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 GreenseekerTM sensor

• 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)

Objective

• Improve the reliability of in-season estimates of yield (INSEY) using a model that incorporates soil moisture

0 1 2 3 4 5 60

1

2

3

4

5

6

f(x) = 0.364994741588337 x + 2.1418444078619R² = 0.30220432065898

Current INSEY--2012 LahomaLinear (Current INSEY--2012 Lahoma)Current INSEY--2012 Lahoma + 1 SDLinear (Current INSEY--2012 Lahoma + 1 SD)

In-season Estimate of Grain Yield (Mg ha-1)

Act

ual G

rain

Yie

ld (M

g ha

-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

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)

Table 1. Model parameter estimates and significance for predicting final wheat grain yield in-season

---All Sites Combined (R2 = 0.37)---Parameter Estimate Std. Err. Pr > |t|Intercept 8.32 2.12 0.0003NDVI -0.09 0.03 <0.0001GDD -10.66 2.48 <0.0001SMF -15.68 3.72 <0.0001NDVI*GDD 0.11 0.03 <0.0001NDVI*SMF 0.22 0.04 <0.0001SMF*GDD 25.80 4.31 <0.0001NDVI*GDD*SMF -0.28 0.05 <0.0001

---Lahoma + Stillwater (R2 = 0.35)---Intercept 9.62 2.82 0.0007NDVI -0.08 0.04 0.0320GDD -13.82 3.17 <0.0001SMF -17.17 4.93 0.0005NDVI*GDD 0.11 0.04 0.0029NDVI*SMF 0.18 0.06 0.0051SMF*GDD 31.44 5.53 <0.0001NDVI*GDD*SMF -0.27 0.07 <0.0001

---Perkins (R2 = 0.55)---Intercept 4.68 3.22 0.1466NDVI -0.06 0.04 0.1261GDD -5.03 4.06 0.2157SMF -13.19 6.26 0.0356NDVI*GDD 0.05 0.04 0.2408NDVI*SMF 0.23 0.07 0.0014SMF*GDD 16.51 7.34 0.0250NDVI*GDD*SMF -0.22 0.08 0.0064

Table 2. Coefficient of determination values (R2) for INSEY models to predict final wheat grain yield throughout the growing season and at specific growth stages for 2011-12 validation sites

All Sites Specific Sites†

Current INSEY New INSEY New INSEY--------------------R2--------------------

Lahoma All Stages 0.30 0.59 0.55 Feekes 4 0.53 0.53 0.53 Feekes 5 0.49 0.61 0.61 Feekes 6 0.38 0.40 0.40 Feekes 7 0.72 0.86 0.86 Feekes 10 0.85 0.90 0.90Stillwater All Stages 0.20 0.31 0.20 Feekes 4 0.12 0.13 0.13 Feekes 5 0.61 0.59 0.59 Feekes 6 0.31 0.30 0.30 Feekes 8 0.77 0.85 0.85 Feekes 10 0.83 0.89 0.89Perkins All Stages 0.07 0.08 0.07 Feekes 4 0.17 0.19 0.17 Feekes 5 0.04 0.04 0.04 Feekes 6 0.05 0.06 0.06 Feekes 8 0.11 0.11 0.11

Feekes 10 0.10 0.10 0.10Hennessey All Stages 0.22 0.35 0.32 Feekes 4 0.22 0.25 0.25 Feekes 5 0.20 0.22 0.22 Feekes 6 0.34 0.39 0.39 Feekes 7 0.82 0.84 0.84LCB All Stages 0.24 0.37 0.33 Feekes 4 0.47 0.50 0.50 Feekes 4 0.20 0.21 0.21 Feekes 5 0.39 0.44 0.44 Feekes 8 0.59 0.68 0.68†New INSEY models developed specifically for soil type. LAH, STW, HEN, and LCB used LAH + STW model; PRK used PRK model.

(A)

(B)

Figure 1. Predictions of INSEY from 2011-12 growing season at Lahoma for new INSEY (A) and current INSEY (B).

0 1 2 3 4 50

1

2

3

4

5

6

f(x) = 0.929915139231393 x + 1.06349813293848R² = 0.585650579950823

New INSEY--Lahoma 2012

Linear (New INSEY--Lahoma 2012)

New INSEY--Lahoma 2012 + 1 SD

Linear (New INSEY--Lahoma 2012 + 1 SD)

In-season Estimate of Grain Yield (Mg ha-1)

Act

ual G

rain

Yie

ld (M

g ha

-1)