Background. Background. Objective. Table of Contents 11/16/2012. Effects of wind erosion on water balance in a crop field in the Sahel, West Africa

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1 11/16/212 Effects of wind erosion on water balance in a crop field in the Sahel, West Africa Table of Contents 1.Background 2.Introduction of lysimeter designed 3.Highlight data showing the effects of soil surface status on water balance in a crop field 4. Summary K. Ikazaki 1, H. Shinjo 2, U. Tanaka 3, H. Ishikawa 2, S. Funakawa 2, T. Kosaki 1 ( 1 Tokyo Metropolitan University, 2 Kyoto University, 3 RIHN) Background Background The Sahel, West Africa South fringe of the Sahara Desert (5 km long 4 km wide) Dry savanna (annual rainfall: 2 6 mm) Pearl millet is grown without fertilizer The Sahara Desert S A H E L Annual Rainfall in West Africa (Brouwer J. and Bouma J. 1997) The Sahel, West Africa Low soil fertility due to very sandy soils (Psamments or Arenosols) limits the growth of crops Food shortage S A H E L Desertification by wind erosion severely affects soil fertility Soil map (FAO/EC/ISRIC 23) Mechanism of desertification by wind erosion 2-3cm Soil loss: 6-8 Mg/ha/yr (4-5 mm/yr) Loose layer (high HC) Crust layer (low HC) References: Ikazaki et al. 29 Trans. 5 ASABE mm (21 Paper Award) Ikazaki et al. 21 Pedologist Ikazaki et al. 211a Trans. ASABE Ikazaki et al. 211b SSSAJ Ikazaki et al. 212 Pedologist Objective To evaluate the effects of soil surface status on the water balance in a crop field in the Sahel using the lysimeter Topsoil of Sahelian soil Loss of loose layer Loss of soil nutrients (e.g., 4-5 kgn/ha) Decrease in HC 1

2 11/16/212 Materials and Methods Site description Niamey IWCA N 2km 2 m 3mm 65mm Study site ICRISAT West and Central Africa Climate Dry savanna Mean annual rainfall: 53 mm Mean annual temperature: 29 C Soil Quartzipsamments Sand:95% Silt:2% Cray:3% Total C:.3% Total N:.3% ph (H 2 O):5 6 (in topsoil of 5cm) 2 cm Surface 2 cm Materials and Methods Design of lysimeter 2 grade Cross section Water tank (D= 2. m, H= 2.3m) Runoff meter Sahelian soil (Sand 9%, Silt 5%, Clay 5%, Bulk density 1.6) Stainless mesh (opening.15 mm) Punching metal (D= 3 mm, P= 5mm) Gravels (size: 2-3 cm) Outlet of discharge Materials and Methods Setting of lysimeter 2 cm Surface Matric potential sensor (Campbell, 253) 2 cm TDR soil water sensor (Campbell, CS616) Temperature sensor (Campbell, 18) Cross section 2

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4 Field hydraulic conductivity (cm s 1 ) Daily rainfall (mm/d) Runoff rate (%) Runoff rate (%) 11/16/212 Treatments in 211 Plot Thickness of Loose Layer Vegetation cm (eroded field) 3 cm (uneroded field) 7 cm (field which trapped eroded soil) Pearl millet Pearl millet Pearl millet Measurements Field hydraulic conductivity Rainfall (every 1min) Runoff (every event) Discharge (everyday) Soil volumetric water content (every 1min) ET (estimated from above-mentioned values) Results and Discussion (Runoff) Jun Jul Aug Sep b Oct Thickness of Bar = SE b Loose Layer Annual runoff 75.1 P<.1 cm 22 mm (46%) 5 3 cm 4 mm (9.5%).5 25 a Jun Jul Aug Sep Oct cm 3 cm 7 cm Annual rainfall: 44 mm 7 cm 21 mm (5%) When Thickness the crust of Loose layer Layer is exposed, the drought condition can be easily reproduced in the soil Results and Discussion (Runoff) Rainfall intensity (mm/1min) Thickness of Loose Layer cm 3 cm 7 cm When crust is exposed, runoff will occur even at 1.2 mm/1min 4

5 Daily rainfall (mm/d) 日降水量 (mm/ 日 ) Discharge (mm/d) Nitrogen loss (kg ha 1 ) Content (%) 日降水量 (mm/ 日 ) 窒素損失量 (%) 11/16/212 Results and Discussion (discharge) Summary Jun Jul Aug Sep Oct Annual rainfall: 44 mm Thickness of Loose Layer Annual discharge cm 3 mm (<1%) 3 cm 41 mm (9.5%) 7 cm 46 mm (1.5%) When crust is exposed, discharge will be negligible 2-3cm 9.5 Loose layer (high HC) Crust layer (low HC) Wind erosion Crust layer (low HC) The exposure of crust layer which results in decrease in HC of topsoil is a major process of desertification by wind erosion <1 Thank you very much for your attention!! Soil physical properties Particle size distribution 5 Clay Silt F Sand ** C Sand 4 Crust layer 3 Loose layer 2 ** * P<.5 1 ** P<.1 ** * * Soil crust was exposed Diameter (μm) Contact to ikazaki@tmu.ac.jp Soil crust will not be formed in the soils with Clay+Silt content < 5% (Ambouta et al. (1996)) Nitrogen loss associated with runoff 窒素の溶脱量 2 年間降水量 :44 mm 2 年間降水量 :44 mm ルーズな砂層の厚さ cm 表面流去による損失量の合計 2.5 kg ha 1 3 cm.3 kg ha 1 7 cm.2 kg ha ルーズな砂層の厚さ 2m 以下への排水量 cm.5 kg ha 1 3 cm 3.5 kg ha 1 7 cm 9. kg ha 1 6 月 7 月 8 月 9 月 1 月 6 月 7 月 8 月 9 月 1 月 流出率の高さを反映し クラスト露出区で損失量が多い 排水量の低さを反映し クラスト露出区では窒素の溶脱が起こらない 5

6 11/16/212 Summary (nitrogen balance) 風食 : 4~5kg/ha 湿性降下物 :5kg/ha 乾性降下物 :3kg/ha 3cm 水食 :<1kg/ha 表面流去 : <1kg/ha(3cm 区 ) 2.5kg/ha( クラスト露出区 ) ルーズな砂層 ( 透水性高 ) クラスト層 ( 透水性低 ) 吸収 :1~2kg/ha 溶脱 :3.5kg/ha(3cm 区 ).5kg/ha ( クラスト露出区 ) 6