You can post the soil data and we can take a look at it. However, when it comes to what happened to soil fertility as the result of growing crops, there are an awful lot of wild cards that might not have much to do with the plants you're concerned with at all. These can include but are not limited to: weed density, uniformity of incorporation, volatilisation, variations in microbial activity, percent organic, C/N ratios, blah blah blah. Another approach may be to use the materials that you're going to use, each on the same plant type, keep cultural practices as uniform as possible, and perform tissue testing to see what the plants actually take up. (the best stage and type of tissue to collect depends on crop type) That too assumes relative uniformity in soil type, fertility levels, and chemistry prior to the application of the above mentioned materials and that's where the soil test info may come in handy, assuming you tested each of the areas separately to investigate differences in the soil from one area to a the next.

Since you mention that this effort is part of a "project," I am guessing that you have access to a university or state testing lab for your soil tests, and that you don't have to pay for the testing. Most of us try to manage without formal soil testing, to keep the cost of gardening down. Also, there is the question of how many samples are needed to ensure that the test results are valid. If you are serious about measuring the amount of soil nutrients taken up by a growing plant, I think you will need to grow your garden plants in a pot. That way, you can limit the volume of soil per plant & you don't have to be concerned about nutrients that might diffuse into your test plot from the surrounding area.

Thanks! Actually I am growing the plants in a greenhouse and they all have the same sized pots with the same amount of soil. I tested the soil and fertilizers/urine before the project and know the minerals in those. I have just got the results back from the soil and plant anaylsis after harvest and I am not really sure how to interpet the data.

If the soil before planting the plants had 80 mg/kg of nitrogen and then after it had only 10 does that mean that the plants took up 70 mg/kg of nitrogen? That example is from the plants given only water (no fertilizers). Thanks.

Not necessarily. Of course, a good percentage of that is probably plant uptake. If you have the crop type and plant data, that would be good to know. Also, does the test break it down into what types of nitrogen (i.e. ammoniacal vs. nitrate vs. urea)? Another thing, do you know if your water is a nitrogen source? A couple of other things to consider are what the planting medium is and how much watering you did. Is your greenhouse temperature regulated?

How did you prevent loss to drainage?

Almost any project needs some controls (You need a really good excuse not to do this.) Did you water pots with no plants in the same manner as you watered the pots with plants?

Results should have a range of some sort 80±[what] before and 10±[what] after?

Hey, I will try to answer as thoroughly as possible. I grew 96 plants. 4 types. 24 peas, 24 basil, 24 lettuce and 24 radish. My project is dealing with utilizing the nutrients in sanitized waste. So basically I collected compost and used it in different concentrations with potting soil.

8 trials (2 x 4 types of plants) with 100% compost, 8 with 80% compost, 60%, 40% and 100% potting soil. I then watered some with just tap water (with very low concentration of nitrogen, ammonia 0.06 mg/l and nitrate I sent the soil away to be analysed and before the soil contained 326 mg/l nitrogen and I fertilized with 100 ml of 51 mg/l nitrogen (from the urine) 6 times before harvest. The resulting soil after harvest contained 205 mg/l nitrogen (almost all in nitrate form).

What I am curious about is the chemical fertilizer trials. They were planted in a 80-70-160 potting soil and given the fertilizer 51-10-43 watered 6 times with 100 ml each time. The resulting soil test shows 10-13-30. It seems strange for it to be so low. Did the plants really take up that much? The % of dry material from the plants show 2.1-0.33-2.0. Does any of this make sense?

There was no urea present because the urine had been stored in air tight containers for 3 months prior to using.

The temperature of the greenhouse was a steady 19 degrees C during the day and 15 at night. It was all automated.

And albert_135 I didn't really prevent loss to drainage, how would I do that? I will comment in my discussion section about that though, possible sources of error. And no I didn't water pots with no plants, that would have been a good idea. But it is so expensive to have the samples analysed so I was trying to keep costs down.

The results didn't give a range, just the plant samples which was +/- 15%.

@Ryder

Are your results/Master thesis published? Is it possible to read your full thesis? I know this thread is years old, but i find your project very interesting.