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The Effects of soil Drainage Conditions on the Morphophysiological Characters of Three Soybean Cultivars.
Thesis Abstract:
Field experiments were conducted to determine the growth performance and physiological responses of three soybean cultivars, Clark 63, UPL, SY2 and Williams, grown on Maahas clay oil under surface drainage conditions of 15, 30, 45 and 60 cm.
Result showed that depths of subsurface drainage significantly affected the growth of soybean plants mostly during the vegetative and early pod filling stages. Shoot dry weight and total and total dry-matter production were high under 15 cm depth but declined as growth progressed. There were slight differences in dry-matter production at drainage depths of 30, 45 and 60 cm,
With 45 cm drainage depth producing the longest root. Root dry weight, however, increased under shallow drainage conditions. Plant height was affected more by varieties than by depths of soil drainage, with UPL-SY2 the tallest and Williams the shortest.
Ratio by weight of soybean components showed high root-top ratio (R/T) and leaf-stem ratio (L/S) values at the shallow depth but high leaf-root ratio (L/R) values at the deep water tables.
Crop growth rate (CGR), relative growth rate (RGR), leaf area index (LAI) and leaf area ratio (LAR) were generally low under drainage depth of 15 cm and high at 30, 45 and 60 cm depths. Conversely, net assimilation rate (NAR) and specific leaf weight (SLW) were high at 15 cm but low at 30, 45 and 60 cm depths.
Although growth performance of the three soybean cultivars were significantly affected by drainage conditions, seed and biological yields and harvest index were mainly influenced by variety. UPL-SY2 had the lowest seed yield and harvest index. Whereas Clark 63 and Williams showed no significant difference. Clark 63 produced the highest biological yield but no significant differences was found between the other two cultivars. The high seed yield of Williams could be attributed to its higher net photosynthetic efficiency.
Result of the study indicated that high soybean yield could be attained at low drainage depth as well as at deeper water tables, and that such growth parameters as R/T and L/R ratios and CGR, LAI, NAR and SLW could be used as indirect indicators of yield.