Thousands of tissue samples from corn and soybeans are evaluated by WinField United labs annually. Trends toward deficiencies of specific nutrients were evident in 2019. Here’s how you can use tissue samples to improve your fertilization program.

Jason Roth, technical agronomist with WinField United, provides insights in this interview with Indiana Prairie Farmer:

What did corn and soybean tissue samples from Indiana farmers show overall in 2019? Over 84% of the 1,100 corn tissue samples submitted were deficient in zinc. Many samples were also deficient or responsive for nitrogen, boron, sulfur, manganese, magnesium or phosphorus.

For soybeans, 73% of samples submitted early in the season were low on copper. By flowering and pod formation, potassium and copper were deficient in more than 65% of samples.

Were samples submitted from fields where problems were suspected? Most samples likely came from routine tissue-sampling programs. Several retailers and agronomists do routine sampling for farmers. Often, they flag an area and pull tissue tests three or even four times per season.

What is the difference between “deficient” and “responsive”? Proper levels for nutrition are established for each nutrient. If the concentration is below a critical level, it’s deficient. If it’s above the critical level but in a range where you would likely see a yield response, it’s responsive. Above a certain level, it’s excessive. Our recommendations suggest keeping nutrient levels in the higher end of the responsive range.

What are the most common nutrients deficient or responsive in corn in any year? Nitrogen and sulfur are the macronutrients which show up as deficient or responsive in tissue sampling. For micronutrients, it’s zinc. Sometimes boron is also low, and occasionally samples test low in manganese.

What about soybeans? Potassium is the No. 1 macronutrient which tends to be deficient or responsive, followed by sulfur. In the past, farmers tended to apply potassium and phosphorus ahead of corn for two years in a corn-soybean rotation. That set up soybeans to potentially run short on potassium, especially if corn yielded over 200 bushels per acre. Some customers who pull off 200 or more bushels per acre only fertilize for 180 bushels per acre or less as a yield goal. Over time, the difference adds up. Today, more farmers fertilize ahead of each crop.

What about micronutrients in soybeans? The No. 1 micronutrient which runs deficient or responsive is manganese. Sometimes we see low zinc, and this year we saw low copper levels. There is little research on copper, and we haven’t confirmed if the copper deficiency is real.

Manganese shows up most often on muck soils or on high-pH soils, and occasionally where lime was recently applied. Soil tests may indicate adequate levels, but manganese can bind up in the soil and be unavailable to plants.

How many leaves are needed for a tissue test? For corn in vegetative stages, pull the uppermost leaf with a collar from plants. Later, pull the ear leaf. You need a mass of material the size of a softball if wadded together.

For soybeans, collect the uppermost, fully extended trifoliate at any growth stage. Collect the three leaflets, not the petioles. Collect the same amount of leaf tissue as for corn.