Pedosphere 29(4): 444–456, 2019 doi:10.1016/S1002-0160(19)60814-3 ISSN 1002-0160/CN 32-1315/P c ⃝ 2019 Soil Science Society of China Published by Elsevier B.V. and Science Press Soil Organic Matter Composition in Coastal and Continental Date Palm Systems: Insights from Tunisian Oases Rawan K. MLIH 1,2 , Martina I. GOCKE 1,∗ , Roland BOL 2 , Anne E. BERNS 2 , Irabella FUHRMANN 1 and Nadhem BRAHIM 3 1 Institute of Crop Science and Resource Conservation, University of Bonn, Bonn 53115 (Germany) 2 Agrosphere Institute (IBG-3), Forschungszentrum J¨ ulich GmbH, J¨ ulich 52428 (Germany) 3 Department of Geology, University of Tunis El Manar, Tunis 2092 (Tunisia) (Received August 7, 2018; revised August 28, 2018) ABSTRACT In Tunisia, the coastal Chenini oasis is characterized by a lush vegetation cover, whereas more inland continental oases (e.g., the Guettaya oasis) have a very scarce vegetation cover. For sustaining date palm production in these areas, organic fertilizers are applied, either spread on the soil surface (in Chenini) or buried under a sand layer (in Guettaya). We examined at a molecular level how these management techniques affect soil organic matter composition in oasis systems. A dominance of fresh plant input for Guettaya was indicated by solid-state 13 C nuclear magnetic resonance spectroscopy signals, which was most pronounced in the uppermost soil close to palms. Evidence for more degraded organic matter was found in deeper soil near the palms, as well as in the soil distant from the palms. Amino sugar contents were low in the uppermost Guettaya soil near the palms. The overall microbial amino sugar residue contents were similar in range as those found in other dryland environments. With increasing distance from trees, the amino sugar contents declined in Guettaya, where the palms grow on bare soil, but this was not the case for Chenini, which has multi-layer vegetation cover under palms. In agreement with the results from previous dryland studies, the soil microbial community in both oasis systems was dominated by fungi in topsoil, and a shift toward bacteria-derived residues in subsurface soil. This might be due to higher variability of temperature and moisture in topsoil and/or lower degradability of fungal remains; however, further research is required to confirm this hypothesis. Key Words: amino sugar, dryland, microbial community, soil organic carbon, solid-state NMR, subsoil amelioration, total nitrogen Citation: Mlih R K, Gocke M I, Bol R, Berns A E, Fuhrmann I, Brahim N. 2019. Soil organic matter composition in coastal and continental date palm systems: Insights from Tunisian oases. Pedosphere. 29(4): 444–456. INTRODUCTION Date palms are one of the most important crops in oasis ecosystems, providing a major source of income for local farmers and the national economy (Tengberg, 2012; Zohary et al., 2012). The productivity of date palm groves in arid regions such as Tunisia is frequent- ly hampered by a negative annual water balance, ex- treme temperatures, wind erosion, as well as weak soil structure and low fertility. This is exacerbated by mis- management at the level of farmers and the removal of plant residues from agricultural land (Kouki and Bouhaouach, 2009). Soil salinity problems, owing to irrigation with salt-affected water (salt contents of up to 7.2 g L −1 ) and saline groundwater (Bouksila et al., 2013; Askri et al., 2014), have contributed to further serious deterioration of soil fertility, which threatens the sustainable production of date palms and other crops (Marlet et al., 2009). Moreover, in the absence of an effective drainage system, the rising of salt along with the groundwater table can occur when farmers flood the palm plots, which then brings additional salts to these plots (Hachicha et al., 2013). Date palm management in Tunisian oases frequent- ly involves addition of organic matter (OM) such as animal manure and plant residues (Rawls et al., 2003; Zem´anek, 2011; Mlih et al., 2016). For decades, far- mers in the continental Kebili region of Tunisia (Fig.1) have traditionally applied ca. 30 t of sheep or goat ma- nure per hectare every third year, which is then bu- ried under a sand layer near the palm trunks. Howe- ver, some individual variation in the actually applied amount occurs among farmers, depending on the avai- lability of manure and precise financial situation of the farmer at the time of application. This organic fertili- zer treatment secures the availability of nutrients for plant growth and helps maintain high moisture levels in the rooting zone of the date palms, with the sand * Corresponding author. E-mail: mgocke@uni-bonn.de.