In the Danish experiments two forms of fertilizer were used. The first consisted of Sikal (Potassium Metasilicate) which was applied at various rates (20-100ppm) to the irrigation water.  It is important to reiterate that the molecule absorbed by plants is silicic acid and not Potassium Metasilicate. So the effectiveness of this fertilizer relates to the amount of freely available silcic acid released to the irrigation water from the Potassium Metasilicate. The other fertilizer used was ActiSil (a stabilized form of silicic acid) applied to the leaves as a foliar spray of 2m/litre active ingredient. The first interesting discovery was that even within different rose varieties the efficiency of silicic acid absorption and the accumulation of silicon was variable. Despite this, all three varieties under trial did accumulate silicon in their leaves following application of Sikal to the irrigation water. In general terms, there was no overal improvement seen in the growth of vegetation or root system.  However in laboratory growth chambers, , the 100ppm rate of application of Sikal reduced mildew development in both young and older leaves in all varieties. Under green house conditions the results were much more variable and less decisive. In the growth chambre, no accumulation of silicon in the leaves was found following the foliar application  of ActiSil. This is thought to be due to the polymerization of silicic acid to silica gel on the leaf surface, effectively blocking any absorption of silicic acid into the underlying leaf tissues. However this physical barrier serves to limit the penetration of fungal spores of mildew into the leaf. A beneficial effect using ActiSil was observed but not due to silicon absorption. Of major importance is that Sikal also contains about 8% Potassium and therefore ordinary fertilizer levels should be aduste accordingly. In addition the product is very alcaline and the irrigation water needs to be corrected bu the addition of acid. This aspect needs to be very carefully tested and monitored by any growers before they make any sich applications.

“FlowerTech” info@reedbusiness.nl www.HortiWorld.nl For further information contact:  the DJF www.agrsci.org and from Conny Wang Hansen, Email: COWH@dffe.dk 

Some further considerations by Edward Bent

Applied research conducted in Italy shows two aspects that should also be taken into account. Firstly that silicic acid in the stabilized forms (ActiSil, AgroForce, SiliForce etc.) applied as a foliar spray will penetrate into the leaf if it is not first allowed to polymerize into colloidal silica and silica gel over the leaf surface. This is much a question of pH, time of day of  application and the type of spreader utilized.

In consideration of Sikal and other silicon salts, experiments need to be conducted to discover the amount of silicic acid released to the irrigation water and under what conditions.  This should also be compared to the addition of one of the above mentioned stabilized forms of silicic acid.  It should also be noted that the physical barrier over the leaf surface created by the deposition of silica, acts as a deterrent to leaf eating insects whose mouthparts are negatively affected and the greater difficulty that lymph sucking insects such as aphids and whiteflies have in penetrating the leaf surface.  Silica deposits in and around the stomata and on the leaf surfaces also help plants control their water balance.

Gerrit Karremans has been working on the application of bioactive silicon to commercial  greenhouse production of roses in Italy. Email: gerritkarremans@yahoo.it

In its grower extension work and research the Department of Horticulture at Cornell University, USA, is now actively promoting the subject of the addition of silicon to container grown plants to improve plant quality and resi stance to biotic and abiotic stresses: www.cornell.edu E-mail: hort@cornell.edu

Research projects on silicon fertirrigation are also being undertaken at the University of Davis, California. Silicon is generally missing from sillessi potting mixtures. The silicon element will be applied by injection. Subsequent distribution and concentration of the element in the plants will be measured and the plants screened for any enhancement in their resistance to diseases and insect pests. E-mail: jabethke@ucdavis.edu

The Agricultural Research Service (ARS,USDA) partecipated in the recent IV International conference on the use of silicon in agriculture , held in October 2008 in South Africa. See: www.siliconconference.org.za The ARS is actively conducting research on the application of silicon in the production of ornamental plants. www.ars.usda.gov