Sugarcane Photosynthesis, Transpiration, and Stomatal Conductance Due to Flooding and Water Table

number of fields now have less than 40 cm of soil (Shih et al., 1998). Second, for every cm of rainfall, the free Sugarcane (Saccharum spp.) is the primary crop on the Histosols water in the soil profile of EAA Histosols can be exof the Everglades Agricultural Area (EAA), where periodic floods pected to rise about 10 cm (Glaz et al., 2002). Finally, and undesirably high water tables are increasing in occurrence and duration. Improved understanding of the physiologic responses of there are regulated and voluntary limits on pumping sugarcane to these conditions could help develop strategies to sustain from farm ditches to public canals as a means of reducing high yields. The purpose of this study was to evaluate the effects of P discharge to the natural Everglades. periodic flooding followed by drainage to different depths on singleThe issues of soil subsidence and P discharge to the leaf net photosynthetic rate (Ps), transpiration (Ts), and stomatal Everglades also provide incentives to maintain higher conductance (SC) of sugarcane. In 2000 and 2001, two sugarcane water tables and short-duration floods. The primary genotypes were planted as split plots in 12 lysimeters filled with Pacause of subsidence in the EAA is microbial oxidation hokee muck soil. Responses of Ps, Ts, and SC to four water-table (Tate, 1980). The factor that most influences the rate treatments were measured for four 21-d cycles each year. Three treatof microbial oxidation is depth of water table in the soil ments consisted of 7-d flooding followed by 14-d drainage to depths profile. Therefore, the rates of oxidation and subsidence of 16, 33, or 50 cm. The fourth treatment was a continuous 50-cm water table. Analyses of individual cycles and analyses repeated over are directly proportional to the depth of the water table. cycles generally identified neutral or positive responses of Ps, Ts, or If the distance between the water table and the soil SC to flood. Drained water-table depth did not consistently affect Ps, surface is halved, the rate of subsidence is halved (SnyTs, or SC, but when differences occurred, 16 cm was often a favorable der et al., 1978). drainage depth. These neutral and sometimes positive responses to Best management practices to reduce P discharge short-duration flood or long-duration high water tables support previfrom the EAA often include strategies to reduce quantious reports of acceptable and sometimes enhanced yields from sugarties and rates of pumping excess water from agricultural cane exposed to high water tables. Previous findings were supported fields (Rice et al., 2002). After EAA sugarcane fields that time of formation of stalk aerenchyma in sugarcane may be a are flooded, which may occur several times during the key factor for sustaining high yields after exposure to flood. summer rainy season, P export to the Everglades could be substantially reduced by allowing floods to subside more by evapotranspiration and less by pumping. DevelT EAA is a 280 000-ha basin of Histosols that lie oping strategies that result in no yield loss to sugarcane on limestone bedrock in the northern region of the after short-duration floods and increasing the duration historic Everglades in Florida. Sugarcane is grown on of flood to which sugarcane is tolerant could facilitate about 148 000 ha in the EAA (Glaz, 2002). Before confarmers’ efforts to conserve soil and reduce P discharge. struction of an extensive public–private system of canals Previous research indicates that sugarcane maintains through the northern Everglades, the EAA was flooded optimum yields through a wide range of water tables. most of the time (Snyder and Davidson, 1994). The Carter and Floyd (1971) reported that maintaining four canal system now facilitates the maintenance of desired constant water tables between depths of 61 and 122 cm water-table depths of 40 to 95 cm in sugarcane fields during the active growth phase of sugarcane did not (Omary and Izuno, 1995). affect cane or sugar yields in Louisiana. Carter and Several factors have gradually resulted in sugarcane Floyd (1975) maintained water tables at 30, 76, and being periodically exposed to higher than desired water 122 cm throughout the year in the second and thirdtables and floods in the EAA. Soil subsidence caused ratoon crops of the plantings reported in their 1971 loss of depth in EAA Histosols at the rate of about study. There were no significant differences in sugar 2.5 cm yr 1 before 1978 (Shih et al., 1978). From 1978 yield in the second-ratoon crop, but in the third-ratoon until the most recent survey in 1997, the rate of soil loss crop, sugar yields decreased as water-table depth rose. declined to 1.4 cm yr 1 (Shih et al., 1998). Some EAA In a field study conducted in Florida, Kang et al. fields had as much as 300 cm of soil above the limestone (1986) compared sugar concentration and cane yields bedrock when they were first drained and used for agriof 16 clones of sugarcane (Saccharum spp.), one of S. culture. Depth of soil to bedrock varies, but a substantial rosbustum Brandes & Jesw. ex Grassl, one of S. officinarum L., and one of Ripidium spp. at water-table B. Glaz and D.R. Morris, USDA-ARS Sugarcane Field Stn., 12990 depths of 30 and 56 cm. Overall mean sugar concentraU.S. Hwy. 441, Canal Point, FL 33438; S.H. Daroub, Everglades Res. tion yields were 15.7 and 17.6% higher in the 30-cm and Educ. Ctr., Univ. of Florida, 3200 E. Palm Beach Rd., Belle water-table depth in the plant-cane and first-ratoon Glade, FL 33430. Received 17 Aug. 2003. *Corresponding author ([email protected]). Abbreviations: CER, CO2 exchange rates; EAA, Everglades AgriculPublished in Crop Sci. 44:1633–1641 (2004).  Crop Science Society of America tural Area; Ps, single-leaf net photosynthetic rate; SC, single-leaf stomatal conductance rate; Ts, single-leaf transpiration rate. 677 S. Segoe Rd., Madison, WI 53711 USA