From a point to a range of optimum estimates for maize plant density and nitrogen rate recommendations

Authors: KING, KYLE - Iowa State University; ARCHONTOULIS, SOTIRIOS - Iowa State University; BAUM, MITCH - Iowa State University; Edwards, Jode

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2023
Publication Date: 12/19/2023
Citation: King, K.A., Archontoulis, S.V., Baum, M., Edwards, J.W. 2023. From a point to a range of optimum estimates for maize plant density and nitrogen rate recommendations. Agronomy Journal. 116(2):598-611. https://doi.org/10.1002/agj2.21516.
DOI: https://doi.org/10.1002/agj2.21516

Interpretive Summary: The three most important variables underlying maize production are choice of hybrid, plant density, and nitrogen fertilization rate, and yet there is little data available on the interactions among all three variables. In collaboration with Iowa State University, USDA ARS scientists estimated the joint response to nitrogen rate and plant density for five hybrids across a wide range of plant densities and nitrogen rates. A key finding in this study was that nitrogen rate and plant density can be varied over wide ranges near optimum values while still maintaining 99% or more of maximum revenue (total value of grain minus seed and nitrogen cost). The shape of response curves was similar among hybrids suggesting that different hybrids have similar response patterns even though the point of maximum return varies among hybrids. Lastly, the study suggested a strong relationship between optimum nitrogen rate and grain yield at optimum nitrogen rate wherein higher optimum nitrogen rates were associated with higher grain yields. This relationship has not been seen in prior studies.

Technical Abstract: The interaction between optimum nitrogen (N) rate, optimum plant density, and hybrid choice on maize productivity and net return to seed and fertilizer cost remains unknown but is important to be addressed given the complexity of agricultural systems. We collected grain yield data from a factorial experiment with five N rates (0 to 291 kgN/ha), five plant densities (3.7 to 11.4 pl m-2), and four hybrids (old versus new) over two years in Iowa, USA. Data were sufficiently modeled with a quadratic plateau model with continuous covariate terms to include N x plant density interactions for each hybrid and year (R2=0.925, n=387). We found a wide range of plant densities (on average 6.7 to 8.4 pl m-2) and N rate (on average 150 to 220 kg N ha-1) combinations to achieve 99% of the maximum net revenue. The economic optimum N rate increased with increasing plant density (from 4 to 7 pl m-2), while the economic optimum plant density increased with N rate (from 0 to 100 kg N ha-1). The fundamental relationships between grain yield response to N fertilizer and plant density were similar across old and new hybrids, however, the absolute values were different, with newer hybrids having 20% higher economic optimum N rate and 23% higher yield than the older hybrids. Our study offers new insights into N rate by plant density by hybrid interactions that can assist future research and development of recommendation systems.