Effect of temperature on soybean germination

Summary

Experiments were conducted in a sandy loam soil, under both laboratory and field conditions. In the laboratory, germination was studied at 5, 10, 15 and 20 per cent soil moisture and in the aerated distilled water at 12±0.5, 20±0.5, 28±0.5, 36±0.5 and 43±0.5°C soil temperatures. Results showed that the optimum soil temperature for soybean germination was 28°C and the optimum soil moisture was between 10–15 per cent in this soil type. At 28°C and 5 per cent soil moisture, the time required for 75 per cent germination was 71 hours which reduced to 47 and 35 hours at 10 and 15 per cent soil moistures, respectively.

In the field, soil temperature was regulated using mulches,viz polythene (Transparant) and three retes of straw (5, 10 and 15 t/ha, referred as S₁, S₂ and S₃, respectively). Two seed rates,viz normal (80 kg/ha) and double (160 kg/ha) were used. Soil temperature at 5 cm depth ranged from 26·6 to 44·6°C under polythene, 24·2 to 32·8°C in S₁, 24.3 to 30.4°C in S₂, 24.5 to 29.0°C in S₃ and 23.0 to 38.4°C in control during the daylight hours. Water uptake by seed was highest under polythene and lowest in control but there was no germination in the polythene-mulched plot due to fungus, attact at 59 hours after sowing. A soil temperature regime of 24.2 to 32.8°C (created in S₁) was optimum for germination. In all the mulched plots, effective germination in the double seed rate was never more than in the corresponding normal seed rate. Also, time taken for 75 per cent germination was minimum (71 hours) in S₁ with normal seed rate and it took about 16 hours more with double seed rate.