Lentil nitrogen fixation response to fertilizer and inoculant in the northern Great Plains

Abstract

Lentil (Lens culinaris Medikus) production in the semiarid northern Great Plains of the United States has increased dramatically over the past two decades. Lentil in rotation provides agroecosystem benefits of more efficient water use, pest cycle disruption, and biological nitrogen (N) fixation. Increasing N fixation could alleviate soil acidification and groundwater impairment, decrease N fertilizer costs, and increase lentil seed yield. Despite widespread farmer adoption of lentil in the region, little is known about the benefits of fertilizer or inoculant type on N fixation. The aim of this study was to determine how nutrients (potassium (K), sulfur (S), and foliar-applied micronutrients) and rhizobial inoculant types (seed-coat powder and granular) influence N fixation of lentil. The study was conducted at two field sites in Montana from 2019 to 2021. Fixed N amounts were calculated using both an N difference approach and 15N natural abundance method. N fixation was highly responsive to climatic conditions and soil characteristics. The amount of N fixed did not respond to K fertilization, likely because soil test K levels were sufficient. In a moderately dry year at a site with low soil sulfate-S, fertilizer application of 5.6 kg S ha−1 increased N fixed by 40%. Inoculated lentil fixed more N than uninoculated lentil in two site-years, but there were no differences in N fixed between inoculant types. Inoculation response was not related to field cropping histories with legumes. The study shows that S fertilization and rhizobial inoculation have potential to increase lentil N fixation amounts in the northern Great Plains.