Just because crop plants start out healthy looking green and growing rapidly doesn’t mean they have the nutrients necessary to carry them through the growing season?

“Even the greenest looking fields can suffer from unseen nutrient deficiencies that prevent crops from reaching their full potential,” related Steve Frack, AgSource Laboratories vice president of laboratory operations. “Farmers do have a way to detect and correct these problems. By using plant tissue testing, in conjunction with routine soil testing, farmers can detect hidden hunger in those plants and optimize crop fertility programs.”

While soil tests indicate which nutrients are available for crop use, tissue analysis shows which nutrients the plants are actually utilizing at a particular point in time. Laboratories can analyze plant tissue for a wide array of measurements, including total nitrogen uptake, phosphorous, potassium, zinc, calcium, sulfur, boron, magnesium, copper, iron, aluminum, manganese and boron. Measured levels then are compared to a set of standards, set by university research, to see what nutrients those specific plants need to get in order to reach the next growth stage.

“In annual crops such as corn and soybeans, tissue testing is a tool that provides a visual picture of the nutrient load within a plant at a particular time. If collected early enough in the growing season, there’s still time to make nutrient corrections at the critical reproductive stage of growth, possibly avoiding a yield reduction during the cropping year.  It won’t tell you the amount of nutrient needed, but it will tell you whether or not you need to apply certain nutrients,” Frack said.

In perennial crops such as grapes, fruit or nut trees, the nutrient evaluation is valuable information for planning the fertilizer purchases for the next growing season, notes Frack. The optimum time to test perennials is at blooming and before fruit set. This is when the plant’s demand for essential nutrients is the greatest. Nutrients determined to be deficient can be applied, with the benefit to be realized in next year’s yield.

Because it provides a snapshot of the plant’s nutrient content at one point in time, it is a very effective tool to validate micronutrient uptake, Frack explains. “It shows what nutrients are being taken up by the plant at that moment in time. It won’t actually tell you what levels of micronutrients are needed, but simply whether or not they are there. For that reason, it’s very important that tissue testing is used in conjunction with field soil tests,” he said.

Frack offers the following tips for getting the best possible results from plant tissue testing:

  1. Time it right. To have an effect on this growing season, corn plants should be in the 8-leaf to 12-leaf stage, soybean plants can be submitted from 4-inches to 8-inches tall and alfalfa from 6-inches to flowering. To get a picture of the soil’s full ability to supply essential nutrients, sample when the plants are absorbing the greatest quantity of nutrients (ie plant reproduction). Use these results to modify nutrient applications for next year’s growing season.
  2. Select the best, most representative samples. Never select diseased, drought stressed or damaged plants. Pick plants that most closely represent actual field conditions.
  3. Collect the proper plant part and amounts. Pick at least half a lunch bag full of plants and choose leaves from the middle of the plant. Never send bottom leaves or immature leaves.
  4. Handle the samples properly. Label your sample bags, make sure the labels match your submittal forms and send them promptly. If possible, collect and ship the samples the same day.  If not, store samples in a refrigerator.

Frack is a strong believer in plant tissue analysis. It should be a routine part of every crop producer's nutrient management program as a way to accurately measure a crop’s health and optimize production, he says. Complete sampling instructions, along with a pictorial sampling guide can be found on the AgSource Laboratories website in the agronomy section at www.agsource.com/PlantTissue.