The Impact of Molybdenum‐Enriched Irrigation Water on Agricultural Soils Near Brighton, Colorado

The Mo concentration in water, soils, and alfalfa (Medicago sativa) was monitored for 1 growing season. The concentration of Mo in irrigation water in this area ranged from 27 to 213 ppB. A significant increase of Mo concentration in alfalfa and available soil Mo was observed at 1 site irrigated with water containing 213 ppB Mo, and the Mo concentration in the alfalfa increased during the growing season from 4.3 to 7.2 ppM which is below the 10 ppM level considered toxic to livestock. Plant Mo was highly correlated (r = 0.94) with resin-extractable Mo in a greenhouse experiment using soils from 3 of the field sites. Field results were less satisfactory (r = 0.51), partially due to limited indigenous levels of Mo in the soils. A simulation model was used to assess the potential hazards of irrigating with water containing from 0 to 600 ppB Mo. The model indicates that a level of 400 ppB Mo in irrigation water applied to soil with 40 percent retention of Mo in an available form would result in toxic levels of Mo in plants within 3 yr. The impact of Mo on the Brighton area during 1 growing season was minimal inmore » relation to uptake of Mo by plants.« less