Defining competition vectors in a temperate alley cropping system in the midwestern USA - 2. Competition for water

A study was carried out in an alley cropping system in the Eastern Maize Be lt of the United States with the objective of quantifying the competition f or water between trees black walnut (Juglans nigra L.) and red oak (Quercus rubra L.) and maize (Zea mays L.). Spatial and temporal variation in soil moisture, tree and maize rooting patterns, tree and maize water uptake, and maize leaf area expansion were determined in three treatments; 'barrier' ( polyethylene root barriers separating maize and tree roots), 'trench' (tren ching without a polyethylene barrier), and 'no barrier' (control). Signific ant temporal variation in soil moisture was observed in both black walnut a nd red oak alley cropping systems. The 'barrier' and 'trench' treatments re sulted in higher soil moisture in the 'maize alley' and lower soil moisture in the 'tree row' than the 'no barrier' treatment. Uptake of water by maiz e was higher in the 'barrier' than the 'no barrier' treatment. However, tre e water uptake was higher in the 'no barrier' treatment than in the 'barrie r' treatment because tree roots utilized water from the 'maize alley'. Maiz e leaf area was negatively impacted by water stress in the 'no barrier' tre atment. Quantification of rooting patterns revealed that maize and tree roo ts were concentrated in the top 30 cm soil layer where water fluctuations w ere greatest. The 'barrier' and 'trench' treatments successfully eliminated the belowground root competition between trees and maize and resulted in g reater leaf area and higher grain yields than the 'no barrier' treatment. T hus, competition for water rather than competition for light seems to be cr itical in defining the productivity and sustainability of this alley croppi ng system.