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Soil Nutrient Distribution Under and Adjacent to Singleleaf Pinyon Crowns¹

ABSTRACT

Soil nutrient concentrations were examined by horizon and distance from the tree stem of singleleaf pinyon (Pinus monophylla Torr. & Frem.). Documenting tree impact on the soil system provided insights into observed understory distribution patterns and variations in understory yield among soil microsites reported previously. Nutrient concentrations were greater under the crowns of trees than in soils between trees. Cluster analysis showed a maximum of 80% similarity in the distribution among exchangeable K⁺, Na⁺, Ca²⁺, Mg²⁺; extractable Zn²⁺, Cu²⁺, Mn²⁺, Fe³⁺, SO^2-₄, PO^3-₄; water soluble C, mineralizable-N, pH, total soluble salts, and HCO^-₃ in relation to soil depth and distance from the tree. Soil nutrients and other measured parameters segregated into two main clusters based on distribution patterns. Extractable PO^3-₄, Fe³⁺, Mn²⁺, Cu²⁺, Zn²⁺, mineralizable-N, water soluble C, and HCO^-₃ were found in highest concentrations at the soil surface. Exchangeable Ca²⁺, Mg²⁺, Na⁺, K⁺, total soluble salts, and pH had highest values in subsurface horizons. Phosphate, K⁺, pH, total soluble salts, and Na⁺ significantly increased from the interspace soils to soils under the tree canopy. Phosphate, mineralizable-N, Zn²⁺, Fe³⁺, and HCO^-₃ declined rapidly in concentration from surface to subsurface horizons under the tree crown. Small root density was directly correlated to concentrations of mineralizable-N, Zn²⁺, Mn²⁺, Cu²⁺, and Fe³⁺. Nutrient accumulation in conjunction with soil moisture, light, and allelopathic effects is speculated to confer a competitive advantage to the tree species at the expense of the associated understory.

¹ Contribution of the Intermountain Research Station, USDA, Forest Service, in cooperation with Oregon State Univ. and the Univ. of Nevada-Reno.

² Project Leader, USDA-USFS, Reno NV 89512; Associate Professor of Range, Rangeland Resources Dep., Oregon State Univ., Corvallis; and Assistant Professor of Soils, Plant, Soil, and Water Dep., Univ. of Nevada-Reno.

Received for publication October 18, 1984.