Improving Bell Pepper Yield and Profit Through Precision Water and Nitrogen Use

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Bell peppers (Capsicum annuum L.) are one of the world’s most valuable crops, contributing over $24 billion annually to the global economy. However, growing them in arid regions like Qatar—where temperatures soar above 33°C and annual rainfall is just 58 mm—poses significant challenges.

A groundbreaking 2025 study published in Agricultural Water Management by researchers from Qatar University and Western Sydney University offers a solution.

By optimizing irrigation (the artificial application of water to crops) and nitrogen use (a key nutrient for plant growth), farmers can achieve 25.7 tons of bell peppers per hectare while using 50% less water and 30% less fertilizer.

Water Scarcity and Nitrogen Overuse

Bell peppers require consistent water and nutrients, but traditional practices in dry climates like Qatar’s often lead to waste and environmental harm.

For example, agriculture consumes 80% of Qatar’s freshwater, mostly from underground brackish water sources (water with moderate salinity, higher than freshwater but lower than seawater). Overwatering and excessive nitrogen use worsen the problem.

Farmers typically apply 100 kg of nitrogen per hectare to boost yields, but 70–90% of this nitrogen is lost through leaching polluting groundwater and releasing nitrous oxide .

Additionally, conventional irrigation methods achieve low crop water productivity (WPC)—a measure of yield per unit of water used—producing just 0.15 kg of peppers per cubic meter of water. To address these issues, the study tested two strategies:

• deficit irrigation (applying less water than traditional methods)
• precision nitrogen management (tailoring fertilizer use to plant needs).

Optimizing Yield in Qatar’s Climate

The research took place at Qatar University’s Agricultural Research Station, located in a region with sandy loam soil (a mix of sand, silt, and clay that drains well but has low organic matter) and high salinity (salt content measured as electrical conductivity, or EC, of 2.25 mS/cm).

The team planted 720 bell pepper seedlings across 18 plots, testing six combinations of water and nitrogen levels. Full irrigation (FI) mimicked traditional practices, providing 60 minutes of drip watering (a method where water drips slowly to plant roots through tubes) every other day, while deficit irrigation (DI) used half that amount.

Nitrogen was applied at three rates: 50 kg/ha (N₁), 70 kg/ha (N₂), and 100 kg/ha (N₃). Over five months, the researchers measured plant growth, yield, water and nitrogen efficiency, and economic outcomes.

 Reduced Inputs Boost Pepper Production

The study revealed that combining deficit irrigation (DI) with moderate nitrogen (N₂) produced the best outcomes. For instance, plants under DI + N₂ grew 34.4 cm tall (vs. 32.3 cm under FI) and developed 13.7 cm roots (vs. 11.3 cm under FI).

These plants also had thicker stems (9.9 mm vs. 8.6 mm) and healthier leaves, with chlorophyll levels (a pigment critical for photosynthesis) 5% higher than those under FI, measured using a SPAD meter (a handheld device that estimates leaf chlorophyll content).

When it came to yield, DI + N₂ outperformed all other treatments, producing 25.7 tons per hectare—a 35% increase over FI + N₃. The peppers were larger, with fruits 12% longer and 9% heavier. Water productivity (WPC) doubled under DI, reaching 0.30 kg/m³ compared to 0.15 kg/m³ for FI.

This means farmers could save 2.8 million liters of water per hectare (enough to fill an Olympic-sized swimming pool) while maintaining high yields. Nitrogen use efficiency (NUE)—defined as yield per kilogram of nitrogen applied—also peaked at N₂, with plants producing 0.37 tons of peppers per kg of nitrogen (vs. 0.21 tons/kg for N₃).

Efficient Water-Nitrogen Use Explained

Deficit irrigation (DI) encourages plants to grow deeper roots, allowing them to access moisture and nutrients even during dry spells. This process, called root adaptation, improves drought resilience.

In contrast, full irrigation (FI) often leads to waterlogged soil (saturated soil with poor oxygen levels), which stunts root growth and reduces nutrient uptake.

Moderate nitrogen application (N₂) provides enough nutrients for healthy growth without overwhelming the soil. Excess nitrogen, as seen in N₃, increases soil salinity (salt accumulation) to 3.01 mS/cm, harming root function and reducing nutrient assimilation (the process by which plants absorb and use nutrients).

Healthy leaves played a critical role in the success of DI + N₂. Plants under this treatment had a leaf area index (LAI) of 0.23 (a measure of total leaf area per ground area) vs. 0.18 for FI, enabling them to capture more sunlight.

Higher chlorophyll levels (66.2 SPAD vs. 61.9 for FI + N₃) further boosted photosynthesis (the process plants use to convert light into energy), fueling fruit development.

Sustainable Farming Benefits for Qatar

For countries like Qatar, where freshwater scarcity is acute and agriculture relies on expensive desalinated water ($0.50 per cubic meter), these findings are transformative.

Adopting deficit irrigation (DI) could cut agricultural water use by 50%, preserving vital resources for future generations.

Reducing nitrogen application from 100 kg/ha to 70 kg/ha would also lower nitrate leaching (nitrogen loss into groundwater) by 55%, aligning with Qatar’s National Climate Change Action Plan, which aims to reduce greenhouse gas emissions by 25% by 2030.

Small-scale farmers stand to benefit significantly. With lower input costs and higher profits, this approach makes farming more sustainable and economically viable.

• For example, a farmer with 10 hectares could save 28 million liters of water and earn $340,000 more annually by switching to DI + N₂.

Overcoming Water-Saving Challenges

Despite its benefits, adopting these strategies requires careful planning. The study noted that brackish irrigation water increased soil sodium levels to 10,294 mg/kg (far above the safe threshold of 1,000 mg/kg), which could harm long-term soil health.

To address this, researchers recommend crop rotation (growing different crops sequentially) with salt-tolerant species like barley, which absorb excess salts and restore soil balance.

Farmer training is another hurdle. Many farmers lack experience with drip irrigation systems (a water-efficient method using tubes to deliver water directly to roots) and precision nutrient management (applying fertilizers based on plant needs).

Governments and NGOs could help by funding workshops and subsidizing equipment like soil moisture sensors (devices that monitor water levels in real time).

Extreme heat remains a concern, as summer temperatures in Qatar often exceed 40°C. Solutions like shade nets and organic mulching can reduce soil temperature by 5–7°C, protecting plants from heat stress (damage caused by excessive heat).

Smart Farming for Resilient Peppers

The team plans to study the long-term effects of deficit irrigation on soil health over 5–10 years, focusing on organic matter content (a key indicator of soil fertility) and microbial activity (beneficial organisms that aid nutrient cycling).

They also aim to test these strategies on other crops, such as tomatoes and cucumbers, which face similar challenges in arid climates.

Integrating smart farming technologies, like IoT sensors (Internet-connected devices that collect field data), could further optimize resource use. For example, sensors could monitor soil moisture and nitrogen levels, automatically adjusting irrigation and fertilizer delivery—a concept called precision agriculture.

Conclusion

This study demonstrates that sustainable farming in arid regions is not only possible but profitable. By using 50% less water and 30% less nitrogen, farmers can grow more bell peppers, protect the environment, and increase their incomes. For Qatar—a nation with 0.6% arable land and 90% desert—these strategies are a lifeline.

As climate change intensifies, such innovations will be essential to feeding a global population projected to reach 9.7 billion by 2050. By adopting deficit irrigation and precision nitrogen management, arid regions can transform agriculture from a resource-intensive challenge into a model of efficiency and resilience.