Validation of deficit irrigation in Northern Italy

New research from Italy shows that Regulated Deficit Irrigation can boost the sustainability of processing tomato cultivation not only under dry environmental conditions, but also under wetter ones. 

The Po Valley in northern Italy is one of the most important areas in Europe for growing processing tomatoes. As climate change brings hotter, drier summers, local farmers are increasingly concerned about water availability. In this context, saving water without sacrificing crop yield or quality has become a top priority.

This study explored a promising approach called Regulated Deficit Irrigation (RDI). This method involves reducing the amount of water given to plants at certain stages of their development—specifically, after the fruits start to turn colour (the “colour-breaking” stage), which signals the start of ripening.

Researchers conducted field trials in two different years and locations within the Po Valley—2019 near Parma, and 2022 near Piacenza. They compared two watering strategies:

1. Full irrigation (FI): Plants received 100% of the water lost through evapotranspiration during the growing season.
2. RDI treatment: Plants received full irrigation until the fruit started to ripen, and then just 50% of the usual amount of water for the remainder of the season.

They used modern tools like satellite imagery from the PlanetScope constellation to track plant health and development over time.

Key Findings

• Water Savings: The RDI method reduced total water use by around 25% compared to full irrigation.
• No Yield Loss: Despite getting less water, the RDI-treated tomato plants produced the same amount of fruit as the fully watered ones. Fruit size, number, and weight remained stable.
• Improved Quality: Tomatoes grown under RDI had higher soluble solids and dry matter content, both indicators of better quality for processed products like paste and sauce.
• Healthy Plants: The satellite images showed that plants under the RDI regime stayed healthy and green during the reduced watering period—meaning they were not visibly stressed by the lower water levels.
• Better Efficiency: When considering how much yield was produced per unit of water used, the RDI method significantly increased water use efficiency, both environmentally and economically.

The results suggest that farmers in the Po Valley—and in similar Mediterranean climates—can adopt regulated deficit irrigation to save water while still producing high-quality tomatoes. The method is simple: water the same as usual until the fruits begin ripening, then reduce irrigation by half.

This strategy makes tomato farming more resilient to drought and reduces pressure on local water supplies, which is especially important as summers become hotter and drier. And since fruit quality actually improves, it may even benefit food processors and consumers in the long run.

This research provides strong evidence that regulated deficit irrigation is a smart, sustainable strategy for growing processing tomatoes. It balances the need to conserve water with the demands of agriculture and food production—offering a practical win-win for both farmers and the environment.

Reference: Burato, A.; Campi, P.; Pentangelo, A.; Parisi, M. Growing Processing Tomatoes in the Po Valley Is More Sustainable Under Regulated Deficit Irrigation. Agronomy 2025, 15, 1805.

Full text: https://www.mdpi.com/2073-4395/15/8/1805