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Plant Tissue Analysis is Good Medicine for Crops

Plant tissue analysis determines essential nutrient concentrations in sampled plant tissues. It complements a proven soil testing plan and helps identify ways to use nutrients more efficiently. Unseen nutrient imbalances or toxicities can be identified, as well. It also measures the efficacy of fertilization and nutrient programs, as well as the levels of nutrients such as, copper, iron, sulfur and others not observed in routine soil tests.

Plant nutrient levels vary depending on the stage of maturity, the part(s) sampled, hybrid or variety and environmental conditions. Sampling earlier in the season identifies deficiencies in time to make corrective nutrient applications, if needed, to help reach yield goals and manage economic risks. Late-season samples tend to offer a “mirror into the past” at how sufficiently nutrients were taken up. This “mirror” can help you plan nutrient needs for the upcoming season.

In addition, plant tissue analysis is a proven diagnostic tool to help compare nutritional variances between normal and abnormal sections of fields. No matter the crop, plant tissue analysis is worthwhile to help determine nutrient needs. As crop values continue to rise, tools such as this and soil sampling are essential to fiscal and yield success. Balancing conservation practices, input use, and tillage to achieve optimum yield and plant nutrition are approached using a holistic point of view.

Bear in mind, plant tissue analysis should not be the sole basis for making fertilizer decisions. It should be used alongside soil test results, records of lime and nutrient applications, cropping history and recent crop protectant applications.

As crop values continue to rise, tools such as this and soil sampling can be essential to fiscal and yield success.

Use analytics to plan nutrient management

Man looking a corn just coming up in the fieldPlant tissue analysis, put simply, is taking a snapshot of the nutrient concentration of a plant part at some point in time. Relating it to medical procedures makes it easier to understand. Plant tissue analysis has two primary uses. One is diagnostic. The other is monitoring.

The latter has been used fairly successfully in crops such as cotton, potatoes, sugar beets, tomatoes, grapes and other high-value crops. With monitoring, growers aim to get a trend over time and use that trend provided by tissue concentrations of nutrients to evaluate overall health.

A diagnostic approach with plants is no different. When we get sick, we go to the doctor. Tests are performed. We find out what’s wrong and determine how to fix it. That’s how the diagnostic or troubleshooting approach works with crops: to determine if there’s a problem or not. If there is, the analysis is the beginning of the reasoning to take corrective action.

Standard values, often established by universities, for each crop and each region guide the diagnosis. These values state that at maturity stage “A,” plant tissue nutrient levels should be at stage “A”, as well. If tissue levels don’t meet those values, it could be that something in the soil supply has been depleted. If it’s early enough in the season, it’s possible more nutrients could be applied, sometimes in a foliar application. Or, perhaps other corrective action is needed.

Take Samples Correctly

When it comes to diagnostics, it’s important to remember there’s a difference between soil deficiencies and plant deficiencies. Some agronomists recommend taking a plant sample and a soil sample at the same time. This way, when you examine results, you may find that you have an uptake problem that’s causing poor plant performance. Soil compaction, moisture levels, tillage practice, insects and other factors can cause variations in results, as well. That’s why it’s important to look at the big picture as often as possible.

Once you start taking samples, it’s critical to get the right plant part at the right growth stage. A general rule of thumb is to use the most recently matured, fully developed leaf for more mature plants. For young plants, you can generally use the entire plant. For high-value crops, the petiole is used.

drawing of petiole and mature leaf

 For a lab to get a solid analysis, 15 to 30 leaves, or roughly a quart of sample material is needed. Shipping is important. Don’t pack them too tightly or take too long to ship to the lab, especially summer. Get samples to the lab as quickly as possible. If you’re taking the samples yourself, check with your lab to be certain of the most appropriate shipping method. Always use a shipper that guarantees delivery by a certain time.

Also, make certain your lab is certified and accredited to perform tissue sampling. If you’re doing things on your own, be sure lab personnel will help you interpret the numbers and determine how you should act upon the results. Using the same lab each time will help you have more accurate trend lines, as well.

Once you receive your analysis, review it carefully. Remember, it is an indicator of what is happening during a specific time. DO NOT rely solely on your tissue analysis numbers to make nutrient decisions. Work with your consultant, agronomist or county Extension agent to compare your analysis to the regional data they’ll have on hand.

In addition compare your analysis to the same hybrids, varieties and soil types, as well as management practices. It’s no different than when a doctor examines you as a patient. None of us is the same and no field is the same.

If you’re fine-tuning your plant tissue analysis program or beginning, try to take samples at the same time and at the same growth stage year after year. The more you can compare “apples to apples,” the more accurate analyses will be over time. Plus, over the years, the analyses will tell you how your soil fertilization is going. It’ll help keep you within usage guidelines and better adhere to recommendations in the 4R nutrient stewardship concept.

Set Goals, Match With a Plan

Stan Grant consults directly with wine grape growers and those who provide services to them. Based in Turlock, Calif., he’s helped growers develop nutrient management plans and identify causes and solutions to nutrient challenges for 11 years.

“While tissue analysis is the most widely used tool to evaluate nutrition levels in wine grape vineyards, I typically use it as one element in a broader approach to mineral nutrient management,” (link to soil sampling piece here) Grant says. “I look at soil survey information and acquire recent soil analysis results so that I have a general idea of the mineral nutrient supply and soil factors that affect it.

“Then I ask the grower about the goals for that vineyard,” he adds. “He may wish to produce the most grapes possible, the best grapes possible, or something in between. The production goal influences decisions regarding the quantity of mineral nutrients applied, the form of mineral nutrient selected, the application schedule and application method. Using this information, I design a mineral nutrient management plan.”

Tissue analysis comes in late for wine grape growers. The best set of guidelines for evaluating tissue is for bloom time. This happens two to three months into the growing season as the seasonal vine development begins to transition from foliage growth to fruit growth. The management objective prior to bloom is to grow enough canopy and ripen the crop, ripen the stem wood and store nutrient reserves in woody tissue for use early next year. Prior to bloom, visual assessment of shoot growth rate, leaf size and foliage color are used to appraise the effectiveness of mineral nutrient management efforts, Grant notes.

Veraison, the onset of ripening, is another period for collecting tissue samples. Veraison tissue analysis results are especially useful for assessing vine potassium status, which when deficient, impairs sugar accumulation in the berries,” he says.

Grant stresses that it’s imperative to look at as many information sources as possible when developing and executing a nutrient management plan.

“Our ability to monitor the mineral nutrient economy of vineyards is limited to two types of information,” Grant says. “The first is visual observations for growth and development, as well as symptoms of nutrient imbalances. The second is lab analysis snap shots of the mineral nutrient supply and factors that affect it, or soil analysis, and grapevine nutrient status, or tissue analysis.”

Agronomists note that you should be cautious if plant analysis levels run too high, as well as too low. The number on a plant analysis report is not a stand-alone value. The general assumption is that a high soil test leads to high nutrient uptake that leads to high plant tissue levels that means green, healthy plants. Not always.

Very high levels may indicate potential plant toxicity of a particular nutrient, especially metals such as manganese, boron and the like. Farmers and advisors often focus on correcting deficiencies, but it’s not uncommon for healthy plants to have lower tissue levels than their poorly growing counterparts. Rapidly growing plants may actually have taken up more total pounds of nutrient than a stunted plant, but proportionately more aboveground growth dilutes it down.

Plants with growth problems may be physiologically younger than healthy plants. Younger plants typically have higher nutrient levels than more mature plants. Alfalfa is a good example. Most farmers know that pre-bud alfalfa has higher nutrient levels, but lower tonnage than full-bloom alfalfa. We often see the higher grain protein levels (e.g. nitrogen levels) during years of poor wheat yields. Plants suffering from iron deficiency chlorosis often have tissue iron concentrations that are sky-high. The total iron in chlorotic plants may be sufficient, but conditions prevent it from mobilizing from the veins to the intervenal tissues.

 

Cost vs. Benefit

Grant and his counterparts repeatedly state that plant tissue analysis is but one element that goes into an overall nutrient management plan. You have to consider soil analysis, crop type, weather patterns and geography, among many other factors.

The cost of tissue analysis should also be considered. While common practice in high-value crops, such as tomatoes, grapes, potatoes and cotton, to name a few, it’s used less in commodity type crops, such as corn and soybeans.

However, its value as a troubleshooting tool is considerable. An analysis can help you make a quick management change, identify a fertility problem and diagnose conditions in plants that may cause yield loss you may have otherwise missed. In these cases, benefits would almost certainly outweigh the costs.

As you deploy plant tissue analysis, you’ll find that it will help guide your nutrient management program toward using them at the Right Rate and Time.