Impact of Irrigation Management Decisions on the Water Footprint of Processing Tomatoes in Southern Spain

The water footprint is an increasingly demanded environmental sustainability indicator for certifications and labels in agricultural production. Processing tomatoes are highly water-intensive, and existing studies on water footprint have uncertainties and do not consider the impact of different irrigation configurations (e.g., surface drip irrigation (SDI) and subsurface drip irrigation (SSDI)) and irrigation strategies. This study presents a two-year experimental investigation to determine the water footprint of processing tomatoes grown in southern Spain (Andalusia) and the impact of SSDI and deficit irrigation. Five irrigation treatments were established: SDI₁ (surface drip irrigation without water limitation), SDI₂ (surface drip irrigation without water limitation adjusted by soil moisture readings), SSDI₁ (subsurface drip irrigation without water limitation and a dripline depth of 15 cm), SSDI₂ (similar to SSDI₁ but with mild/moderate water deficit during the fruit ripening stage), and SSDI₃ (subsurface drip irrigation without water limitation and a dripline depth of 35 cm (first year) and 25 cm (second year)). Measurements included crop vegetative growth, leaf water potential, leaf gas exchange, nitrate concentration in soil solution, and crop yield and quality. The soil water balance components (actual evaporation, actual transpiration, deep drainage), necessary for determining the total crop water footprint, were simulated on a daily scale using Hydrus 2D software. Results indicated that SSDI makes more efficient use of irrigation water than SDI. The water footprint of SSDI₁ was 20–35% lower than that of SDI₁. SSDI₂ showed similar water footprint values to SDI₁ under highly demanding environmental conditions and significantly lower values (≈40%) in a year with lower evaporative demand. The dripline depth in SSDI was critical to the water footprint. With a 35 cm installation depth, SSDI₃ had a significantly higher water footprint than the other treatments, while the values were similar to SSDI₁ when the depth was reduced to 25 cm.