Análise de Risco Edafoclimático para a Soja Cultivada na Região do Cone Sul de Rondônia: Diagnóstico Atual e em Cenários Futuros do Clima

Abstract

The present study aimed to calibrate and validate the mechanistic model CSMCROPGRO-Soybean for the climatic conditions of the mesoregion of the Southern Cone of Rondônia (CSRO), located in the southern portion of the Amazon, more precisely in the transition zone between the Cerrado and Amazonian Forest biomes. For the execution of the parameterization process, six early cycle cultivars were chosen, with relative maturity (GMR) greater than 7.0 and distinct growth habits (indeterminate and determined), sown regularly by farmers in the western and southern regions, respectively, Mato Grosso and Rondônia. During two experimental harvests, 2017/2018 (calibration) and 2018/2019 (validation), climatic data of air temperature and relative humidity, wind direction and speed, precipitation, short-wave solar radiation and soil moisture were collected, as well as information on the physical and chemical characteristics of the local soil, as well as data on phenology, growth and biomass (leaves, vegetables, stems and grains) of the cultivars used in the study, necessary to make the simulations of the agricultural model more robust. The results obtained during the validation season consolidate the application of the model in the CSRO, mainly because concurrently with the process of adjusting the model parameters, an analysis of future climate projections for the course of the 21st century in that region was carried out. The research, based on simulations of 41 global climate models (MCG's), projects temperature increases ranging from 2° C to 3.2° C, as well as reductions of 1.5 mm day- 1, reaching 3 mm day-1, in the CSRO rainfall indexes. A worrying situation already in the short and medium terms, as from the preparation of the climatological water balance (BHC) for the CSRO, it appears that from the middle of the century onwards the water recharges expected for the rainy season will fall well below the current conditions. This new reality, if materialized, will prolong the dry season and intensify the deficits of moisture in the soil, due to the potential evapotranspiration (ETP) overcoming the precipitation (P), especially between 2081-2100, with the months of September and October becoming very dry, and extremely low replenishment in water stocks between December and March. Under this new perspective, agricultural practice in the CSRO may become impractical, especially for soybeans, whose sowing and development will occur in the months (September to January) that will most suffer these impacts (estimated losses of approximately 1200 mm) in the future scenario of the end from the century. Therefore, in view of the above, this study will allow CSRO farmers and decision makers to make use of another mechanism, properly adjusted and validated, for the management and guidance of agricultural practices in the local edaphoclimate. Added to this, the fact that the CROPGRO-Soybean model, after calibrated and validated, also has the ability to simulate and project the potential productivity of soybeans under limited water and high temperatures, as expected for CSRO in the coming decades.