S06 - Session O8 - Silicon accumulation by sunflowers impacted at low substrate pH.

Authors: Jennifer Boldt *, Mona-Lisa Banks, James Altland

Supplemental silicon (Si) is becoming more-widely applied to mitigate abiotic crop stresses. The objective of this study was to evaluate the effect of soilless substrate pH on Si accumulation. Sunflowers ( Helianthus annuus L. 'Pacino Gold') were grown in 11.5-cm diameter pots filled with an 85 peat : 15 perlite (v:v) substrate amended with 0 to 4.75 kg·m -3 lime, in treatment increments of 0.59 kg·m -3 , and supplemented weekly with 150 mL of either 0 or 2 mM potassium silicate. Plants were grown in a greenhouse with ambient irradiance and photoperiod. Mean air temperatures were 24.5 +- 1.5 °C day/20.4 +- 0.4 °C night, and mean daily light integral was 13.1 +- 7.0 mol·m -2 ·d -1 (mean +- SD). Substrate pH increased and electrical conductivity (EC) generally decreased with increased lime incorporation rate. Five weeks after transplant, pH ranged from 3.27 to 5.66, and EC ranged from 2.12 to 1.41 mS·cm -1 (pooled across Si treatments). Leaf Si concentration was lowest in the 0 and 0.59 kg·m -3 lime treatments and increased quadratically with lime rate. Overall, substrate pH did not impact supplemental Si accumulation in sunflower across the substrate pH range typically used for ornamental crop production.