Salinity evolution and crop response to secondary soil salinity in two agro-climatic zones in Lebanon

Abstract This paper reviews the human impact on land degradation through the integrated effect of fertilization and irrigation on secondary salinization for the different cropping patterns and agro-climatic zones of Lebanon. Agricultural operations in the semiarid northern areas of Lebanon are characterized by intensive open field and low tunnel production. Soil degradation has occurred because of the combined effect of mismanaged crop rotation, poor fertilization and irrigation policies. Monoculture and other agricultural practices caused salt accumulation in the soil (9.0 dS/m), which was then deserted after several years of exploitation. Under arid Mediterranean climate, these practices increased the vulnerability of an already fragile ecosystem. Because of water shortage, farmers relied on drip irrigation despite higher investment cost, although, the deterioration of soil quality was associated with the use of drip irrigation. The monitoring of soil quality indicated a self-recovery after several years of fallowing or a switch to a barley-based rotation. Instead of enhancing water use efficiency and properly managing the fertigation system, a replacement of drip by sprinklers is practiced. This is an indication that the introduction of modern irrigation systems is not sufficient, an improvement of agricultural practices and an upgrading of farmer's skills are required. Along the subhumid coastal strip, the area of greenhouses has expanded to 5000 ha. It is the most intensive cropping system in the country with a manure input reaching 60 t ha −1 added every 2 years and fertilizer input exceeding 1800 kg ha −1 of compound soluble and low-solubility fertilizers per season. Consequently, secondary soil salinity has reached 15–20 dS/m. A six-fold increase of soil salinity inside the greenhouses in comparison with the soil outside them was observed. A 5-year monitoring of the status of groundwater and soil on the Lebanese coast showed that the deterioration of soil quality is also linked to the mismanagement of fertilizer input and irrigation with low quality waters. Several zones are irrigated with well water which was subjected to seawater intrusion. In the southern coastal region, water salinity fluctuated around 3 dS/m. In regularly sampled wells, the chlorine content explained only 12% of the variation in total salinity of irrigation water (ECw). ECw explained 34% of soil salinity (ECe). Indeed, the level of ECw cannot justify the extent and seasonal fluctuation of ECe, which showed a peak of 50 dS/m. Replacing drip by sprinklers is not the proper solution in an area with severe shortage in fresh water. Instead, improving the management of water and nutrients inputs and increasing their use efficiency is a necessary step to conserve the limited natural resources in the country.