Evaluating critical nitrogen dilution curves for assessing maize nitrogen status across the US Midwest

Authors: SHAO, HUI - University Of Minnesota; MIAO, YUXIN - University Of Minnesota; FERNANDEZ, FABIAN - University Of Minnesota; KITCHEN, NEWELL - Retired ARS Employee; Ransom, Curtis; CAMBERATO, JAMES - Purdue University; CARTER, PAUL - Farmer; FERGUSON, RICHARD - University Of Nebraska; FRANZEN, DAVID - North Dakota State University; Laboski, Carrie; NAFZIGER, EMERSON - University Of Illinois; SAWYER, JOHN - Iowa State University; SHANAHAN, JOHN - Agoro Carbon Alliance

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2023
Publication Date: 7/23/2023
Citation: Shao, H., Miao, Y., Fernandez, F.G., Kitchen, N., Ransom, C.J., Camberato, J.J., Carter, P.R., Ferguson, R.B., Franzen, D.W., Laboski, C.A., Nafziger, E.D., Sawyer, J.E., Shanahan, J.F. 2023. Evaluating critical nitrogen dilution curves for assessing maize nitrogen status across the US Midwest. Agronomy. 13(7):1948. https://doi.org/10.3390/agronomy13071948.
DOI: https://doi.org/10.3390/agronomy13071948

Interpretive Summary: To maximize maize grain production, farmers must ensure that the crop has adequate nitrogen (N). Determining if the maize crop is N stressed can be very difficult. One approach is to take plant samples and measure the amount of N in the plant tissue. One issue with this approach is that the critical N concentration decreases as plants increase in biomass. Researchers have developed mathematical models that relate the critical plant N concentration to biomass; however, they have not been evaluated for the U.S. Midwest. The aim of this research was to evaluate two such models (termed critical nitrogen dilution curves; CNDC) developed in France and China using data from N rate response trials conducted across eight US Midwest states over three years. Results showed that of the two models, the French CNDC was considerably more accurate and described 38 to 56% of the variability in soil nitrate-N content. Overall, the French CNDC is a suitable diagnostic tool for assessing maize N status in the US Midwest. However, further work is needed to improve model performance across the entire US Midwest. These improvements could include incorporating remote sensing technology as a surrogate to plant tissue sampling.

Technical Abstract: Plant N concentration (PNC) has been commonly used to guide farmers in assessing maize (Zea mays L.) N status and making in-season N fertilization decisions. However, PNC varies based on the development stage and therefore a relationship between biomass and N concentration is needed (i.e., critical N dilution curves; CNDC) to better understand when plants are N deficient. A few CNDC have been developed and used for plant N status diagnoses but have not been tested in the US Midwest. The objective of this study was to evaluate under highly diverse soil and weather conditions in the US Midwest the performance of CNDCs developed in France and China for assessing maize N status. Maize N rate response trials were conducted across eight US Midwest states over three years. This analysis utilized plant and soil measurements at V9 and VT development stages and final grain yield. Results showed that the French CNDC (y=34.0x^-0.37, where y is critical PNC, x is aboveground biomass) was better with a 91% N status classification accuracy compared to only 62% with the Chinese CNDC (y=36.5x-0.48). The N nutrition index (NNI), which is the quotient of the measured PNC and the calculated critical N concentration (Nc), based on the French CNDC was significantly related to soil nitrate-N content (R^2=0.38-0.56). Relative grain yield on average reached a plateau at NNI values of 1.36 at V9 and 1.21 at VT, but for individual sites ranged from 0.80 to 1.41 at V9 and from 0.62 to 1.75 at VT. The NNI threshold values or ranges optimal for crop biomass production may not be optimal for grain yield production. It is concluded that the CNDC developed in France is suitable as a general diagnostic tool for assessing maize N status in US Midwest. However, the threshold values of NNI for diagnosing maize N status and guiding N applications vary significantly across the region, making it challenging for guiding specific on-farm N management. More studies are needed to determine how to effectively use CNDC to make in-season N recommendations in the US Midwest.