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Forest, Range & Wildland Soils

Enrichment over Time of Organic Carbon and Available Phosphorus in Semiarid Soil

^a Dep. of Biological Sciences, Idaho State Univ., Pocatello, ID 83209-8007
^b Idaho National Lab., P.O. Box 1625, Idaho Falls, ID 83415-2203
^c Currently at: Dep. of Botany, Brandon Univ., Brandon, MB R7A 6A9, Canada

^* Corresponding author (mcgoniglet{at}brandonu.ca)

Rates of accumulation of organic C and associated changes in available P in surface layers are not well characterized, yet are important for development of subsoil exposed by disturbance. Subsoil was placed experimentally in 1993 into field trenches to simulate waste burial by soil caps in the semiarid western USA, planted, and sampled in 2001 to investigate rates of enrichment of surface soil with organic C and available P in relation to plant canopies. Various soil cap designs and irrigation regimens were studied. Under ambient moisture levels, organic C in the surface soil below Wyoming big sagebrush Artemisia tridentata wyomingensis Beetle & Young increased annually at an average rate of 0.5 g kg^–1. We estimate 32 yr would be needed for exposed subsoil to increase to the level of soil surface organic C below sagebrush in undisturbed steppe. Soil surface bicarbonate-available P increased under ambient moisture inputs below sagebrush at a rate of 3.6 µg g^–1 annually and had after 8 yr advanced more than half way from levels in exposed subsoil to those in established steppe. Irrigation stimulated enrichment of organic C and available P, and annual rates of increase across the experiment were 0.9 g kg^–1 for C and 6 µg g^–1 for P. Cap design effects were mostly absent. Enrichment of surface organic C and available P below shrub canopy, compared with intercanopy space, was evident in both the experimental and undisturbed plots. Corresponding increases in C and P were less pronounced under bunchgrass canopies.

Abbreviations: DOE, Department of Energy • EBR-1, Experimental Breeder Reactor-1 • IB, impermeable barrier • INEEL, Idaho National Engineering and Environmental Laboratory • PCBE, Protective Cap Biobarrier Experiment