Shallow saline groundwater use by Black cumin (Nigella sativa L.) in the presence of surface water in a semi-arid region

• Groundwater contribution by Black cumin was studied under different saline and water table conditions.
• Increasing groundwater salinity and WT depth resulted in a significant reduction in groundwater contribution.
• Surface irrigation can be managed to increase crop water requirement from shallow groundwater.
• The planting of Black cumin under shallow water table depth and low salinity condition is recommended.

Lysimetric experiments were conducted to investigate the percentage of groundwater contributions made by Black cumin (Nigella sativa L.). The plants were grown in 27 columns, each with a diameter of 0.40 m and packed with Silty clay soil. The factorial experiments were carried out using three replicates with randomized complete block design and different treatment combinations. Nine treatments were applied during each experiment via maintaining groundwater with an EC of 1, 2 and 4 dS m−1 at three different water table depths (0.6, 0.8 and 1.10 m). The groundwater contribution was measured as a part of crop evapotranspiration by taking daily readings of water levels in Mariotte tubes. The additional irrigation water requirement for each treatment was applied by adding surface water with EC of 0.5 dS m−1. The results showed that for different treatments with EC values of 1, 2 and 4 dS m−1 and different water table levels of 0.60, 0.80, and 1.10 m, the average percentage of groundwater contributions were determined to be 67.25, 55 and 45.75%, 60.75, 50 and 41.5% and 54.25, 43.5 and 36% of the average annual Black cumin water requirements, respectively. This investigation shows that groundwater use and crop yield decrease as both groundwater salinity and water-table depth increase.