Impact of different irrigation regimes on nitrogen dynamics in moderately saline soil

Irrigation management strongly controls nitrogen (N) availability, movement, and loss in saline agricultural soils, directly affecting crop productivity and environmental sustainability. This study investigated the influence of different irrigation regimes on soil nitrogen dynamics, depth-wise nitrogen distribution, and plant nitrogen uptake in a moderately saline clay soil using okra (Abelmoschus esculentus L.) as a test crop. A pot experiment was conducted under a completely randomized design with six irrigation treatments, ranging from no irrigation to excessive irrigation (200% field capacity), with three replications. Soil samples were collected after harvest from six depth intervals (0–30 cm) to quantify total nitrogen and soil organic matter, while shoot and root tissues were analyzed for nitrogen uptake. The results showed that irrigation regime, soil depth, and their interaction significantly affected soil nitrogen and organic matter distribution. Moderate irrigation (50–75% field capacity) enhanced nitrogen retention in the root-active zone (10–20 cm) and supported higher plant nitrogen uptake. In contrast, no irrigation restricted nitrogen mobility and uptake due to water stress, while full and excessive irrigation increased nitrogen redistribution to deeper layers and reduced plant nitrogen concentration, indicating greater risks of leaching and denitrification. Soil organic matter declined consistently with depth, but moderate to high irrigation promoted its retention in mid and lower soil layers. Plant presence was a key factor regulating nitrogen retention and utilization across all irrigation regimes.

Overall, nitrogen response to irrigation was non-linear, with moderate irrigation providing the most favorable balance between nitrogen availability, plant uptake, and reduced losses. The findings emphasize that optimized irrigation scheduling is essential for improving nitrogen-use efficiency and maintaining soil fertility in moderately saline soils under irrigated agriculture.

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