Quantifying nitrogen fixation of agroforestry shrub species by the 15N natural abundance and dilution techniques under the greenhouse condition

Abstract

The land use systems of the province of Saskatchewan has agroforestry trees such as sea buckthorn (Hippophae rhamnoides L.), caragana (Caragana arborescens Lam.) and buffaloberry (Shepherdia argentea Nutt.) as important components. They have been employed within the systems to perform functions such as ameliorating soil moisture, light and temperature through wind speed reduction and trapping snow. However, their N2-fixation capability has not been determined. Therefore in a greenhouse experiment conducted at the Agriculture greenhouse at the University of Saskatchewan, Saskatoon, SK, Canada from January 2012 ̶ April 2012, the N2-fixation rates in the test species were evaluated to know their contributions to on-farm nitrogen management. After 120 days after planting, the shoot N derived from the atmosphere (%Ndfa) in the species ranged from 20-59%, 21-70% and 3-15% for caragana, sea buckthorn and buffaloberry, respectively. Also the whole plant %Ndfa in the species ranged from 18-47%, 49-54% and 38-41% for caragana, sea buckthorn and buffaloberry, respectively by both estimation methods. The contributions of the species to soil N were 73-91, 25-261 and 15-110 kg N ha-1 for caragana, sea buckthorn and buffaloberry, respectively by both methods. The amount was sufficient to meet the N requirements of most of the forage and grass species in the province which would progressively reduce the overreliance on synthetic fertilizers and minimize the risk of agrarian-derived soil and water pollution from inorganic nutrient sources.