Effect of surfactant as adjuvant for irrigation/ fertigation in vegetables production: preliminary results on lettuce

In crop management, the use of surfactants (surface active agents) in the formulation of different pesticides and herbicides has rapidly increased and, more recently, their use as adjuvant for irrigation water has been proposed. In order to assess possible synergistic or antagonistic effects between the application of surfactants and the mineral fertilization, a first agronomical trial on lettuce, by testing a non-ionic surfactant formulation (45% fatty acid ester, 45% sorbitan sesquioctanoate and 10% propylene glycol), was carried out. The surfactant was administered to lettuce (Lactuca sativa 'Iceberg') in 2 or 3 application, through irrigation water, in presence or absence of mineral fertilization (granular urea). After 21 days, biometric parameters, nutrient uptake and potential interaction effect between the surfactant and the fertilizer were evaluated by ICP-AES and vector analysis. After 3 surfactant applications and in absence of fertilization, results highlighted a probable detrimental and/or phytotoxic effect on plant growth. Root growth was more influenced by surfactant applications, interacting with the mineral fertilization: without fertilization, a negative effect on root fresh and dry weight was noticed, but on the contrary, in fertilized lettuce, the same biometric parameters significantly increased. The vector analysis allowed to highlight an increased nutrient use efficiency both in ipogeic and epigeic lettuce after 2 surfactant applications, after 3 applications plus fertilization and, for the epigeic, portion of lettuce, after 2 applications plus fertilization. Since in fertilized soils the surfactant induces improved roots robustness, together with a better efficiency of nutrient use, it is reasonable to hypothesize that the tested formulate could act at soil/root interface, probably by favouring root water uptake and, consequently, the nutrient assimilation by lettuce.