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Heat damage can be manifested in many ways, from a reduction in emergence, to increased flower abortion and reduced seed vigor. Soil temperatures at or above 100F cause soybean cotyledons to deteriorate rapidly. High soil temperatures at plant emergence is thought to be a primary reason for “heat canker” or “pinched stems at surface” (sunken necrotic lesions near the soil surface). Nodule formation, development and nitrogen fixation are reduced when soil temperatures rise above 90F. Day temperatures in excess of 95F, coupled with low humidity, have been shown to reduce seed set and potential seed vigor. In general, the soybean plant can tolerate short periods of high temperatures if supplied with adequate soil moisture. |