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Agro-physiological adaptation and nitrogen fixation of soybean Glycine max L. varieties to three flooding regimes and growth stages
Dissertation Abstract:
The study conducted two experiments, namely: pot experiment at the Crop Science Cluster, University of the Philippines Los Baños (CSC, UPLB) from May to September 2009 and field experiment at the Central Experimental Station, UPLB from January to May 2010, to determine the physiological, morphological, and agronomic responses of 12 soybean varieties to flooding stress; and to evaluate the sensitivity of biomass accumulation, N2 fixation, and yield reduction due to flood duration at different growth stages among three varieties.
Three-day flooding at vegetative stage reduced the functional leaf area, leaf area ratio, net assimilation rate at flowering stage, and total dry matter yield at both flowering and pod setting stages in the pot experiment. Three-day flooding at vegetative and reproductive stages also reduced the RGR. However, specific leaf weight and root volume increased at three-day flooding at vegetative stage. Grain yield plant-1 increased when flooded for one day at pod setting stage as compared with control. It was reduced when there was flooding for three days which was not significantly different from the control. Path coefficient analysis showed that higher soybean grain yield for one day flooding than control was due to significant contribution of numbers of pod plant-1 and seed pod-1.
Among the 12 varieties tested, IPB Sy 96-27-21 was the most resistant variety with highest grain yield because of higher hundred seed weight, seed pod-1, and high physiological parameters (leaf area, leaf area ratio, net assimilation rate, and total dry matter yield). The second most and intermediate resistant varieties were Tiwala 8 and Tiwala 10, respectively. NSIC- Sy-9 was the susceptible variety due to poor grain yield, seed pod-1, functional leaf area, and filled pods plant-1.
In the field experiment, three-day flooding reduced functional leaf area (FLA) and leaf area index (LAI) at pod setting stage. One-day flooding had the highest FLA and LAI. There was no reduction in total dry matter yield, nitrogen fixation, grain yield plant-1, and grain yield ha-1 due to flooding at one and at three days. Among the varieties, Tiwala 8 had the highest total dry matter yield at three growth stages while Tiwala 10 had the lowest. NISC- Sy-9 had the highest nitrogen fixation for both flowering and pod setting stages while Tiwala 8 for only vegetative stage.
Flooding for one day at flowering stage significantly increased grain yield ha-1 by 17 percent compared with the control. At pod setting stage, flooding for three days significantly reduced grain yield by 16 percent compared with the control. However, it was not significantly different with that for control at vegetative and flowering stages. Path coefficient analysis revealed that there was no yield component that positively and significantly contribute to higher grain yield but percent nitrogen fixation had positive and high significant correlation with hundred seed weight for one day flooding at flowering stage, positive and non-significant correlation for control at pod setting stage, and in turn positively and indirectly affected grain yield via its effect on hundred seed weight.