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SOIL BIOLOGY & BIOCHEMSITRY

Oxygen Effects on Carbon, Polyphenols, and Nitrogen Mineralization Potential in Soil

USDA-ARS Integrated Farming and Natural Resour. Res. Unit, 2413 E. Hwy. 83, Weslaco, TX 78596-8344

^* Corresponding author (lzibilske{at}weslaco.ars.usda.gov).

Crop residue decomposition is affected by environmental factors and residue biochemical properties. These factors may contribute to management protocols that enhance soil organic matter accumulation in hot climates, which have characteristically high oxidation rates. The purpose of this experiment was to determine O₂ effects on soil polyphenol oxidase (PPO), peroxidase (PO), water-soluble polyphenolics (WEP), arginine ammonification (ARG), and water-extractable C (WEC). Cowpea (Vigna unguiculata L.) and sorghum [Sorghum bicolor (L.) Moench] residues in soil were incubated with headspace O₂ concentrations of 0.5, 10, or 21% (ambient) for up to 110 d. The PPO and PO were negatively related to WEP and WEC, mostly at 10 and 21% (P < 0.05). The WEP and WEC were significantly (P < 0.05) and negatively related to O₂ concentration. The WEP ranged from 0.5 mg kg^–1 soil at 0.5% O₂ to near 0 at 10 and 21% O₂. The WEC ranged from about 350 mg C kg^–1 soil at 0.5% O₂ to <25 mg C kg^–1 soil at 10 and 21% O₂. The ARG rates were also negatively related to O₂ level with cowpea, but not as strongly as with sorghum. The ARG and WEC were negatively correlated. The ARG ranged from 6 mg N kg^–1 soil at 0.5% O₂ to <0.5 mg N kg^–1 soil at 21% O₂ through 110 d. The WEC and WEP varied independently during incubation. Our results suggest that soil organic C accumulation may be stimulated by (i) using cover crops with higher polyphenolic content, which could slow C mineralization, and (ii) restricting soil O₂ availability via reduced tillage.