Silicon accumulation by sunflowers at low substrate pH

Supplemental silicon (Si) is becoming more-widely applied in soilless substrates to mitigate crop stress. The objective of this study was to evaluate the effect of soilless substrate pH on foliar 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 dolomitic lime, in increments of 0.59 kg m^‑3, and supplemented weekly with 150 mL drenches of 0 or 2 mM potassium silicate. Plants were grown in a greenhouse with ambient irradiance and photoperiod. Pour-through leachate pH increased with increased lime incorporation. Five weeks after transplant, pH ranged from 3.27 to 5.66 (pooled across Si). Leaf Si concentration was lowest in the 0 and 0.59 kg m^‑3 lime treatments and increased quadratically with lime. Maximum dry mass occurred at 3.18 kg m^‑3 lime (final substrate pH of 5.27) and maximum leaf Si concentration occurred at 3.62 kg m^‑3 lime (final substrate pH of 5.39). Overall, substrate pH values between 4.53 and 5.66, corresponding to lime rates of 1.19 to 4.75 kg m^‑3, did not impact growth or supplemental Si accumulation in sunflower.