GROWTH AND YIELD OF MODERN DEEP-WATER RICE - COMPARISONS WITH MODERN IRRIGATED RICE

Deepwater rice (DWR) is grown in flood-prone areas at water depths of 50 to 100 cm or more. Growth and yield of two modern DWR cultivars gro wn at a water depth of 80 cm were compared with high-yielding irrigate d rice grown at 10 cm water depth during the wet season. Plant types o f DWR which differed in tillering characteristics were produced by gro wing plants at different densities, and these were compared with irrig ated rice cultivars to try and identify ideal plant types for DWR, Yie ld was higher in DWR plants (cv. HTA 60) with large numbers of mainste ms per unit area and no nodal tillers. HTA 60 with many mainstems yiel ded more than 5 t ha(-1) during the wet season, similar to the yield o f irrigated rice (cv. IR 72) grown under the same nutrient inputs. Yie ld of DWR planted at different densities was positively correlated wit h LAI at flowering (r(2) = 0.87), total dry matter at harvest (r(2) = 0.82), number of spikelets m(-2) (r(2) = 0.90) and number of mainstems m(-2) (r(2) = 0.76). While nodal tillering ability is an important tr ait for DWR in the event of stem reduction due to damage, DWR crops wi th a large portion of nodal tillers always had smaller LAI and lower y ields than crops with no nodal tillers, In experiments where there was no stem damage and differences in LAI were accounted for, nodal tille rs had no effect on yield as indicated by (i) the same yield/LAI in on e field experiment and (ii) the same yields when plants with different portions of nodal tillers were grouped into canopies at flowering al either small or large LAI (LAI = 3 or 6). Ideal DWR plant canopies sho wn here have high densities and large LAI, and this is associated with plants that have a large portion of mainstems or primary tillers and no nodal tillers. Results are compared with other research where produ ctivity of DWR and irrigated rice are grown in the field.