SEED QUALITY AND VIGOR OF SOYBEAN CULTIVARS AS INFLUENCED BY CANOPY TEMPERATURE

The objective of this study was to quantify the effects of canopy temperature on seed quality and vigor of soybean planted on different dates. An experiment was conducted at the Agriculture Research Farm of the KPK Agricultural University, Peshawar, during 2003 and 2004. Determinate cultivars (Epps, maturity group [MG] V) and indeterminate cultivar, Williams 82 [MG] 111) were planted on May 1(st) to August 1(st) at one month interval during both years. Data was recorded on canopy temperature, seed quality and vigor attributes of soybean. Heat indices were calculated from canopy maximum and minimum temperatures for the periods between growth stages starting from beginning of bloom to physiological Maturity (R3-R7). Seed quality and vigor attributes were regressed on different heat indices. Canopy temperature during reproductive growth stages of R4-R5, R5-R6 and R6-R7 had pronounced effect on both seed quality and vigor of soybean. Increase in mean averaged temperature in the range of 23-30 degrees C during growth stage of R6-R7 improved germination, field emergence, and increased seedling dry weight, protein and oil contents of soybean seed. Whereas, increase in mean temperature averaged in the range of 23 to 30 degrees C during reproductive growth stage of seed initiation to full-seed (R5-R6) reduced germination, field emergence, protein and oil contents of soybean seed and increased electrical conductivity. Increase in maximum temperature in the range of 32 to 37 degrees C during growth stage of full bloom to seed initiation (R4-R5) decreased seedling dry weight and oil content of soybean seed.