How Smart Water Management is Revolutionizing Rice Farming
Alternate Wetting and Drying irrigation is transforming agriculture in Northeast China, addressing water scarcity and soil degradation while maintaining rice yields.
Imagine a surgical technique that not only saves a patient's life but also improves their long-term health—this is the agricultural equivalent happening in China's precious black soil region. Alternate Wetting and Drying (AWD) irrigation is emerging as a transformative practice that simultaneously addresses two critical challenges: water scarcity and soil degradation. In Northeast China, known as the nation's "granary," this innovative approach is rewriting the rules of rice farming, demonstrating that we can indeed produce more with less while healing the very land that feeds us.
Studies reveal that after a century of cultivation, soil organic matter has plummeted from 150.6 to 50.2 g kg−1, with available nitrogen, phosphorus, and potassium decreasing by 50-70%, 20-30%, and 30-60% respectively 1 .
The black soils of Northeast China represent one of the planet's most precious agricultural resources, yet decades of intensive farming have taken their toll. This degradation threatens the foundation of China's food security in a region that produces about one-quarter of the country's grain 7 .
Against this backdrop, AWD irrigation isn't merely an efficiency improvement—it's a necessary evolution toward sustainable agriculture that aligns with China's new "Law on the Protection of Black Soil" enacted in August 2022 7 . This article explores how this innovative watering method is helping rescue China's black soils while maintaining the rice production that millions depend on.
Alternate Wetting and Drying (AWD) is a water-saving irrigation strategy that cycles between saturated soil conditions and controlled drying periods. Unlike traditional continuous flooding—where rice fields remain submerged throughout the growing season—AWD allows fields to dry to a specific moisture level before reapplying water 1 .
The practice might sound simple, but its implementation requires precision. Farmers typically monitor water levels using specially designed field water tubes that visually indicate when irrigation is needed. The specific drying threshold—how dry the soil is allowed to become before rewetting—proves critical to the technique's success, with research pointing to -10 kPa as the optimal soil water potential for black soil regions 1 .
For generations, rice farmers have operated under the assumption that their crop requires constant submersion. This continuous flooding method has dominated rice agriculture worldwide, consuming an astonishing 40% of global irrigation water—up to 2500 liters of water per kilogram of rice produced 2 .
The AWD method challenges this convention by introducing controlled dry periods that create fluctuating redox conditions. This cycling fundamentally changes the soil environment, affecting everything from microbial communities to nutrient availability. The benefits are substantial: research demonstrates that AWD can reduce irrigation water use by 15.7-35% compared to conventional flooding 1 , while simultaneously altering nutrient dynamics in ways that can benefit both crops and soil health.
Field is flooded to establish rice seedlings
Water level drops naturally until soil reaches predetermined moisture level
Field is re-irrigated to shallow depth before soil becomes too dry
Process continues throughout growing season except during flowering
Often called "the pandas of the soil world," black soils are characterized by their thick, dark humus topsoil layers with high organic matter content and exceptional fertility 7 . Northeast China is home to one of only four major black soil regions worldwide, alongside the Mississippi River Basin in North America, the Pampas of South America, and the Russia-Ukraine Great Plain 4 .
China's black soil region, often called the "bedrock of food security," has seen its grain output skyrocket from 3.70×10⁷ tons in 1980 to 17.35×10⁷ tons in 2020 4 . This incredible productivity comes at a cost—the very resources that make the region productive are being depleted at an alarming rate.
The statistics paint a concerning picture of a resource in decline. Beyond the dramatic drops in organic matter and available nutrients, the physical structure of black soil is deteriorating. After decades of cultivation, soil bulk density has increased by up to 59.49%, while total porosity has decreased by 22.68%, and field water holding capacity has plummeted by 53.90% 4 .
The economic pressure to maintain high yields has led to overexploitation of these soils without sufficient investment in their long-term health. Between 2000 and 2023, the proportion of water used for irrigation relative to total water consumption in the region decreased from 28.5% to 25.6% 1 , creating additional pressure to use water more efficiently.
Increase in soil bulk density after decades of cultivation 4
Decrease in total soil porosity 4
Decrease in field water holding capacity 4
The situation became sufficiently dire that China passed specialized legislation—the "Law on the Protection of Black Soil"—which took effect in August 2022 7 . This law specifically promotes conservation practices like crop rotation, reduced tillage, and the application of organic fertilizers to restore soil health.
To understand how AWD specifically affects black soils, researchers conducted a comprehensive two-year study at the Qixing National Agricultural Science and Technology Park in the Sanjiang Plain—a representative black soil region in Northeast China 1 . The experiment investigated different AWD intensity levels on the growth of "Longjing 31," a local rice cultivar.
The research team established three distinct AWD treatments based on soil water potential thresholds:
These were compared against CK (Control), which used traditional continuous flooding irrigation. The researchers meticulously measured rice growth indicators at five critical growth stages: tillering, jointing, heading, milk ripening, and yellow ripening 1 .
The findings revealed compelling differences between the treatment groups, with the light AWD (LA) emerging as the clear standout for black soil conditions.
The yield advantage of LA over the more intense AWD treatments was striking—9.1% higher than MA and 14.1% higher than SA in the first year, with similar advantages in the second year 1 . Even more notably, LA actually outperformed traditional flooding by approximately 9%, suggesting that mild AWD doesn't just save water—it can genuinely enhance productivity.
The LA treatment consistently maintained higher levels of available nutrients in the soil 1 . The researchers concluded that the light treatment facilitates the release of available nutrients, while moderate and severe treatments increasingly hinder this process.
| Treatment | Panicles per unit area | Grains per panicle | Seed setting rate (%) | Thousand-grain weight (g) | Yield (kg hm⁻²) |
|---|---|---|---|---|---|
| LA (-10 kPa) | 456 | 95 | 92.5 | 25.1 | 10,033 |
| MA (-20 kPa) | 424 | 93 | 91.8 | 24.8 | 8,947 |
| SA (-30 kPa) | 411 | 92 | 91.5 | 24.7 | 8,512 |
| CK (Flooded) | 442 | 94 | 92.1 | 24.9 | 9,215 |
Data derived from experimental results 1
| Treatment | NO₃⁻-N (mg/kg) | Available P (mg/kg) | Available K (mg/kg) |
|---|---|---|---|
| LA (-10 kPa) | 42.5 | 35.2 | 185.6 |
| MA (-20 kPa) | 38.1 | 32.4 | 169.8 |
| SA (-30 kPa) | 36.4 | 31.5 | 161.4 |
| CK (Flooded) | 39.8 | 33.1 | 172.3 |
Data synthesized from experimental measurements 1
Perhaps most impressively, all AWD treatments significantly improved water use efficiency (WUE) compared to continuous flooding. By reducing evaporation, percolation, and other water losses, AWD achieved much higher productivity per unit of water applied—a critical advantage in regions facing water scarcity 1 .
The improved nutrient availability under mild AWD conditions stems from complex biochemical processes in the soil. The drying cycles introduce oxygen into the soil profile, fundamentally changing the redox conditions that govern nutrient availability 3 .
Under continuous flooding, ferric iron (Fe(III)) reduction leads to the dissolution of iron-bound phosphorus (Fe-P), making it available to plants 3 . However, AWD creates alternating conditions that affect multiple phosphorus sources.
Similarly, nitrogen availability shifts under AWD. While flooded conditions favor ammonium (NH₄⁺) as the dominant nitrogen form, AWD introduces nitrification during dry periods, making nitrate (NO₃⁻) more available 8 .
Perhaps the most fascinating aspect of AWD is how it reshapes the soil microbiome. The fluctuating moisture conditions create what scientists call a "variable redox environment" that selectively favors certain microorganisms over others 8 .
Research shows that AWD increases the abundance of specific bacterial groups like Proteobacteria and Actinobacteria while enhancing the fungi-to-bacteria ratio 8 .
This microbial shift matters because these microorganisms become tiny nutrient factories and distributors. They accelerate the decomposition of organic matter and the release of nutrients in plant-available forms.
AWD doesn't just change the soil—it changes the plant itself. The alternating moisture conditions encourage rice plants to develop deeper, more extensive root systems as they seek water during drying periods.
These enhanced root networks allow plants to explore a larger soil volume and access more nutrients 1 . Additionally, research shows that AWD can increase arbuscular mycorrhiza abundance 3 —the symbiotic fungi that effectively extend the plant's root reach, further improving nutrient and water uptake.
This root development creates a positive feedback loop: healthier roots support more robust above-ground growth, which in turn supports more extensive root systems.
One study found that AWD increases microbial allocation of phosphorus to phospholipids—essential components of cell membranes—indicating robust microbial growth and activity 3 . Though microorganisms compete with plants for nutrients, this vibrant microbial life ultimately creates a more efficient nutrient cycling system that benefits the entire ecosystem.
The success of AWD can be amplified when combined with other sustainable practices:
For farmers in Northeast China's black soil region considering AWD, research points to specific recommendations:
| Aspect | Recommendation | Rationale |
|---|---|---|
| Soil water potential threshold | -10 kPa | Optimal for balancing yield and water savings in black soils 1 |
| Water depth at re-irrigation | 30 mm | Appropriate upper limit for the Sanjiang Plain region 1 |
| Key growth stages for monitoring | Tillering, jointing, heading, milk ripening, yellow ripening | Critical phases where water management most impacts yield 1 |
| Complementary practices | Biochar amendment, controlled-release fertilizers, conservation tillage | Enhance AWD effectiveness and protect soil health 2 4 8 |
The transition to AWD requires careful monitoring, ideally using simple tools like field water tubes to visually determine when to irrigate. Government support through technical guidance and possibly subsidies—as encouraged by the Black Soil Protection Law—can facilitate this transition 7 .
The research from Northeast China's black soil region offers a hopeful message: we don't have to choose between productivity and sustainability. Alternate Wetting and Drying irrigation represents a rare win-win solution that addresses both water scarcity and soil degradation while maintaining—and in optimal cases, even improving—rice yields.
The light AWD approach (-10 kPa soil water potential) emerges as the gold standard for black soil conditions, demonstrating the principle that in agriculture, as in medicine, the most effective treatments often involve subtle interventions that work with natural systems rather than against them.
As China and other rice-producing regions face increasing pressure from climate change, water scarcity, and soil degradation, practices like AWD offer a path forward. By embracing these science-based, sustainable approaches, we can protect precious resources like the black soils while ensuring food security for future generations. The story of AWD in Northeast China represents more than just an irrigation upgrade—it's a blueprint for the future of sustainable agriculture.
The experimental data presented in this article are based on peer-reviewed research conducted at the Qixing National Agricultural Science and Technology Park in the Sanjiang Plain, published in 2025 1 .