Nutrient dynamics of rangeland burns in southeastern Arizona

Abstract

Burning of vegetation generally increases surface runoff and erosion and potentially can change the nutrient dynamics of an ecosystem with loss of nutrients. Nitrogen, phosphorus, and potassium nutrient status of soil and aboveground biomass were determined before fall and spring burns and 1 year later at 2 different soil and vegetation type locations in southeastern Arizona. The evaluations were repeated in subsequent years to evaluate a year effect. Potential nutrient loss in surface runoff and sediment was assessed with rainfall simulations conducted immediately after prescribed burns and after a second burn one year later. Nutrient loss in the runoff water and sediment from burned areas was compared to paired unburned. The soil contained >98% of the total nutrient and was not significantly influenced by the burn treatment. The nutrient concentrations in the regrowth biomass were generally greater. Immediately after the first burn, nutrient loss in surface runoff 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 losses on the burn treatment were significantly greater than the unburned treatment and similar between locations. The nutrient loss in surface runoff was primarily associated with the sediment and influenced by an interaction between biomass and soil. The nutrient loss in runoff and sediment was small compared to the nutrient in the aboveground biomass and insignificant compared to the soil nutrient. The implication is that increased surface nutrient loss from burning could take place for many years before a significant amount of nutrient would be lost from the large soil pool and change the nutrient status of the ecosystem. Year and season were also important factors influencing nutrients in the soil, biomass, and in runoff and sediment losses, irrespective of a burn treatment effect.