Foliar fertilization is an application technique that is increasingly being used in agriculture and offers the possibility of providing nutrients directly to the site of highest demand. Especially for phosphorus (P), the foliar application is an interesting alternative to soil fertilization, but foliar uptake mechanisms are poorly understood. To gain a better understanding of the importance of leaf surface features for foliar P uptake, we conducted a study with tomato (Solanum lycopersicum) and pepper (Capsicum annuum) plants, which have different leaf surface traits. For this purpose, drops of 200 mM KH2PO4 without surfactant were applied onto the adaxial or abaxial leaf side or to the leaf veins, and the rate of foliar P absorption was evaluated after one day.
Additionally, leaf surfaces were characterized in detail by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), also estimating leaf surface wettability and free energy, among other parameters. While the leaves of pepper hardly contained any trichomes, the abaxial side and the leaf veins of tomato leaves were densely covered with trichomes.
The cuticle of tomato leaves was thin (approximately 50 nm), while that of pepper was thick (approximately 150-200 nm) and impregnated with lignin. Due to the fact that trichomes were most abundant in the leaf veins of tomatoes, dry foliar fertilizer drop residues were observed to be anchored there, and the highest P uptake occurred via tomato leaf veins, resulting in a 62% increased P concentration. However, in pepper, the highest rate of P absorption was recorded after abaxial-side P treatment (+66% P). Our results provide evidence that different leaf parts contribute unequally to the absorption of foliar-applied agrochemicals, which could potentially be useful for optimizing foliar spray treatments in different crops.
Henningsen, Jon & Bahamonde, Héctor & Mühling, Karl & Fernández, Victoria. (2023). Tomato and Pepper Leaf Parts Contribute Differently to the Absorption of Foliar-Applied Potassium Dihydrogen Phosphate. Plants. 12 2152. 1-14. 10.3390/plants12112152.
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