Productivity and belowground competition vectors of a temperate alley cropping system
Abstract
Novel alley cropping systems in the humid temperate Midwestern USA are being developed as alternatives to the conventional practice of growing hardwood trees and agronomic crops in monocultures. There are several issues concerning management of the black walnut (Juglans nigra L.) alley cropping system, which include consideration of the sufficiency of belowground and aboveground plant resources and whether toxins exuded by the trees inhibit crop growth. Tree management activities were examined for their impacts on tree and maize (Zea mays L.) productivity in an alley cropping system located in southern Indiana. Tree root pruning in year 11 after system establishment (year 1 = 1985) improved crop access to nutrients and water resulting in little detectable difference in crop yield between mid alley and alley edge rows. This response dissipated by year 16 when crop production declined by up to 96% as trees continued to grow and light became limiting across the 8.5 m-wide alley. However, tree branch pruning in year 17 returned crop yields to up to 81% of the year 11 values in the mid alley, but only 30% at the alley edge. Root pruning was associated with reduced soil organic matter levels and organic nitrogen fertility as well as increased inorganic nitrogen concentrations in soil leachates below the effective rooting zone. Water appeared to limit maize productivity particularly during a late summer droughty period in year 12; however, more typically frequent summer rainfall in this humid region may provide sufficient water for resource demanding alley crops. Juglone (5-hydroxy-1,4-naphthoquinone) exudation by walnut tree root seedlings was confirmed in a pot study and soil pore-water concentrations estimated from extracts of surficial soil from beneath the alley cropping system were as high as 6.6 × 10−6 M, which is below levels known to inhibit crops considered for intercropping with black walnut. Further assessment of the likely persistence of juglone in soils indicated that juglone is both microbially and abiotically degraded, and that it will be particularly short-lived in soils supporting microbial activity. The potential increase in overall productivity and conservation of the landscape unit justifies efforts to overcome the challenges of managing mixed-cropping systems.
Degree
Ph.D.
Advisors
Gillespie, Purdue University.
Subject Area
Environmental science|Soil sciences|Forestry
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