Variation in interference relationships have been shown for a number of crop-weed associations and may have an important effect on the implementation of decision support systems for weed management. Multiyear field experiments were conducted at eight locations to determine the stability of corn-foxtail interference relationships across years and locations. Two coefficients (IandA) of a rectangular hyperbola equation were estimated for each data set using nonlinear regression procedures. TheIandAcoefficients represent percent corn yield loss as foxtail density approaches zero and maximum percent corn yield loss, respectively. The coefficientIwas stable across years at two locations and varied across years at four locations. Maximum yield loss (A) varied between years at one location. Both coefficients varied among locations. Although 3 to 4 foxtail plants m−-1row was a conservative estimate of the single-year economic threshold (Tc) of foxtail density, variation inIandAresulted in a large variation inTc. Therefore, the utility of using common coefficient estimates to predict future crop yield loss from foxtail interference between years or among locations within a region is limited.

Physical and chemical properties of minesoil reclaimed for forest land use in southwestern Indiana were evaluated to determine suitability for reforestation according to specifications of Public Law 95–87, The Surface Mining Control and Reclamation Act of 1977. Properties of reconstructed minesoil and unmined reference soils were compared. Soil types on the reference area were primarily Ava (Typic Fragiudalf) and Parke (Typic Hapludalf) silt loams and were similar to soils on the mineland prior to excavation. Both the reclaimed mineland site and reference site supported mixed upland hardwood trees and shrub vegetation prior to surface mining. Chemical properties of minesoil were similar to or more favorable for plant growth than unmined reference soils. However, physical properties in the rooting zone were less favorable in minesoil than reference soils. Minesoil had higher bulk density, lower porosity, lower permeability, higher coarse fragment and clay content, and lower available water‐holding capacity than reference soils at comparable depths. Mean bulk density of minesoil, adjusted for rock fragments > 2 mm, ranged from 1.53 Mg m−3 (g cm−3) in topsoil to 1.77 Mg m−3 in graded cast overburden. Mean available water‐holding capacity was 16.5% in topsoil and 10.8 to 11.7% (kg kg−1) in graded cast overburden layers of minesoil. Chemical properties of minesoil should be adequate for cover crop and tree seedling establishment after liming and fertilization to recommended soil test levels of NPK. However, physical properties could adversely affect plant survival and growth.

Measurements of above-ground plant volume were used to quantify corn interference with common cocklebur and velvetleaf. Separate experiments were carried out for each weed species in which neighborhoods with a radius of 50 cm were established around target plants of both species, selected from a range of corn plus cocklebur or velvetleaf densities. Height and canopy area of target plants and neighbor corn and weed populations were measured periodically during the growing season. Target plant (corn, cocklebur, or velvetleaf) size as well as corn and weed population size within each neighborhood were quantified as cylindrical volumes. Regression analysis was used to quantify the relationship between target plant seed production and cylindrical volumes of the target and neighbor species. Both target and neighbor plant volumes were correlated with target plant seed production for all species. The ratio of target plant volume to total neighborhood plant volume (volume ratio) was the independent variable that accounted for the most variation in target plant seed production. These volume-based variables may be used to develop competitive indices in physico-empirical based interference models.

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