Materials & Methods Research Sites Lahoma , Oklahoma (LAH) Grant silt loam, 1 to 3 percent slopes

1. Improving In-Season Estimation of Yield Using Soil Moisture Data to Make Nitrogen Fertilizer Recommendations in Winter Wheat Jacob T. Bushong1, Jeremiah L. Mullock1, William R. Raun1 1Department of Plant & Soil Sciences, Oklahoma State University • Introduction • Ability to predict wheat grain yield in-season allows producers to make proper agronomic management decisions such as nitrogen (N) fertilizer recommendations • Current methods incorporate measure of biomass accumulated over a period of growing degree days, but do not adjust for amount of plant available water • Materials & Methods • Research Sites • Lahoma, Oklahoma (LAH) • Grant silt loam, 1 to 3 percent slopes • Preplant N Rates (kg N ha-1): 0, 22, 45, 67, 90, 112 • Stillwater, Oklahoma (STW) • Kirkland silt loam, 1 to 3 percent slopes • Preplant N Rates (kg N ha-1): 0, 40, 90 • Perkins, Oklahoma (PRK) • Konawa fine sandy loam, 1 to 3 percent slopes • Preplant N Rates (kg N ha-1): 0, 56, 112, 168 • Hennessey, Oklahoma (HEN) • Bethany silt loam, 0 to 1 percent slopes • Preplant N Rates (kg N ha-1): 0, 28, 56, 84, 112, 140, 168, 224 • Lake Carl Blackwell, Oklahoma (LCB) • Port silt loam, 0 to 1 percent slopes, occasionally flooded • Preplant N Rates (kg N ha-1): 0, 28, 56, 84, 112, 140, 168, 224 • Weather Data • Downloaded from www.mesonet.org • Data retrieved using Microsoft Access Queries & Reports • Statistical Parameters • Normalized Difference Vegetation Index (NDVI) • Measured with GreenseekerTMsensor • Growing Degree Days (GDD) • Days from planting to sensing • Average Temperature > 4 °C • Fractional Water Index > 0.30 • Soil Moisture Factor (SMF) • Amount of plant available water at sensing divided by the estimated amount of water usage from sensing to estimated harvest date (June 10) • Cannot exceed 1.0 • Model Development & Validation • Models developed for 22 site years combined and separated into different soil types • Loamy textured mollisols and alfisols (STW, LAH) • Coarse textured alfisols, inceptisols, entisols (PRK) • Models validated using 2011-12 grain yield data • Loamy textured sites (LAH, STW, HEN, LCB) • Coarse textured sites (PRK) • Results & Conclusions • Soil moisture at the time of sensing had a significant effect on final wheat grain yield for all locations (Table 1) • INSEY models that included soil moisture parameters typically outperformed current INSEY models at all locations (Table 2) • Objective • Improve the reliability of in-season estimates of yield (INSEY) using a model that incorporates soil moisture (A) (B) Figure 1. Predictions of INSEY from 2011-12 growing season at Lahoma for new INSEY (A) and current INSEY (B).