Tracking the Impact of Nutrient Management Practices on Domestic Farms

A research team examines the impact of nutrient management practices on crop production.

Nutrient management practices are the different kinds of strategies that farmers employ to be able to make sure they have enough fertilizer to have the best crop yields possible, while also making sure that that fertilizer doesn't run off into the environment. Molly Sears and James Sears, assistant professors in the Department of Agricultural, Food, and Resource Economics (AFRE) at Michigan State University (MSU), are collaborating with researchers at University of California, Davis and California Sea Grant to evaluate the effectiveness of nutrient management practices on fields in California’s Central Valley and provide recommendations on efficient nitrogen application.

Nitrogen, phosphorus, and potassium are the macronutrients that are applied in fertilizer to help plants grow. Given the current California policy initiatives on nitrogen runoff, the research team chose to focus on Nitrogen.  Nitrogen is the nutrient that's typically applied in the greatest amount and can be a limiting factor for production. If you don't have enough nitrogen in your soil, you can hit a yield barrier.

“There are eight nitrogen efficiency related practices that we included in our study sample,” Molly Sears shared. “Many people adopt several of these practices, so the way we ended up deciding on an analytical strategy both really made sense from an agronomic perspective, but also from an economic perspective, which excited me a lot.”

With this study, the team had an advantage in their data collection. As part of the Irrigated Lands Regulatory Program in California, farmers are required to fill out a nitrogen management plan annually with the state water board.

“The data is fully anonymized,” Sears explained. “We don't know where the fields are, we don't know who owns the fields. But for every field for this study, we know what crops they grew, and we know what kinds of irrigation systems they use. We also know their nitrogen application rates and their nitrogen efficiency, and what nitrogen erosion and pesticide practices that they're engaged in.”

The team took the data and analyzed it in two different stages. First, they looked at how management practices influenced  nitrogen application rates, and then how the practices and application rates influence nitrogen efficiency. Utilizing a two-stage least squares strategy allowed the team to identify how all of the individual practices had an impact.

“Most of our nitrogen application practices implemented on operations dramatically improved nitrogen efficiency,” Sears shared. “One of the things that makes me especially excited about this is that split nitrogen had a huge impact, and split nitrogen application is something that almost 90% of farmers do in our sample. It's the easiest possible nitrogen management practice, where a producer applies it twice throughout the year, instead of dumping a whole bunch [of nitrogen] on at the beginning of the year.”

The research team wants to replicate the study in Michigan, but currently there are no policies in Michigan that collect these kind of data. While it may be hard to replicate outside of California, there are still benefits that can be gleaned by farmers across the U.S. The team is continuing to run analyses for individual crops and meet with stakeholders to pursue further results wherever they may lead.

Sears shared, “I do think that these results provide a lot of optimism for what farmers in Michigan are doing because I know that many Michigan producers are already implementing these practices, and this study has some pretty strong implications for the nitrogen efficiency results we're seeing there.”

Members of the research team included MSU AFRE’s Molly Sears and James Sears, Mark Lubell and Sat Darshan S Khalsa (UC Davis), and Jessica Rudnick (California Sea Grant)

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