Conclusions
Results from this research demonstrate that low soil pH and
high concentration of AlKCl resulted in a significant reduction
in sunflower growth and yield. Plant mortality, height, NDVI,
and relative seed yield with potassium-chloride-extractable
Al also showed significant negative relationships in most site-
years. Critical soil pH and AlKCl differed by soil types and
years for all growth and yield parameters evaluated. At the
Perkins site, Teller sandy loam, a plant loss of greater than
10% occurred at a pH of 4.7 and corresponding AlKCl level of
41 mg kg−1. Both plant height and NDVI were maximized at
a soil pH of 4.9. At Perkins the relative yields values fell below
the point of 90% at a soil pH of 5.1. At the Haskell location,
Taloka silt loam, plant stand was significantly impacted at
a pH of 4.0 and negatively linearly correlated with AlKCl
level with no critical point being found. A soil pH of 4.