IN THE FIELD
TRIALS FINE-TUNE NITROGEN USE On-farm nitrogen use efficiency assessments can guide nitrogen management for economic and water quality gains. by Abby Augarten
acre or lbs./ac), or “How much did the field produce at a given N rate?” Fields with lower efficiencies not only provide an economic incentive to improve NUE but also have a need to reduce their risk to water quality. N balance, or N applied minus N removed (lbs./ac), measures the amount of unused N in a system.
Some of this unused N will be lost to volatilization, denitrification, and ammonia loss, but the main pathway of N loss is through nitrate leaching. Therefore, N balance is a good indicator of potentially leachable N and is a valuable tool to assess water quality impacts of N applications. Fields with PFP metrics in the low
Figure 1. Fields with lower efficiency have higher risk to water quality N Balance (N applied - N removed)
D
iscovery Farms’ Nitrogen Use Efficiency Project provides farmers and agronomists opportunities to evaluate their N management to determine economic and environmental impacts of current practices. With five growing seasons of data collection and 300 fields in our database, we have established benchmarks for different nitrogen use efficiency (NUE) categories. The benchmarks found in “Nitrogen Use Efficiency: Statewide Benchmarking for NUE in Corn Grain and Corn Silage” (bit.ly/JNM-NUE-benchmarking) would be applicable to corn production in the Upper Midwest. An individual producer can calculate NUE for their field, compare their value to these benchmarks, and use decision trees to determine what shifts in management would be valuable for improvements in profitability and water quality. Simple NUE assessments are a quick evaluation tool to identify if, and how, NUE can be improved. The first step is to evaluate partial factor productivity (PFP) on a given field. PFP is yield divided by N applied (pounds per
250 200 150
Median: 53 lb. N/ac
Median: 26 lb. N/ac
Low to mid use efficiency 1.1-1.3 bu/lb. N
Mid to high use efficiency 1.3-1.5 bu/lb. N
100 50 0
Median: 2 lb. N/ac
Median: 106 lb. N/ac
-50 Low use efficiency <1.1 bu/lb. N
High use efficiency >1.5 bu/lb. N
Partial factor productivity (PFP) efficiency category
Table 1: Practices for improving low efficiency fields Increasing yield at a given N rate
Decreasing N rate while maintaining yield
Nitrogen management (timing, placement, and source)
Nitrogen management (rate, timing, placement, and source)
Soil health
Manure management (rate, timing, and placement)
Soil fertility
Crediting other forms of N (manure testing and crediting, and credits from alfalfa)
Pest management
Crop rotation and legumes
Variety selection
Soil health (organic matter and nutrient cycling)
6 | Journal of Nutrient Management | August 2020
F2 6-7 Aug 2020 In the Field.indd 1
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