Desenvolvimento do arroz e do arroz vermelho: modelagem e resposta à mudança climática

Abstract

Increases of 1.1 to 6.4°C in temperature are projected by the end of the XXI century in several locations, including Brazil. Among processes that may be affected by increasing temperatures is the duration of the developmental cycle of crops. Simulation models are tools that allow to describe the possible interactions that take place in agroecoystems and their response to climate change scenarios. The objectives of this dissertation were (i) to simulate the development of irrigated rice and red rice comparing a linear (thermal time model) with a non-linear (WE model) model, and (ii) to investigate the response of the development of rice and red rice to climate change scenarios in Santa Maria, RS, Brazil, considering symmetric and asymmetric increases in minimum and maximum daily air temperatures. Data from a four-year experiment conducted during the 2003-2004 (five sowing dates), 2004-2005 (five sowing dates), 2005-2006 (three sowing dates), and 2006-2007 (two sowing dates) growing seasons in Santa Maria, RS, Brazil were used. Plants were grown in 12 liter pots during the four years, and in a paddy rice field during the 2006-2007 growing season. Nine cultivated rice genotypes (IRGA 421, IRGA 416, IRGA 417, IRGA 420, BRS 7 TAIM, BR-IRGA 409, EPAGRI 109, an Hybrid, and EEA 406), and two red rice biotypes (awned blackhull- ABHRR, and awned yellowhull-AYHRR) were used. Developmental data available and used in this study were dates of emergence (EM), panicle differentiation (R1), anthesis (R4), and all grains with brown hulls (R9) recorded in five plants per replication in each sowing date. Data collected in the 2004-2005 and 2005-2006 growing season were used to estimate the coefficients of the two models and data collected in the 2003-2004 and 2006-2007 growing season were used as an independent data set for models evaluation. A one hundred years climate scenarios of 0°C, +1°C, +2°C, +3°C, +4°C, and +5°C, with symmetric and asymmetric increases in minimum and maximum daily air temperatures were created with the LARS-WG Weather Generator using a 1969-2003 database. Date of developmental stages in each climate scenario was calculated with the non-linear model (WE model). The root mean square error (RMSE) for all developmental stages varied from 4.9 to 10.5 days with the thermal time model and from 4.3 to 10.9 days with the WE model. The WE model gave better predictions in six out of eleven genotypes, with better predictions for early (R1) than for later (R4 and R9) developmental stages. The duration of the EM-R1 phase in general decreased whereas the duration of the R1-R4 and R4-R9 phases most often increased as temperature increased in the climate change scenarios. The simulated rice development response to elevated temperature was not the same when the increase in minimum and maximum temperature was symmetric or asymmetric. Current rice genotypes may be less competitive with red rice in future climates.