Effect of Wood Biochar Amendment to Sand on Leachate Water Quality with Repeated Dairy Manure Application: A Soil Column Study
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The full proceedings paper is at: http://www.extension.org/72741 Agricultural operations can pose a threat to the quality of nearby water sources, particularly from nitrogen and phosphorus losses following land application of manure. Biochar application to soils has the potential to ameliorate degraded soils and reduce nutrient leaching to groundwater. The effects of amending sand soil columns with hybrid poplar biochar made by a slow pyrolysis process at 450°C at varying rates (0, 1, 2 and 5% by weight) with repeated dairy manure applications over a 56-week period was examined to evaluate the impact to leachate water quality.
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Effect of Wood Biochar Amendment to Sand on Leachate Water Quality with Repeated Dairy Manure Application: A Soil Column Study
- 1. Effect of Wood Biochar Amendment to Sand on Leachate Water Quality with Repeated Dairy Manure Application: A Soil Column Study Alysa Bradley UW-Madison, WI April 2, 2015
- 2. Presentation Outline Introduction Experimental Design Leachate Results Retention Results Conclusions Limitations and Recommendations for Future Work
- 3. Introduction
- 4. Introduction Biochar - a carbon-rich substance produced as a co- product by the thermal degradation of organic matter under a limited supply of oxygen.
- 5. Experimental Design: Biochar • Hybrid poplar chips • Slow pyrolysis at 450°C • Applied at rates of 1, 2 and 5 % by weight.
- 6. Experimental Design: Soil columns 5% 2% 1% 0% C
- 7. Experimental Design: Leaching – Volume – pH – Biological Oxygen Demand (BOD5) – Nitrite (NO2) – Nitrate+Nitrite (NO3+NO2) – Total Phosphorous (TP) – Total Nitrogen (TN) – Total Kjeldahl Nitrogen – Ammonia
- 8. 5% 2% 1% 0% C
- 17. Nutrient Retention Results: TP
- 18. Conclusions Hybrid poplar biochar in sand: • Increased leachate pH • Decreased leachate BOD5 • Decreased leachate nitrogen • Some increased TP in leachate
- 19. Limitations and Recommendations• Limitations • Simulated precipitation • Relatively constant temperature • No plantings • No measured soil emissions • Recommendations • N cycling and mechanisms for change • Effect on emissions and crop yields • Field trials • Alternative application strategies
- 20. Questions?
Editor's Notes
- Pause (start presentation) Alright, so this presentation is on the (read).
- Pause (give the organization of presentation topics) Here is a quick overview of the presentation – We’ll have a brief introduction, I’ll describe the experimental design, then we’ll take a look at the leachate results and some of the nutrient retention results (what was left in the columns at the end after we cut them open). Then I’ll give some of the conclusions we took from the study. As a laboratory soil column study, there were some inherent limitations which I will address at the end along with some recommendations for future work that I think would be relevant and useful. And then we should have a few minutes for questions!
- Pause (establish problem – pollution from fertilizer use) In this study, we focused on nutrient leaching to groundwater. Nitrate is a particular concern because it is easily leached, potentially toxic to fish, has human health impacts and in WI it’s our most prevalent groundwater contaminant. The EPA drinking water limit is 10 mg/L and contaminated wells tend to be concentrated in areas of high cultivation. The pie chart here (from Shaw, 1994 in a WI DNR report) shows sources, with 90% attributed to agriculture.
- Pause (introduce biochar) Biochar is a byproduct of biomass pyrolysis. Pyrolysis can be used to produce energy and bio-oil, which has some potential as a petroleum substitute in the future. It is carbon-rich, typically very porous (which you can see in the Scanning Electron Microscope image here (From pp 25, Chapter 2 of Biochar for Environmental Management) with high surface area and very low density. The exact properties of a given biochar are highly dependent on the feedstock material, and also dependent on pyrolysis type and temperature. Biochar amended to soils in previous studies has been shown, with some variability, to decrease nutrient leaching.
- Pause (introduce experimental design – biochar) The biochar we used was from hybrid poplar woodchips made by a slow pyrolysis process - about an hour - at 450°C. We sieved to a particle size of 2mm or less. Treatments were sand and biochar mixtures at 0, 1, 2 and 5% by weight.
- Pause (show/explain picture) This is just a photo of our columns - There were four replicates of each treatment. From left to right the treatments are 5% biochar (point), 2% (point), 1% (point), 0 (point) and a control which was leached but did not receive manure (point). The manure used was a liquid dairy manure with an average solids content of 5.6%, which is pretty typical. The application rate was high, corresponding to roughly 20,000 gallons per acre, which is about twice the local recommendation. Manure was reapplied once every 3 months (14 weeks) for a total of four applications over about a year (56 week study period). All columns were packed to an 8” depth, which is about 20 cm, and is a typical plough depth. (Because of biochar’s low density the total mass in columns was not uniform.)
- Pause (give details on experimental design – leaching events) All columns (including the control) were leached once every other week with deionized water. Columns were allowed to drain completely and leachate volume (point) and pH (point) were measured as well as BOD5 (point). Nitrite (point) and Nitrate+Nitrite (point) were both measured for all leaching events and Nitrate was calculated from those. TP (point) was measured for all leaching events. TN (point) was measured for all but the first two leaching events. TKN (point) was measured for the first and last manure application cycles, mostly as a double check for the TN method. Ammonia (point) in leachate was measured starting with the 2nd manure application. Organic N was calculated starting with the the 2nd manure application by subtracting the ammonia and nitrate+nitrite values from the TN value.
- Pause (show/explain picture) This is a picture of the leachate shortly after the third manure application, which I think is just a nice visual. From left to right the treatments are 5% (point) 2% (point), 1% (point), 0% (point) and control (point). You can sort of see that the no biochar leachate is darker than the rest and the color gets lighter with greater biochar amendment rate (point). We suspect that the color is from solids or organic matter, but these were not measured in the study.
- Pause (present pH results – explain figure) This figure shows the average pH (note the axis range) at each leaching event (point out horizontal axis) for each treatment (point out legend – 5%, 2%, 1% and no biochar treatments). Overall, increasing biochar amendment rate increased leachate pH, which made sense because the biochar pH was slightly higher than the sand pH - biochar was a little over 9, sand was 8.85. These drops in pH that you can see (point) occurred at the 2nd (point), 3rd (point) and final (point) manure applications. This is likely due to some bypass flow because the pH of the treatments was higher than the applied manure.
- Pause (present BOD results – explain figure) BOD in the leachate peaked with the first leaching event after each manure application and dropped off sharply for all treatment columns. This figure shows the average BOD (point out vertical axis) at the leaching event immediately following each manure application (point out horizontal axis) for each treatment (point out legend). The data are presented this way partially because we had some missing data (my estimates were off and there’s only one shot with this type of analysis) and because the values dropped off so sharply.
- Pause (present cumulative TN results – explain figure) TN in the leachate increases after each manure application (point – 1st, 2nd, 3rd, and 4th manure applications). And as you can see in this figure, increasing biochar amendment rate reduces TN leaching (point out treatments and colors).
- Pause (present cumulative nitrate results – explain figure) Like TN, leachate NO₃ increases more sharply after each manure application. Also like TN, increasing biochar amendment rate reduced NO₃ leaching (point out treatments and colors).
- Pause (present nitrate concentrations related to drinking water requirements – explain figure) So I wanted to show nitrate on a week-to-week basis so we can see how the concentration in leachate can decrease with biochar amendment. I mentioned earlier that the drinking water limit for nitrate is 10 mg/L and you can see that the maximum concentrations leached are very large (point out vertical axis), especially at the third peak nitrogen leaching event after the third manure application.
- Pause (present cumulative ammonia results – explain figure) This is leachate ammonia, which we started measuring after the second manure application cycle (point to axis). Leachate ammonia followed a similar pattern to TN and NO3, with very clear differences between the treatments. There are pretty sharp increases after each manure application. And as you can see in this figure, increasing biochar amendment rate reduces ammonia leaching (point out treatments and colors).
- Pause (present cumulative TP results – explain figure) So TP in leachate followed the opposite trend from the nitrogen species and actually increased with increasing biochar amendment 5 (point), 2 (point) 1 (point) and 0 (point). But if you look at the total amount leached (point out axis) it was still pretty low compared to the total P input, which was about 300 mg for the treatment columns (285 – 318).
- Pause (present N mass balance – explain figure) So this figure is from a mass balance of nitrogen in the columns. It’s shown by percent (point out vertical axis) because the total N in each column was not uniform. For each treatment (point out horizontal axis), there’s the percent leached (point), the percent retained (point) and the leftover, which was assumed to be emitted (point). The emissions were not measured directly, so there’s no way to know whether the emitted N was N₂, N₂O, or NH₃. Because of the high pH, at least some ammonia volatilization was probable.
- Pause (present P mass balance – explain figure) And here we have a similar balance for P. I mentioned earlier that the total amount of P leached was low compared to applied – you can see that the vast majority was retained for all treatments (point). The largest percentage of leaching was in the 5M treatment, but was still under 10%, and actually when we looked at it as a function of the total mass of substrate (sand and biochar) in the column, there was no difference between treatments.
- Pause (briefly present conclusions) So, some of the conclusions we came to from the study - increasing amendment rates of biochar were found to increase leachate pH, and TP leaching, but decrease leachate BOD5, and N species (Total Nitrogen, Nitrate, Ammonia and Organic N). However, N emissions were increased with increasing biochar amendment levels, though the form of those emissions was not measured in this study.
- Pause (outline study limitations and make recommendations for future study) So some of the limitations to this study were inherent to soil column studies, like the simulated precipitation and laboratory temperatures throughout the course of the year. Also, there were no plantings on our soil columns, so we don’t know the potential effects on plant productivity. We also didn’t directly measure the emissions from soil, so we don’t know these effects either. Some of the recommendations for moving forward are additional study into the effects on N cycling and trying to at least narrow down the mechanisms responsible for the observed changes. Also field trials with emissions measurements and to determine the effect(s) on crops. Other application strategies should also be studied. In our columns the biochar was mixed into the soil as homogeneously as possible, which would be difficult to accomplish in the field. Mixing biochar with liquid manure before application or biochar applied as a filter, for example in a filter strip, should also be studied.