The correlation of ECa to yield at the sixty sites was 0.51. The moderate correlation between yield and ECa suggests that some soil properties influencing ECa measurements may also influence cotton yield, making an ECa-directed soil sampling strategy a potentially viable approach at this site. The similarity of the spatial distributions of ECa measurements and cotton yield in Figure 16.1 visually confirms their close relationship.
Exploratory statistical analysis was conducted to determine the significant soil properties influencing cotton yield and to establish the general form of the cotton yield response model. The exploratory statistical analysis consisted of three stages: (1) a preliminary multiple linear regression (MLR) analysis, (2) a correlation analysis, and (3) scatter plots of yield versus potentially significant soil properties. Both preliminary MLR and correlation analysis showed that the 0 to 1.5 m soil depth increment resulted in the best correlations and best fit of the data; consequently, the 0 to 1.5 depth increment was considered to correspond to the active root zone. Preliminary MLR analysis indicated that the following soil properties were most significantly related to cotton yield: ECe, LF, pH, percentage clay, 8g, and pb. Table 16.1 reveals that the correlation coefficients between ECa and 8g, ECe, B, percentage clay, pb, Cl-, LF, and SP were significant at the 0.01 level. The correlation coefficients were 0.79, 0.87, 0.88, 0.76, -0.38, 0.61, -0.50, and 0.77, respectively, indicating high correlations between ECa and the properties of 8g, ECe, B, percentage clay, and SP. However, B is a property not measured by ECa. Rather, the high correlation of B to ECa is an artifact due to its close correspondence to salinity (i.e., ECe) stemming from the leaching process. The high correlation of ECa to both percentage clay and SP is expected because it reflects the influence of texture on the ECa reading. So, in this particular field, ECa is highly correlated with salinity, 8g, and texture. Table 16.1 also indicates the correlation between cotton yield and soil properties, with the highest correlation occurring with salinity (ECe).
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