Abstract
Tree-based intercropping (TBI) systems, consisting of a medium to fast-growing woody species planted in widely-spaced rows with crops cultivated between tree rows, are a potential sink for atmospheric carbon dioxide (CO2). TBI systems contribute to farm income in the long-term by improving soil quality, as indicated by soil carbon (C) storage, generating profits from crop plus tree production and potentially through C credit trading. The objectives of the current study were: (1) to evaluate soil C and nitrogen (N) stocks in soil depth increments in the 0–30 cm layer between tree rows of nine-year old hybrid poplar-hay intercropping systems, to compare these to C and N stocks in adjacent agricultural systems; and (2) to determine how hay yield, litterfall and percent total light transmittance (PTLT) were related to soil C and N stocks between tree rows and in adjacent agricultural systems. The two TBI study sites (St. Edouard and St. Paulin) had a hay intercrop with alternating rows of hybrid poplar clones and hardwoods and included an adjacent agricultural system with no trees (i.e., the control plots). Soil C and N stocks were greater in the 0–5 cm depth increment of the TBI system within 1 m of the hardwood row, to the west of the poplar row, compared to the sampling point 1 m east of poplar at St. Edouard (p = 0.02). However, the agricultural system stored more soil C than the nine-year old TBI system in the 20–30 cm and 0–30 cm depth increments. Accumulation of soil C in the 20–30 cm depth increment could be due to tillage-induced burial of non-harvested crop residues at the bottom of the plow-pan. Soil C and N stocks were similar at all depth increments in TBI and agricultural systems at St. Paulin. Soil C and N stocks were not related to hay yield, litterfall and PTLT at St. Paulin, but hay yield and PTLT were significantly correlated (R = 0.87, p < 0.05, n = 21), with lower hay yield in proximity to trees in the TBI system and similar hay yields in the middle of alleys as in the agricultural system. Nine years of TBI practices did not produce significant gains in soil C and N stocks in the 0–30 cm layer, indicating that the total C budget, including C sequestered in trees and unharvested components (litterfall and roots), must be assessed to determine the long-term profitability of TBI systems in Canada.
Highlights
Canadian agricultural operations contribute approximately 8% of national greenhouse gas (GHG)emissions each year, mainly from fertilizers, enteric fermentation and manure management [1]
Tree-based intercropping (TBI) systems, which combine widely-spaced tree rows of a medium to fast-growing woody species, such as poplar (Populus spp.), were one of the technologies prioritized for investigation by Agricultural Greenhouse Gases Program (AAGGP), because trees can be a sink for atmospheric carbon dioxide (CO2), as well as a long-term source of farm income [2,3]
Soil C and N stocks were greater in the 0–5-cm depth increment of the TBI system within 1 m of the hardwood row, west of the poplar row, than at the sampling point 1 m east of poplar at St
Summary
Canadian agricultural operations contribute approximately 8% of national greenhouse gas (GHG)emissions each year, mainly from fertilizers, enteric fermentation and manure management [1]. With improved management of cropland and forests, it is possible to mitigate GHG emissions through carbon (C) sequestration while enhancing soil and crop productivity. Agroforestry technologies, including TBI systems, provide opportunities for C sequestration, and other environmental and financial benefits [4]. Canadian farmers require evidence of the economic benefits of TBI systems to consider adopting this technology. Studies on the productivity (yield of trees and crops) and the economic profitability of Canadian TBI systems have considered tree species, tree planting density and height and crown diameter, crop species, manure and fertilizer application rates and timing, soil type and the age of a system [5,6]. Tree species assessed for Canadian TBI systems included hybrid poplars and high-valued hardwood species, such as Juglans nigra L., Quercus rubra L., Prunus serotina Ehrh., Fraxinus americana L. and Fraxinus pennsylvanica Marsh. Crops grown in Canadian TBI systems included grain crops, like corn (Zea mays L.) and cereals, oilseeds, such as soybean (Glycine max (L.)
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