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.

The goal of this research was to determine the potential for use of site-specific management of corn hybrids and plant densities in dryland landscapes of the Great Plains by determining (1) within-field yield variation, (2) yield response of different hybrids and plant densities to variability, and (3) landscape attributes associated with yield variation. This work was conducted on three adjacent fields in eastern Colorado during the 1997,-98, and-99 seasons. Treatments consisted of a combination of two hybrids (early and late maturity) and four plant densities (24,692, 37,037, 49,382 and 61,727 plants ha)1) seeded in replicated long strips. At maturity, yield was measured with a yield-mapping combine. Nine landscape attributes including elevation, slope, soil brightness (SB) (red, green, and blue bands of image), EC a (shallow and deep readings), pH, and soil organic matter (SOM) were also assessed. An analysis of treatment yields and landscape data, to assess for spatial dependency, along with semi variance analysis, and block kriging were used to produce kriged layers (10 m grids). Linear correlation and multiple linear regression analysis were used to determine associations between kriged average yields and landscape attributes. Yield monitor data revealed considerable variability in the three fields, with average yields ranging from 5.43 to 6.39 mg ha)1 and CVs ranging from 20% to 29%. Hybrids responded similarly to field variation while plant densities responded differentially. Economically optimum plant densities changed by around 5000 plants ha)1 between high and low-yielding field areas, producing a potential savings in seed costs of $6.25 ha)1. Variability in yield across the three landscapes was highly associated with landscape attributes, especially elevation and SB, with various combinations of landscape attributes accounting for 47%, 95%, and 76% of the spatial variability in grain yields for the 1997,-98, and-99 sites, respectively. Our results suggest site-specific management of plant densities may be feasible.

No abstract

No abstract

Nitrogen fertilization and irrigation practices can affect durum [Triticum turgidum subsp. durum (Desf.) Husn.] grain quality, especially protein content. The purpose of this study was to determine if irrigation frequency during grain fill influences the effectiveness of N applied near anthesis in increasing durum grain quality. A field study was conducted at Maricopa, AZ on a Casa Grande sandy loam soil (fine‐loamy, mixed, superactive, hyperthermic, Typic Natrargid). Durum was grown with recommended amounts of N fertilizer until anthesis when 0, 3.4, and 6.7 g N m−2 were applied and irrigation based on 30, 50, and 70% depletion of plant‐available soil water was initiated. Irrigation during grain fill had no effect on grain yield or grain quality except in 1996, when irrigating at 30, 50, and 70% depletion resulted in hard vitreous amber counts (HVAC) of 813, 870, and 934 g kg−1, respectively. Nitrogen application near anthesis of 0, 3.4, and 6.7 g N m−2 resulted in grain protein contents of 115, 127, and 140 g kg−1 in 1995 and 132, 141, and 151 g kg−1 in 1996, respectively. Nitrogen application near anthesis increased grain protein yield and HVAC in both years of the study and increased grain yield, grain volume weight, and kernel size in 1995. The results of this study suggest that N fertilizer application near anthesis has a primary influence on durum quality and that effects of irrigation frequency during grain fill are inconsistent or relatively minor.