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How, When And Why To Tissue Test

It’s likely that most farmers would only consider plant tissue testing to diagnose visible problems with their crop. While it is a powerful tool for confirming or discovering nutrient deficiencies, the value of tissue testing has longer-term implications. A plant tissue test can give you a heads up on impending problems before they become acute or may alert you to adverse soil conditions or nutrient imbalances that have yet to show up in the crop.

“Fifteen years ago I may have said that tissue testing and foliar applications of nutrients wasn’t worth it, but it’s amazing what one shot of the right nutrient can do when a plant is stressed,” says Elston Solberg, president of Agri-Trend Agrology. Micronutrients are largely immobile in the soil but are well absorbed by leaves, making them a good fit for late-season, foliar applications.

It’s also an excellent tool for anticipating problems before they start eating yield. “For example, if I’m testing a canola crop and the copper levels come back low, I won’t likely worry about that canola crop (because canola is a low user of the nutrient),” says Solberg, “but I might consider adding copper the following year with my wheat crop because I know that a high-yielding wheat crop may run out during the growing season.”

And what about healthy crops? Plant tissue testing is also becoming more accepted as a fertility management tool, versus simply a diagnostic tool, says Solberg. The value here is in evaluating a nutrient management program or change to a program, as a means of measuring if what’s being put on below is making a difference above ground.

Brunel Sabourin, agronomist with Cargill based at Morris, Man., says that when tissue testing, you’re not just determining if the crop has enough of each micro-and macronutrient at a specific growth stage — you’re also evaluating if these nutrients are in the correct balance. “There are well-established acceptable ranges for each nutrient by crop type and stage,” Sabourin says. “But you’re also looking at key ratios for these nutrients. From a tissue test, we can rank the most limiting nutrients and advise action from there.”

WHEN TO SAMPLE

All experts agree that if you’re puzzled by symptoms showing up in the field, the earlier you test the better. “Early testing and diagnosis allows for the maximum amount of time to correct the problem, if possible,” says John Lee, soil scientist with AGVISE Labs, based in North Dakota, U.S. “Allowing

an issue to go on for more than 10 days could induce other nutrient deficiencies,” he says, further complicating the problem and, perhaps, eliminating any chance of fixing the problem or preserving enough yield to make it worthwhile.

How you test and the amount of tissue you send depends

somewhat on the plant you’re sampling and the crop stage. For cereals, sampling at the five-to six-leaf stage (or equivalent for pulses or canola) offers a snapshot of what’s to come. “Early on, you’ve got time to adjust for macronutrient deficiencies, such as nitrogen or sulphur,” says Solberg. Early tests also foreshadow what micronutrients may become deficient later on in the growing season. Testing at the boot/early flag leaf or equivalent for canola and pulses is typically done to check for micronutrient deficiencies, as these nutrients are largely immobile in the soil. Foliar applications, of a usable form of the nutrient, late in the season are the only effective way to top up nutrients like sulphur, copper or manganese, for example.

SAMPLE THE RIGHT PART

When sampling early in the growing season, it’s important to snip off about 50 plants at ground level. “When plants are small, we need the entire plant in order to get enough volume for testing,” says Lee. “We don’t ever need roots.

“It’s also important to send plant samples and soil samples from both healthy and unhealthy parts of the field if you are trying to diagnose the problem,” Lee says. Later in the season, you need at least 50 flag leaves in order to have enough volume for testing in the lab. Plant material is dried and ground before being tested in the laboratory, Lee says. “Since plant material is mostly water, a large amount of plant tissue is needed for testing.”

Sabourin adds that it’s important to take a clean sample as well. “Dust or clay on the plants will really inflate the test results for certain nutrients (such as iron and manganese),” he says.

INCLUDE A SOIL SAMPLE

Lee also says that your most thorough analysis is going to come from including a soil sample with the tissue sample. “You only need to sample the top six inches,” he says, “but including a soil sample can help eliminate other issues, such as compaction or a root problem.” And, when testing for a deficiency, it’s imperative to include plant and soil sample from both affected and unaffected areas for comparison.

A key indication of this could be a field that typically tests high for nitrogen but never produces a stand-out, high-protein cereal crop. “Sulphur can affect nitrogen uptake in wheat, for example. A tissue test could help identify if sulphur is a limiting factor that may be indirectly affecting protein. Nitrogen may not be the problem at all,” Sabourin says.

PRICING

Depending on your agronomist or lab, you can expect to pay about $90 per tissue test. Some agronomists or companies will do the testing and analysis for you and develop recommendations. Agri-Trend is just one company that does this and Solberg says it costs about $0.50 per acre on a quarter section. That’s a ballpark figure of course — ask your local agronomist what their rates are.

Producers of high-value crops, such as potatoes, are the most likely to use a tissue test throughout the growing season, but Lee says that the value of the analysis shouldn’t be underestimated. “A deficiency has to be pretty severe for a plant to show visual symptoms,” he says. If you can see the plant is stressed, it’s likely already cost you yield or quality.

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If you can see the plant is stressed, it’s likely already cost you yield or quality

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how, when and why totissue test

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Three Steps To TheBest Tissue Test

1) Test early

When it comes to identifying a nutrient deficiency, time is of the essence if you’re to have any chance of correcting the problem. Sending off a representative sample as soon as possible gives you the maximum amount of time to develop a game plan. Wait too long, and by the time you decide to add a nutrient, you may have already lost too much yield to make it worthwhile. What’s more, as one nutrient becomes deficient, it begins to impact the availability of other nutrients — even if there’s more than enough available in the soil.

2) Sample the correct part and amount of plant

Depending on the age of the plant and what you’re testing for, you’ll need to send a specific sample (sample bags from the lab contain directions or ask your agronomist). You also need to send enough material to ensure a usable result. Plants are mostly water — by the time they dry down some, there’s very little actual plant tissue to test. If the lab wants 50 seedling plants, send 50 seedling plants and send the entire plant from the base. At no time do you need to send anything from below ground except for…

3) Include a soil sample When using tissue testing as a

diagnostic tool, it’s important to send a soil sample from the top six inches. Why? Because, for example, there may be plenty of phosphorus in the soil, but the soil is very compacted, making P unavailable. In this case, adding more phosphorus will not correct the problem. In order for the lab to make an educated assessment of the problem, they’ll need to know what is in the soil and compare it to what the nutrient concentration is in the plant.

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