Light availability, weed cover and crop yields in second generation of temperate tree-based intercropping systems

Abstract

An experimental network representing a new generation of widely spaced tree-based intercropping (TBI) systems, which are more adapted to large-scale annual crops than narrowly spaced ones, was established in southern Quebec. Over two consecutive growing seasons (2016-2017), we determined effects of these TBI systems on percent total light transmittance (PTLT), soil moisture, weed cover and crop yield. We studied six experimental sites that included different annual crops (maize, soybean, wheat, black bean) or forage crops. Age of TBI systems varied between 3 and 22 years, and spacing between tree rows ranged from 25 to 90 m. Variables were measured in control (non-tree) farm plots and in TBI alleys at four distances from the row of trees. Spatial variation in crop yield in TBI alleys was crop-specific. Yield reductions for maize, soybean and black bean were observed at the closest distance to the tree row (½H, where H = tree height). These yield reductions were associated with a decrease in PTLT or an increase in weed cover. Soil moisture changed little with distance from the row of trees and no significant relationship between crop yield and soil moisture was measured, which suggested that competition for water between trees and crops was marginal. Our results indicate that forage crops are less sensitive than annual crops to changes in environmental conditions that were incurred by TBI systems. Overall, the second-generation TBI systems under study exerted neutral net effects on integrated crop yields (i.e., all distances combined), except for black bean in 2016. Second-generation TBI agricultural yields appear to be more promising than those obtained in first-generation TBI systems.