The objective of this paper was to assess the performance of Hydrus-2D model to simulate the effects of different on-farm irrigation strategies applied on potato crop. The ability of the model to simulate the stress coefficient (K_s), obtained as the ratio between actual and maximum transpiration, and to define the productive function of potato crop under the semi-arid conditions of central Tunisia were also evaluated. Experiments were carried out on potato crop under full (FI) and deficit irrigation (DI) and two different water qualities supplied by means of a subsurface drip irrigation system. Results evidenced that the model, despite some discrepancies locally observed, can fairly accurately predict soil water contents and electrical conductivity around buried emitters. Furthermore, under water and salt stress conditions, “measured” K_s, based on crop water stress index (CWSI) obtained on thermal images, resulted in a good correlation with the corresponding estimated by the model (R² = 0.8). The database collected during the three growth seasons also allowed the definition of the crop productive function represented by a linear relationship between the relative yield loss and K_s. This function represents a useful guidelines for the sustainable use of irrigation water in countries characterized by a semi-arid climate and a limited availability of water for irrigation.

Water supplies have been decreasing in several semi-arid regions, and it is therefore necessary to adopt irrigation strategies aimed at maximizing water use efficiency. In this paper, the effects of saline and deficit irrigation on water use efficiency and on potato crop response, based on observations of soil and plant water status, were investigated. Experiments were carried out in Central Tunisia, by monitoring potato crop growth during two seasons in four distinct treatments (T1–T4), represented by two different irrigation doses and two water qualities. For irrigation scheduling purposes, thresholds of soil matric potential, soil water content and Crop Water Stress Index (CWSI) were identified with the aim to quantify the effects of water and/or salinity stress on the achievable yield. Experiments allowed verifying that crop yield is strongly affected by the seasonal amount and quality of applied water. Despite differences of crop yield between treatments T2, T3 and T4 not being statistically significant (P < 0.05), crop yield varied between 26.3 t/ha (T3 in 2015) to 16.3 t/ha (T4 in 2015). However, crop yield decline of 17.0 t/ha and 12.0 t/ha per each 100 mm decrease of applied water were observed under the application of water electrical conductivity of 1.6 dS/m and 4.1 dS/m respectively. On the other hand, an increase of 1.0 dS/m in water electrical conductivity caused a yield decline rate of about 10%. The results achieved showed that under the semi-arid climate of Tunisia, potato crop irrigation should be scheduled to avoid water deficit; however, the possibility to reduce water supply can be envisaged when water availability is limited, but with the awareness to accept the shortage of production. Finally, when saline water is the only source available to the farm, it is necessary to avoid the reduction of irrigation doses, to prevent excessive salt accumulation in the root zone with unavoidable effects on crop yield.

Current trends in the intensification of olive cultivation including irrigation have dictated a need to reconsider amendment management practices. The addition of organic wastes to agricultural soils is becoming a common practice as a disposal strategy and to improve the physical and chemical soil properties This study examines physiological varieties of young olive trees (Olea europaea L.) grown on deficit irrigation under four different amended soil. We evaluated the short-term effect of different amended soil under deficit irrigation on soil, plant water status, level of soil, and leaf Nitrogen. Water stress was considered to be insignificant or absent with an irrigation amount of 50% of daily evapotranspiration. Leaf relative water content was between 65 and 88% for the Chemlali cultivar, while that of the Koroneiki was between 60 and 70%. Under conditions of water stress, photosynthesis of trees planted in soil amended with biochar decreased from 8.5 to 1.5 μmol.CO₂.m⁻²s⁻¹, compared to the control for both cultivars.To conclude, amendment addition, used as a tool for sustainable agriculture, could improve plant growth, although soil fertility. The type and amount of amendment should receive special attention to be efficient.

Improving soil fertility by adopting several sustainable management practices that are a prime concern for plant growth. Organic waste addition to agricultural soil is becoming a common practice that improves physical, chemical and hydrodynamic properties and minimizes environmental impact. The use of some alternative nutrition sources as biochar and compost has been tested on two-year-old olive varieties ‘Chemlali’ and ‘Koroneiki.’ Three treatments were established “Cont” soil didn’t amended, “Comp” soil amended with Compost (90% soil+10% compost), and “Bioc” soil amended with biochar (90% soil+10% biochar). All treatments were conducted under deficit irrigation receiving 50% of daily evapotranspiration. We evaluated soil–plant water status and relationships between all studied parameters. Results showed that soil water content was the lowest in non-amended treatments and did not exceed 10%. During experiment, compost amendment induced a better water plant status for both studied varieties less than −2 MPa for mean seasonal leaf water potential, while the biochar amendment induced a weak stress level indicated by the lower potential that reached a minimum value equal to −2.9 MPa. Crop Water Stress Index on biochar-amended soil was more important than that measured on other treatments which confirms the sensitivity of biochar treatment to hard conditions. High negative relationships have been found between soil water statuses and plant water statuses. The highest determination coefficient was between crop water stresss index and leaf water potential was about 0.85. In conclusion, the use of organic amendment is an approach for sustainable olive orchards under low water avaibility.

The progress in computer technology has enabled the development of crop models reproducing the behavior of a crop in a wide range of pedoclimatic conditions and technical itineraries. This work aims to study the impact of total available soil water in the root zone (TAW) on durum wheat yield (Triticum durum Desf.) as affected by irrigation regime in Mediterranean climatic conditions of Tunisia. In this work, STICS model was used to simulate effects of farmer’s irrigation practices in wheat in the pedoclimatic conditions of the irrigated area of Oued Rmel in Tunisia over a 20-year period. Assessment of irrigation practices in the study area was performed, compared to rainfed system, in terms of yield and produced biomass at harvest. The model was calibrated to simulate the growth and development of winter wheat using the field observed crop data collected from three growing seasons in two locations in Tunisia. To carry out the study, three types of soil (S1, S2 and S3) in the Oued rmel irrigation scheme were chosen on the basis of their available soil water in the root zone (TAW). The study showed that the model adequately predicts crop yield and biomass. Simulation results showed that the farmers’ irrigation practice results, in higher grain yield and dry matter at harvest as compared to rainfed system. Simulated grain yield was significantly higher in soil with high TAW than in the other soils. Results showed that the highest difference (30%) in simulated grain yield, between the two water regimes, was obtained in soil having high TAW. Depending on the soil type, simulated dry matter at harvest increased from 4% to 12% compared to rainfed system.