ORGANIC SOIL OXIDATION POTENTIAL DUE TO PERIODIC FLOOD AND DRAINAGE DEPTH UNDER SUGARCANE

Organic soils subside when they are drained continuously, primarily because of aerobic microbial activity. The purpose of this study was to determine the organic matter oxidation potential of an organic soil that is the result of intermittent flooding and draining in combination with different water table depths, some suitable for the culture of sugarcane. A 2-year outdoor study was conducted with lysimeters filled with a Pahokee muck soil (Euic, hyperthermic Lithic Haplosaprist) and planted to sugarcane (interspecific hybrids of Saccharumspp.). Treatments were flooding for 7 days, followed by drainage for 14 days to 16-, 33-, or 50cm water table levels below the soil surface. A continuous drain treatment to a 50-cm water table was included as a control. Soils were sampled during four flood/drain cycles in both years. Oxidation of 14 C (carboxyl)-benzoate applied to soil was used to estimate oxidation potential. In the continuously drained treatment, oxidation potential remained constant at 457 nmol CO 2 kg !1 soil h !1 . In the treatments of flood followed by drainage to 33- and 50-cm depths, soil organic matter oxidation potential increased immediately upon drainage and reached close to maximum activity (384 and 473 nmol CO 2 kg !1 soil h !1 , respectively) in 3 to 7 days. Oxidation potential in the 16-cm water table declined from 339 to 289 nmol CO 2 kg !1 soil h !1 during the drainage cycle, possibly due to inhibitory influences in the sugarcane rhizosphere on microbial activity. Histosols may not need to be submerged continuously to reduce oxidation potential substantially. Two weeks of drainage to a 16-cm water table depth after 1 week of flooding resulted in an organic matter oxidation potential similar to flood in this lysimeter study. (Soil Science 2004;169:600‐608)