Biological nitrogen fixation and tuber yield of yam bean in central Mexico

the mexican tuber bearing edible pachyrhizus erosus is widely grown and consumed in central mexico. the aim of this research was to study the relationships between the dynamics of n2 fixation and biomass accumulation and final tuber yield of two phachyrrizus species, p. erosus bred cultivar san juan ec550 and p. ahipa accession 102 introduced from bolivia. the experiment was established on april 2nd, 2005 at the bajio experimental station located near celaya, guanajuato, mexico. plant samples from one m2 were periodically taken from 67 days after planting (dap) onwards, on those, nodule number and mass, as well as plant biomass and leaf area index (lai), were recorded. for tuber yield an area of 3.8 m2 was harvested per plot. p. erosus reached the highest number of nodules at 170 dap, while p. ahipa at 123 dap. p. ahipa had a higher number of nodules than p. erosus, but of smaller size, thus, nodule dry mass was significantly higher (p<0.05) in p. erosus in most sampling dates. fresh tuber yield of p. erosus was significantly (p<0.01) higher than that of p. ahipa and p. ahipa displayed a larger dry tuber weight that was due to a higher concentration of solids and fiber in the tuber. higher tuber yield in p. erosus was related to a longer growth cycle, higher lai and biomass accumulation.