Measurement and analysis of the spatial variability of fields are two important aspects of site-specific crop management. In this study, data for wheat yield, ground slope and aspect were intensively collected from five fields in the Palouseregion of Washington using a set of sensors and a Global Positioning System (GPS) receive,: A Geographic Information System (GIS) database was developed to manage the field-collected data and information from topographic maps and to group the data fromeach field into different regions for analysis. Relative elevation differences across the five fields ranged from 29 to 70 m. Slope steepness ranged from 0 to 30° with field means of 9 to 12°. Geostatistical analyses showed that the spatial patterns ofvariability in wheat yields differed not only from one field to another but also from one region to another within a field. The ranges of influence in wheat yield for the five whole fields were from 55 to 86 m, while those for the within-field regionsvaried from 20 to over 100 m. Regression analyses indicated that topographic attributes including elevation, slope and aspect had significant effects on wheat yield. These topographic attributes could explain 13 to 35 of the variability in wheat yieldfor the whole fields, though 49 to 84 of the yield variability could be explained by topography in some regions within the five fields. These results provided useful quantitative information about the influence of topography on crop yield in the Palouseregion.
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