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A New Sediment Catcher to Evaluate the Effect of Wind Erosion on Soil Fertility

Description

       Wind erosion causes enormous negative effects on the soil fertility through soil loss and associated soil nutrient loss in the Sahel or the semi-arid zone of West Africa, one of the most major desertification front lines in the world. Although coarse organic matter (COM), which is defined as free organic debris larger than 0.2 mm, plays a prominent role in soil nutrient dynamics in the semi-arid agro-ecosystems, we have not been able to quantify the flux of COM by wind erosion. The Big Spring Number Eight (BSNE) sampler, the most used sediment catcher, can trap COM blown higher than 50 mm above the ground but cannot estimate the COM flux accurately because most of the COM moves below 50 mm. Therefore, we aimed to develop a new sediment catcher, named as the Aeolian Materials Sampler (AMS), which can trap with better efficiency both the COM and soil particles moving below 50 mm during wind erosion events like frequent sand storms. As shown in Figure 1, the AMS has been designed to have three special features for the improvement of its trapping efficiency, 1) wedge-shaped with two mouths which draw the air and blown materials into the sampler by the Venturi effect, 2) an apron in front of the mouth which prevents scouring effects at the inlet, and 3) a collection pan which is long enough to ensure that the entering materials settle into it.
　　Wind-tunnel experiments showed that the trapping efficiency of the AMS for COM, TEcom (%), was constant at the range of wind velocities used, and is well described by the following equation (Fig. 2, r2 = 0.94 when TEcom was averaged for each angle):

TEcom = 61.0 + 18.0 exp (-0.06x)

　　where x stands for the angle of AMS to the wind direction (° ). It was also revealed that the AMS does not selectively trap COM, so that the particle size distribution of the original COM is preserved in the trapped COM.
The performance of the AMS was verified in the field of the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT-Niamey), Niger. The amount of remaining COM on the soil surface was calculated by subtracting the loss of COM measured using the AMS and the BSNE sampler from the initial amount of COM, which corresponded with the actual amount (Fig. 3). Thus, we can estimate how much nitrogen (N) or carbon (C) moves along with the COM blown in wind erosion events, when measuring the N or C content of the trapped COM.
Since the AMS is a buried type sampler and is unable to rotate (Fig. 1), it is effective in limited wind direction ranged ±45° against the set AMS. Therefore, it is necessary to use at least four AMS to cover all wind direction.

Figure, table

  1.  

    Fig. 1 Appearance of the AMS equipment at the study site.
    Fig. 1 Appearance of the AMS equipment at the study site.

  2.  

    Fig. 2. Trapping efficiency of the AMS for COM as a function of its angle to the wind.
    Fig. 2. Trapping efficiency of the AMS for COM as a function of its angle to the wind.

  3.  

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    Fig. 3. Changes in the actual amount of remaining COM on the soil surface as compared with the estimated amount by using the AMS and BSNE samplers(ralative value).
    The bars represent standard error.
Affiliation

Japan International Research Center for Agricultural Sciences Crop Production and Environment Division

Kyoto University

Term of research

FY2005～2007

Responsible researcher

IKAZAKI Kenta ( Kyoto University )

KAKEN Researcher No.: 70582021

SHINJO Hitoshi ( Kyoto University )

ORCID ID
0000-0002-7244-9558
KAKEN Researcher No.: 70359826

TANAKA Ueru ( Kyoto University )

KAKEN Researcher No.: 10231408

TOBITA Satoshi ( Crop Production and Environment Division )

ほか
Publication, etc.

IKAZAKI Kenta, SHINJO Hitoshi, TANAKA Ueru, TOBITA Satoshi, KOSAKI Takashi.（2007）：Development of a new sediment catcher to evaluate the effect of wind erosion on carbon dynamics in the Sahel, West Africa. International Symposium on Organic Matter Dynamics in Agro-Ecosystems, Poitiers, France, 16th -19th July, 2007

IKAZAKI et al. (2007) Abstracts from annual meetings of Japanese Society of Soil Science and Plant Nutrition, 118 

IKAZAKI Kenta, SHINJO Hitoshi, TANAKA Ueru, TOBITA Satoshi, KOSAKI Takashi. （2008）： Sediment catcher to evaluate the effect of wind erosion on carbon dynamics and nutrient cycling. Trans. ASABE （in press）

Japanese PDF

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