ALLELOPATHY IN BLACK-WALNUT (JUGLANS NIGRA L.) ALLEY CROPPING - I - SPATIOTEMPORAL VARIATION IN SOIL JUGLONE IN A BLACK WALNUT-CORN (ZEA-MAYS L.) ALLEY CROPPING SYSTEM IN THE MIDWESTERN USA

A study was conducted to quantify the spatial and temporal variation i n soil juglone (5-hydroxy-1,4-naphthoquinone) in a 10-year-old black w alnut (Juglans nigra L.)-corn (Zea mays L.) alley cropping system. Two treatments ('root barrier' and 'no barrier') were applied to determin e if soil juglone in the alley can be minimized by preventing black wa lnut root growth into the alley. Although no significant seasonal vari ation in soil juglone existed, a distinct spatial pattern was observed . Juglone concentration decreased as much as 80% as the distance incre ased to 4.25 m from the tree row. Installation of polyethylene root ba rriers minimized juglone concentration to trace levels in the alley. H owever, this treatment increased juglone levels within the tree row as compared to the 'no barrier' treatment, probably as a result of incre ased rooting density within a limited volume of soil.