Opportunities and Challenges to Managing the Beneficial Nutrient Silicon in Plant Production Systems.

The element silicon (Si) is ubiquitous in nature, but can vary in its bioavailability in different soil types and rooting materials. Although silicon is not considered an essential plant nutrient, there are clear benefits of adding supplemental Si to some cropping systems in both field and greenhouse environments; reduction of fungal and viral pathogens, mitigation of heavy metal toxicity, decreases in population growth of insect pests, mitigation of both salt and drought stress, and reduced damage from heat stress. While the mechanisms for these effects are still being elucidated, Si generally activates existing plant pathways allowing plants to effectively defend against stresses. The benefits from silicon could be particularly significant in sustainable or organic production now that the National Organic Program is allowing applications of potassium silicate into organic systems. We have evaluated different Si-containing materials and correlated Si release rates with plant uptake. Some Si-extraction procedures accurately predict Si availability while others significantly underestimate potential Si supply. Beneficial effects from supplemental Si are clear, but accurately predicting Si availability remains a challenge. Because of this, recommendations about Si application in different production environments can be difficult.