Nutrient dynamics of rangeland burns in Southeastern Arizona

Burning of vegetation generally increases surface runoff and erosion and po tentially can change the nutrient dynamics of an ecosystem with loss of nut rients. Nitrogen, phosphorus, and potassium nutrient status of soil and abo veground biomass were determined before fall and spring burns and 1 year la ter at 2 different soil and vegetation type locations in southeastern Arizo na. The evaluations were repeated in subsequent years to evaluate a year ef fect. Potential nutrient loss in surface runoff and sediment was assessed w ith rainfall simulations conducted immediately after prescribed burns and a fter a second burn one year later. Nutrient loss in the runoff water and se diment from burned areas was compared to paired unburned. The soil containe d >98% of the total nutrient and was not significantly influenced by the bu rn treatment. The nutrient concentrations in the regrowth biomass were gene rally greater. Immediately after the first burn, nutrient loss in surface r unoff and sediment was not affected by the burn treatment, but one location was greater than the other. After 1 year and a second burn, nutrient losse s on the burn treatment were significantly greater than the unburned treatm ent and similar between locations. The nutrient loss in surface runoff was primarily associated with the sediment and influenced by an interaction bet ween biomass and soil. The nutrient loss in runoff and sediment was small c ompared to the nutrient in the aboveground biomass and insignificant compar ed to the soil nutrient. The implication is that increased surface nutrient loss from burning could take place for many years before a significant amo unt of nutrient would be lost from the large soil pool and change the nutri ent status of the ecosystem. Year and season were also important factors in fluencing nutrients in the soil, biomass, and in runoff and sediment losses , irrespective of a burn treatment effect.