Martinho António dos Santos Martins: The effects of Biochar concentration in soil on erosion and infiltration

STSM at Institute of Water and Environmental Sciences, Volcani Center, Israel

The purpose of this Short-term Scientfic Mission was to identify the relationships between biochar concentration in soil and erosion of soil and biochar particles, for a sandy loam soil. The ‘perforated tray rotating disc type rainfall simulator’ of the host institute will allow for collecting both the run-off and the water percolated through the soil. The experimental facilities also facilitate running replicate rainfall simulation experiments (RSEs). Both types of water samples will be analysed for pH, electrical conductivity, optical density, sodium absorption ratio and particle size (soil and biochar). The Soil and soil with the bioxar will also be analysed for turbidity with a new plastic optical fibre-based sensor (Bilro et al. 2010), which has been developed at the University of Aveiro. The infiltration rate will be calculated from the measured percolated water.
The working hypotheses were:

i) the contrasting soils have different relationships between biochar concentration and soil hydrology (infiltration/erosion)

ii) water samples with suspended biochar will require modified calibration values for optical turbidity sensing.

Description of the work carried out during the STSM


During this STSM was run a total of five different rainfall simulations (Control with no soil incubation, soil+biochar (80ton/ha rate) without incubation, control with incubation, soil+bichar (80ton/ha rate) with incubation, and soil+bichar (20ton/ha rate) with no incubation.
Soil preparation and incubation
The soil from an agricultural field at the host institute were passed through a 4 mm sieve and then packed to a mean bulk density of 1.56 (±0.03) Mg m-3 as a 0.02 m layer in 0.5 x 0.3 m perforated tray used as the control for this study. The soil was homogenously packed without any pressure through the tray and water added to 60% of water holding capacity. Four trays were selected to be incubated in a dark room at 30°C during two days, than water to 60% of water holding capacity was added again. This procedure was repeated every two days until a maximum of 7 days of incubation. The other four trays were used in the rainfall simulation experiment without incubation.
With the same soil type, twelve trays were mixed with biochar (69% C, 19% ash, 12% volatile matter). The soil and biochar were mixed at selected proportions of 4.1% (w/w) equivalent to 80 Mg/ha in eight trays and 1.3% (w/w) equivalent to 20 Mg/ha in the last four trays, this mix resulted in a bulk density of 1.65 (±0.03) Mg m-3 in the 80/ha trays and 1.52 (±0.03) Mg m-3 in the 20 Mg/ha trays. The soil + biochar was homogenously packed without any pressure through the tray and water added to 60% of water holding capacity. After four of the 80 Mg/ha trays were selected to be incubated using the same procedure as the incubated control plots and the other four trays with 80 Mg/ha and the four with 20 Mg/ha were used in the rainfall simulation experiment without incubation.

Rainfall simulation Experiments (RSEs)

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Fig 1: Control tray (left) and Soil+ Biochar tray (right) for the rainfall simulation experiment

A ‘perforated tray rotating disc type rainfall simulator’ was used, with the rainfall simulation as described by Ben-Hur and Wakindiki (2004).Before the placement of the trays in position, the rainfall hose and the rotate system, are tested to assure that the speed and intensity are in accordance to the plan. Each tray is placed in one of the 5 positions of the rotating disc at a gradient of 9%, and the fifth tray is used as a control to the rainfall intensity (54 mm/h).
Each RSE are divided in 4 time periods (approximately 20 minutes), according to a total rainfall of 18 mm, performing a 0-18, 18-36, 36-54, 54-72mm of cumulative samples. In each period the runoff volume of each tray was measured and collected for further analysis. The leaching volume was measured using a fraction method, where every 2 minutes the volume of a completed round in the simulator were measured and the liquid joined according the correspondent period (18, 36, 54, 72 mm) to further analysis.
After the RSE ended the last bottles was kept in place for 5 min to collect all the remaining runoff and leaching. The trays were then taken out and left drying during 3 days to assess the crust formation on the soil. After measuring the total volume, a small amount (100 mL) was taken and kept at 0°C for further analysis of pH, electrical conductivity, optical density, sodium absorption ratio from every of the 32 runoff and 32 leaching samples. The rest of the sample was left for sediment content, and particle size distribution analysis.

 

Main Results

1) Infiltration

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Fig. 2: Infiltration results

 

The Infiltration data suggest that there is no significant difference between a rainfall simulation experiments (RSE) with incubation and without for control soil and soil+biochar. Also there were no significant difference in the infiltration rate between an application of 80ton/ha and 20ton/ha.

2) Runoff

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Fig. 3: Runoff results

The runoff data suggest that the RSE with incubation decreases the difference between the control soil and soil+biochar. Without incubation there is a significant difference in the cumulative runoff between the biochar and the control.

3) pH

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Fig. 4: pH results

The pH in the control trays with and without incubation shows no relevant change. However, the biochar trays reveal a decrease in pH for the greater biochar application rate (80 t/ha), but no significant difference betweenwith and without incubation.

4) Electrical conductivity (EC)

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Fig. 5:  EC results

The EC data suggest that there are no significant difference between the control Soil and Soil+biochar after the incubation. Whereas without incubation, the control soil seems to be lower with the cumulative rain increasing.

Besides these preliminary results, there are more data that will be analyzed in the near future by the applicant in the University of Aveiro (applicant institution), such as sediments eroded, sodium absorption ratio, optical density, particle size distribution, nutrients, organic carbon and optical turbidity calibration.

Future collaboration with the host institution


The host and the applicant institutions appreciated the opportunity of collaborating through this STSM. Many data were generated in a relatively short time period. Plans are being discussed between the host and applicant institutions for follow-up research using successive rainfall simulation experiments to ascertain the longevity of the observed effect on infiltration.


Foreseen publications/articles resulting or to result from the STSM


The work performed as part of this STSM will be elaborated upon and analyzed statistically before consideration of submitting it as an original research article to an appropriate ISI journal, e.g. Science of the Total Environment, in which the COST Action will be duly acknowledged.
In addition, the data already analyzed will be submitted to a poster communication the ESF- Exploratory Workshop: impact of natural and anthropogenic pyrogenic carbon in Mediterranean ecosystems, 5th – 7th November, 2013 Sevilla (Spain). The COST Action will be duly acknowledged in the poster.

References


Ben-Hur, M. and Wakindiki, I.I.C. Soil mineralogy and slope effects on infiltration, interrill erosion, and slope factor (2004).
Bilro, L., Prats, S.A., Pinto, J.L., Keizer, J.J., Nogueira, R.N. TECHNICAL DESIGN NOTE - Design and performance assessment of a plastic optical fibre-based sensor for measuring water turbidity. Meas. Sci. Technol. 21 (2010).
Busscher, W.J., Novak, J.M., Evans, D.E., Watts, D.W., Niandou, M.A.S., Ahmedna, M. Influence of pecan biochar on physical properties of a Norfolk loamy sand Soil Science 175 (1) , pp. 10-14 (2010).
Tryon, E.H., 1948. Effect of charcoal on certain physical, chemical, and biological properties of forest soils. Ecological Monographs 18(1): 83-113.
Verheijen, F.G.A. , Jeffery, S., , Bastos, A.C. , van der Velde, M. , Diafas, I.(2010) Biochar Application to Soils - A Critical Scientific Review of Effects on Soil Properties, Processes and Functions. Joint Research Centre (JRC) Scientific and Technical Report. Luxembourg. Office for the Official Publications of the European Communities, Luxembourg. 149. pp