A/Prof. Soh Sugihara1, Mr. Kazuaki Murayama1, Dr. Kenta Ikazaki2, Dr. Dougbedji Fatondji3, A/Prof. Haruo Tanaka1, Prof. Takashi Kosaki4, Prof. Shinya Funakawa5

1Tokyo University of Agriculture and Technology, , Japan, 2JIRCAS, , Japan, 3ICRISAT, Niamey, Niger, 4Aichi University, , Japan, 5Kyoto University, , Japan

Nutrient-poor sandy soils are widely distributed in the Sahel region, causing hunger and poverty in combination with a severe dry climate. Generally, fallow management is expected to increase the stable SOM associated with clay minerals or aggregates, but in Sahelian sandy soil, this might not occur and there are likely to be alternative mechanisms of SOM restoration. In this study, we verified the hypothesis that fallow management in Sahel mainly increases labile OM, e.g., plant residues, and that it significantly contributes to SOM restoration. We collected soil samples from continuously cultivated (C plot) and long-term preserved plots, i.e., fallow plot (F plot; > 30 yrs) in ICRISAT West and Central Africa, Niger (5 layers from 0–30 cm depth; 5 replications). We measured the total carbon (TC) and nitrogen (TN), clay contents, and bulk density. Then, we also measured light fraction (LF; < 1.6 Mg m−3) as labile OM and heavy fraction (HF; ≥ 1.6 Mg m−3) as stable OM. Increases in TC and TN were observed in all soil layers, particularly at the surface in F plots. TC was 11.8 and 7.7 Mg C ha−1, LF-C was 3.3 and 0.9 Mg C ha−1, TN was 809 and 468 kg N ha−1, and LF-N was 202 and 59 kg N ha−1 (0–30 cm depth) in F and C plots, respectively. Long-term fallow management clearly increased SOM, and the increase in LF-OM largely accounted for the increase in TC (59%) and TN (42%). In addition, we found there was no difference in HF-C per clay contents between F and C plots, indicating that the increment of HF-C in F plots was mainly caused by clay accumulation because of the capture of Harmattan dust. Thus, our hypothesis was confirmed, and the significance of clay accumulation by fallow management was also suggested.


Soh Sugihara is A/Professor for Soil Science at the Tokyo University of Agriculture and Technology, Japan. He received his Ph.D. from Kyoto University in Soil Science (2010). His research interest is C/N/P dynamics in the tropical agro-ecosystems, and those management for sustainable agriculture.

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