Soybean yield and protein concentration are limited by nitrogen (N) supply, especially in high-yield environments. However, yield response to N fertilizer is inconsistent and usually not cost-effective. Here we plan to develop a method that allows in-season diagnosis of plant nitrogen status that can be used to better inform soybean producers with respect to when and how much N fertilization can be applied on soybean to more consistently achieve a profitable yield response. To develop and validate this method, we propose a 3-year project during which we will conduct N fertilization trials in producer fields in Nebraska. Each experiment will include three treatments: (i) a ‘zero-N’ treatment that receives no N fertilizer; (i) a ‘full N’ treatment in which the crop will grow under ample N supply, and (iii) an ‘optimal N’ treatment in which we will apply N fertilizer during flowering with the goal of delivering an economically profitable yield response to N. We plan to conduct 24 replicated trials per year at various NE farm sites. Soil and plant samples will be collected during the growing season for N determination, with seed yield and other crop parameters measured at maturity. Ultimately, this project expects to generate a decision tree tool that can guide producers on their decisions about N fertilizer application in soybean.

The goal of this project is to fine tune nitrogen application in soybean.

There is currently no tissue-based diagnostic tool available for NE and US soybean producers that helps guide producers’ decisions in relation to N fertilizer application in soybean. Here we propose a novel approach consisting of an in-season diagnosis of N limitation based on N concentration in stems around flowering stage. This approach will be evaluated via two years of field trials. Our ultimate goal is to develop a decision tree that can help NE producers to make decisions on soybean N fertilizer application, providing them with a range of possible economic outputs considering typical fertilizer & soybean prices.

The project will have a total duration of 36 months (Oct 1, 2021 – Sep 30, 2024). We are proposing two years of field experiments to account for variation in weather and possible unmanageable factors (such as hail or killing frost). Because the harvest of the second year of field experiments occurs in October (after the end of the 2nd fiscal year on 30 Sep), we are requesting a third final project year (1 Oct to 30 Sep) to be able to complete the 2nd year seed harvest, perform the seed constituent assays, undertake the data analysis & interpretation, and then prepare and write the scientific and extension publications. But, if the two-year results appear to be promising, we would consider working with the NE On-Farm Research Network to develop some protocols that could be used by soybean producers in 2024 to do their own on-farm research tests. The proposed project timeline is shown below.

Milestones: We will conduct field experiments in 24 soybean producer fields each year. A tool will be developed to guide N fertilizer addition in soybean. Results will be published in high-impact agronomic-oriented journals and conveyed to NE soybean producers via field days and extension material.

Updated May 26, 2023:

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Findings from this study will be used to develop a decision tree that can help NE producers to make decisions on soybean N fertilizer application, providing them with a range of possible economic outputs considering typical fertilizer & soybean prices.

This project is expected to provide guidelines on how to detect an in-season nitrogen limitation in soybean and help soybean producers to inform their decisions on N fertilizer application in soybean.