Assessing soil quality of Ramli agricultural plots (northern Tunisia): a FAO globally important agricultural heritage system

The Ramli is an agricultural practice involving the cultivation of crops on sandy substrates in the lagoons of the Ghar El Melh area in northern Tunisia. These unique 17th-century gardens were created due to a lack of cultivable land and fresh water. The Ramli system at this site has been recognised by the Food and Agriculture Organization of the United Nations (FAO) as a Globally Important Agricultural Heritage System (GIAHS) because of its unique traditional practices, which have been adapted to sandy and wetland environments. This agricultural practice involves growing crops in sandy soil. The plant roots are supplied with rainwater that floats on the surface of seawater and is moved by the tides. This agro-environmental system allows crops to be grown all year round, even during periods of drought, without the need for an artificial water supply. However, this site is affected by climate change, rapid urban growth, and intensive human activity, which have damaged the ecosystem and reduced agricultural production. This study aims to determine the physicochemical properties, fertility status and elemental composition of agricultural soils in Ramli using laser-induced breakdown spectroscopy (LIBS). The chemical and fertility indicators were determined, including organic matter, cation exchange capacity (CEC), the C/N ratio, pH, total and active carbonates, electrical conductivity, and the concentrations of exchangeable cations (Sodium, potassium, Magnesium and Calcium) and micronutrients (Fe, bromine and Chloride). The results of soil analysis of Ramli crops show that the soil texture is silty-sandy, with a predominance of sand. The soils are alkaline, with levels ranging from 7.88 to 8.26. Salinity values range from 0.273 to 1.68 mS/cm, with higher values localised in the southwest and northeast zones. This indicates the influence of low rainfall and weak communication between the lagoon and the sebkha, promoting the retention of soluble salts. The cation exchange capacity (CEC) values range between 3.54 and 9.55 mS/cm, and the C/N ratio in the study area varies between 7.02 and 10.01. The percentage of organic matter is less than 14%. Nutrient analysis of Sodium (g/kg), Chloride (g/kg), Potassium (g/kg), Magnesium (g/kg), Calcium (g/kg), Phosphorus (mg/kg), and Total Kjeldahl Nitrogen (%) shows that the plots in the study area are generally poor in these elements. The presence of bromine (Br) in soil samples can indicate pesticide or herbicide contamination. Indeed, the Ramli soils are associated with low water retention and limited fertility, making them vulnerable to drought and nutrient deficiencies. These results highlight the importance of adopting appropriate agricultural practices to ensure the sustainability of agriculture in the region.

Funding

The present work was funded by the research and innovation action “Soil Health and Agriculture Resilience through an Integrated Geographical information systems of Mediterranean Drylands” (SHARInG-MeD) funded by the “Partnership for Research & Innovation in the Mediterranean Area” (PRIMA Foundation) under the grant agreement number 2211.