Alfalfa Case Study

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The differences seen in the soil may be due to addition of carbon/ nitrogen which can change and alter the C:N ratio. The greater C:N ratio the more extracellular polymers are released which help hold the aggregates together and better its stability. The lower the C:N ratio the worse the aggregate stability and the faster the aggregate will crumble away as can be seen in both a slaking test and the alfalfa treatment. The water which is added into the 100 grams of soil has the highest aggregate water stability. The alfalfa has a higher nitrogen amount thus will exhibit a low C:N ratio. Thus the treatment in alfalfa will have limited excretion of extracellular polymers that can help bind the aggregate thus the stability of the aggregate for this treatment will be quite unfavorable as is seen in the table. The sucrose treatment will …show more content…

(3 pts) Which of the four treatments most favored the growth of Azotobacter and why (base your answer on qualitative observations of Azotobacter incubations)?
> The most favored growth of Azotobacter are seen in the addition of Na2HPO4 thus (HPO42-) a moderately reduced compounds. It is stated in the manual that the Na2HPO4 helps provide the Azotobacter with its demand for phosphorous. The phosphorous used by this nitrogen fixing bacteria may be a selective inhibitor toxic to other bacteria yet, beneficial to the Azotobacter. In the addition of Na2HPO4 there are multiple tiny, shiny gray spots all across the silver colonies.
2. (2 pts) Contrast the potential contributions of Azotobacter versus Rhizobia/Bradyzhizobia to the nitrogen budget in soils. Discuss why they are so different.
3. (4 pts) Include a drawing of each of the following: an Azotobacter cell, nodules attached­ to plant root system; a Rhizobia/Bradyrhizobia cell the plant nodules; and the ectomycorrhyzal fungi. Include a scale for the two cell drawings.
Azotobacter cell Nodules to Plant

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