Reduced soil nutrient leaching following the establishment of tree-based intercropping systems in eastern Canada

Abstract

Tree-based intercropping (TBI) systems, combining agricultural alley crops with rows of hardwood trees, are largely absent in Canada. We tested the hypothesis that the roots of 5-8 years old hybrid poplars, growing in two TBI systems in southern Québec, would play a ''safety-net'' role of capturing nutrients leaching below the rooting zone of alley crops. TBI research plots at each site were trenched to a depth of 1 m on each side of an alley. Control plots were left with tree roots intact. In each treatment at each site, leachate at 70 cm soil depth was repeatedly sampled over two growing seasons using porous cup tension lysimeters, and analyzed for nutrient concentrations. Daily water percolation rates were estimated with the forest hydrology model ForHyM. Average nutrient concentrations for all days between consecutive sampling dates were multiplied by water percolation rates, yielding daily nutrient leaching loss estimates for each sampling step. We estimated that tree roots in the TBI system established on clay loam soil decreased subsoil NO 3 -leaching by 227 kg N ha -1 and 30 kg N ha -1 over two consecutive years, and decreased dissolved organic N (DON) leaching by 156 kg N ha -1 year -1 in the second year of the study. NH 4 ? leaching losses at the same site were higher when roots were present, but were 1-2 orders of magnitude lower than NO 3 -or DON leaching. At the sandy textured site, the safety net role of poplar roots with respect to N leaching was not as effective, perhaps because N leaching rates exceeded root N uptake by a wider margin than at the clay loam site. At the sandy textured site, significant and substantial reductions of sodium leaching were observed where tree roots were present. At both sites, tree roots reduced DON concentrations and the ratio of DON to inorganic N, perhaps by promoting microbial acquisition of DON through rhizodeposition. This study demonstrated a potential safety-net role by poplar roots in 5-8 yearold TBI systems in cold temperate regions.

Plant: soil interactions in temperate multi-cropping production systems

“…Such effects were tested in two different soil types, a sandy soil and a clay loam (Bergeron et al 2011). The hypothesis was found to be true in two separate studies, where N losses could be significantly reduced in a clay loam (Bergeron et al 2011;Wang et al 2011), but not in a sandy soil where leaching rates exceeded N uptake; although sodium leaching was reduced where tree roots were present (Bergeron et al 2011). Apart from a deeper root system, reduced N inputs and reduced lateral surface flow reduce N losses in agroforestry systems (Wang et al 2011).…”

Review: Redesigning Canadian prairie cropping systems for profitability, sustainability, and resilience

“…Benefits include increased soil organic C and greater C sequestration (Thevathasan and Gordon 2004;Peichl et al 2006;Oelbermann and Voroney 2011); reduced leaching of water contaminants including nitrate and E. coli (Thevathasan and Gordon 2004;Dougherty et al 2009;Bergeron et al 2011); reduced N 2 O emissions (Beaudette et al 2010); enhancement, diversification and stabilization of arbuscular mycorrhizal fungi populations (Chifflot et al 2009;Lacombe et al 2009;Bainard et al 2012); and augmentation of earthworm, bird and insect populations (Thevathasan and Gordon 2004). Some of these effects have been observed in relatively young agroforestry systems, only 5 to 8 yr old.…”

Branching out: Agroforestry as a climate change mitigation and adaptation tool for agriculture

“…Additionally, emissions may be further reduced through tree uptake of excess N (Allen et al 2004;Bergeron et al 2011). Referred to as the safety-net feature of agroforestry, tree roots have the potential to take up excess N in time and in space that would otherwise be available for N 2 O emissions on-or off-site.…”