By Chris Henry, Assistant Professor and Water Management Engineer
A noticeable and concerning change across the countryside that has recently been noticed is many more rice fields using poly pipe. This practice, termed Multiple Inlet Rice Irrigation (MIRI) which started in the early 1990’s has many benefits, including reducing the cold water effect on the first levee, reducing total water use by 25%, allowing for the implementation of alternating wetting and drying, and a quicker flooding. Being able to quickly flood up a field is beneficial for being able to get the flood established for water management as well as weed control and ensuring fertilizer efficiency. Delta Plastics and the University of Arkansas, Division of Agriculture have had programs to promote the implementation of MIRI, so help is available for farmers that want to use MIRI.
However, this year on thing that is more noticeable is that while poly pipe is being used, the use of blue gates, are not. Two and a half inch blue gates and a plan are a key component of a MIRI implementation. The blue gates allow for a wide range of flow, the key with MIRI is to balance the flow to each levee so that the field floods up evenly. If holes are punched without any way to adjust them, then some levees will cascade over the other. Thus if too much flow ends up at the bottom of the field, then it will take longer to flood up a field than without poly pipe. While the current weather pattern has blessed many of us with ample rainfall, in dryer time periods, pumps will run longer. More importantly additional irrigation capacity may be needed to meet crop water demand, which could result in reduced yield. Effective implementation of MIRI should only have water going over levee gates during high rainfall periods. Levee gates should be set higher than for cascade irrigation as they are essentially overflow devices when MIRI is used.
Help is available, through local county Extension offices, Delta Plastics and Natural Resource Conservation Service Field offices. The process is simple and mobile apps and on-line tools are available to develop a plan for the most complicated fields. Determine your flow rate, use a plumb bob or borrow a flow meter from your local Extension or NRCS office. Please do not punch and pray, punch with a plan. More information on MIRI can be found at https://extension.msstate.edu/sites/default/files/publications/publications/p2338_0.pdf