Jon Zuk

Jon Zuk, WinField United agronomist.

SHOREVIEW, Minn. – More and more, growers are turning to in-season tissue sampling of their crops to get an idea of where that crop is at nutritionally. In 2018, WinField United collected nearly 5,800 corn tissue samples from across the state and analyzed what trends could be seen in the samples.

“In corn, we could see certain nutrients were becoming deficient at certain times,” said Jon Zuk, a WinField United agronomist, during a recent phone interview. “For example, micronutrients zinc and boron, we were finding zinc deficiencies early at V5 and boron deficiencies at tassel, so timing of the tissue sample was critical.”

Zuk recommends taking three tissue samples of corn at different times throughout the growing season – the first one at V5, then at V9 and the last one at tassel.

“We are trying to recognize the trend of that nutrient going down before we actually visualize the deficiency in hopes to give us enough time to get out there and make an application,” said Zuk.

The biggest focus among growers is usually on the macronutrients, nitrogen, phosphorus, potassium and sulfur. While the 2018 tissue results do show deficiencies of these nutrients at times, it may not necessarily be due to a nutrient deficiency in the soil or fertilizer application.

“I always challenge the grower to think about what the most limiting factor is,” he said. “What our tissue sample data has shown was sometimes you might be deficient in nitrogen and the answer to fixing that is not always adding more nitrogen.”

A closer examination of results reveals that an application of potassium may be more beneficial to the crop. This is based not only on the tissue sample results, but also keeping the grower’s soil data and crop management practices in mind.

Potassium is a key nutrient to bringing nitrogen into the plant. While the plant could have access to all the nitrogen it needs, the lack of potassium is preventing its uptake.

The interaction of nutrients and minerals in the plant is important to how well the plant can use those nutrients. When looking at tissue sample data, it is important to consider not just the levels of nutrients, but the ratios of nutrients to each other as well as how the nutrients act within the plant and soil.

There is a reason corn plants often show deficiencies of zinc early in the growth stages.

“What we know about zinc is that zinc is not mobile in the plant,” he said. “Maybe the plant has enough zinc when it is at three- or four-leaf stage, but when it grows to the five-, six-, eight- and 10-leaf stage, it cannot remobilize the zinc from the bottom of the plant to the top of the plant.”

There are four ways to manage zinc in the crop. It can be put directly on the seed, applied in furrow, through foliar application or broadcast applied with other nutrients.

“When I talk about zinc, I maybe don't talk about, ‘Hey you need to use a foliar,’” he said. “What I would suggest is out of those four ways, you should be trying three of those ways to get zinc into your crop.”

In the case of late season deficiencies of boron around tassel, a foliar application might be the best option. Zuk explains that boron is very mobile in the soil and not mobile in the plant.

“There is really no way for us to do a soil applied application of boron and still have it available at tassel,” he said.

The recommendation of a late season foliar application of boron works well with many growers’ crop management plant. It coincides with the fungicide applications, so it does not require an additional pass over the crop.

When looking at soybean tissue sample results, there is still more work that needs to be done to better understand how the nutrients and minerals interact within the plant.

“Corn, I feel like we have a process of when we get the sample, we know how to read it, and with soybeans, we are getting to that point,” said Zuk. “One thing with soybeans is the micronutrient, especially manganese, is probably the most critical.”

Not only is manganese essential for photosynthesis, in soybeans, it is the signal nutrient to turn on nitrogen fixation in the rhizobium nodules.

“That is a critical process. If we do not have good manganese, that means we do not have good nodulation or production of nitrogen and then we are deficient in our macronutrients,” he said.

Zuk recommends tissue sampling of soybeans at three separate times – the first one during the vegetative stages, then one right at the start of flowering, R1, and the last one at R3-R4.

“The test at R3-R4 is probably not going to make a decision for application, because we are probably done driving through that crop, but it's going to give me an indicator of how well I did on (corrective field applications for) the first two ,” he said. “Maybe have the chance, if there is something really odd, to go back and do something.”