Pools of organic carbon in the solum (A and B horizons) were 1.5-fold greater beneath the oak canopy as compared to the open grassland. The majority of this increase is due to accumulation of organic matter in the A and AB horizons; however, concentrations were significantly greater throughout the entire profile. A large portion of this increase is due to above-ground litterfall which returns 9100 kg/ha/yr of organic matter or 4500 kg/ha/yr of organic carbon to the soil surface. While not quantified in this study, below-ground components are also believed to contribute appreciable amounts of detrital material to thesoil organic matter pool.
Similar to organic matter, pools of nitrogen and phosphorus in the solum were 1.5-fold greater beneath the oak canopy. Nutrient pools were increased in all horizons, but most strongly in the A and AB horizons. The strong similarity between the organic matter pool and the nitrogen and phosphorus pools suggests that the primary source of these nutrients is from the soil organic matter. Annual returns of nitrogen and phosphorus in above-ground litterfall were 84 and 8 kg/ha/yr for nitrogen and phosphorus, respectively. Among the pools of exchangeable cations, potassium and calcium showed significantly higher nutrient pools beneath the oak canopy. As shown earlier, calcium and potassium are the two base cations cycled in the greatest quantities by blue oak. The increased pools of calcium and potassium are found largely in the A horizons where increased organic matter concentrations provide greater CEC to retain nutrient cations.