Silicon Nutrition

for Healthy  Plants

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

Powdery  Mildew on Greenhouse Pumpkin

MAY 4, 2012          MAY 16,  2012

Harsco Metals & Minerals

www.harsco-m.com/54/Agriculture.aspx

Axner Pottery Supply

www.axner.com/wollastonite-w30.aspx

Levy Group

www.edwclevy.com/aboutus.aspx

RT Vanderbilt Company Inc.

www.rtvanderbilt.com

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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