Growers frequently are concerned about the response of corn (Zea 1968). The optimum planting date in the Corn Belt mays L.) to planting date. Early planting of corn is recommended because full-season hybrids utilize the entire growing season, achieve typically occurs between 20 April and 10 May (Benson, physiological maturity before a killing frost, and start to dry, thereby 1990). While some studies show an advantage for plantincreasing profit through reduced drying costs. The objective was to ing before 20 April, other areas in the northern Corn evaluate the influence of planting date and hybrid maturity on corn Belt may yield well when planted around 20 May (Cargrain yield and harvest moisture in Wisconsin. Two or three corn ter, 1984). hybrids ranging in relative maturity from 80 to 115 d were planted Several researchers have described planting date efbetween 19 April and 22 June at six locations in Wisconsin from 1991fects on corn (Alessi and Power, 1975;Benson, 1990; to 1994. In southern Wisconsin locations, the optimum planting date Johnson and Mulvaney, 1980;Imholte and Carter, 1987; for grain yield of full-and shorter-season hybrids ranged between 1 Nafziger, 1994;Swanson and Wilhelm, 1996). Our objecand 7 May, and was still at 95% of optimum between 9 and 18 May.Abbreviations: MN RM, Minnesota relative maturity [rating]. Published in Agron.

Core Ideas The geographic scope, scale, and unique collaborative arrangement warrant documenting details of this work. The purpose of this article is to describe how the research was undertaken, reasons for the research methods, and the project's potential value. The project generated a valuable dataset across a wide array of weather and soils that allows evaluation of N decision tools. Due to economic and environmental consequences of N lost from fertilizer applications in corn (Zea mays L.), considerable public and industry attention has been devoted to the development of N decision tools. Needed are research and databases and associated metadata, at numerous locations and years to represent a wide geographic range of soil and weather scenarios, for evaluating tool performance. The goals of this research were to conduct standardized corn N rate response field studies to evaluate the performance of multiple public‐domain N decision tools across diverse soils and environmental conditions, develop and publish new agronomic science for improved crop N management, and train new scientists. The geographic scope, scale, and unique collaborative arrangement warrant documenting details of this research. The objectives of this paper are to describe how the research was undertaken, reasons for the methods, and the project's anticipated value. The project was initiated in a partnership between eight U.S. Midwest land‐grant universities, USDA‐ARS, and DuPont Pioneer. Research using a standardized protocol was conducted over the 2014 through 2016 growing seasons, yielding a total of 49 sites. Preliminary observations of soil and crop variables measured from each site revealed a magnitude of differences in soil properties (e.g., texture and organic matter) as well as differences in agronomic and economic responses to applied N. The project has generated a valuable dataset across a wide array of weather and soils that allows investigators to perform robust evaluation of N use in corn and N decision tools.

An extensive literature review was conducted of corn and soybean research that compared yields of no‐tillage to conventional fall tillage systems. The objective was to test the hypothesis that no‐till has a different effect on corn and soybean yields in different regions of the United States and Canada. The trial results were mapped to look for geographic and environmental patterns in the relative performance of no‐tillage to conventional tillage on corn and soybean yield. The national average difference in corn and soybean yield between no‐tillage and conventional tillage was negligible. A map of the tillage yield comparisons was created for the U.S. and Canada. No‐till tended to have greater yields than conventional tillage in the south and west regions. The two tillage systems had similar yields in the central U.S., and no‐till typically produced lower yields than conventional tillage in the northern U.S. and Canada. No‐tillage had greater corn and soybean yields than conventional tillage on moderate‐ to well‐drained soils, but slightly lower yields than conventional tillage on poorly drained soils. Corn and soybean yields tended to benefit more from crop rotation in no‐till as compared to continuous cropping. Future tillage research should focus on optimizing successful high residue no‐tillage or strip‐tillage production systems instead of making comparisons to conventional tillage systems.

Uneven emergence of corn (Zea mays L.) may occur when soils are dry at the time of planting. This research was conducted in seven environments in Illinois and Wisconsin during a 2‐yr period to measure the effect of uneven emergence on grain yield. Two hybrids (Pioneer Brand 3732 and 3615), chosen to represent differing responses to plant density, were hand planted in early May (E), 10 to 12 after E (M), and 21 to 27 d after E (L) to produce various patterns of among‐row and within‐row unevenness. There was no consistent interaction of hybrid with emergence patten, and responses were quite consistent among environments. Across environments, uniform E, M, and L plantings produced 11.8, 11.1, and 10.4 Mg ha−l, respectively. Uniform E rows bordered by M rows [E(M)] produced 11.4 Mg ha−l, while the other among‐row treatments E(L), M(E), L(E), and M(L) produced 12.2, 10.5, 7.9, and 11.8 Mg ha−l, respectively. The within‐row, repeating patterns of 3E:1M, 1E:1M, 3E:3M, and 1E:3M produced yields of 11.0, 10.7, 10.9, and 10.9 Mg ha−l, respectively, while the 3E:1L, 1E:1L, 3E:3L, and 1E:3L treatments produced grain yields of 10.5, 9.2, 9.4, and 9.1 Mg ha−l, respectively. Comparison of uneven within‐row patterns with incomplete stands showed that in no case did the presence of late‐emerging plants cause yield loss. While uneven emergence decreased yields, these data do not show a yield benefit to replanting in order to attain uniformity, with the possible exception of cases where one‐half or more of the plants are delayed in their emergence by at least 3 wk.

Not all fields, nor even portions of fields, have the same economically optimal corn plant density. However, until the recent introduction of precision farming, producers could not benefit from these accepted intrafield differences. This field study was conducted on 170 cooperating farmer fields throughout the Midwestern U.S. Corn Belt between 1987 and 1996 and consisted of over 42 000 individual experimental units. At each location, corn (Zea mays L.) was overplanted and thinned to 44 000 to 104 000 plants ha−1. The objective of our field research was to estimate the economic value, to the farmer, of variable rate seeding (VRS) as compared with uniform rate seeding (URS). We first estimated the correlation between field quality and economically optimal plant density. The economically optimal uniform plant density for the Midwest Corn Belt was 67 900 plants ha−1. For every tonne per hectare increase in site quality, as measured by yield potential, the predicted value of the site‐specific economically optimal plant density increased by approximately 1200 plants ha−1. We compared differences in revenues minus seed costs on four simulated fields. The value of VRS, ignoring the costs of VRS equipment and services, ranged from $12.83 ha−1 for farmers with VRS technology and full information to $0.15 ha−1 for farmers with VRS technology but only partial information. Profitable implementation of VRS will require detailed and expensive information regarding site characteristics, production inputs, and stochastic factors. Therefore, VRS will remain economically infeasible for most commercial corn growers until the cost of obtaining such information decreases considerably.