Soil constraints with distinctive coralloid nodulation and nitrogen fixation of “Mecca” alfalfa

Abstract The evolutionary origin center of alfalfa within the extensive subhumid Transcaucasia has been a valuable source of Medicago spp. for development of improved alfalfa cultivars. Centuries of natural outcrossing within the perennial, allogamous Medicago species complex resulted in numerous polymorphic plants with desirable genetic characteristics adaptive to harsh climatic and soil environs. Characteristic large coralioid noduiation of M. media (M. falcata X M. sativa) provides means for improved symbiotic nitrogen fixation. The compositae, “Mecca”, (M. sativa spp. falcata Arcemgeli) was selected for desirable noduiation and nitrogen fixation attributes. The objective of this study was to determine soil fertility factors governing its nodulation, nodule histology and cytosol enzymology essential for symbiotic nitrogen fixation. Adequate available soil P was a first limiting factor. Growth, noduiation and nitrogen fixation resulted in significant response to increases in K and Ca only with P combina...