed and dried, and then sent to a lab for nutrient analysis. Farmers can do the same for their crops, such as corn. Often soil nutrient analysis is done to get a bigger picture of fertilizer needs. Credit: Jaclyn Fiola

Ideally, tissue analysis should be used in conjunction with other methods of checking if plants’ nutrient needs are being met. Farmers can do a soil analysis and check for visual symptoms of nutrient deficiencies. The most effective nutrient program is one informed by both soil and tissue analyses. Tissue nutrient analysis gives a snapshot of the nutritional status of the plant. Soil analysis indicates the pool of nutrients and other properties (e.g., pH) that influence plant nutrient availability.

Tissue nutrient analysis is a nifty tool for both checking on your plants and for monitoring a field over many years. Hopefully, all my leaf washing will help farmers make better decisions about their nutrient management, and in my case, better wine!

Answered by Jaclyn Fiola, Virginia Tech

About us: This blog is sponsored and written by members of the American Society of Agronomy and Crop Science Society of America. Our members are researchers and trained, certified, professionals in the areas of growing our world’s food supply while protecting our environment. We work at universities, government research facilities, and private businesses across the United States and the world.

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