Reservoir siltation because of water erosion is an important environmental issue in Mediterranean countries where storage of clear surface water is crucial for their economic and agricultural development. The high density of gully systems observed in Mediterranean regions raises the question of their contribution to reservoir siltation. In this context, this study quantified the absolute and relative contributions of rill/interrill and gully/channel erosion in sediment accumulation at the outlet of small Tunisian catchments (0·1–10 km2) during the last 15 years (1995–2010). To this end, a fingerprinting method based on measurements of caesium‐137 and total organic carbon combined with long‐term field monitoring of catchment sediment yield was applied to five catchments in order to cover the diversity of environmental conditions found along the Tunisian Ridge and in the Cape Bon region. Results showed the very large variability of erosion processes among the selected catchments, with rill/interrill erosion contributions to sediment accumulated in outlet reservoirs ranging from 20 to 80%. Overall, rill/interrill erosion was the dominant process controlling reservoir siltation in three catchments whereas gully/channel erosion dominated in the other two catchments. We identified the presence of marly gypsum substrates and the proportion of catchment surface covered by soil management/conservation measures as the main drivers of erosion process variability at the catchment scale. These results provided a sound basis to propose guidelines for erosion mitigation in these Mediterranean environments and suggested to apply models simulating both rill/interrill and gully/channel erosion in catchments of the region. Copyright © 2015 John Wiley & Sons, Ltd.

BACKGROUND: The agricultural production system and cultivation practices are critical factors in determining yield and food nutritional quality. Controversy remains regarding whether or not organic foods have a nutritional advantage when compared with their conventionally produced counterparts. In this study the effect of conventional and organic production systems on yield, physicochemical and nutritional properties of four field tomato cultivars (Perfectpeel, Rio Grande, Hypeel 108 and Firenze) was determined. In the organic system, different fertiliser combination treatments were used.

Purpose: Approximately 74% of Tunisian agricultural soils are affected by water erosion, 44 leading to the siltation of numerous man-made reservoirs and therefore a loss of water storage 45 capacity. The objective of this paper is to propose a methodology for estimating the relative 46 contributions of gully/channel bank erosion and surface topsoil erosion to the sediment 47 accumulated in small reservoirs. Materials and methods: We tested an approach based on the sediment fingerprinting technique 49 for sediments collected in a reservoir installed in 1994 at the outlet of a pilot catchment 50 (Kamech, 2.63 km²). Sampling efforts were concentrated on the soil surface (in both cropland 51 and grassland), gullies and channel banks. A total of 17 sediment cores were collected along a 52 longitudinal transect of the Kamech reservoir to investigate the sediment origin throughout 53 the reservoir. Radionuclides (particularly caesium-137) and nutrients (organic matter, total 54 phosphorous and total nitrogen) were analysed as potential tracers. 55 Results and discussion: The applications of the mixing model with caesium-137 alone or 56 caesium-137 and total organic carbon provided very similar results: the dominant source of 57 sediment was surface erosion, which was responsible for 80% of the total erosion within the 58 Kamech catchment. Additionally, we showed that the analysis of a single composite core 59 sample provided information on the sediment origin that was consistent with the analysis of 60 all successive sediment layers observed in the core. We demonstrated the importance of the 61 core sampling location within the reservoir for obtaining reliable information regarding 62 sediment sources and the dominant erosion processes. 63 Conclusions: The dominance of surface erosion processes indicates that conservation farming 64 practices are required to mitigate erosion in the Kamech agricultural catchment. Based on the 65 results from 17 sediment cores, guidelines regarding the number and location of sampling 66 cores to be collected for fingerprinting purposes are proposed. We showed that the collection 67 of two cores limited the sediment source apportionment uncertainty due to the core sampling 68 scheme to less than 10%.

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The efficiency of two mycorrhizal bio-inoculants on the mineral uptake during the growth stages of a Mediterranean forage legume sulla (Hedysarum coronarium L.) was studied in the field on a highly calcareous soil. The first inoculum (Mm) was made up of a mixture of native arbuscular mycorrhizal fungi (AMF) isolated from calcareous soils: Septoglomus constrictum, Funneliformis geosporum, Glomus fuegianum, Rhizophagus irregularis and Glomus sp. The second was a commercial inoculum (Mi) containing one AMF species: R. irregularis. Both mycorrhizal inoculants increased total and arbuscular colonization of sulla roots. Inoculation with Mm showed a positive effect on sulla shoot dry weight (SDW) when compared to Mi and non-inoculated plants (control). Mineral contents (P, Mg, Mn, Fe) were higher in the shoots of sulla plants cultivated on mycorrhiza-inoculated plots compared to non-inoculated ones. This enhancement was observed during the flowering stage for P, Mg and Mn and during the rosette stage for Fe. An increase in P content of 50 % in plants inoculated with Mm compared to non-inoculated ones may be explained by the induction of root alkaline and acid phosphatase activities. Higher efficiency of native AMF species adapted to calcareous soils opens the way towards the development of mycorrhiza bio-fertilizers targeted to improve sustainable fertilization management in such soils.

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