Assessment of nitrogen fixing trees for soil amelioration in degraded agricultural lands

Abstract:

According to Environment and Climate Change Canada, roughly 7.4 million hectares of former cropland in the Prairie provinces are classified as degraded, with organic carbon levels too low to support profitable grain production without heavy fertiliser input. Nitrogen fixing trees (NFTs) offer a biological path to rebuild these soils, yet species performance data under Saskatchewan’s cold semi-arid climate are scarce. This research compared three NFT species—red alder (Alnus rubra), black locust (Robinia pseudoacacia), and Russian olive (Elaeagnus angustifolia)—planted on degraded cropland at Prairie Agricultural University, Saskatoon, from May 2018 to October 2023. Soil organic carbon, total nitrogen, bulk density, pH, microbial biomass carbon, and earthworm density were measured under each species and compared with an unplanted degraded control and an adjacent undisturbed grassland reference. After five years, A. rubra raised soil OC from 1.12% to 2.31% and total N from 0.084% to 0.168%—recovering approximately 86% and 87% of the undisturbed reference values, respectively. R. pseudoacacia performed nearly as well. Microbial biomass carbon doubled under both species. These results confirm that NFT plantations can substantially restore fertility in degraded Prairie soils within a five-year timeframe.