Open-cycle drip vs closed-cycle subirrigation: Effects on growth andyield of greenhouse soilless green bean

Closed-cycle management of soilless cultivation is one of the promising strategies to prevent pollution,while increasing the efficiency of water and fertilizer use. However, in order to encourage the adoptionof closed-cycle cultivation even in countries characterized by a low-tech greenhouse industry, effectiveeasy-management systems need to be developed.A greenhouse experiment was carried out to determine the influence of two irrigation methods (dripirrigation open-cycle and subirrigation closed-cycle) and two nutrient solution (NS) concentrations (100and 80% of the macro-element concentration normally used for soilless cultivation) on substrate electricalconductivity (EC), plant growth, gas exchange, yield, fruit quality, and water-use efficiency of green bean(Phaseolus vulgaris L., cv. Saporro).Subirrigated plants showed higher substrate EC and higher Na+and Cl−concentrations, especially inthe upper layer of the growing medium, while moisture distribution throughout the substrate profileshowed an opposite trend and was more uniform in drip irrigation. The total fresh and dry biomass ofthe drip-irrigated plants were higher than in those grown in subirrigation, while whole plant dry matterpercentage was lower. Differences in terms of plant height, number of leaves, leaf area, root growth,chlorophyll content, net photosynthesis, stomatal conductance and transpiration rate were recorded,with higher values in drip-irrigated plants. With closed-cycle subirrigation, green bean total and mar-ketable yield (598 and 574 g plant−1, respectively) were, on average, 33% lower than for drip irrigation, butfruit quality was higher in terms of “extra class” number of pods (93.6 vs 88.3%) and dry matter percent-ages. On average, both total and marketable yield were 9% higher with NS 80%, with a 13% higher waterconsumption, while slight or no effects were observed on net photosynthesis, stomatal conductance andshoot growth. The highest WUE (11.2 kg m−3) was obtained with subirrigation, where recirculating NSwas never discharged, compared to drip irrigation (8.5 kg m−3). The green bean response to closed-cyclesubirrigation showed a general decrease in productive performance. Detrimental effects were reducedby reducing the NS concentration. Lower yield could be compensated by savings of water and fertilizersand lower environmental impact.