Investigating the relationship of increased biomass and nutrient content of soybean (Glycine max merr)
Type of DegreeMaster's Thesis
Crop Soils and Environmental Sciences
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Declining nutrient concentration in higher yielding cultivars is evident in literature meta-analyses assessing cultivars developed over the last century and studies performed under elevated CO2 to artificially increase yields and study nutrient concentrations. In meta-analyses covering soybean yield improvement and nutrient decrease, data has been collected over decades during which farm management and varieties have changed concurrently. More efficient agricultural management and breeding for higher yielding cultivars greatly improved overall soybean production but also resulted in unintended mineral nutrient decreases. Whether the nutrient decrease is due to management practices, cultivar improvements or a combination of both is still unknown. For this reason, it is necessary to study nutrient and yield relationships with old and new cultivars grown under similar conditions and practices. By growing old and new cultivars under 4 different nutrient regimes under equivalent farm practices, differences in yield, soil nutrient availability and nutrient uptake can be studied with the aim of understanding if the nutrient decrease observed in high yielding cultivars is due to a dilution of minerals, increase nutrient efficiency, or to a limitation of nutrient absorption by roots. Using these cultivars, we then determined an old and a new cultivar with the greatest difference in nutrient uptake for which we then grew under elevated CO2 concentrations ([CO2]) in open top chambers. This increased yield in both cultivars, allowing us to study the nutrient response in cultivars that accumulate nutrients differently under ambient [CO2]. Using elevated [CO2] allowed us to study nutrient and yields under conditions known to alter photosynthesis and transpiration. Decreased nutrient concentrations and transpiration rates were observed in the larger biomass produced under elevated [CO2]. Therefore, transpiration should not be excluded as a factor behind dilution in larger yields. Understanding climate change factors that influence nutrient content is essential for meeting future food demands.