1. Using Remote Sensing to Characterize Yield Loss due to Water and N stress in Corn. David E. Clay, K. Kim, J. Chang, S.A. Clay, C.G. Carlson, and K. Dalsted

2. N and water stress NASA North Central Soybean Board SD Corn Utilization Council USDA-CSREES PPI SD Soybean Research and Promotion council.

3. We also know that multiple factors interact to influence reflectance Reflectance = f(water, nutrients, light, energy, diseases, insects, other)

4. August 24, 2001 Bare soil, 2001

5. Objectives Determine the influence of water and N stress on yields and reflectance.

6. Field experiment N and water experiment was conducted between 2002 and 2004. Remote sensing was measured with a crop scan. Carbon and N budgets were determined

7. Need to separate N and water stress from each other 13 C natural abundance approach was used to quantify N and water stress in the plants

8. N and water response Natural + irrigation Natural

9. N budget Soil yield zone Yield Mg/ha N min. Kg/ha WUE Kg/ha cm N from soil (kg N/ha) Low850072.021880 High960086.019092 P-value0.0040.0620.0060.027

10. N effects N rateYield (Mg/ha) WUE kg/ha cm N from soil 0751017080 56904020499 112989022396 168980021970 P value0.001

11. Sampling dateParameterYieldYLNSYLWS 12 JulyNDVI0.24*-0.41**0.20 V8-V9GNDVI 0.67**-0.73**0.02 Green-0.22*0.24*-0.02 Red-0.140.23*-0.11 NIR 0.19-0.48** 0.34*

12. Sampling dateParameterYieldYLNSYLWS Aug. 1-4NDVI 0.65**-0.22 -0.61** R1GNDVI 0.63** -0.65**-0.04 Green -0.55** 0.49**-0.14 Red -0.48**0.05 0.58** NIR0.16 0.27* 0.12

13. Summary Stuff changes –Early on reflectance sensitive to N but not water –At R1 (silking) water and N both impacted reflectance Green N Red water

14. Models Sampling dateModelRMSE N needed Model YLNS V8-V9 12-14 JulyN stress16.226.429000 Yield model21.630.232500 Yield & water stress21.723.646400

15. Summary Water and N stress both impact reflectance. N stress early, water stress later 13 C discrimination can be used separate the factors.

16. Summary Remote sensing models can be used to develop corrective treatments. The models can be developed using a variety of approaches.

17. Summary The model based on N stress had lowest lost opportunity and RMSE. Attributed to the water and N cycles being interrelated and that the low and high water regimes had similar optimum N rates. Water increased N mineralization and N increased water use efficiency. A sandy soil may have different results.