Fertigation matches nutrient application with plant needs

ST. LOUIS — Fertigation provides the ability to alter nutrient application timing to more accurately match the crop nutrient uptake needs.

“Fertigation is at the crossroads of precision nutrient management and precision water management,” said Matt Yost, assistant professor and agroclimate extension specialist at Utah State University.

“Data from the National Ag Statistics Service indicates fertigation frequency is greatest for corn silage followed by wheat, corn, alfalfa and other hay,” Yost said during a presentation at the InfoAg Conference, hosted by The Fertilizer Institute.

“Nearly one-third of the corn silage acreage in the U.S. is fertigated and about 25% of the wheat acres,” he said. “Fertigation frequency increased for all these crops except corn from 2013 to 2018, indicating fertigation use and acceptance is on the rise.”

There are several benefits of using fertigation, Yost said, including reduced chemical exposure to applicators, saved time and labor, flexible timing especially at late growth stages and reduced soil compaction and crop damage.

“It provides the ability to incorporate chemicals with irrigation which makes it well suited to no-till or conservation till settings,” he said.

Yost also identified some negative aspects of fertigation including the increase wear and tear on irrigation systems, the large initial investment in equipment, additional technical expertise required and the risk of water source contamination.

“There is potential environmental pollution because of drift and runoff, and it may require longer application times,” Yost said.

“We can spoon-feed crop nutrients and this can help make great strides for nutrient management that might not otherwise be possible or economical,” he said. “However, it also means that two to three fertilizer decisions can turn into eight to 10 decisions which rapidly increases complexity for growers.”

Most pivots sold during the past two decades have sector control capabilities, Yost said.

“Developing and implementing sector programs often requires additional prescriptions that can be purchased for less than $500 per pivot per year,” he said.

However, variable nitrogen rate prescriptions are generally not conducive to sector-based applications, Yost said.

“So, zone control may be vital for applying variable rate nitrogen to irregular zones throughout the field,” Yost said.

“Zone control requires upgraded pivot panels and smart control valves on each sprinkler which usually costs $20,000 to $25,000 per pivot and it requires the additional prescription necessary for programming variable rate irrigation applications,” he said.

Due to the high cost of zone control irrigation, Yost said, it only makes sense in certain conditions.

“Variable rate irrigation may make sense when we have high value crops or when a pivot passes over a ditch where we cannot apply chemicals,” he said.

In irrigated fields, Yost said, water is the key driver of yield.

“Developing robust variable rate irrigation plans is extremely challenging and on top of this there’s little consensus that exists about optimal ways to develop plans,” he said. “Most plans include combinations of soil moisture, elevation and crop yield.”

For the nitrogen management of corn, Yost said, most experts recommend that fertigation represent less than 50% of the total nitrogen application.

“It is also important to remember that most fertigation should occur during the vegetative stages of crop growth,” he said. “As the crop moves into the reproductive stage, fertigation can sometimes limit corn yield.”

As corn gets past the V6 stage, Yost said, farmers should monitor and sample tissue and maybe the soil as well as nitrogen zones which could include remote sensing.

“Identify areas of chlorosis or hot spots that might need nitrogen,” Yost said.

“Careful monitoring is critical because chlorosis can be nitrogen, water or other issues,” he said. “If the need for nitrogen is identified in zones, then fertigation becomes a great option to remedy it by applying nitrogen only where needed.”

More economic assessments of variable rate irrigation is necessary because it is the key to precision fertigation, Yost said.

“We have to have the water correct or we’ll always struggle with fertigation,” he said.

“Currently precision fertigation is probably most applicable for sensitive, high value, specialized applications where we need to rescue nitrogen or other nutrients to meet crop needs,” Yost said.

“However, as we go into the future and as zone control options become greater and the cost comes down, I think precision fertigation could be a more important aspect of nutrient management on many farms,” he said.