TREATMENT OF SWINE WASTEWATER USING A SATURATED-SOIL-CULTURE SOYBEAN AND FLOODED RICE SYSTEM

Abstract

Constructed wetlands have potential for treatment of livestock wastewater, but they generally contain wetlandplants rather than agronomic crops. We evaluated two agronomic crops, saturated-soil-culture (SSC) soybean and floodedrice, in a constructed wetland system used for swine wastewater treatment. Both crop production and treatment efficiencywere evaluated from 1993 to 1996 in two 4-m 33.5-m constructed wetland cells that were connected in series. The firstcell contained SSC soybean four cultivars planted in a randomized complete block design with four replications.Flooded rice Maybelle was planted in the second cell. From the first to fourth year, wastewater application rates weregradually increased to obtain rates of 2.0 to 8.8 and 0.5 to 2.2 kg ha 1 d 1 for total N and P, respectively. The bestsoybean grain and dry matter yields were 4.0 and 9.1 Mg ha 1 , respectively. These were obtained with soybean Young atthe lowest wastewater application rate. Increasing total N loading rates and the associated higher NH 4 -N concentrationsdepressed soybean seed yield and dry matter production. On the other hand, both rice grain and dry matter productionwere stable over the application range; mean values were 4.0 and 10.9 Mg ha 1 , respectively. Nutrient mass reductionswere good; removal values increased linearly with loading rates (y = 0.69N load + 0.45 , R 2 = 0.99 and y = 0.45P load +0.20, R 2 = 0.95). At the highest loading rate, the system removed 751 and 156 kg ha 1 yr 1 N and P, respectively. Itappears that the SSC soybean and flooded rice system could be useful for liquid manure management in confinedlivestock production. The system produced comparable treatment to systems with natural wetland plants; moreover, thesoybean and rice are marketable crops. However, the flooded rice seems to be the more robust component for highwastewater application rates.