Nitrogen Mineralization and Nitrification in Mineral Soils of Pinyon‐Juniper Ecosystems

The mineral soils in the interspaces and under canopy of three pinyon ( Pinus edulis Engelm.)‐juniper [ Juniperus osteosperma (Torr.) Little] woodland communities were analyzed to determine their nutrient status and potential N mineralization and nitrification. A >400‐yr‐old ungrazed, a 300‐yr‐old grazed, and a 35‐yr‐old burned and grazed site were represented. Significant differences were noted in soil pH, texture, bulk density, total N, organic C, and NaHCO 3 extractable P between the canopies and the respective interspaces of the mature sites. No differences were noted between the canopy soils of the ungrazed and grazed nature sites. The 35‐yr‐old canopy soils showed significantly less total N and organic C than the mature sites. Interspaces exhibited relatively few differences between sites. Both canopy and interspace soils exhibited linear rates of mineralization and nitrification over the 60‐d incubation. On all sampling dates there were significant differences in mineralization and nitrification rates between the canopy and interspace soils. The proportion of total N mineralized was highest for the most disturbed (burned, grazed) canopy soils and lowest for the least disturbed (ungrazed). The results obtained indicate that nitrification is not inhibited in mature pinyon‐juniper woodlands, but suggest that the rate of N mineralization and nitrification may be enhanced by disturbance.