Effects of cultivation on chemical and biochemical properties of dryland soils from southern Tunisia

• In drylands, organic amendments, irrigation, and plant activity improve soil fertility.
• In drylands, enzymatic activity occurred also at soil depth.
• Soil organic C storage occurred by the formation of organo-mineral encapsulation.
• Chemical fertilization and drip irrigation favor organic matter mineralization at depth.

The progressive degradation of cultivated drylands has been mainly ascribed to adoption of intensive soil use, namely repeated soil cultivation with external inputs and disturbances. Consequently, soil managements in equilibrium with environmental and social constrains are required to conserve and improve the soil fertility. We evaluated the impact of soil cultivation and management on chemical and biochemical properties of dryland soils from the Tunisian Jeffara Plain. This study considered three sites (Chenini Nahel, Matmata Nouvelle, and Menzel Habib), with both non-cultivated and cultivated soils. These latter were subjected to different soil management: organic fertilization and irrigation by submersion, chemical fertilization and drip irrigation, no fertilization and sporadic watering. The results showed that the addition of organic matter as compost or manure combined with irrigation may favor pH reduction, with consequently higher enzymatic activity and organic matter storage. The latter occurred because of the encapsulation of organic particles into collars made of re-precipitated gypsum and calcite. In cases where chemical fertilization and drip irrigation were applied, the organic matter stabilization occurred only at the surface; at depth we observed a reduction of organics due to microbially-mediated mineralization processes. When neither organic amendment nor water was supplied, no substantial difference occurred between cultivated and non-cultivated soils. We concluded that, in drylands, agricultural managements providing the use of water and organic amendments is the way to increase soil organic matter storage and improve physical, chemical and biological properties so to enhance the soil fertility.