Visualizing clogging up of soil pores in the tropical degraded soils and their impact on green water productivity

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Poster prepared by Tigist Tebebu, Christine Baver, Cathelijne Stoof, and Tammo Steenhuis for the Nile Basin Development Challenge (NBDC) Science Workshop, Addis Ababa, Ethiopia, 9–10 July 2013

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Visualizing clogging up of soil pores in the tropical degraded soils and their impact on green water productivity

  1. 1. MethodsIntroduction Restrictive soil layers commonly known as hardpans restrict water and airflow in the soil profile and impede plant root growth below the plow depth (Busscher and Bauer 2003). Preventing hardpans to form or ameliorate existing hardpans will allow plants root more deeply, increase water infiltration and reduce runoff, all resulting in greater amounts of water available for the crop (i.e. green water). However, there has been a lack of research on understanding the influence of transported disturbed soil particles (colloids) from the surface to the subsurfaceto form restrictivesoil layers, which is a common occurrence in degraded soils. In this study we investigated the effect of disturbed soil particles on clogging up of soil poresto form hardpans. Tigist Tebebu*, ChristineBaver, CathelijneStoof, and Tammo Steenhuis Department of Biological and Environmental Engineering, Cornell University Visualizing clogging up of soil poresin thetropical degraded soilsand their impact on green water productivity *: Presenter, e-mail tyt7@cornell.edu a Results& Discussion Time series images in Fig 4. & a decrease in leachate sediment concentration with time in thelight absorbance graph in Fig 5. showed that accumulation of significant amount of soil particles occur in between sand particles and at air-water interfaces, indicating theclogging of soil pores occurs as a result of disturbed fine soil particles transported from thesoil surfaceto thesubsurface. FutureWork Further infiltration measurements are in progress to determine theeffect of moisturecontent, clay mineralogy, ionic strength, pore structure and infiltration rate on the transport and accumulation of clay particlesto form hardpans. Fig. 2Apictureshowing compacted soilsin the upper 60 cmabovethemacro porenetworksin a soil profilein theEthiopian highlands. Fig 3. Illustration of infiltration measurement showing themicroscopeconnected to thecamera capturing the vertical movement of soil solution in thecolumn. Image adapted from(Sang, 2012). References 1.Busscher, W. and P. Bauer. 2003. Soil strength, cotton root growth and lint yield in a southeastern USA coastal loamy sand. Soil and tillageresearch 74:151-159 2.FAO. 2005. Field preparation and planting. http://www.fao.org.Accessed February, 2013. 3.Sang, W., 2012. How Hydrofracking Flowback WastewaterInfluencesColloid Transport in Unsaturated PorousMedia. Soil and Water Lab Fig 1. Illustration of plant root deformed bya hardpan (left) and plant root growth in a ripped hardpan (right) (FAO, 2005). 10-60cm Hardpan Unsaturated sand column infiltration measurements were performed by applying 0.04g/ml soil/DI water solution on 0.00025-0.000425 & 0.000425-0.000625 mm diameter sand texture. The sand columns were exposed to constant influent rate of 0.5 ml/min for an hour and half controlling the inflow rate by a peristaltic pump. The leachates draining from the sand column were collected in cuvettes at five minute intervals at a five cm suction that was controlled by the bubble tower. Concurrently, transportation, circulation and deposition of clay particles (soil colloids) were visualized using a bright field microscope and time series images and short videos were captured. The experimental set up isshown in Fig.3 Soil solution Sediment concentration in the leachate was measured by determining the absorbance of radiation at a wavelength of 590 nm with a spectrophotometer. y = -0.0003x + 3.0 R² = 0.55 2.95 2.96 2.97 2.98 0 20 40 60 80 LightAbsorbance Time to leachate collection (minutes) Light absorbance at 590nm Linear (Light absorbance at 590nm) Figure4: Imagesof infiltration measurement showing thesand column at thestart of themeasurement, 30minutesof soil solution application, 1hr application and 2hrsafter thesecond soil solution infiltration on the previoussand column respectively. Figure5: Light absorbance plotted against leachates collection time. Our experiment show that forming of the hardpan in the Ethiopian soils can be related to the infiltration of sediment rich water after the soils are tilled and the soil cover is removed by plowing. Ameliorating of these pores clogging or preventing them to form can help to improve the rainwaterstoragecapacity of degraded soils. NBDC Science Workshop, 9-10 July, 203, Addis Ababa, Ethiopia This document is licensed for use under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License July 2013

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