On-Farm Studies of Water Use and Water Quality for Rice Production

One of the major rice producing areas of the US, the L'Anguille River watershed in eastern Arkansas, has been experiencing declining groundwater levels and has been designated for a total maximum daily load (TMDL) limit for total suspended solids. Previous on-farm water-use studies in Arkansas conducted during the 1999 through 2002 growing seasons compared traditional flooded rice production to an alternative method known as multiple-inlet rice irrigation. Those studies showed that the multiple-inlet system required an average of 24% less irrigation water than conventional flooding without yield loss. A shortcoming of the studies, however, was that they did not address any effects on quantity or quality of the runoff water. A multidisciplinary project was started in 2003 to investigate the impact of multiple-inlet irrigation on water use, runoff volume, and quality of the runoff water within the L'Anguille River watershed. In 2004, two paired rice fields within the watershed were equipped to allow computation of a complete water balance throughout the flood period, with sampling of inflow and runoff water. In 2005, the project expanded to three paired fields. Based on a field in St. Francis County, Arkansas, the relative difference between inflows for two production systems (conventionally flooded and multiple inlet) appeared consistent throughout the season. Based on three pairs of fields located within 25 km of each other, water quality entering and leaving the field did not differ for samples collected on 5 August, 2005. The concentration of total nitrogen was significantly lower for the multiple inlet system. However, the limited data included in this report should not be used to make broad inferences about water use or water quality associated with rice production.