Nitrogen Use Efficiency and corn silage

By: Abby Augarten and Kevan Klingberg

While Nitrogen Use Efficiency (NUE) is commonly discussed in reference to corn grain systems, there is little data on corn silage production systems. Wisconsin is the top producer of corn silage and there is a lot to be gained by fine-tuning nitrogen (N) management for these systems for both water quality and economic efficiency. The Discovery Farms Program is finishing its fifth year evaluating NUE on WI fields. Since the beginning, we’ve realized how much NUE for corn grain and silage differ and have assessed N management for these two end uses independently. It is not only important to analyze these two datasets separately, but also it is valuable to look at the entire farming system surrounding corn silage production to improve NUE.

Corn silage fields, on average, have higher NUE than corn grain fields

In corn silage production, the entire above-ground plant is removed at harvest, whereas when corn is harvested as grain, the stalks are typically left in the field to decompose. This is significant because it means that we are removing more N with corn silage harvest compared to grain. Based on Discovery Farms averages, corn silage removes ~80 lbs/ac more N than grain. Because of these differences in N removal rates, we see greater NUE values for our monitored silage fields and think that NUE for corn grain and silage should be evaluated independently. We’ve created specific benchmarks for corn silage fields so that WI farmers can assess their own field’s efficiency relative to other silage systems and see if improvements can be made to reach an above-average NUE. Benchmarks for corn grain and silage fields can be found here: https://bit.ly/2kwbmA0

Focus on ways to replenish organic matter

On average, N balance (N applied-N removed) in our corn silage fields was -20 lb N/ac, compared to 48 lb N/ac in our corn grain dataset.

	Average N applied	Average N removed	Average N balance
Corn grain	180 lb N/ac	132 lb N/ac	48 lb N/ac
Corn silage	190 lb N/ac	210 lb N/ac	-20 lb N/ac

For the majority of our monitored corn silage fields, harvest actually removed more N than what was applied. In removing corn stalks at harvest, we need to consider alternative ways to replenish N and rebuild organic matter (OM). This can be done through manure applications, diversified rotations including legumes, and cover crops, if managed properly within the system.

Managing multiple N sources creates a challenge to achieving a higher NUE

In our entire dataset, fields that used two or more sources of N (fertilizer, manure and/or legume credits), on average had higher N rates. Higher N rates do not always contribute to a proportionate yield gain, and can cause a lower NUE and risk to the environment. Additionally, we assign credits for manure and alfalfa the best we can, but, organic N sources are dependent on variable weather conditions, nutrient content and management to transform N into a plant-available form. Lastly, logistical constraints such as storage and transport often determine when and how manure is applied to fields, which might differ from what would be best for N management and water quality. Corn silage systems are most reliant on manure and alfalfa as N sources, meaning that there is an inherent lack of control and uncertainty in N management.

Best management practices for corn silage systems include manure management, cover cropping and zero-N test strips

Manure can create a challenge to achieving higher efficiencies, so use these tips to help maximize returns to manure.

Conduct a manure analysis to best assess its nutrient content, assign credits, and adjust manure and fertilizer rates accordingly.

Seed a fall cover crop that will capture and store N (grass species such as rye) from applied manure and experiment with N inhibitor products.

Use zero-N test strips or low-N test strips to assess how much N is being supplied by your corn silage system. A zero-N test strip does not receive any manure or fertilizer and will be an indicator of how much N is supplied by the soil. For fields where you are concerned about removing more N from a system, this would be a good test to assess if you’ve been able to replenish N stores and maintain OM over many years of corn silage production.

Fine-tuning N management in corn silage production systems will protect water quality and improve economic efficiency of inputs. Evaluating NUE for your corn silage fields is a great first step to assess what improvements in management can be made.

Corn silage is a primary feed source for many dairy farms in Wisconsin.