Oxidation Potentials of Soil Organic Matter in Histosols under Different Tillage Methods

Organic soils in the Everglades Agricultural Area (EAA) of southern Florida, USA, are subsiding due primarily to oxidation by aerobic microorganisms. Since there are large C losses in drained Histosols, it is not certain if minimum tillage will significantly reduce soil C losses below the background levels. The objective of this experiment was to determine if increasing the surface soil disturbance through tillage significantly increases the soil organic matter oxidation potential (OP) in Histosols. Tiliage treatments from lowest to highest soil disturbance consisted of (i) no-till; (ii) tine implement cultivation, one pass; (iii) tine implement cultivation, two passes; (iv) heavy harrow disking; and (v) switchplowing. Treatments were conducted on two fields (bare fallow and plant residue covered). Surface soil samples (0-15 cm) and all microbial measurements were taken on 0, 1, 4, 13, 28, and 42 d after tillage. The switchplow treatment had the greatest OP ( 14 C oxidation of benzoate) and soil microbial CO 2 respiration (RESP) averaged across the 42-d period compared with the other treatments. No-till tended to have the lowest OP and RESP. Other tillage treatment effects were intermediate depending on field type. Correlation analyses indicated that greater quantities of extractable N (EXN) were related to increased OP in both fields, while higher quantities of extractable C (EXC) were related to increased RESP in both fields, This research demonstrates that minimum tillage can be used on Histosols to reduce C loss and thereby reduce soil subsidence.