Water, tillage and weed management options for wet seeded rice in the Philippines

The recent shift from transplanted to wet seeded rice (Oryza sativa L.) in South East Asia has resulted in major weed problems which require more labour and energy for their control. Field experiments were conducted during 1994-1996 on a Chromic Vertisol in central Luzon, the Philippines, to study the effect of water, tillage and herbicide levels on total water use, weed growth and yield of wet seeded rice. The treatments included three water regimes (i) shallow-water pending (5 +/- 2 cm) throughout the crop growth period (W1), (ii) shallow-water pending until panicle initiation and then saturated soil (W2), and (iii) saturated soil (W3); two tillage levels (i) one ploughing + two harrowings (T1), and (ii) two ploughings + two harrowings (T2); and three herbicide levels, pretilachlor at a rate of (i) 0.30 kg a.i. ha(-1) (H1) and (ii) 0.15 kg a.i. ha(-1) (H2), and (iii) no herbicide (H3). Water pending effectively suppressed weeds, irrespective of the herbicide dose applied. Both, the herbicide levels (H1 and H2) were equally effective and produced statistically similar rice yields. More intensive tillage (T2), produced significant positive effect in controlling weeds in the dry season. The T2-W1-H1 combination produced the highest rice yield. Saturated soil (W3) saved about 40% of water compared to continuous shallow pending (W1) and produced statistically the same rice yield when weeds were controlled by herbicide. Proper use of herbicide can thus substitute the excessive water-consuming practice of continuous submergence in rice fields. (C) 1999 Elsevier Science B.V. All rights reserved.