plants Review The Effects of Foliar Sprays with Different Silicon Compounds Henk-Maarten Laane ReXil Agro BV, Demmersweg 92a, 7556 BN Hengelo (OV), The Netherlands;
[email protected] Received: 7 March 2018; Accepted: 6 June 2018; Published: 7 June 2018 Abstract: The use of foliar sprays with silicon compounds is relatively new. Initially (in 1990) foliar sprays with silicates were used. In 2003, foliar sprays with (stabilized) silicic acid were introduced, and more recently foliar sprays with silica nanoparticles have also been applied. Foliar sprays with silicates are effective as pesticides, while (stabilized) silicic acid sprays increase growth and yield and decrease biotic and abiotic stresses. The limited data on foliar silica-nano sprays show a tendency to decrease biotic stress and to stimulate a limited increase in growth and yield. Keywords: foliar spray; silicates; stabilized silicic acid; silica nanoparticles; growth; yield; quality; biotic stress; abiotic stress 1. Introduction Foliar fertilization (or foliar feeding) is the application of nutrients, plant hormones, biostimulants, other beneficial substances and pesticides to the leaves and stems of plants. The application of these substances during growth and development can improve the nutrient balance of crops, which, in turn, leads to increased yield and quality, greater resistance to diseases and insect pests and improved drought tolerance. The literature on the application of foliar sprays starts in the 1850s [1,2] and covers 100 years or so [3,4]. From the 1950s onwards, foliar feeding in agriculture was used on an ever-increasing scale, with macro- and micro-nutrients such as nitrogen, potassium, phosphorus, zinc, copper, boron, manganese, cobalt, chromium, calcium, fluoride, iodine, iron, molybdenum, and selenium [5,6], as well as pesticides.