Interspecific interactions in alleycropping: The physiology and biogeochemistry

This research was designed to determine the critical ecological interactions between trees and crop plants in an alleycropping system with black walnut (Juglans nigra L.)/red oak (Qeurcus rubra L.) and corn (Zea mays L.) in the Eastern Corn Belt of the U.S. The below-ground competition for water and/or nutrients (and possibly phytotoxicity in black walnut alleycropping) was isolated by either \u27trench\u27 (trenching 1.3 m deep on both sides of tree rows) or \u27barrier\u27 (installing polyethylene root barrier) treatments. The \u27no barrier\u27 treatment served as a control where tree and crop roots intermingled. Several measurements were taken during 1995-1997 with the objective of quantifying the competition for light, water, and nutrients. The spatio-temporal variation in soil juglone and its effect on crop (corn and soybean) growth and physiology was also studied. Further, the role of tree leaves and fine roots in enhancing soil fertility was also examined. Competition for light was not a major at this stage of system development. For example, although light (measured as PAR) was inhibited as much as 41% near tree rows (in red oak alleycropping), corn yield was not significantly affected. In general, avoiding root competition through the \u27barrier\u27 treatment resulted in normal growth and yield in corn. Competition for water was found to be critical, especially following a late season drought. Water uptake by corn was severely inhibited when tree roots had access to the \u27corn alley\u27. This led to less leaf area and lower yield in corn in the \u27no barrier\u27 treatment than in the \u27trench\u27 or \u27barrier\u27 treatments. Due to supplemental fertilization, competition for nitrogen was minimal at this stage of system development. Both corn and soybean were found to be sensitive to juglone in solution culture. The \u27barrier\u27 treatment was successful in minimizing juglone in the \u27corn alley\u27. It was found that tree leaves and roots could add significant amounts of carbon and nutrients into the system through mineralization. The ecological potential of this system seems to be defined by below-ground processes and resources, and light at this stage of system development, plays only a secondary role