Yield Traits and Water Productivity Responses among Rice Varieties (Oryza sativa L.) Grown in A Fadama Ecosystem in Akure, Southwestern Nigeria

Drought is the most important factor limiting rice productivity under rainfed system of the humid tropics. Field experiments were conducted to determine the effects of soil water management strategies (growth on residual soil moisture at the vegetative stage supplemented with irrigation at the reproductive stage and growth under full irrigation throughout) on water use, yield and yield components of four varieties of rice grown in the dry season in an inland valley swamp (fadama). The four selected varieties were two upland (Ekpoma local and upland Nerica 4) and two lowland (lowland Nerica 1 and 2). The first planting (December, 2010) adequacy of soil moisture from planting to date of first flowering was assumed, thereafter irrigation was imposed during reproductive growth. In the second sowing (Janaury, 2011), rice plants were drip-irrigated from planting to seed harvest. The results indicated that differences between the December and January sowing dates were found significant for most of the traits measured (root and shoot weight, leaf area, plant height, number of tillers, weights of panicle and 100-seed and harvest index). Total seed yield and harvest indices (3.19 t ha-1:10.1) were higher in January over December (1.24 t.ha-1: 6.3) sowing in addition to higher water use efficiencies (0.053 and 0.031 t.ha-1.mm-1). The seed yield reduction was associated with reductions in plant height (103.4:76.8 cm), leaf area (51.9: 76.1 m2) and shoot weight (103.7: 76.8 g) across all tested lines. Seasonal soil moisture storage ranged from 186 to 223 mm for the respective first (December) and second (January) sowing dates. The two best lines (Upland cultivars: Ekpoma and Nerica 4), had similar yield performance when grown under irrigation from planting to maturity (harvest) but differed significantly in their trait combinations. Over other varieties, upland Ekpoma and Nerica 4 exhibited superior ability to produce tillers, panicle and seed weights in both first and second sowing dates. Functional relationships between some weather variables and growth and yield characteristics of rice which gave high regression coefficients (R2) showed that, the differences in shoot biomass and seed yield production between the sowing dates were explained by a combination of weather parameters. The evaluated varietal yield potential and related traits measured under variable soil moisture regimes were discussed in relation to genotypic adaptation (drought tolerance) among the tested rice varieties. It is concluded that, in a cultivar, higher yield potential may be related to ability to tolerate multiple and concurrent abiotic stresses of soil and air moisture deficit and temperature stresses.