Crop yield and tree-leaf production in three planting patterns of temperate-zone alley cropping in Oregon, USA

The objective of this study was to determine crop and tree productivity in several alley cropping planting patterns. The four- year study was conducte d in western Oregon, United States and involved irrigated sweet corn (Zea m ays) intercropped between hedgerows of red alder (Alnus rubra) and black lo cust (Robina pseudoacacia). Three alley cropping planting patterns with var iable plant populations and tree-crop proximity were tested with each tree species in a randomized block design. Space available to trees and crops de termined yield of both plant components. High crop yield coincided with low pruning yield, and vice versa. Compared to monocropping, yield reductions in traditional alley cropping planting patterns with widely spaced, double tree rows ranged from 5% to 15%. A. rubra and R. pseudoacacia coppiced read ily and produced 0.9 to 4.7 tons of dry matter pruning biomass per growing season, depending on planting pattern and year. A. rubra yield continually increased during the trial, while the ability of R. pseudoacacia to produce green manure after frequent coppicing appeared to weaken. After four years , soil organic matter was 4 to 7% higher in the topsoil of an alley croppin g system compared to a monocropping system. However, continuous growing of sweet corn resulted in decreased soil organic matter levels in both croppin g systems compared to original levels. Crop yield reductions and the need f or additional management inputs constrain the implementation of alley cropp ing in temperate climates. Only if benefits other than minor soil fertility improvements are realized is alley cropping a feasible alternative in temp erate climate regions.