Soybean

• It is basically of temperate origin. Climatic requirements of soybean are similar to those of maize. Therefore, soybean can be grown wherever maize is produced. Most of the varieties require a temperature range of 30 to 33oC. Minimum, optimum and maximum cardinal temperature for germination are 5, 30 and 40oC respectively.
• A day temperature of 25oC or less may delay the flowering and prolonged period of cloudy weather may tend to extend the vegetative phase at the expense of seed yield. Soybean growth is limited by soil temperatures in excess of 33oC. At 27oC, nodule formation, development and nitrogen fixation were found to be most rapid.
• Nodulation is slow if temperatures are below or above this. Freezing temperature can result in almost complete damage of leaves up to pod filling stage and in low seed yield when exposed before pod filling.
• High temperature during flowering and ripening increases fat but reduces nitrogen content.
• In subtropical climates, about 65 cm of rainfall during growing season is sufficient for a successful crop.
• They are usually less sensitive to drought during the vegetative growth, but it is particularly sensitive to moisture stress during flower bud differentiation and pod filling stage.
• Moisture stress during pod filling stage may result 20 to 50% reduction in grain yield. An excess of soil moisture also inhibits nitrogen fixation.