Grain yield as a function of rainfall, soil moisture and solar radiation in upland rice ( Oryza sativa L.)

Abstract

Rainfall, soil moisture tension (SMT), and solar radiation were monitored in upland rice ( Oryza sativa L.) yield trials during the 1984–1989 wet seasons at the International Rice Research Institute (IRRI) dryland farm and two farmers' fields in Southern Luzon, Philippines. The goal was to identify environmental parameters during the vegetative, reproductive, and maturation stages that influence grain yield of upland rice. Three varieties, IR43, Kinandung Patong and UPLRi-7, and one line, IR9560-2-6-3-1, were used. Regression techniques were used to identify the environmental variables that have a major impact on the yield of each variety and line. The final models included reproductive stage rainfall (R-RF) and maturation stage solar radiation as independent variables for IR43 ( R 2 = 0.58 ∗∗ ), R-RF for IR9560-2-6-3-1 ( R 2 = 0.38 ∗∗ ), R-RF for Kinandung Patong ( R 2 = 0.67 ∗∗ ), and R-RF and reproductive stage SMT at 20-cm soil depth for UPLRi-7 ( R 2 = 0.65 ∗∗ ). The models indicate that the lines used were most sensitive to rainfall during the reproductive stage. This result suggests that the planting of upland rice should be timed so that the reproductive growth stage falls in a predicted rainy period.