US maize yield gains have decoupled from the need for higher plant densities

Abstract

Context: The improvement in US maize grain yield has been a remarkable success, increasing 3-fold since 1950. A large component of this improvement has been the synergy between long-term breeding selection of genotypes with tolerance to crowding stress and the increase in plant densities sown by farmers. However, survey data shows that US farmers are today barely increasing their plant densities, in central states (Iowa, Illinois, Indiana, Minnesota) the rate for the last 10 years is around 20% of the historical increase. Methods: The first experiment began in 1987 and continuously tested new cohorts of pre-commercial genotypes (on average 44 genotypes per year) in a range of plant densities (3.4–12.4 plants m−2) across the US Midwest (on average 34 locations per year). A second experiment conducted in the same region from 2020 until 2025 (2–4 locations per year) simultaneously evaluated genotypes commercially released from 1936 to 2020 (61 genotypes) across different plant densities (3.0–8.5 plants m−2). Results: The experiment testing pre-commercial genotypes released from 1988 until today showed that the number of plants needed to maximize yield has not increased for genotypes released after 2010; genetic yield improvements are today driven by increases in yield per plant. The second experiment showed the potential individual plant yield without resource competition (at 3.0 plants m−2) remained stable at 275 g plant−1 for genotypes released until 1990, while modern genotypes achieved 380 g plant−1. These results demonstrate that during the last decades US plant breeders have released genotypes that continue to increase yield but without the need for higher plant densities. Conclusions: The plant density that maximizes yield across the US is stabilizing and yield increases have decoupled from plant density increases. Our findings represent a paradigm change around the constant need to have more plants to achieve greater maize yields, genetic yield improvements are today driven by increases in yield per plant and not by enhanced crowding tolerance.