Soybean development and thermal requirement under the climatic conditions of Paragominas, Pará state, Brazil

Abstract

The degree-days or thermal time theory has been widely used to simulate crop development because of its simplicity; in addition, it represents a good indicator of crop phenological evolution compared with the days after sowing scale. We investigated the development and thermal requirements of soybean (Glycine max (L.) Merrill), BRS Tracajá cultivar, grown in an agricultural border area of advance in eastern Amazon. The field experiment was carried out in the 2007 and 2008 growing seasons in the municipality of Paragominas, Pará state, in a completely randomized experimental design at six sowing dates with three replicates. The soybean thermal time required, from emergence to flowering, at cardinal temperatures of 10, 31 and 40 °C was 642±70 degree-days and the thermal time of the Ve-R8 stage was 1,753±16 degree-days.

EN-U 4H 9 P lts were submitted to principal component analysis (PCA) to obtain the correlation circles. In the circle of eigenvectors, in the slope with soft undulating relief, most vectors are located in the negative sector, both for physical and chemical properties with the latter being closer together. Also, the relationships between Ca, Mg, K and aluminum are evident. This way, chemical and physical properties are listed in the two slopes, and the level of correlation depends on the existing interactions. In addition, young soils with different characteristics and behavior were different from the others. Effective depth and structure were limiting attributes, but other favorable attributes were observed. The relationships among the attributes are differentiated along the slopes, and are influenced by the physicochemical nature of the geological substrate.