Influence of tillage and plant residue management on respiration of a Florida Everglades Histosol

Subsidence of drained, high organic matter Histosols in the Everglades Agricultural Area (EAA) is a concern for the sustainability of crop production in southern Florida. Histosol subsidence is primarily due to oxidation of organic matter by aerobic microorganisms, but far less is known about the influence of agricultural practices. The use of shallow tillage, as opposed to deep tillage, combined with proper plant residue management, may help to reduce the present rate of subsidence and soil CO2 emissions. The present study was conducted on a Lauderhill soil (euic, hyperthermic, Lithic Haplosaprist) previously cropped in sugarcane (Saccharum spp.). The objectives were to (1) determine the effects of tillage depth on short-term CO2 losses in a herbicide-killed weedy residue covered field and another field kept fallow without residue cover, and (2) compare soil respiration measurements made with two different dynamic closed-system portable chamber techniques. Four tillage practices common to the EAA were used to produce soil disturbance ranging in depth from approximately 20 to 300 mm. These practices included switch plowing, disk harrowing, and single and multiple tine cultivation. Twenty-four hours after tillage, cumulative CO2 loss from the deepest tillage treatment (switch plow; 300 mm deep) was as much as 33 times greater than that from the no-till (control) treatment. Cumulative CO2 loss following intermediate tillage (disk harrow; 78-145 mm deep) was as much as 2.3-fold greater than the no-till treatment, but shallower tillage (tine cultivation; 20-41 mm deep) was generally not different. Short-term tillage-induced CO2 loss was primarily related to soil moisture content and soil porosity. Soil respiration measurements made with the two chamber techniques agreed well with each other except for the deepest tillage treatment, where the larger chamber measured CO2 flux that was approximately 10 times greater than for the smaller chamber. Results indicate that minimum or no-tillage may reduce short-term tillage-induced CO2 emissions on organic soils, thus minimizing soil subsidence.