An Evaluation of the Influence of Biodynamic Practices including Foliar-applied Silica Spray on Nutrient Quality of Organic and Conventionally Fertilised Lettuce (lactuca Sativa L.)

Evidence for the role of silica in plants is reviewed with respect to the application of silicate based sprays in biodynamic agriculture. There is research indicating improved resistance to pests, disease, drought and other stresses on plants from application of silica fertilisers and sprays. There is also evidence of improved nutrient uptake. Experiments with field grown lettuce were undertaken to evaluate the effects of the biodynamic field-spray preparations and organic composts on lettuce yield, nutrient uptake, nitrogen metabolism, antioxidant activity and soil organism activity. Higher fresh yields of field lettuce were observed with organic composts than with a mixture of diammonium phosphate and calcium ammonium nitrate applied at similar N and P application rates. Although lettuce yields were higher when the compost and plants were treated with biodynamically prepared silica sprays, the variation in lettuce fresh yield in the field was high (c.v. 28%) and the effects of the sprays were not statistically significant (p 0.05). Irrespective of fertiliser source, composts or soluble fertiliser, silica sprays produced lettuce at harvest (47 DAT) with higher dry matter content and crude protein in fresh leaves. However, application of silica spray had no statistically significant effect on lettuce fresh head yield, N uptake, plant sap nitrate concentrations, NO3 to TKN ratio, and amino acid content. Further investigation of management practises, such as the use of biodynamic field sprays, which may contribute to nutrient uptake and assimilation and improved product quality within an organic system, is recommended.