Effect of Sun and Shade on Soybean Plant Growth and Physiology Under Potassium Fertilized and Non Fertilized Conditions.

The effect of sunlight and low light intensity due to shading in potassium (K) applied soybean plants were evaluated in a greenhouse experiment to determine if the plants fertilized with K will have preferable growth in shade compared to non fertilized plants.  The experiment was  divided in 4  groups  of  6 replicates; group 1 as  control  and  group 2  treated  with 1.75%  foliar K at V3 stage, both grown under full sun.  The 3^rd and 4^th groups were placed under the shade with no treatment as control and K treated pots respectively. The results were analyzed on the basis of morphological assessment and physiological parameters. Plant heights measured in the first week (wk) were taller under the shade (21.75cm) compared to plants in the sun (16.35cm),  whereas  at the end of  two wks the plants in the sun increased in height (35.46cm) comparable to the shade plants (35.36cms).  The shade plants had longer internodes and looked fragile in comparison to the sun plants. To evaluate the physiological effects of shading we measured chlorophyll and stomatal conductance in the leaves. Results taken over 5 weeks showed higher chlorophyll concentration in the leaves of the plants grown in sun (wk2:32.53; wk 5: 38.6) than in shade (wk 2:28.78; wk 5: 35.57).  Application of K did not show any changes in the chlorophyll measurements.  Stomatal conductance measured higher in plants the first 2 wks in the sun [wk 1:14.55 mmol/(m²-s); wk 2: 10.5mmol/(m²-s)] compared to plants in the shade [wk 1: 9.28mmol/(m²-s); wk 2:7.91mmol/(m²-s)].  Stomatal conductance increased in the K treated plants [wk 5: 18.55mmol/(m²-s)] in the sun compared to control [wk 5: 11.67mmol/(m²-s)], however, no clear trend was observed in the shade measurements. From the above study we conclude that stomatal conductance of soybean plants grown in shade increased transiently with application of potassium.