Constraints to High Yield of Dry-Seeded Rice in the Rainy Season of a Humid Tropic Environment

Abstract

Dry seeding advances establishment and harvest of rainfed rice and may help the crop escape late-season droughts.Early establishment, however, may expose the crop to early and mid-season droughts and periods of low radiation during the grain formation phase.We conducted experiments in the 1992 and 1993 rainy seasons at Tarlac, Philippines, to investigate factors that may hinder the performance and yield of dry-seeded rice cv.IR72.The treatments included three seeding dates and three water regimes(totally rainfed, irrigated from seeding to complete emergence followed by rainfed, and fully irrigated).Drough stresses between panicle initiation and flowering, with a matric potential of -25 kPa to -60 kPa in the 0-10 cm soil layer, reduced final biomass by 20%-30%.The same stresses occurring during the vegetative stage delayed flowering 3-5 d, but did not reduce total biomass at harvest.High plant density of the dry-seeding culture(325-450 seedlings m^-2)resulted in excessive vegetative growth(1600-2200 tillers m^-2 at maximum tillering stage).Inter- and intra-plant competition and low radiation(especially in typhoons)during anthesis and grain filling resulted in a high rate(40-70%)of tiller abortion, delay in flowering of later tillers, low percentage of filled spikelets(30-60%), and low yield(2.5-4.3 t ha^-1), despite high blomass production(13-15 t ha^-1).Selecting new varieties and devising cultural practies that ensure adepuate plant population and weed competitiveness in drought years and avoid excessive vegetative growth in years with low radiation are research challenges to make full use of the potential of dry seeding to increase the productivity of rainfed lowland rice.