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    Tissue Testing: A Key Tool for Deficiency Diagnosis

    Fine-tuning your soil fertility approach might start with understanding what the crop is feeling when it’s feeling it.

    Tissue testing used to be a practice reserved for “high-value” crops like fruits, vegetables and cotton. But in the era of 200-plus bushel corn and 50-plus bushel soybean yields, notions of “high-value” crops are shifting. Row crops, for which in-season management decisions can have significant impacts on yield, benefit from tissue sampling as a regular part of the plan for balanced crop nutrition.

    When it comes to in-season diagnosis of plant nutritional needs, tissue sampling is one of three information sources needed for a complete understanding of what’s happening in a field, according to Dr. Ross Bender, senior agronomist for Eastern North America at The Mosaic Company.

    “The most important concept with tissue testing is that it should always be verified with a soil test and with crop scouting,” says Dr. Bender. “So it’s three pieces: tissue test, soil test and crop scouting. When it’s done right, tissue testing is a really informative diagnostic and preventive tool. It has real-world implications, and it can help growers and retailers evaluate the effectiveness of their nutrient management program.”

    Bender advises that tissue testing has two uses for crop farmers: diagnosis and prevention of nutrient deficiencies.

    “If we go out to the field and there are visible signs of deficiency, we can use tissue testing as a diagnostic tool to identify its presence and magnitude,” he explains. “We can also tissue-test to help prevent nutrient deficiencies from occurring. When we see nutrient concentrations getting lower and lower, even though there might not be a visible sign of deficiency yet, we can potentially identify this pattern in advance. This is what the fertilizer industry calls ‘hidden hunger.’”

    Plant nutrition expert Dr. Rob Mikkelsen notes that when you see symptoms of deficiency, you have already lost yield. Tissue testing helps uncover ‘hidden hunger,’ and allows farmers to make timely nutrient adjustments before major yield losses have occurred, he says.

    Tissue testing can help the farmer meet the economic and environmental ideal expressed in the 4Rs of Nutrient Stewardship: putting on the Right product, at the Right time, at the Right rate and in the Right place, according to Mikkelsen, a director at the International Plant Nutrition Institute and former professor of soil chemistry at North Carolina State.

    “Foliar analysis or tissue sampling is one important part of getting those 4Rs correct,” Mikkelsen says. “For instance, if you know what the right rate is, tissue testing can help you adjust to meet that rate during the season. A deficient reading means you can decide you need to correct it, or you need to add a little more fertilizer next year. Tissue sampling can also tell us that we need to find out why the plant is not taking up those nutrients, if something like root health is at fault.”

    Tissue testing helps the farmer put a finger on the connection between nutrition and yield, adds Bender.

    Tissue sampling reports provide the concentrations of macronutrients and micronutrients in the sample through interpretable data in multiple forms, one of which is a sufficiency range. It ties the concentration of nutrients in the plant to what the expected yield would be. The higher the concentration of the nutrient, presumably, the higher the yield level.

    Low concentrations of a nutrient may mean that nutrient is limited, and as a result will limit yield.

    Bender also notes that many farmers have begun to use tissue sampling as a kind of report card on their nutrient management program.

    “For example, let’s say a farmer was trying a new application method this year,” Bender says. “Conventionally speaking, he would normally broadcast a set of nutrients on the surface, work them into the soil, and then plant. This year, he wants to try a new practice: banding nutrients in a subsurface band right beneath the crop row. Afterward, he can compare tissue concentrations of one practice versus his new practice. Looking at the nutrient concentrations, he can compare the effectiveness of different fertilizer sources, different application methods and different rates.”

    From a practical standpoint, there are two occasions when row crop farmers may find it especially useful to take tissue samples: whenever visible crop deficiency appears, and also a week or two before a planned application.

    “If you start to see visible signs of a deficiency in the field, you should get out there and test it,” Bender advises. “Test a good area of the field — one without visible signs of a deficiency — and then the part where you are seeing the symptoms. Include the soil test for each spot with the tissue test, so you get two data points. And then compare the results.”

    Another great time to perform a tissue test, according to Bender, is in the week or two before the farmer plans to make a pass over the top of the field. If he knows he is going to be making a herbicide application in one or two weeks, or he knows he is going to be coming back with a fungicide or an insecticide, it may be advantageous to do a tissue test immediately before that; because if some deficiency is apparent in the results, the farmer may be able to make an application of some nutrient source to limit how badly that deficiency may impact yield. Combining that application with one previously scheduled is more time efficient and cost effective.

    Mikkelsen agrees with Bender that scouting and linking samples to a GPS-derived location is a powerful data point.

    “Often,” he says “when I think of the fourth R — putting the fertilizer in the right place — I think of the right place in the root zone so the plants can access it, but another way to describe the right place is to put the fertilizer in the right place in the field. If there is a spot in the field that is prone to iron deficiency, you don’t need to treat the whole field. The tissue sampling can help you know what the right place in the field is, so you are not spreading that nutrient everywhere.”

    Mikkelsen says tissue testing is part of a thought process: “If there is a deficiency or perhaps a toxicity, we can ask, ‘Why is this happening? Is it a problem with the plant, or with our fertility program?’ If it’s a problem with the plant, it may be drainage or flooding or cold weather or insect damage. If it’s not that, then, okay, what about the fertility program? Let’s see what we could have done differently.”

    Bender believes that tissue testing can also help farmers pay more attention to something they often miss — micronutrients.

    “The most successful farmers, who are growing the highest value commodities, already tissue-sample,” Bender explains. “It’s really a necessity. My personal philosophy is that if farmers are not experimenting with new practices to move their operation forward, they may be falling behind. The industry evolves so rapidly, and new technologies are brought into the market all the time. So it’s imperative to continually test the effectiveness of the current nutrient management program. As we continue to drive yields with new genetics, better equipment and management practices, as well as improved nutritional sources, we increase the rate at which nutrients are removed from the field. We need to replace those nutrients; however, many farmers forget about micronutrients. As a result, these nutrients are at risk of becoming increasingly deficient over time, and tissue testing can be used as a means to evaluate your program’s effectiveness.”