METHODS FOR COMPARING SPATIAL VARIABILITY PATTERNS OF MILLET YIELD AND SOIL DATA

This paper investigates methods to compare spatial patterns of pearl m illet [Pennisetum glaucum (L.) R. Br.] yield with spatial patterns of soil variables in a farmer's 1-ha field on an undulating sand plain in Niger near ICRISAT-SC. Spatial pattern comparisons are important for precision farming applications. Methods included the correlation coeff icient, linear regression, a distance measure to compare separate maps and the cross-correlation function. Millet grain yield varied from 0 to 2885 kg ha(-1) on 5 by 5 m sub-plots. Pearl millet yield was correl ated with measured soil variables at three different depths, elevation , and crust formation for two successive years. Only 30% of the total variation in millet dry yield was explained by regressing yield agains t soil variables. Detrended elevation showed a significant negative re lation with yield (r = -0.421). The cation-exchange capacity (CEC) at all the depths showed a significant negative relation with yield (r of -0.238 to -0.290) because crusting and erosion increase with CEC exte nding to distances up to 30 to 40 m. Pattern comparison using the cros s-correlogram related local hillocks in the area with high yields and local dips with low yields at a distance of 15 to 20 m. From this stud y, we concluded that the cross-correlogram was beneficial to compare d ata at various distances. Yield patterns are best explained by soil va riables related to erosion as the major determining factor in the area .