Discussion

1. Evaluating the Effect of Soil Acidity on Grain Sorghum and Sunflower Production Katy Butchee, D. Brian Arnall, Chad Godsey, Hailin Zhang, and Jerry May Department of Plant and Soil Sciences, Oklahoma State University, Stillwater, OK Soil pH 4.2 Results Introduction • Many Oklahoma producers are converting to no-till production systems and integrating crop rotations to break weed, disease, and insect cycles. • Grain sorghum and sunflower are well suited for these crop rotations but have typically been grown on calcareous soils with a soil pH of >6.5. • 2005 soil test results from the Potash and Phosphate Institute reported that 46% of soil samples in Oklahoma had a soil pH of <6.0. • Monoculture winter wheat is the most widely produced crop in Oklahoma and is considered to be more acid tolerant than grain sorghum and sunflower. As producers integrate grain sorghum and/or sunflower into their production systems they may not be accustomed to liming soils with low pH. Soil pH 5.3 Soil pH 6.1 y=1.31x-5.00 joint=4.45 r2=0.70 y=0.49x-1.56 joint=5.02 r2=0.72 • Figure 2. Grain sorghum relative plant height (left) reached a linear plateau at soil pH 4.45, and sunflower relative plant height (right) reached a linear plateau at soil pH 5.02. Height measurements were taken in grain sorghum at 5-8 leaf stage and in sunflower at reproductive stage 1-3. (Relative height was calculated as [(x/y)*100] where x=height and y =greatest height reported for that site) Soil pH 3.9 Soil pH 4.2 Objectives • To evaluate the effect of soil pH (4.0-7.0) on grain sorghum and sunflower production • To develop relative yield values as related to soil pH for grain sorghum and sunflower Soil pH 4.9 Soil pH 5.3 Soil pH 5.9 y=0.41x-1.21 joint=5.20 r2=0.84 y=0.51x-1.48 joint=4.76 r2=0.59 Materials and Methods • Randomized complete block design with 12 treatments replicated three times • 3 sites at Perkins, Haskell, and Lahoma, Oklahoma • Treatment soil pH was raised with hydrated lime (Ca(OH)2) and lowered with aluminum sulfate (Al2(SO4)3) to a range of 3.7 to 7.3. Rates were determined in a previous lab study. • Crop performance variables used for evaluation were plant height, plant biomass using the GreenSeekerTM sensor to collect NDVI readings, and grain yield. • 1.2 meter soil samples taken from each location are currently being analyzed for soil pH to determine the depth that soil treatment pH changes occurred. • 15 centimeter soil samples from each plot are currently being analyzed for aluminum concentration and base saturation. • Figure 3. Grain sorghum relative NDVI (left) reached a linear plateau at soil pH 5.20, and sunflower relative NDVI (right) reached a linear plateau at soil pH 4.76. NDVI readings were taken in grain sorghum at 3-5 leaf stage and in sunflower at reproductive stage 1-3. (Relative NDVI was calculated as [(x/y)*100] where x=NDVI and y =highest NDVI reported for that site) • Figure 4. Grain sorghum relative yield (left) and sunflower relative yield (right) were not highly correlated with soil pH. The Haskell, OK yield data was not included due to pest damage. (Relative yield was calculated as [(x/y)*100] where x=yield and y=average of the 3 highest yields reported for that site) Discussion • Plant height and NDVI were highly correlated with soil pH. • The effect of soil pH diminished as crop maturity progressed, hence the less significant correlation of yield and soil pH. This may be due to the rooting depth exceeding the 10-15 cm depth of soil that was acidified as the crop reached maturity. • If weather conditions are favorable throughout the growing season, roots may penetrate the acidic subsurface soil (10-15 cm) and reach neutral subsoil, which could reduce the negative effects of soil acidity on these crops. • Grain sorghum and sunflower maximum predicted relative yield occurred at soil pH 5.91 and 6.18, respectively. • Figure 1. Grain sorghum (top) and sunflower (bottom) at Perkins, OK demonstrate the reduction in plant height and plant biomass associated with soil acidity. For more information contact: Katy Butchee Graduate Research Assistant Department of Plant & Soil Sciences Oklahoma State University katysb@okstate.edu