Nitrogen Use Efficiency and Partial Nitrogen Balance Assessment

Overview

Efficient use of nitrogen (N) is essential for crop production, whether the nitrogen source is commercial fertilizer, manure, legumes, or some combination. Assessing the efficiency of N applications on a per-field basis is a valuable first step in evaluating your N fertilizer management. Metrics such as Nitrogen Use Efficiency (NUE) and partial N balance can be relatively simple and offer insight into how N is currently being managed and implications for productivity, profitability, and water quality.

This protocol provides an easy and effective entry point for farmers interested in investigating the agronomic, economic, and water quality impacts of their current nitrogen management. Through this assessment, participants will:

Receive resources, tools, and guidance to support on-farm data collection and sampling.
Investigate nitrogen cycling and management on their farms.
Receive an individualized report with nitrogen use efficiency and nitrogen balance indicators, how they compare to statewide benchmarks, and what these signify for agronomics, economics, and water quality.
Learn together with other NOPP participants about strategies to optimize nitrogen management

Projects derived from this protocol are designed to provide insight into field-specific nitrogen use efficiency.

The project requirements described in this protocol align with the research requirements of the DATCP’s Nitrogen Optimization Pilot Program (NOPP) grant Option 2 but can be used independently on your own farm to investigate nitrogen use efficiency. Current funding opportunities for NOPP can be found here.

This protocol was developed by the UW-Madison Department of Soil and Environmental Sciences and Division of Extension.

If you’re applying for a NOPP grant, specific project details can be discussed with UW NOPP Research Director Monica Schauer. If interested in implementing this research protocol independently on your own farm, reach out to Extension’s On-Farm Research Coordinator Abby Augarten.

Project Design

Overview

Overview: With the Nitrogen Use Efficiency and Partial Nitrogen Balance protocol, you will:

Investigate nitrogen metrics as a group of 3 or more farmers across 2 years.
Track nitrogen throughout the season through N inputs, exports and soil and plant analyses.
Implement a zero-nitrogen test strip, which is a test strip that does not receive any synthetic N (besides from starter, if < 40 lb N/ac).
Calculate field-level nitrogen use efficiency and partial nitrogen balance for corn grain or silage fields.

Collaboration

Participants may benefit from collaborating with local partners for assistance in implementing the zero-N test strip and/or collecting samples throughout the season. Consult with your agronomist, local land and water conservation departments, or UW Extension regional educators or outreach specialists about collaborating on this project prior to applying.

This assessment will provide information on the following metrics:

Yield produced per pound of N (partial factor productivity)
Fertilizer use efficiency: How efficiently the applied nitrogen was used to increase yields
Yield with zero synthetic nitrogen inputs: How much the soil (and organic N sources, if applicable) can yield without any N inputs
Partial N balance: An estimation of N that could potentially be leached to groundwater
How these metrics compare to other fields in Wisconsin and implications

This protocol is based on the Discovery Farms’ program nitrogen use efficiency assessments. Learn more about Discovery Farms and explore Wisconsin-specific agriculture water quality work here.

Field Selection

Participants should select corn grain or corn silage fields to monitor. Ideal fields will be relatively uniform, accessible for routine data collection and scouting, and representative of other fields/management histories on the farm.

If using a yield monitor to determine yield, fields need to be at least 350 ft long. However, selecting a field that isn’t too long (ideally 350-750 ft long) will make it easier to implement a field-length zero-N test strip without incurring too much yield loss.

Establishing a Zero-Nitrogen Test Strip

A zero-N strip is a test strip that does not receive any synthetic nitrogen, besides from starter fertilizer, if less than 40 lb N/ac. Yield from this strip will inform how much nitrogen was supplied by the soil (and organic sources like manure or legumes if included in the system). Follow the guidance below on how to establish a zero-N test strip:

Select a representative spot in the field with a uniform soil type.
You will have a zero-N strip and a with-N strip, which is a nearby strip that receives the full N rate and will serve as a direct comparison to the zero-N strip.
Zero-N strip width is dependent on your equipment, including N application and harvester widths. It is recommended that zero-N strips are at least 3 combine widths and a length of at least 350 feet. Note that the longer the length, the easier it will be to obtain accurate yield data; however, be mindful of the cost of potential yield loss.
If you are equipped to do so, creating a GPS boundary or a prescription for the zero-N test strip can make it easier to avoid in-season N applications and obtain yield data from the monitor, if available.
Additionally, or if you do not have GPS software, flag off the four corners of the zero-N strip using tall stakes and flags so that you can see the plot during in-season applications. This is especially important if you will not be the one applying N. Also, at the field’s edge, mark off the strips where the zero-N is located, so you look out for the strip during applications.

Zero Nitrogen Rate Field Setup

>350 ft.
in
length

Zero-N Strip
↓	↑ Yield Data	↓
3 Combine Widths

⤒
|
|
|

Buffer

With-N Strip
↓	↑ Yield Data	↓
3 Combine Widths

Arrows indicate the direction of the combine. Yield data from the middle combine pass is used to provide a buffer between treatments.

As you consider how best to lay out and mark the test strip, connect with the UW team to receive assistance.  

Data Collection

Required sampling and data collection will provide crucial insights into how nitrogen is entering, cycling and leaving the field being monitored. Participants can investigate additional metrics of interest (see optional data below) as their budget allows. In the data collection information below, “treatment” refers to the “zero-N strip” and “with-N strip.”

Required Data and Sampling – All Sites 

Maintain zero-nitrogen test strip
Field history and management data (data collection survey will be provided)
Routine soil (pH, OM, P, K, etc.) sampled across trial area as one composite sample.
Pre-plant soil nitrate and ammonium at 0-1’ and 1-2’ prior to nitrogen application: 1 each per treatment.
Pre-sidedress soil nitrate and ammonium (or in-season sampling if all N was applied at plant) at 0-1’: 1 per treatment.
Post-harvest soil nitrate and ammonium at 0-1’ and 1-2’: 1 each per treatment.
Yield data from calibrated yield monitor or weigh wagon.

Required Data and Sampling – If Applicable

Manure analysis (if manure applied during this crop year): 1 sample per application.
Cover crop sample if field has cover (see UW sampling resources linked in the NOPP protocol library): 1 composite field sample at time of termination.
Grain nitrogen content (for corn grain fields): 1 sample per treatment.
Irrigation nitrogen content (for irrigated fields): 1 sample per field.

Optional Data Collection and Sampling Examples

Soil nitrate and ammonium sampling the following spring: 0-1’ and 1-2’, 1 each per treatment. This sampling is highly recommended for those interested in investigating potential nitrate leaching risk during the shoulder season following corn
Cover crop forage quality: 1 composite
Whole plant nitrogen content (whole-plant silage or stover for grain fields): 1 per treatment just prior to harvest
Corn silage forage quality: 1 per treatment just prior to harvest
Leaf tissue samples: 1 per treatment
Soil health metrics: Recommend 1 per field, prior to nitrogen application. Overview of common soil health metrics can be found here.

Project Timeline

Timeframe	Activities
Winter through spring	Select field(s) you want to monitor   Cover crop biomass sampling/analysis (prior to winter kill or termination, if applicable)  Manure analysis if manure is being applied
Spring (before planting)	Approximate test strip location (sampling will occur in this area) Take a routine soil sample Take a pre-plant soil sample for nitrate and ammonium Flag out/implement zero-N and with-N strips with flags, or by using a shapefile Optional sampling: soil health sampling
In-Season	Pre-sidedress soil sample for nitrate and ammonium Irrigation nitrate (if applicable) Calibrate your yield monitor and review yield monitor data collection instructions Optional sampling: leaf tissue sampling, soil health sampling
Harvest	Harvest Grain N content (for corn grain fields) Optional sampling: whole plant N content, corn silage forage quality
Post-Harvest	Submit soil, agronomic, and yield data to NOPP team  Receive results (early spring)  Optional sampling: post-harvest soil nitrate and ammonium

Projects derived from this protocol are designed to provide insight into field-specific nitrogen use efficiency.

This protocol was developed by the UW-Madison Department of Soil and Environmental Sciences and Division of Extension.