While many Corn Belt no-tillers have suspected it for years, it took researchers at North Dakota State University to demonstrate how continuously no-tilled soils require less nitrogen.

What has taken place in regard to nitrogen recommendations for long-term no-tilled soils is unprecedented with these new North Dakota guidelines. And there’s no doubt this fertility research represents a major step forward in no-till fertilization.

Soil scientist Dave Franzen has determined that when it comes to growing corn, fields that have been in continuous no-till for over 6 years require 40 to 50 pounds less nitrogen per acre than conventionally tilled soils. These recommendations follow on the footsteps of earlier North Dakota work with spring wheat and durum that indicated a 50-pound-per-acre nitrogen credit for long-term no-till.

North Dakota is apparently the first land-grant school in the country to adjust soil fertility recommendations to account for the nitrogen-reducing benefits of no-tilling. Like is the case in many states, fertility recommendations for corn grown in North Dakota were based on data published 40 years ago.

“My inspiration for doing this work came from my first winter in North Dakota when some founders of the Manitoba-North Dakota Zero-Tillage Association came up to me during a social time at one of their meetings,” Franzen says. “They welcomed me to North Dakota and then told me that they didn’t follow the university recommendations for nitrogen anymore. They found they could decrease their nitrogen rate once a field had been in no-till for a series of years.

“I decided to test their ideas, and they were correct.”

Nitrogen Timing Critical

Instead of simply encouraging growers to apply less nitrogen, Franzen created tables that analyze nutrient needs, expected yields and the price of both nitrogen and corn.

Franzen says the new recommendations are based on data collected from 2010 through 2013 from 77 North Dakota nitrogen-rate trials. Plus, he looked at relevant data from recent nitrogen studies in northwestern Minnesota, southern Manitoba and the northern tier of counties in South Dakota.

He says the answer to higher yields in many North Dakota soils often is not the rate of applied nitrogen, but the timing of the applications.

“Application of half or more of the recommended nitrogen at the V6 to V8 stage would greatly increase yields and nitrogen efficiency in wetter years,” he says. “Considering the tendency for our high-clay soil to have sticky, mucky characteristics in wet conditions, the use of a coulter sidedressing applicator with a UAN solution is recommended.”

With conventionally tilled soils, Franzen found medium-textured soils with historic yields over 160 bushels per acre were the most productive, nitrogen-efficient soils. These soils do not require sidedressed nutrients to be nitrogen efficient.

On the no-till side, the most inefficient soils for nitrogen were medium-textured soils with the potential for producing less than 160-bushel yields. Since these soils are highly susceptible to leaching, they benefit dramatically from sidedressed nitrogen.

Franzen says the increased acceptance of diverse crop rotations has dramatically boosted the biology activity in no-tilled soils. Additional soil microbiology activity and storage of more nitrogen with no-till is the main reason behind trimming these nitrogen needs.

Continuous No-Till Is Key

Franzen knows of no other university researchers who collect this kind of nitrogen data. His impression is that most researchers don’t see any differences for nitrogen usage between tillage systems.

Will other universities adapt these nitrogen guidelines for no-tilled soils? The jury is out since fertility recommendation changes come slow and conducting costly nitrogen studies with no-tilled soils may not be a priority for many scientists.

“It’s hard to know how far away from North Dakota that continuous no-till would increase the efficiency of nitrogen in the soil, as I have seen in both our wheat and corn work,” Franzen says.

“I think these results may have the potential to encourage researchers in other states to collect data from continuous no-till fields, as well as conventional fields, to see if the data can be segregated by tillage practice.”