Weed infestation causes great yield reduction in rice. However, application of herbicides under proper water management may control weeds and could increase the yield of irrigated lowland rice. This study aimed to determine the effects and appropriate water regimes and chemical herbicides; and assess the weed population and profitability ha-1 of using different chemical herbicides and water regimes in lowland rice production. The experiment was laid out in a nested design with complete block design in three replications. Different water regimes: M1-continuous submergence at 5cm and M2-Saturated condition as main plots and different herbicides as the sub plots T0- Control (unweeded and no herbicide application), T1- Butachlor, T2- Propanil + Butachlor, T3- Metsulpuron Methyl + Chlorimuron Ethyl, T4- Butachlor + 2,4D, T5- Cyhalofop butyl + Pyribenzoxim and T6- Manual weeding at four weeks after transplanting. Results revealed that lowland rice under continuous submergence at 5cm significantly produced more number of productive tillers, 1,000 seed weight and resulted to the increased total grain yield (tha-1). Application of chemical herbicides under different water regimes showed significant differences on the number of productive tillers, grain yield and harvest index. Moreover, rice plants treated with Butachlor + 2,4D (T4) and Cyhalofop butyl + Pyribenzoxim (T5) produced the highest grain yield of 7.78t ha-1 and 7.89t ha-1, respectively. Lowest weed population of 3.50 was observed in plants applied Butachlor + 2,4D (T4) while highest on Cyhalofop butyl + Pyribenzoxim (T5). All chemical herbicide treatments had high weed control efficiency except Butachlor (T1). Highest net income was observed in T5 with a net income of PhP85,027.20 ha-1 that is equivalent to 46% higher than the control plants with a net income of PhP38,945.20 ha-1.
submerged, saturated, herbicides, weeds and income