With an increase in precision agriculture and more closely monitored in-season crop fertilizer applications, we’ve also seen an increased interest in plant tissue testing. But before you begin sampling in the field this season, you need to do what you can to ensure you’re getting the best sample and making the most from your time spent.

“It’s very important to take a plant tissue sample from the correct plant part when submitting samples to the lab for testing,” says Jim Friedericks, outreach and education adviser for AgSource Laboratories, based at Ellsworth, Iowa. “Timing is important, too. For example, to get the earliest effective reading 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 first flowering.”

Results help fine-tune fertilizer application
The test results can then be used to fine-tune an expected sidedress application or for a “rescue” nutrient application for the current crop.

The results from plant tissue samples are typically reported in comparison to the range of nutrient concentrations sufficient for that plant at that growth stage, he explains. Because these ranges shift with the growth of the plant it is important to identify the growth stage when submitting a plant sample to the laboratory. It’s normal for crop nutrient levels to vary throughout the season, therefore it’s important for these nutrients to be available when the crop needs them.

Alternatively, taking plant tissue samples multiple times throughout the growth cycle reveals the seasonal trends of your crop, and differences in your individual fields, says Friedericks. Reports from these frequent plant tissue samples can be used to make corrections or additional nutrient applications, as long as your field equipment makes it feasible to spray the canopy or dribble nutrients onto the soil surface.

Know nutrient status of crops
Plant tissue sampling provides a picture of the nutritional status of your crops. Combined with a soil testing program, you can build a 360-degree view of your fields and crops to make better management decisions that could drive higher yields and reduce input costs throughout the growing season.

Plant tissue testing is also helpful when checking for suspected nutrient deficiencies. Often, a common visual sign of a macronutrient deficiency can be mistaken for what is actually a micronutrient deficiency. One example is molybdenum (Mo), which is required for nodule formation in nitrogen-fixing crops. What visually appears as nitrogen deficiency in alfalfa may in fact be inadequate supply of molybdenum.

CORN SAMPLE: Guidelines to properly take a leaf sample for tissue testing depends on growth stage of the crop.

While creating your crop plant tissue sampling plan, Friedericks says to keep these points in mind:

• Sample your fields using appropriate zones. Pull plant or leaf samples from the same variety or hybrid; one sample equals one variety.

• Combine with a soil sample. Consider a routine soil sample that includes nitrate in the analysis. Pull this sample in the same location as your plant tissue sample. This approach can determine the soil’s ability to supply nutrients in the growing season and identify confounding problems such as low soil pH.

• Avoid trouble spots. Stay away from sampling close to field boundaries or gravel roads, or visually damaged field zones. Trouble spots should be a separate sample.

• Collect the proper plant part and amounts. Collect 15 to 20 leaves, or at least half a paper lunch bag full, and choose mature leaves from the middle or upper part of the plant. Never send bottom leaves or immature leaves. Consult a sampling guide for more specific instructions.

• If the leaves are contaminated with soil, rinse them briefly under a stream of distilled water and allow to air-dry.

• Consistency is key in plant tissue sampling. Pull samples at the same time of day throughout the season.

• Handle the samples properly. Label your sample bags; make sure the labels match your submittal forms and send them promptly. Pack the shipping box loosely to include some air space. If possible, collect and ship the samples the same day. If not, store samples in a refrigerator.

“Shipping and handling is critical,” Friedericks says. “When samples are shipped wet and in plastic bags, we end up with moldy tissue. We can’t test moldy samples, and growers end up having to go back out to the fields and resample. For best results, use a paper bag and ship dry samples. We hate having to call clients to tell them their samples have to be tossed.”

Source: AgSource Laboratories