Originally Posted by bsgospel
It's through a certificate platform called edX.org- The three part program is called Sustainable Food Security. In order, I'm taking crop production, systems analysis, and security & access.
I believe I've mis-worded my objective. You're correct, though. What I mean to ask or investigate are the steps, beginning to end/ gigajoule to yield. The program is very detailed but also condensed where math steps are necessary. And I don't think the math is hard but I can't visualize or connect certain steps:
600 joule per m2 per second (Clear day, middle of summer)
40 kg Co2 per HA per Hour (C3 plant, single leaf at normal temperature. 80 kg CO2 per HA per hour assimilated by a closed canopy)
Gross Assimilation Maximum (Amax) (best possible outcome without greenhouse influence or assistance)
Next remove energy spent on respiration
[hazy on this- respiration coefficient .01-.03 kg of assimiliates per kg of standing phytomass. What do I even do with that?]
Net assimilation in kg CO2 per HA per hour
[hazy again- use the assimilation here to drive growth and quantify biomass, I think? But now we've gone from joules to gigajoules per HA per Day...]
It's between net assimilation and yield that I can't wrap my brain around. So when a question like this:
"Tree biomass contains a considerable amount of core wood, that is no longer metabolically active and therefore does not require maintenance respiration. So this implies all other organs require maintenance respiration. The maintenance coefficient of the remaining active tree components amounts to 0.1 ton (CH2O or assimilates)per ton-1 (dry matter) per year. Information collected from a Douglas fir plantation in 1924 and 1983 is given in Table 1. [table given] Q. Express the maintenance coefficient in ton CH2O per ton dry matter per day.
answer with 6 decimals, e.g. 1.234567"
Is posed, my hair blows back.
ok, so first that last question. I looked up the specific question so I could also see the table given with it.
the thing here is that the table lists FM(fresh matter), and a water content. while you need DM(dry matter). so this excercise is mostly just calculating between fresh/dry matter, and reading the question well enough to know you have to ignore the core wood. other than that it's just multiplying by the given maintenance respiration.
the first question after the info given, the one you copied, is actually really, really simple. you don't need the table at all for that. it's just a step to make the next question easier, it's asking you to convert the given maintenance respiration, which is per year, to a value per day.
so it's just 0.1/365
after that you have to calculate the maintenance respiration of that specific douglas fir plantation from values given in the table.
so for 1924:
33.3 tons needles, 70% moisture content, 0.3*33.3=9.99 ton dry matter per ha
42.0 ton branches, 50% moisture, 0.5*42=21 ton DM
(core wood, not relevant since it doesn't require maintenance respiration)
200.0 tons sap wood, 40% moisture, 0.6*200=120 tons DM
40 t roots, 60% moisture, 0.4*40=16 t DM
so together: 9.99+21+120+16=166.99 ton DM per ha
maintenance respiration given= 0.1 ton (CH2O or assimilates) ton-1 (dry matter) per year.
so 166.99*0.1=16.699 ton assimilate per ha per year.
but, you have to answer per day, not per year.
16.699/365=0.04575068493 ton assimilate per ha per day, for 1924.
for the other comments:
I think you need to look into respiration a bit more.
the step between gross assimilation and net assimilation is using respiration.
so gross assimilation is your total production by photosynthesis. it's a certain amount of energy from the sun, which assimilates a certain amount of CO2, which is converted into sugars(assimilates).
so you then have this amount of sugar, but it can't be all used for growth. the are a few different kinds of respiration, which are things that cost energy, so to provide that energy sugars/assimilates produced by photosynthesis are used.
first you have the loss from photorespiration(only aplicable with C3 plants). this is the loss from the chemical that binds CO2 from the leaf pores to bring it into the leaf, this chemical also binds O2, which has to be split off again before it can be re-used for CO2, but with O2 it doesn't give a CO2, so it's a loss in energy.
then you get maintenance respiration. this is the sugars used just to maintain all the plant matter that's already there. this is also what was calculated in that question above. it's expressed as a amount of assimilates per total DM(but in the specific question above it was about a douglas fir plantation, so a tree, so therefor you have to deal with corewood which is dead, so doesn't require maintenance respiration. with annual crops that's irrelevant)
what you have leftover after the 2 respirations above is what can be used for new growth. however, new growth is not directly equal to the weight of the assimilates. your assimilates are sugars, but new growth also contains other compounds(more complex carbohydrates like starches, proteins, fats). converting assimilates into those compounds also costs some energy, so that's growth respiration.
if you know a conversion factor for how much new growth you get per amount(kg or ton or whatever) of assimilates, you can calculate how much new growth you get. and that conversion factor also depends on what is grown, for example a plant setting seed with oily seeds will have a different conversion factor from a plant with starchy seed.