Assessing cotton irrigation scheduling strategies under rotational delivery schedules in Pakistan

In Punjab, Pakistan, the “Warabandi” principle guides the distribution of surface water in tertiary canal networks to each farm. The allocated amount is proportional to farm size and provided according to a predetermined schedules in a 7-day fixed rotation. Limited canal water and rigid rotations of the Warabandi-guided water allocation led to unsustainable pumping of groundwater and relatively low field application efficiency. Using both site monitoring and modelling, we assessed cotton irrigation scheduling under current practices and the planning options in the context of the Warabandi principle. The farming practices of two raised-bed furrow cotton fields were intensively monitored at the Mungi distributary canal command area in Punjab. The AquaCrop model was parameterized and validated using 2019 and 2020 datasets and then applied to assess four irrigation scheduling scenarios. Scenario 1 reflects the current irrigation practice under canal water and groundwater use, while for scenarios 2, 3, and 4, solely canal water was considered and irrigation followed a fixed rotation of 7-days, 14-days, and targeted intervals, respectively. According to simulations’ outputs, scenarios 2, 3, and 4 resulted in better performance compared to the current practices in both fields by reducing percolation substantially up to 90% below the root zone and lowered soil evaporation by up to 27% enebling similar yields ∼2.2 ton/ha raw cotton and higher water productivity. Under the frame conditions of Warabandi, scenario 4 was a promising option for introducing more flexible and demand-oriented irrigation at the farm level targeting cotton's water-stress sensitive growth stages by adapting irrigation application to rainfall events and refilling the soil slightly below field capacity level during each irrigation event to reduce percolation. The study delivered detailed information about cotton irrigation scheduling for on-farm water management, considering a bottom-up approach in Punjab.

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