Irrigation de précision des agrumes et cultures maraichères : cas de la plaine de la Mitidja

Abstract

Located in northern Algeria, the Mitidja Plain is a vast alluvial region known for its groundwater resources and agricultural importance. However, since the 1980s, the water table has significantly dropped (by more than 40 meters) due to drought and the over-exploitation of water for irrigation (1.3 million hectares irrigated). Poor irrigation management by farmers has further worsened the situation. To improve irrigation systems in the Mitidja Plain and provide better water management through a decision-support tool for farmers, we proposed conducting soil physical studies and water infiltration assessments. This involved determining the impact of organic mulching and studying its combination with drip irrigation systems at different depths for tomato crops. Finally, we compared the most efficient irrigation systems to optimize plant growth while conserving significant amounts of irrigation water for orange trees. Our thesis results show that the soil where tomatoes and orange trees were planted mostly consists of silt, with generally less dense soil, but potential clogging in soils with higher density values. The modified Kostiakov model was the most efficient in the study area. Additionally, analysis of the irrigation water used in the field showed that it was of good quality for plants. For the tomato plots, the mulch made of equal parts wood chips, sawdust, and wheat straw was the most water-conserving over two years (37% - 50%) and required the least irrigation. Furthermore, the comparison of this mulch with BRF (which had also proven effective in past studies), coupled with surface and 15 cm depth drip irrigation, revealed that this same mulch, when combined with subsurface irrigation, saved 29.6% of water and increased yield by 2.9%. The study also confirmed the impact of mulching on soil moisture retention, temperature regulation, and pH, while stabilizing soil salinity over time. This mulching method also showed its importance in improving soil organic matter, with increases of 0.86% - 1.35% in Block A and 0.19% - 0.77% in Block B across the different mulches studied. For the orange tree plots, soil pH ranged from 6.63 to 7.36 over a one-meter depth profile. Comparing the three irrigation systems (S1, S2, S3) revealed that the 30 cm depth drip irrigation system (S3) was the most water-efficient, saving between 14% (2022) and 32% (2023) compared to the surface drip irrigation system (S2). The reduced water consumption was mainly due to drainage or percolation outside the root zone. Root concentration for the orange trees at the station ranged from 40 to 60 cm deep. The 15 cm (S1) and 30 cm (S3) subsurface irrigation systems showed better alignment with Kc and ETc, suggesting more efficient water management, which could be particularly beneficial for maximizing orange production in the Mitidja Plain.