Definição de áreas aptas e épocas de plantio para a cultura da soja no nordeste e sudeste do Estado do Pará.

Abstract

The aims of this study is the identification of the most suitable areas and sowing periods for the establishment of soybean crop in northeastern and southeastern Para State region (Brasil). It takes into consideration the water availability for crop cycle as well as the climatic risk for its sowing. For this, a ten-day-period-frequency analysis of the rainfall was performed at levels of 20%, 50% and 80% for the years that were considered being of low, medium and high climatic risk respectively. Water balance simulation for crop was performed by using SARRA model and the SGI (Geographic Information System) for spatial analyses. The main input data for these are: daily rainfall, reference evaporation, duration of crop cycle and phenological phases of crop and its coefficient. The last date input are used for determining ISNH (Fulfillment of Water Need Indexes) for the growing phase which goes from flowering to grain filling (crop's critical phase). Water balance simulation for soybean crop was performed by combing twelve planting periods, two varieties and three usable soil water reserve of 25mm, 35mm and 50mm in order to obtain the ISNH. The definition of the appropriate area for soybean cropping was based in the spatial medium variation of ISNH for the crop critical phase. This was mapped through GIS Agroclimatic zoning maps for soybean crop in Eastern Para. It map of this shows differences concerning the appropriate period for cropping caused by the variations in the rainfall regime, soybean variety cycle and soil water reserve, as well as the suitable, intermediate suitable and unsuitable sowing periods. The study also shows that the biggest studied area presents suitable areas for soybean-crop in the period that goes from 1 to 31 of January. However the last 10 days of this period are the most suitable ones due to cropping season coincide with the beginning of rainfall decreasing. Its the sowing period advances, there's an increase in the South to North direction, of the areas which final themselves unfit for soybean sowing the results of this work will furnish subsidy to reduce or minimize economical damages caused by soybean crop sowing in areas and periods that are unsuitable for such to take place.