Go to body Go to Main Menu Go to Submenu Go to footer

Rural Development Administration National Institute of Crop Science

Environmental condition


Environmental condition

 

(1) Varities released
Sandy loam soil and clay loam soil are preferable to grow soybeans. Also, soils for soybean cultivation are required rich in organic matters and sufficient in phosphorus, potassium, and lime. Neutral soil is suitable and acidic soil affects reduction in growth, vigour of Rhizobia, and yield. Therefore acidic soils need to be improve to neutral soil by application of lime. Saline soils are not suitable for soybean cultivation. The growth of soybeans is greatly decreased in the growth and yield of soybeans above 0.03% in salt concentration. Excessive soil moisture severely restricts germination and early growth of soybeans. These effects are apparently the result of restricted oxygen movement to the seed and plant roots. Once soybeans are established, the effect of an excess or deficiency of moisture will depend on the stage of plant growth at which stress occurs and its duration. Flooding causes yield reduction at all times except near the end of the growth cycle.

 

(2) Climate condition
Soybeans are temperate crop which can be cultivated under wide range of weather conditions from tropics and the far eastern Russia and mid Canada. However, even extremely early cultivars need above 2,000°c in cumulative temperature for economic yield. The ideal temperature for growth is about 30°c. Higher or lower temperatures slow development. Vegetative growth, flowering, and seed sets are also affected by temperature. Differencebetween varieties in time of flowering are due to chiefly to their response to day length. But the year-to-year variations in the time of flowering of the same variety planted on the same date each year are due to the effect of temperature. Temperatures below 24°c will normally delay flowering by 2 or 3 days for each decrement of 0.5°c.
Temperatures above 40°c have an adverse effect on the rate of node formation, internode growth rate, and flowering initiation. Heat stress of 40~46°c results in pod abscission. Even though the growth rate declines at high temperatures, soybeans tolerate high temperatures better than corn. A study of 10 soybean cultivars at 25 tropical sites indicated that the number of days from emergence to flowering increases at higher altitudes (Whigham et al., 1978). Minimum and maximum temperatures were negatively correlated with altitude. Altitude was positively associated with plant height.
The level of light saturation for photosynthesis in soybean leaves depends on the light intensity of the environment in which plants are grown. In greenhouse conditions, the saturation level is reached at 20 Klux. In growth chambers, the rate of photosynthesis in soybean seedlings increases with light intensities up to 43 klux. Leaves of field-grown soybeans are not saturated at 150 klux. A controversy exists among scientists concerning of light intensity at which soybean become light saturated. The top leaves of the soybean canopy have a higher light saturation intensity and a higher rate of photosynthesis than those lower in the canopy. A high rate of pod abscission occurs in light intensities of approximately 5 klux. Soybean yields of 20 cultivars were reduced significantly when light intensity was decreased by 40% during shade studies in Philippines. The average yield reduction due to shading was 32%. The number of pods was reduced by 28% and seed weight was also decreased under shade.