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

a mineral soil (Farnham and Finney, 1965), which provides a high potential for diffusion and storage of O2 Organic soils in the Everglades Agricultural Area (EAA) of southfor microbial utilization in the organic soil. Neller (1943) ern Florida, USA, are subsiding due primarily to oxidation by aerobic microorganisms. Since there are large C losses in drained Histosols, reported that soil O2 ranges between 15 and 17% at an it is not certain if minimum tillage will significantly reduce soil C 81-cm depth in Histosols during January and February. losses below the background levels. The objective of this experiment Water table levels were at 91 cm. When soil air contains was to determine if increasing the surface soil disturbance through 0.1% O2, microbial activity is only 20% less than microtillage significantly increases the soil organic matter oxidation potenbial activity at a soil air concentration of 21% O2 (Broadtial (OP) in Histosols. Tillage treatments from lowest to highest soil bent (1960). Since O2 concentrations in drained Histodisturbance consisted of (i) no-till; (ii) tine implement cultivation, one sols may not be low enough to inhibit microbial activity, pass; (iii) tine implement cultivation, two passes; (iv) heavy harrow it is not certain if reducing soil tillage will have an impact disking; and (v) switchplowing. Treatments were conducted on two on reducing soil subsidence. fields (bare fallow and plant residue covered). Surface soil samples In mineral soil, short term (within 24 h) gaseous C (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 losses as CO2 can occur when surface soils are disturbed. OP (14C oxidation of benzoate) and soil microbial CO2 respiration Reicosky and Lindstrom (1995) used a large, portable (RESP) averaged across the 42-d period compared with the other photosynthesis chamber and reported substantial shorttreatments. No-till tended to have the lowest OP and RESP. Other term gaseous losses of CO2 immediately after tillage to tillage treatment effects were intermediate depending on field type. partially explain long-term CO2 losses from tilled minCorrelation analyses indicated that greater quantities of extractable eral soils. The moldboard plow was the most intensive N (EXN) were related to increased OP in both fields, while higher tillage implement and caused more CO2 loss than lessquantities of extractable C (EXC) were related to increased RESP disruptive tillage methods. No-till or no soil disturbance in both fields. This research demonstrates that minimum tillage can be lost the least amount of CO2, suggesting minimal enviused on Histosols to reduce C loss and thereby reduce soil subsidence. ronmental impact with these systems. Moldboard plowing was reported to have two major effects: to loosen and invert soil and allow a rapid CO2 loss and oxygen M of the soils in the EAA are classified as entry, and to incorporate and mix residues to enhance Histosols, many of which have organic matter microbial attack (Reicosky and Lindstrom, 1995). Simicontents 85% (Snyder et al., 1978). To grow agricullar results for less intensive tillage were found by Ellert tural crops (mostly sugarcane, Saccharum spp.), these and Janzen (1999) and Rochette and Angers (1999). soils must be drained. Drainage promotes organic matter This interaction of soil and residue mixing enhances decomposition by heterotrophic, aerobic microorganisms aerobic microbial decomposition of the incorporated (Tate, 1980). These microbes efficiently utilize certain residue to cause a net decrease in soil organic C (Reifractions of the soil organic matter for their cellular growth cosky et al., 1995). (biomass) and respiration (loss of CO2), resulting in soil Short-term soil C losses in Histosols could be different subsidence. Recent data from soil marker posts in the than in a mineral soil. An organic soil during the winter EAA have indicated that such oxidation from drainage may contain 4 to 6% CO2 (Neller, 1943). The impact results in subsidence at an average of 1.4 cm yr 1 (Shih of tilling Histosols on increasing short-term gaseous C et al., 1998). Most of these cultivated soils now have 30 losses (CO2) compared with undisturbed soil that is alto 150 cm of soil remaining on top of limestone bedrock ready losing gaseous C by diffusion through the large (Ingebritsen et al., 1999). soil pore spaces has not been investigated. One way to increase soil C in mineral soils ( 5% orSoil organic matter formation and development is ganic matter) is through minimum tillage practices, but highly dependent on management decisions that influorganic matter decomposition in Histosols due to tillage ence intensity of tillage and the amount and placement may not be the same as in mineral soils. At 0.5 MPa of residue. Minimum tillage methods that leave most of water potential, a highly decomposed (saprist) organic the crop residue on the surface with limited soil contact soil may have 50% more pore volume compared with preserves organic matter (Reicosky, 1997). Methods to maintain soil C levels and aggressive tillage are not D.R. Morris, USDA-ARS, Sugarcane Field Station, 12990 U.S. Hwy. compatible. Concern for soil conservation requires new 441, Canal Point, FL 33438; R.A. Gilbert, Everglades Research and knowledge to minimize agriculture’s impact on the enviEducation Center, Univ. of Florida, 3200 East Palm Beach Road, Belle Glade, FL 33430; D.C. Reicosky and R.W. Gesch, USDA-ARS, North Central Soil Conservation Research Laboratory, 803 Iowa Ave., Abbreviations: EAA, Everglades Agricultural Area; EXC, extractMorris, MN 56267. Received 21 Feb. 2003. *Corresponding author able organic carbon (mg C g 1 soil); EXN, extractable total nitrogen ([email protected]). (mg N kg 1 soil); MBC, microbial biomass carbon (mg C g 1 soil); MBN, microbial biomass nitrogen (mg N kg 1 soil); OP, organic matter Published in Soil Sci. Soc. Am. J. 68:817–826 (2004).  Soil Science Society of America oxidation potential (nmol CO2 kg 1 soil h 1); RESP, microbial respiration ( mol CO2 m 2 s 1). 677 S. Segoe Rd., Madison, WI 53711 USA