This study analyzed the condition of stress in soybean associated with environmental factors and physiological plant. Data were collected in a field experiment during the cultivation of soybean (Glycine max (L.) Merrill, BRS) Tracajá cultivar sown in a soil classified as Typic Clayey texture ranging from sandy loam to heavy clay, from February 24 to June 17, 2007. The experiment was conducted at the commercial production of soybeans, with about 200 hectares in the of Paragominas municipality (020 38 'S; 0460 27' W), middle region of the northeastern state of Para. The climate of the region is of type Aw according to the classification of Koeppen. The stress condition in the culture was analyzed by three methods that we call: Canopy-air temperature difference method (MDT), Evaporative method (MEV) and Crop coefficient method (MKC). The result of the performance of all methods showed that the stress condition in the culture did not exist when the analysis was made in the daily scale. However, when examined in the hourly scale, the performance of MDT (only one allowed) on a typical day (dry and rainy), the phases beginning, middle and end of growing season, it was found that the plants reached a high level stress, especially at the initial stage of cultivation in dry day. On the other days analyzed, also found that there was stress condition the plants, but at level ranged from mild to moderate
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