Wheat Variety Response to a Soil pH and Al Concentration Gradient.

Soil acidification due to the use of ammonium based fertilizers has become a major yield limiting factor for winter wheat (Triticum aestivum L.) production in the southern Great Plains. Our objective was to evaluate the susceptibility of modern wheat varieties to a soil pH and aluminum (Al) concentration gradient under both dual-purpose (forage and grain) and grain-only management. A two-way factorial treatment structure was arranged in a split-plot design with three replications. Main plots were six target levels of soil pH ranging from 4 to 7, achieved by incorporating either aluminum sulfate or hydrated lime to the soil, and subplots were the wheat varieties 2174, Duster, Ruby Lee, and TAM 203. The experiment was conducted during three growing seasons (2013, 2014, and 2015 harvest years) in an Easpur loam at Stillwater (dual-purpose site) and in a Dale silt loam at Chickasha (grain-only site), Oklahoma. The addition of soil amendments resulted in a soil pH range of 4.1 to 7.4 at Stillwater and 4.4 to 7.6 at Chickasha. Stand homogeneity, assessed as the coefficient of variation (CV) of normalized difference vegetative index (NDVI) readings within a given subplot, increased with an increase in soil pH, with NDVI CV being reduced to <10% at a soil pH of 4.9 or above. Wheat forage and grain yields increased with an increase in soil pH and a consequent decrease in soil Al_sat, and were variety- and site-year- specific. All varieties had lower pH thresholds required to maximize relative grain yields (4.8 to 5.8) as compared to the threshold to maximize forage yield (5.5 to 6.0). Duster and 2174 showed better tolerance to low soil pH than Ruby Lee or TAM 203. Our results indicate that dual-purpose wheat systems may have a greater penalty than grain-only systems under acidic soil conditions, and that wheat variety selection can be an effective method to improve wheat productivity on acid soils.