Effect of prescribed fire on nitrogen and phosphorus in Arizona chaparral soil‐plant systems

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Abstract
To improve understanding of how prescribed fire affects N and P in chaparral soil‐plant systems, a study was conducted to compare the distribution and availability of N and P in soil‐plant systems before and after a burn. Distribution of N and P in biomass components, litter, and soil was measured for five Cercocarpus betuloides and eight Quercus turbinella soil‐plant systems and compared to the distribution of biomass, N, and P in the same 13 soil‐plant systems following a prescribed burn. Individuals of C. betuloides accumulated more dry matter, N, and P in their shoots, litter, and upper 2 cm of mineral soil than those of Q. turbinella. Burning resulted in a loss of dry matter and N and a redistribution of N and P in soil‐plant systems of both species. Nutrient availability of soil collected under the 13 shrubs before and after the burn was assessed using a pot culture technique with barley as a test plant. The availability of P was greater in postburn soils than in preburn soils, while availability of N was similar in preburn and postburn soils. The effect of fire on N mineralization in soils collected under the 13 shrubs was assessed with an incubation study of soil collected before and after the burn from the 0‐ to 2‐cm and 2‐cm to 10‐cm soil layers. Although NH+ 4 production increased and NO3 ‐production decreased with fire, cumulative N mineralized did not differ between preburn and postburn soils. Fire resulted in a loss of N and a redistribution of N and P to system components that are highly susceptible to erosion. While mechanisms for replenishment of N are known for chaparral systems, P is replenished very slowly, primarily by weathering of parent material. Hence, long‐term productivity of these systems may depend on how P is managed.

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