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Spatiotemporal Analysis of Rice Yield Variability in Two California Fields

^a Graduate Group in Ecol., Univ. of California, Davis, CA 95616, USA
^b Dep. of Agron. and Range Sci. and Dep. of Biol. and Agric. Eng., Univ. of California, Davis, CA 95616, USA
^c Instituto Nacional de Investigaciones Agropecuarias, Treinta y Tres, Uruguay

View larger version (104K): [in a new window]   Fig. 1. Gray-scale renditions of false-color infrared aerial images taken on 8 Aug. 1998 of the two study fields. (a) Field 1. Note that in the image the field becomes darker as one moves from west to east. This corresponds to higher near-infrared values in the original image. (b) Field 2. The dark areas in this image correspond to areas of very sparse vegetation in the field. The field had recently been laser-leveled and brought into production, and these dark areas in the image were areas where considerable topsoil had been cut off in the leveling process.

View larger version (42K): [in a new window]   Fig. 2. Yield monitor data (every 10th data point) of Field 1 plotted in the order in which records were entered into the database. Abscissa is the difference between the GPS clock time for that record and the lowest GPS time of the data set. Ordinate is yield (kg ha–1) converted to common moisture content. Arrows placed at gaps in the GPS time record indicate that the harvest had been stopped and restarted.

View larger version (47K): [in a new window]   Fig. 3. Yield monitor data (every 10th data point) of Field 2 plotted in the order in which records were entered into the database. Abscissa is the difference between the GPS clock time for that record and the lowest GPS time of the data set. Ordinate is yield (kg ha–1) converted to common moisture content. Arrows placed at gaps in the GPS time record indicate that the harvest had been stopped and restarted.

View larger version (14K): [in a new window]   Fig. 4. Relationship between the means of sequences of 10 yield monitor data points recorded next to each other in Field 1. Error bars show 95% confidence intervals based on standard deviation of the 10 data values.

View larger version (59K): [in a new window]   Fig. 5. Sequence of maps of Field 1 data as analyzed for each of the years 1998 through 2001. Yield data are in kg ha–1. Outliers have been deleted, and data have been resampled to a common grid representing 30-m square cells (Grid 1).

View larger version (61K): [in a new window]   Fig. 6. Sequence of maps of Field 2 data as analyzed for each of the years 1998 through 2001. Yield data are in kg ha–1. Outliers have been deleted, and data have been resampled to a common grid representing 30-m square cells (Grid 1).

View larger version (11K): [in a new window]   Fig. 7. Experimental and fitted variograms of yield data in Field 1. Values of the fitted variogram sill, co + c1; range, Ao; and model fitness, r2; are given in the figures. (a) 30- and (b) 60-m sampling grid. Variograms for Field 2 are very similar.

View larger version (40K): [in a new window]   Fig. 8. Spatial distribution of the temporal variance (Mg ha–1)2 for (a) Field 1 and (b) Field 2. Each figure consists of Thiessen polygons surrounding each sample point.

View larger version (15K): [in a new window]   Fig. 9. (a) Cluster behaviors defined by standardized yields in 4 yr in Field 1. (b) Cluster behaviors defined by standardized yields over the three years 1998–2000 in Field 2.

View larger version (48K): [in a new window]   Fig. 10. (a) Thiessen polygons interpolated clusters in Field 1 (1998–2001). (b) Thiessen polygons interpolated clusters in Field 2 (1998–2000).