Abstract
The use of water surfactants in fertigation constitutes a viable approach to increase soil wetting, potentially improving crop nutrient uptake and quality. An in-field demonstration test was carried out by applying an innovative, eco-friendly, non-ionic surfactant to fertigation water in Lactuca sativa (var. Iceberg) production to increase nutrient use efficiency and improve the crop’s access to water. A non-ionic methyl-oxirane surfactant (methyl-oxirane + 2-methyl-oxirane) was added at an increasing rate to the fertigation solution (Hoagland). Upon harvesting, the main growth and nutritional parameters were determined on the aboveground and belowground portions of the lettuce. Leaf nitrate content, water, and nitrogen use efficiency were recorded; the relationship of lettuce aboveground dry biomass with nutrient uptake was evaluated using vectorial analysis; and ultrastructural analysis of lettuce roots was performed by scanning electron microscopy. The surfactant, applied by fertigation at the rate of 1.0 mL × LHoagland−1, improved crop P, K, Mn, and Fe use efficiency. When applied by fertigation, although the surfactant did not increase the water use efficiency index, it induced a significant decrease of the specific leaf water content (−8.8%) and an increase of the leaf area (+13.3%). By comparison with the recent literature, we inferred a positive physiological response by more expanded and less thick leaves in lettuce, likely by the optimization of the crop water and nutrient root uptakes mediated by the abundant but shortest lateral roots. This finding corresponded to the lowest leaf nitrate content, indicating an improvement of the lettuce quality without losing the crop yield.
Highlights
Under the effects of climate change, high temperatures and extreme weather events occurring within a short period of time, especially in areas with poor vegetation cover or bare soil, lead to soil erosion, aridity, and loss of organic matter
The surfactant acted at the soil/root interface, modulating the water and nutrient uptake on the basis of their soil nutrient availability and the availability of nutrients in the soil, as well as their mutual chemical affinity with the surfactant
Since a theoretical model recently explained how non-ionic organosilicone surfactants affect soil capillary and adsorption processes in horticultural systems [11], we may correctly refer to the MOS ability to optimize lettuce water uptake and specific nutrients assimilation, in particular that of P, K, Fe, and Mn
Summary
Under the effects of climate change, high temperatures and extreme weather events occurring within a short period of time, especially in areas with poor vegetation cover or bare soil, lead to soil erosion, aridity, and loss of organic matter. The supply of adequate water and nutrients to crops is becoming an issue [1]. Even if excessive fertilization does encourage great yields, at the same time it results in water and soil pollution; the possibility of reducing nutrient inputs and improving crop nutrient use efficiency may instead reduce the amount of fertilizers employed by farmers. Water 2018, 10, 613 increasing water infiltration rate, and limiting runoff in Pacific Northwest soils [5]. This would indicate an improvement of the water use efficiency, guaranteeing that an adequate amount of nutrients reaches the crops
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