by Joseph Heckman, Ph.D.
From ACRES USA MARCH 2013
Silicon (Si) is one of the most abundant elements present in soil minerals. This abundance is probably one of the reasons why silicon has not been given, until recently, much attention as a limiting factor in soil fertility and crop production.
Agronomists are becoming more aware of the valuable function of silicon nutrition in crops and soils and even animal life. Research conducted on many soils worldwide has shown that supplying crops with plant-available silicon can suppress disease, reduce insect attack, improve environmental stress tolerance and increase crop productivity.
In 2012, silicon became officially designated as a plant beneficial substance by the Association of American Plant Food Control Officials (AAPFCO). Plant available silicon may now be listed on fertilizer labels.
Of the many benefits associated with enhanced silicon nutrition, the one that appears most outstanding is suppression of powdery mildew disease on a variety of different crops. Wheat, pumpkin, Kentucky bluegrass and dogwood are examples of crops where adding soluble silicon to soil helped to control powdery mildew disease in field trials and/or greenhouse studies conducted in New Jersey. More research is currently under way to study silicon needs of other soils and crops.
Generally silicon supplementation of soil is more effective for suppressing plant diseases than spraying silicon on the plant foliage.
Calcium silicates are the most widely used silicon soil amendments. Besides supplying plant available silicon, they are also effective liming materials. Calcium silicates are variable in composition depending on source. Some commercial calcium silicate products also supply some magnesium.
The manufacturing of steel provides a common source of calcium silicate. The
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calcium originates from the limestone and the silicon is primarily coming from the iron ore that is placed inside the steel mill smelter. The by-product is often called steel mill slag or calcium silicate slag.
Research on New Jersey soils has found that calcium silicate slag is an effective liming material that can be substituted about one to one for limestone. The calcium silicate slag has the additional advantage of being a good source of plant-available silicon.
Organic growers usually prefer naturally mined materials as soil amendments. Wollastonite is a naturally occurring calcium silicate mineral mined in New York State. Another type of silicon fertilizer, volcanic ash, is mined in Montana. Organic growers should check with their organic certifier before using a particular silicon product on their farm.
Calcium silicate amendments may be applied at rates comparable to regular agricultural liming materials. A recent soil test may be used to guide the application rates based on calcium concentration or the need for soil pH adjustment.
While freshly applied silicon soil amendments are the most effective, there is significant residual availability that can benefit crops for several years after the initial application to soil.
The calcium silicate materials should be applied in advance of rotating to crops that are most vulnerable to pow- dery mildew disease. Pumpkin, cucumber and wheat are examples of crops where silicon has been demonstrated to effectively suppress powdery mildew disease. See table for data on powdery mildew disease severity on pumpkin as a result of applying silicon supplements to a Sassafras sandy loam soil.
Based on our field and greenhouse experience with pumpkin, silicon delays the onset of powdery mildew. Although silicon soil amendments may not entirely prevent powdery mildew disease, it should significantly reduce the need for sprays and other control measures for this disease.
Joseph Heckman, Ph.D. is a soil science professor at Rutgers University. The current issue of his newsletter provides a comprehensive summary about silicon and soil fertility (njaes. rutgers.edu/pubs/soilprofile).
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Of the many benefits associated with enhanced
silicon nutrition, the one that appears most outstanding is suppression of powdery mildew disease on a variety of different crops.
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