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Agroclimatology

Modification of a Crop-Specific Drought Index for Simulating Corn Yield in Wet Years

^a High Plains Regional Climate Center, Univ. of Nebraska, Lincoln, NE 68583-0728
^b Current address: Texas Inst. for Appl. Environ. Res., Tarleton State Univ., Stephenville, TX 76402

^* Corresponding author (khubbard1{at}unl.edu)

Received for publication August 27, 2004. Drought occurs when there is a deficit in soil water supply to the plant. Severe drought limits crop yield by causing the plant's water use to be limited compared with a well-watered crop. Too much water (flooded soils) also causes stress to the plant whose roots are in saturated soil for long periods. Both situations lead to crop water stress, ultimately resulting in reduced crop yield. Since flood and drought can occur intermittently in cropping, an effective yield predictor should contain both flood and drought stress components for better representation of the range of natural conditions the plant might encounter during its growth period. This paper details the modification of the Crop-Specific Drought Index (CSDI) model by introducing a soil saturation factor, resulting in a Crop-Specific Stress Index (CSSI) model. The study was conducted in eastern Nebraska and southeastern Minnesota. The coefficients used in the CSSI model were estimated by a jackknifing procedure based on 1971–2002 climate data, nonirrigated yield data of corn (Zea mays L.), and soil information retrieved from the STATSGO database in the crop districts. Results show that all indicators of agreement between the estimated and actual yields show improvement of the new CSSI model over the old CSDI model in all districts. Results also show that the CSSI model outperforms the CSDI model in years characterized by soil saturation. For instance, the CSDI for 1993 overestimates the relative yield in northeastern Nebraska by about 28% while the CSSI underestimates the 1993 yield by 3%.

Abbreviations: COOP, Cooperative Weather Station Network • CSDI, Crop-Specific Drought Index • CSSI, Crop-Specific Stress Index • ET, evapotranspiration • RMSE, root mean square errors • STATSGO, State Soil Geographic database