Data Exploration: Lower conductivity by aging manure outside? and a pH Calcium relationship

Hi Everyone, I wanted to start 2021 with a fresh look at the Midwest data now that I have compiled all of the questionnaire data. I had to contact many producers to clarify some questions, so thank you all for getting back to me so quickly and apologies again for the unclear questions.

I am going to start by sorting the same graphs from the previous posts by percent total manure added. It took me a bit to think how to do this because we have 6 different kinds of manure (horse, cow, rabbit, goat, chicken, sheep and fish?). Some had mixed manures and different treatments which we'll get into a bit as well. To simplify this variability I summed up the all the manures and ordered the samples from least to most % total manure from left o to right (Figure below).


As expected, there appears to be some correlations with increased manure amounts having higher phosphorous. We see that generally the samples with less or 0% manure tend to have lower phosphorus levels. I first want to point out that #8 has 5% fish poop (manure?), but is currently grouped with the non manure samples for now.

Sample #6 jumps off the charts here which is likely due to the 30% rabbit manure added which is maybe more concentrated than horse and cow manure. It is the only sample with rabbit manure, so it's hard to draw firm conclusions.

Samples #5 and #19 are somewhat outliers here. My suspicion is #5 has an amendment or a special food-waste component. With producer #19, perhaps spent brewers grain has a phosphorous concentration similar to that of manure? I think further investigation is likely required here.

Conductivity (Salts)

Conductivity you will notice has similar trends to phosphorous, but with some pretty big discrepancies especially if you look at the higher manure content samples. I expect higher manure content samples to also have higher conductivity due to the urine mixed in. Composting manure tends to lead to increased conductivity because it is essentially a concentration of manure and the salts typically aren't removed. I was confused as to why some higher % manure samples could have conductivity levels relative to those of mainly food waste and leaves and still maintain high phosphorous levels.

Phosphorous Relative to Conductivity

To explore what what could be causing the high phosphorous and lower conductivity levels, I graphed the phosphorous to conductivity ratio. The higher the ratio the more phosphorous and less conductivity. What stands out here now? Samples 8, 13, 9, 1, 4, 15, and 18 all kind of sit above the rest and they all have manure (if you count the 5% fish poop in #8). Other than that, I don't see a clear trend so let's look at other factors. Fish poop from the bottom of the pond might have low salt content because the salts would dilute into the water. Samples #1 and #4 are actually from the same vermicompost operation, but different sampling times. They both contain manure that had not been "composted" but aged outside in a pile. If I had to guess, sample #4 was made with manure left outside longer or rained on more than #1. Samples #9 and #18 are both composted in an outdoor windrow type system. These types of systems would allow the salts to infiltrate the ground. Sample #15, with the highest phosphorous to conductivity ratio, was a mystery because it was pre-composted indoors and vermicomposted indoors. I had to inquire if the dairy manure used was aged outside at all. Sure enough, it had been aged outside for 3-4 months. I still need to confirm with other manure producers like #7 and #12 if their manure was left outside much prior to the composting process. Also, producer #13 only had 5% manure with the bulk of the input being food waste and pine bedding. Perhaps with a more granular breakdown of the foodwaste input that outlier can be better understood as well.

pH and Calcium

I wanted to leave you with one more observations pH and calcium. If you look at the graph below, there is a weak trend with calcium and an increase in pH with some pretty serious outliers in #10 and #16. Clearly there are other factors at play.

This confused me at first because calcium doesn't directly affect pH. However, calcium carbonate (CaCO3) or lime is a common form of calcium in the soil. Carbonate can donate an (OH-) which can absorb an H+ ion thus reducing acidity. Sample #2 I believe also had a calcium booster added to it which could have contained lime. Samples #15, 8, 4, 9, 1, and 17 all have wood-chips, hay, or leaves added added to them. All of these inputs could have been on the ground and perhaps enough dirt was added to buffer the system and keep the pH from dropping to much. Is this too much of a stretch? I'm curious to hear any other theories.

It's nice to see the questionnaire data begin to help make sense of the the Midwest results. I would not call these ideas presented firm conclusions, but I hope you can start to see the power of comparative analysis. Much of the sequencing analysis will largely be based on a similar process. Given the amount of variability in samples, we not be able to much with 100% certainty, but it's already leading to some interesting hypothesis.

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