Published as FARA Research Report Volume 3 No: 6 (2018)
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Durum wheat (DW) is a major crop in Tunisia as it is the base of the local diet. It occupies more than 50% of the area occupied by cereals and the mean production cover about 70% of national demand (Bachta, 2011). This deficit penalizes the country’s trade balance since it is filled by importation of variable quantities of DW and bread wheat depending of the annual production. In fact DW production is highly variable and closely linked to variability of the precipitation amount during growing season (Latiri et al., 2010). On the other hand, soil degradation due to intensive land cultivation based on multiple tillages poses serious challenges to agricultural sustainability and on food security of the country.
In fact, the tillage-based agriculture contributes to soil structure disruption, soil organic matter and associated soil life and biodiversity depletion (Gathala et al., 2011). In Tunisia, soil erosion is the main threat causing on-site and offsite damages in wheat growing-area. These disturbances will be accentuated in the future due to climate change, seriously striking all Tunisian regions (GIZ, 2007; Lhomme et al., 2009), which has been qualified as the « hot spot for climate change» (Giorgi and Lionello, 2008). This alarming situation requires a sustainable intensification of wheat based-system by improving the natural resources uses. In this perspective a group of crop management practices termed “conservation agriculture” (CA) are widely promoted to increase crop yields, reduce soil degradation and develop systems that are more resilient to climate change (Kassam et al., 2009; Mrabet, 2011).
CA is based on three complementary pillars: i) reduced tillage, ii) retention of adequate levels of crop residues and permanent soil surface cover, iii) Crop diversification and use of adequate crop sequences.
CA is well known as a mean to restore soil degradation and to maintain soil security. CA allows to increase water infiltration and to reduce water evaporation and erosion (Thierfelder and Wall, 2009). By protecting the soil surface from direct impact of high-energy raindrops, soil surface cover in CA prevents surface-sealing and thus maintains the soil’s infiltration capacity, while at the same time minimizing soil evaporation (Jemai et al., 2012). Moreover, CA-practicing farmers stabilize their rainfed cereal production, even in slight-drought years, securing therefore a minimum income (Fredenburg, 2012). The economic benefits of CA include savings in expenditures on fuel, labor and time as well as water conserving.
In Tunisia, CA was introduced since 2000 and nowadays more than 200 farmers are practicing this system, over an area of 12000 ha mainly in durum wheat. Apart of limited availability of affordable no till seeder, this low adoption of CA is in part due to the CA strict proscriptive approaches followed by farmers. So, the use of a no till seeders, even considered as a key component of CA, specific agronomic practices (management and crop rotations) should be developed and fine-tuned to optimise the wheat production. For example we assume that the use of the no till seeder combined with legumes-based rotation would change the nitrogen dynamic in the soil-plant system under semi-arid condition of northern Tunisia. On the other hand the mistaken perception of farmers that soil tillage is essential for production inhibit the adoption of CA. Farmers and policy makers should be encouraged to adapt the CA-general concept to meet their specific situations leading to extension of CA surface across the cereal production area. Nitrogen (N) is the nutrient most commonly limiting Durum wheat production for no-legume crops N can be provided by soil through soil organic matter mineralization et/or through mineral nitrogen fertilizer application. In this context, this study aims to assess the effect of nitrogen fertilization of DW under tow tillage systems (CA vs CV) combined with two contrasted crop rotation (cereal monocropping, forage legume/cereal), on (i) crops yields, (ii) water and nitrogen efficiencies and (iii) soil quality.