Sensitivity of redox conditions to irrigation practice and organic matter decomposition in a rotational flooded rice (Oryza sativa) cropping system.

Abstract

Agricultural practices in the Everglades Agricultural Area (EAA) of South Florida have focused on managing accelerated organic matter (OM) decomposition in Histosols, which leads to soil subsidence. Rotating flooded rice (Oryza sativa L., variety Diamond) during the summer fallow period of sugarcane (Saccharum officinarum L.) has been proposed to reduce soil oxidation and loss by creating anaerobic conditions. However, limited research exists on the oxidation-reduction (redox) dynamics of these unique organic soils under rice cultivation and the associated OM decomposition, hindering the development of effective water management practices. This study aimed to understand the effects of flooded rice cropping on OM decomposition and loss by unraveling the intricacies of the redox conditions and their relationship with irrigation practices. Soil redox indicators, including dissolved oxygen (DO) and redox potential (E_h), along with flood depth, soil temperature, and acidity level (pH) were monitored in two rice fields. Soil samples were collected before planting and after harvest and their OM and active carbon concentrations were compared to quantify the effects of rice cultivation. Results showed that prolonged flooding shifted the soil from aerobic to moderately reduced conditions. Increased flood depth, elevated soil temperatures, and higher pH from alkaline limestone mixing contributed to lower DO and E_h. The observed reduction in active carbon suggests that flooded rice cultivation can slow the rate of OM decomposition and loss. Improved water management practices, including extended irrigation periods, consistent water levels, and optimized field conditions, are recommended to further mitigate soil loss and support sustainable farming in the EAA.