Resource competition across the crop-tree interface in a maize-silver maple temperate alley cropping stand in Missouri A. W. Miller and S. G. Pallardy* Department of Forestry, University of Missouri, Columbia, MO 65211, USA (*Author for correspondence: E-mail: pallardys@missouri.edu) Key words: Acer saccharinum, grain yield, photosynthesis, soil water, Zea mays Abstract In order to improve the management of temperate alley cropping, it is important to study the growth and physiological responses of plants arising from competition across the crop-tree interface. Maize ( Zea mays L.) was established between rows of seven-year-old silver maple (Acer saccharinum L.) trees in north- central Missouri, USA with four imposed treatments: (1) an unmodified control with a standard rate of N fertilization (179.2 kg N (as NH 4 NO 3 ) ha –1 ), (2) trenching with root barrier installed, (3) supplemental fertilization treatment (standard N + 89.6 kg ha –1 N), and (4) a combination of trenching with root barrier and supplemental fertilization. Whereas soil N status had little effect on maize physiology and yield at the interface, competition for soil water was substantial in both years. Without a root barrier, soil water content, predawn and midday water potential, and midday net photosynthesis of maize plants adjacent to the tree row were reduced compared with those of plants in the alley center, but no differences across the maize crop were evident in the presence of a barrier. Grain yield of border row maize plants lacking an adjacent barrier was depressed compared with that for maize plants with a root barrier present (8.42 vs. 6.59 Mg ha –1 in 1997; 5.38 vs. 3.91 Mg ha –1 in 1998). However, the barrier did not completely restore yield to that in the alley center, suggesting that reductions in light near the tree row also limited pro- duction. Top ear height showed a similar pattern of response to the presence of a root barrier. Silver maple trees responded to root barrier installation with reduced annual diameter growth and reduced water status on some sample days. Agroforestry Systems 53: 247–259, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. Introduction Alley cropping as an agroforestry practice can increase profitability, diversification, and envi- ronmental protection (Garrett and Buck, 1997). Some of the competitive interactions for resources (water, light, and mineral elements) between the tree component and the crops in alley cropping have been documented in a variety of practices in the tropics (e. g., Cannell et al., 1996; Akonde et al., 1996); however, there is less complete infor- mation available for temperate regions. In maize (Zea mays L.) alley cropping practices in south- eastern Indiana, USA employing black walnut (Juglans nigra L.) or northern red oak (Quercus rubra L.) as the tree crop, root trenching with or without barrier installation slightly increased soil water content and elevated whole-plant water uptake rate and grain yields in maize plants adjacent to the tree row (Gillespie et al., 2000; Jose et al., 2000a). In another study conducted in Ohio, USA, Ssekabembe et al. (1994) reported that black locust (Robinia pseudoacacia L.) hedgerows would deplete the adjacent soil of water after irri- gation, but also that there was no influence of below ground competition from roots on maize grain yield unless soil water content declined because of drought (Ssekabembe and Henderlong, 1991). Hence while there is some evidence of tree root