Foliar Application of Potassium Salts to Olive, with Focus on Accompanying Anions

Abstract

Potassium (K) is an essential element, which is often supplied to horticultural crops via foliar spraying. Some studies have investigated the effect of different foliar-applied K compounds; however, most studies have focussed on crop quality and yield parameters, or were performed with isolated leaf cuticles. The aim of this study was to evaluate the rates of the foliar ion penetration and leaf surface deposition of 130 mM K sprays of compounds with markedly different point of deliquescence (POD) and efflorescence (POE) values, the rates having been previously estimated in climate chamber trials. Shoots of field-grown, commercial olive trees were sprayed with K-nitrate (KNO3), K-sulphate (K2SO4), K-chloride (KCl), K-phosphate (K3PO4), K-carbonate (K2CO3) and K-bicarbonate (KHCO3), and leaf samples were collected after 3 and 24 h. Cation and anion concentrations were determined in the leaf tissues, and in a preliminary leaf water wash for estimating surface-deposited ion concentrations. No significant leaf tissue K increments were recorded between the K sprays. Olive tissue anion concentrations showed different patterns, and a chloride (Cl−) increase was detected 3 h after the foliar KCl supply. On the other hand, the foliar K applications led to leaf nitrate changes regardless of the K source supplied. High amounts of K and accompanying ions were recovered in the washing liquid of the foliar K-supplied leaves. Some foliar K treatments increased the leaf surface concentration of sulphate and chloride, suggesting a potential effect on leaf cell anion extrusion. Hence, despite no evidence of foliar K uptake, an effect of leaf anion concentrations was observed, indicating that foliar nutrient sprays may influence leaf and leaf surface anion balance.

Leaf surface features of maize cultivars and response to foliar phosphorus application: effect of leaf stage and plant phosphorus status

“…One day after the foliar P spraying, one plant per replicate (n = 4) was sampled for tissue P analysis. Leaves were first cleaned following a three‐step washing procedure which involved leaf surface scrubbing with acidulated 0.1% detergent, followed by a thorough rinse in tap and distilled water (Bahamonde et al, 2023). Subsequently, leaves were oven‐dried at 65°C until they were constant in weight and were then ground, dry‐ashed and digested with acid prior to mineral element determination by inductively coupled plasma optical emission spectroscopy (ICP‐OES, Optima 3000, PerkinElmer), following the UNE‐EN ISO/IEC 17025 standards for calibration and testing laboratories (CE‐ BAS‐CSIC Analysis Service) as previously described by Henningsen et al (2023).…”

“…three/four leaves unfolded, plants were sprayed with 200 mM KH 2 PO 4 and 0.1% Genapol X‐80 (pH 6.6) as described by Henningsen et al (2022). Genapol X‐80 is a non‐ionic surfactant that significantly reduces surface tension approximately 27 mN m −1 , thus significantly decreasing the contact angle of aqueous solutions to low values (Bahamonde et al, 2023). Genapol X‐80 has been used at a 0.1% concentration in previous foliar fertilisation studies (e.g.…”

“…Genapol X-80 has been used at a 0.1% concentration in previous foliar fertilisation studies (e.g. Bahamonde et al, 2023;Barlas et al, 2023). To prevent soil P contamination due to KH 2 PO 4 spraying, the pots were covered with aluminium foil and absorbent paper.…”

Mineral Particles in Foliar Fertilizer Formulations Can Improve the Rate of Foliar Uptake

“…The physio-chemical characteristics of spray formulations have been recognised as key factors affecting foliar absorption rates [ 4 , 5 , 6 , 7 ]. The properties of both mineral elemental compounds and formulation adjuvants (e.g., surfactants or humectants), such as point of deliquescence (or deliquescence relative humidity) [ 8 , 9 ], point of efflorescence (or efflorescence relative humidity) [ 10 , 11 , 12 ], solubility [ 7 ], or physiological effects [ 13 ] should be considered when designing a foliar spray formulation [ 2 ].…”

“…The highest rate of foliar absorption takes place during the drop-drying process (i.e., shortly after foliar fertilizer application) [ 2 ], but many factors may influence foliar uptake efficiency as described above. Hence, for evaluating the performance of foliar formulations, short-term leaf uptake trials are often performed [ 7 , 9 , 11 , 12 ]. The methodology employed in such foliar penetration investigations is directed towards estimating the amount of nutrients that are transported across the cuticle or leaf surfaces [ 2 , 3 ], and not towards evaluating mineral element cell uptake in plant organs, which is affected by additional factors including, for instance, long-distance transport and membrane cell transporters [ 1 ].…”