Cornbelt: Reducing Nutrient Loss – Understanding the Variables

Corn fertilizer application. ©Debra L Ferguson Stock Photography

This article reviews USDA-funded agricultural research seeking to apply data, technology and a full range of science to the challenge of managing farm nutrients.

Using the 4Rs is Key

A key component of the strategy to reduce nutrient loss is improving the application of fertilizers, particularly nitrogen in corn production.

The “4Rs” approach to nutrient management covers:

  1. Right source of fertilizer
  2. Right rate or amount
  3. Right timing
  4. Right place for the crop as a method to help reduce losses

Failure to adhere to the 4Rs can result in fertilizer not being consumed by the growing crop and the residual nutrients in the field after harvest are very susceptible to being exported from the field and lost to waterways.

Tile-drained fields lose on average nearly half of the nitrogen remaining after harvest, but can lose as much as 85%. Achieving each corner of the 4R strategy is particularly challenging given the vast uncertainties caused by the weather, especially precipitation, given its influence on both crop growth (nutrient consumption) and nutrient loss from leftover nutrients.

Traditional Methods for Nitrogen Applications

Historically (from 1970 to 2005), the basic method for farmers in applying nitrogen was a yield-based recommendation; estimate yield under ideal conditions and apply N fertilizer at 1.2 times that grain yield.

If the farmer, for example, expected 200 bushels per acre in a field then this rule would advise the application of 240 pounds of nitrogen per acre in the field.  Subsequent research has concluded, however, that expectations for corn yield is not an effective method for nitrogen recommendations.  Recent research calls into question the original research and the validity of the conclusions that supported the 1.2 yield recommendation.

Since 2005, recommendations in the seven states of the Corn Belt have used the Maximum Return to Nitrogen (MRTN) method. MRTN demonstrates progress in nitrogen recommendations largely because recommendations are based on corn yield response research, as well as economics and profitability analysis, rather than simple yield goals.

Many universities, as well as some commercial software, continue to use yield-based methods for providing nitrogen recommendations, however.  The efforts to create economically optimal nitrogen rates have significant drawbacks, including that they are based on after-harvest data when, for example, the weather and production conditions are known; farmers will not know weather and growing conditions in advance.

In 2016, The National Institute of Food and Agriculture (NIFA) through the competitive research funding of the Agriculture and Food Research Initiative (AFRI), awarded a grant to a group of researchers led by David Bullock at the University of Illinois at Urbana-Champaign for a project titled, “Using Precision Technology in On-Farm Field Trials to Enable Data-Intensive Fertilizer Management.” 

AgFax Weed Solutions

At $4 million in funding, the grant is for research through February 2020 that seeks to apply precision agricultural technologies that were developed using full-field, on-farm agronomic trials to improve the application rate for nitrogen fertilizers.

In short, the research seeks to develop better fertilizer recommendations based on agronomic experiments and statistical analysis techniques.  More importantly, it seeks to make use of modern precision farming and data analytics to conduct randomized on-farm field trials.

Figures 1 through 3 provide examples of the randomized on-farm field trials using the software and statistical analysis method; more information can be found on the project’s website (DIFM). Figure 1 is the trial design for nitrogen application (side dress) and Figure 2 is the actual applied, randomized nitrogen in a central Illinois field.

Each set of blocks by color in the design is a different application rate. Figure 2 illustrates the accuracy of the machine in matching to the trial design, as well as what the randomized trial for nitrogen rates looks like on the field. Figure 3 is an example of a randomized nitrogen field trial in Ohio.

One outcome of these randomized trials is that yields can be compared against nitrogen application rates across the field.

Click Image to Enlarge

Click Image to Enlarge

Click Image to Enlarge

The DIFM project conducted approximately 40 randomized field trials in 2018. The goal of properly-designed trials such as these is to better account for the impacts on crop yields from both variations in growing conditions (e.g., soils, weather, etc.) but also different management decisions.

The research may be able to better untangle the impacts on yields that can be attributed to weather or soil from those attributed to management practices such as nitrogen application. Results could help improve the methodology for providing nitrogen recommendations and advance towards the 4R goals for reducing nutrient losses from farming.

Concluding Thoughts

A challenge as vast and complicated as reducing nutrient losses from farming will require substantial research and should be helped by advances in technology and data analytics.  It will also require significant efforts to translate that research through outreach, demonstration and Extension; feedback from the experiences and interactions on the ground valuable for further research questions and agendas.

Even the best research, data and analysis, however, will be left with substantial uncertainties because of unpredictable weather.  Such unpredictability may become more complicated under climate change scenarios (IPCC).

It may be that the best we can do is to better understand the variables we know, continue to research the ones we do not and always be ready, able and willing to adapt to changing circumstances and understandings; fitting, in fact, for farming.

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