Abstract:
Water scarcity during the dry season is one of the major constraints for rice (Oryza sativo) production in
Sri Lanka. The objective of this study was to evaluate alternative water-saving irrigation regimes
developed for rice cultivation in the dry season oh Red Yellow Podsolic soils in Minuwangoda area with a
view of reducing total water input while ensuring minimum yield reductions. The study was conducted in
a protected house with Bg 300 rice variety. Five water-saving irrigation treatments were imposed as
following: Standing water (SW) throughout (T l); SW during vegetative (VEG) and reproductive [REP)
stages and saturated soil conditions (SAT) during grain-filling, GF, (T2); SW during VEG followed by SAT
during the rest (T3); SW during VEG followed by SAT during REP and allowing to dry down to crack
formation (CF) during GF (T4); SAT throughout (T5). Grain yield and water productivity showed
significant (P<0.01) reduction with decreasing water availability. Total dry weight, harvest index and
percentage of filled grains showed significant positive correlations to grain yield. All water-saving
irrigation regimes cause yield reductions. While ensuring minimum yield reductions, it is only possible to
reduce the water inputs during the vegetative stage from standing water to saturated soil conditions.
There is a scope for increasing water productivity in rice cultivation on Red Yellow Podsolic soils in
Minuwangoda of Gampaha District up to an upper limit of 0. 99 g kg'1 by reducing water input through
water-saving irrigation regimes.
