Effects of Rhizobium Strains and DAP Fertilization on Nodulation and Growth Parameters in Grass Pea (Lathyrus sativus L.)

Abstract

This study evaluated the effects of Rhizobium strains isolated from different leguminous forage crops and varying diammonium phosphate (DAP) doses on nodulation and growth traits of grass pea (Lathyrus sativus L.). Experiment was conducted under controlled conditions using the cultivar Gürbüz-2001 in a randomized plot design with three replications. Seeds were inoculated with Rhizobium strains derived from alfalfa (A), vetch (V), soybean (S), and field pea (F), along with a non-inoculated control. DAP fertilizer was applied at 0, 4, and 10 kg da⁻¹. At 50% flowering, nodulation parameters, growth parameters, and root and shoot biomass were recorded. Nodule number per plant ranged from 1.33 to 59.66, and nodule weight varied between 0.003 and 0.282 g. The highest plant height (88.88 cm) was obtained from the vetch-derived strain with 10 kg da⁻¹ DAP, while the longest roots (23.44 cm) were observed in the non-inoculated control group at the same dose. The field pea-derived strain combined with 10 kg da⁻¹ DAP produced the highest branch number and biomass values, whereas soybean-derived strains showed consistently low nodulation. Correlation analysis revealed strong positive relationships between nodulation traits and shoot biomass. PCA indicated that nodulation and biomass-related traits were the main contributors to total variation, clearly separating inoculation-fertilizer combinations. Overall, the results demonstrate that Rhizobium strain origin and DAP dose significantly influence nodulation efficiency and growth in grass pea, highlighting the importance of strain-specific inoculation combined with appropriate phosphorus management.