Arbuscular Mycorrhizae and Fertilizer Phosphorus Effects On Symbiotic Nitrogen Fixation and Phosphorus Availability In Pulse Crops.

Pulse crops have a high requirement for phosphorus (P) due to their nitrogen (N) fixation symbiosis. Soil P deficiencies and their effect on pulse crop growth may be particularly important in the northern Great Plains, where a high percentage of soils test low to medium for available P as a result of high soil calcium levels. A greenhouse study was conducted to evaluate the effect of arbuscular mycorrhizal fungi (AMF) inoculum and P fertilization on aboveground biomass, N and P uptake, and N fixation of pea and lentil, two common pulse crops in this region. Plants were grown in an unsterilized, low P soil and treated with P fertilizer (0, 4, or 8 mg P kg^-1) with or without commercial AMF inoculum. Aboveground biomass was sampled at flower, and N fixation was estimated with the ¹⁵N natural abundance method, using non-nodulating pea as a reference crop. Phosphorus fertilization increased biomass yield and tissue N and P uptake for both crops. Additionally, P fertilization increased N fixed by pea, yet there was no additional benefit in N fixed from the higher P fertilizer rate. Across all P rates, AMF inoculum had little effect on biomass, N or P uptake, or N fixed; however, when P levels were moderate, AMF inoculation resulted in an increase in biomass and plant N uptake compared to non-inoculated treatments. Future work will be required to further investigate the interaction between AMF inoculation and P level on pulse production.