Strategies for Mitigating the Decline in Productivity of Irrigated Wells

Over-irrigation to ensure high crop yields in North China Plain (NCP) has led to a sharp groundwater table decline over the past decades. We conducted a scenario analysis from1980 to 2017 with 12 irrigation strategies from T1W0M0 to T12W3M2 (T is treatment and numbers of irrigation times in wheat (W) and maize (M) seasons, 75 mm each) for the dominant winter wheat-summer maize rotation using the soil-water-atmosphere-plant (SWAP) model in the NCP. After model calibration and validation with 4-year experimental data, we analyzed the long-term simulated annual crop yield, actual evapotranspiration (ET _a ), water productivity (WP), groundwater table change and economic benefit to the different irrigation practices.

Keywords: irrigation strategy, rained treatment.

The optimized irrigation strategy is based on an integral analysis for different precipitation year-types. Results showed that annual yield and WP increased with increased irrigation until these reached a plateau. Treatment T4W2M1 was the turning point with an annual yield of 15335 kg·ha ^-1 , significantly higher than T2W1M1 (26 %) and T1W0M0 (63 %), but not significantly different from 4 to 5 irrigations in wet and normal years. ET _a increased with increased irrigation from 456 to 644 mm yr ^-1 . The annual WP followed a similar trend as annual crop yield for all irrigation schedules. T4W2M1 had an annual WP of 2.47 kg cm ^-3 , significantly higher by 15 % than T2W1M1 and 24 % higher than T1W0M0, with no significant difference seen with 4–5 irrigations. The rained treatment mitigated groundwater table decline the best, even reversing the trend during the past four decades to 0.11 m yr ^-1 rise. This was followed by two irrigation treatments (−0.30 m yr ^-1 ), three irrigations (−0.55 m yr ^-1 ), four irrigations (−0.72 m yr ^-1 ), and five irrigations (−0.86 m yr ^-1 ). The latter corresponds to typical farmer practice. Using the productivity indicators, including irrigation WP, marginal benefit and economic index, T4W2M1 showed the best performance. Therefore, we recommend T4W2M1 (two irrigations at pre-wintering and jointing stages for wheat and one irrigation at maize sowing stage) as the best irrigation strategy for the wheat-maize rotation to mitigate groundwater table decline, and sustain grain yields and water productivity in the NCP; another a thesis irrigation for winter wheat is recommended during extreme dry years to sustain grain yield.

Irrigated agriculture plays a pivotal role in global food security, providing sustenance for billions of people worldwide. Central to this system are irrigated wells, which supply water to crops, ensuring their growth and productivity. However, over time, the productivity of irrigated wells can decline due to various factors, posing a significant challenge to agricultural sustainability. This essay explores the causes of declining productivity in irrigated wells and proposes strategies to mitigate this issue.

Causes of Declining Productivity in Irrigated Wells:

1. Over-Extraction of Groundwater: One of the primary reasons for the decline in productivity of irrigated wells is the over-extraction of groundwater. As water is continuously pumped from aquifers to irrigate crops, the water table drops, leading to decreased well yields and increased pumping costs.
2. Aquifer Depletion: The excessive extraction of groundwater can result in the depletion of aquifers, reducing the overall water availability for irrigation. As aquifers are depleted, the remaining water may become more saline or contaminated, further impacting crop productivity.
3. Sedimentation and Clogging: Irrigated wells are susceptible to sedimentation and clogging over time, especially in areas with high sediment loads or poor water quality. Sedimentation reduces the effective capacity of wells, leading to decreased water flow and lower productivity.
4. Infrastructure Degradation: Aging infrastructure, including well casings, pumps, and distribution systems, can contribute to declining productivity in irrigated wells. Leaks, corrosion, and mechanical failures can reduce water delivery efficiency and increase operational costs.
5. Climate Change: Climate variability and change can exacerbate the challenges faced by irrigated agriculture, affecting both water availability and demand. Shifts in precipitation patterns, increased temperatures, and more frequent droughts can strain water resources, leading to reduced productivity in irrigated wells.

Strategies for Mitigating Declining Productivity:

1. Sustainable Groundwater Management: Implementing sustainable groundwater management practices is essential for preserving aquifer health and maintaining well productivity. This includes setting pumping limits, promoting water conservation measures, and implementing groundwater recharge initiatives.
2. Improved Irrigation Efficiency: Enhancing irrigation efficiency can help reduce the demand for groundwater and alleviate pressure on irrigated wells. Adopting precision irrigation techniques, such as drip irrigation and soil moisture monitoring, can optimize water use and improve crop yields.
3. Rehabilitation and Maintenance: Regular maintenance and rehabilitation of irrigated wells and associated infrastructure are crucial for ensuring optimal performance and longevity. Cleaning, desilting, and repairing wells can help mitigate sedimentation and clogging issues, restoring productivity.
4. Investment in Modern Technologies: Investing in modern technologies, such as solar-powered pumps, efficient irrigation systems, and remote monitoring devices, can enhance the efficiency and reliability of irrigated wells. These technologies can reduce energy consumption, improve water management, and mitigate the impacts of climate change.
5. Integrated Water Resource Management: Adopting an integrated approach to water resource management can help balance competing demands for water and ensure its sustainable use across sectors. This involves collaboration among stakeholders, including farmers, policymakers, and water resource managers, to develop and implement comprehensive water management plans.
6. Promoting Crop Diversification: Encouraging crop diversification can help reduce the reliance on water-intensive crops and alleviate pressure on irrigated wells. By promoting the cultivation of drought-resistant crops and implementing agroforestry practices, farmers can improve resilience to water scarcity and enhance overall agricultural sustainability.

The declining productivity of irrigated wells poses a significant threat to global food security and agricultural sustainability. Addressing this challenge requires a multifaceted approach, encompassing sustainable groundwater management, improved irrigation efficiency, infrastructure rehabilitation, technological innovation, and integrated water resource management. By implementing these strategies, stakeholders can mitigate the impacts of declining well productivity and ensure the long-term viability of irrigated agriculture.

References:

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