Optimizing irrigation and drainage rates in sri paddy fields

A quantified study to optimize furrow irrigation and drainage rates for SRI paddy fields has been carried out over three different planting seasons. It is very crucial to maintain soil conditions where the water level sustains soil moisture at around saturation and air-entry values. In the present study we report on a simulator program which applies a saturated water flow equation in one dimension for which boundary conditions at both ends formed water rates (Neumann type). A spreadsheet optimization using an imbedded Solver in MS Excel was employed alongside the simulation. Daily rainfall, evapotranspiration and percolation rates as sink-source functions were incorporated into the equations. Our study shows that optimizing irrigation and drainage rates gives an effective water level for SRI paddy fields within a range of -5 to 0 cm for all planting seasons. The highest value for irrigation rate within the furrow was about 6 mm per day, while the optimizing drainage rate was about 0.5 mm per day. Water table profiles are significantly affected by planting season. Our study confirmed that conserving drained water from one planting season is desirable to provide sufficient irrigation water for the next planting season