Submitted to: National Conservation Tillage Cotton and Rice Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: November 1, 2005
Publication Date: February 1, 2006
Citation: Vories, E.D. 2006. Conserving water with multiple inlet rice irrigation. 9th Annual National Conservation Systems Cotton and Rice Conference, February 1-2, 2006, Tunica, Mississippi. p. 27 Technical Abstract: Rice production is an important component of Arkansas' and other southern states' agriculture. In fact, when combined with the rice processing, agricultural equipment, and other businesses supporting rice production, it is apparent that rice is important to the overall economy, and not just in the rice-producing states. Almost all US-produced rice is grown in a flooded culture, with typical values reported for the amount of irrigation water applied to rice in Arkansas ranging from 24 to 48 inches. Even at the low end of the range (24 inches), rice production in Arkansas over the years 1998 through 2002, based on figures from Arkansas Agricultural Statistics Service, required applying an average of nearly one trillion gallons of water per year. The large amount of water applied to rice has resulted in two problems. The energy costs associated with pumping make up a significant portion of the rice production budget, with the cost influenced by fluctuations in energy prices. In addition, groundwater and surface-water shortages are being observed in some rice-producing areas. Reducing the water requirements for rice has been a goal of farmers and researchers for many years. Studies where rice was produced with sprinkler or furrow irrigation rather than with continuous flood resulted in lower yields. Producers cannot afford to abandon flooded production for an alternative system that produces lower yields. Conventional flooded production utilizes a well or riser in the highest-elevation portion of the field. Contour levees are constructed at approximately every 0.2 ft in elevation drop and adjustable spills are placed in the levees. When water is released from the well or riser, it fills the first paddy and then flows over the spills into lower paddies. Since the paddies must be overfilled to allow water to pass to the next lower paddy, there is quite a lot of skill and/or guesswork in knowing exactly how much water to pump so that all paddies are filled with little runoff from the lowest paddy. An alternative method for applying flood water is known as side-inlet or multiple-inlet irrigation. The name side inlet comes from the fact that a supply pipe is often, but not always, installed on the side of the field. Rather than discharging directly from the well or riser into the paddy, the riser is connected to a pipe and gates or holes are placed in the pipe for each paddy. In this way, each paddy is watered concurrently, instead of receiving overflow from a higher paddy. By adjusting the gates, the operator can fill all paddies simultaneously. The spills are left in the levees to provide a spillway for rainwater. Since it is not necessary to overfill the paddies with multiple inlet irrigation, deep percolation and seepage through the outside levees should be reduced. In addition, since each paddy fills at the same time, it is easier to apply the exact amount of water needed without excessive runoff. More efficient water management for rice will result in lower costs to the producers and allow more effective irrigation of other crops that share the water supply. It will also help relieve some of the water shortages being encountered in rice-producing areas. In order to study water requirements for rice on a production scale, on-farm water use studies were conducted in Arkansas during the 1999 through 2002 growing seasons. The studies consisted of paired fields located close together, with the same cultivar, soil type, planting date and management practices. One of the fields was randomly assigned as conventionally flooded and the other was assigned as multiple-inlet rice irrigation, with flowmeters installed in the inlets to both fields. When the farmer was ready to begin the flood period, University of Arkansas Extension personnel installed the flowmeters and assisted in setting up the multiple inlet irrigation fields. Disposable plastic irrigation tubing was connected to the well or riser and run over the tops of the levees through each paddy. Holes were punched or adjustable gates were installed within each paddy to allow the proper amount of water. The flow rate for each paddy was determined from the total flow rate multiplied by the ratio of individual paddy area to the total irrigated area. Once the field was set up, the flow to the individual paddies could be adjusted so that all paddies filled simultaneously. During the flood period, Extension personnel periodically visited the fields to ensure that everything was working correctly. After the final draining of the fields, Extension personnel recorded the amount of water pumped on the field. The farmers provided yield data for the fields from their farm records. The farm personnel managed the fields after the initial set up was completed. During the four-year study period (1999-2002), data for comparisons were collected from 14 pairs of fields ranging in size from 30 to 80 acres. The farms represented the northern, central, and southern portions of the rice-growing region in Arkansas, and the range of soil types used for rice production. The multiple inlet method required 24% less irrigation water than conventional flooding, with 37 inches for the conventional and 28 inches for the multiple inlet systems. Rice grain yields were not reduced with the multiple inlet system, with 147 bushels/acre for the conventional and 152 bushels/acre for the multiple inlet systems. Such large water savings without yield reductions can allow the producers to reduce their production costs substantially and at the same time address some of the water shortages being experienced.