SIMULATION OF WITHIN–FIELD YIELD VARIABILITY IN A FOUR–CROP ROTATION FIELD USING SSURGO SOIL–UNIT DEFINITIONS AND THE EPIC MODEL

Abstract

Soil data were collected from a 30 ha commercial field using a 60 m sampling grid. Monitored yield data werealso collected in this field between 1996 and 1999, when it had a wheatprocessing tomatobeansunflower crop rotation.A comparison between SSURGONRCS soilunit definition and fieldmeasured soil data showed that in this field the formerare a good approximation and starting point for precision agriculture studies and management. In a second test, the EPICmodel, using the SSURGO database soil type definitions, was found to reproduce the yield variability within this field withreasonable accuracy. The models performance was not as good when tested with data from soil samples, apparently due tothe way EPIC simulates water holding capacity from texture information and the lack of some key variables (not sampled),such as water content at fieldcapacity (FC), wiltingpoint (WP), and soil saturated conductivity. A set of runs was performedto simulate the yield at 13 pointlocations in the field using FC, WP, and bulk density. Although the accuracy of the simulationdid not improve greatly, the model reproduced the yield trend of two of the crops (wheat and sunflower).