Geoscience Reference
In-Depth Information
similarity of the spatial distributions of EC
a
measurements and cotton yield in Figure 16.1 visually
confirms their close relationship.
16.3.2 e
x P l of R a t of R y
s
t a t i s t i c a l
a
n a l y s i s
Exploratory statistical analysis was conducted to determine the significant soil properties influenc-
ing 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 indi-
cated that the following soil properties were most significantly related to cotton yield: EC
e
, LF, pH,
percentage clay, θ
g
, and ρ
b
. Table 16.1 reveals that the correlation coefficients between EC
a
and
θ
g
, EC
e
, B, percentage clay, ρ
b
, 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 EC
a
and the properties of θ
g
, EC
e
, B, percentage clay, and SP. However, B is a
property not measured by EC
a
. Rather, the high correlation of B to EC
a
is an artifact due to its close
correspondence to salinity (i.e., EC
e
) stemming from the leaching process. The high correlation of
EC
a
to both percentage clay and SP is expected because it reflects the influence of texture on the EC
a
reading. So, in this particular field, EC
a
is highly correlated with salinity, θ
g
, and texture. Table 16.1
also indicates the correlation between cotton yield and soil properties, with the highest correlation
occurring with salinity (EC
e
).
tAble 16.1
Simple Correlation Coefficients between eC
a
and
Soil properties and between Cotton yield and
Soil properties
Soil property
a
fixed Array eC
a
b
Cotton yield
c
θ
g
0.79**
0.42**
EC
e
0.87**
0.53**
B
0.88**
0.50**
pH
0.33*
−0.01
% clay
0.76**
0.36*
ρ
b
−0.38**
−0.29*
NO
3
-N
0.22
−0.03
Cl
−
0.61**
0.25*
LF
−0.50**
−0.49**
SP
0.77**
0.38*
Notes:
* Significant at the
P
< 0.05 level; ** significant at the
P
<
0.01 level. θ
g
= gravimetric water content; EC
e
= electrical
conductivity of the saturation extract (dS m
-1
); LF = leaching
fraction; SP = saturation percentage.
a
Properties averaged over 0 to 1.5 m.
b
Pearson correlation coefficients based on sixty observations.
c
Pearson correlation coefficients based on fifty-nine observations.
Source:
Modified from Corwin, D.L., Lesch, S.M., Shouse, P.J.,
Soppe, R., Ayars, J.E.,
Agron. J.
, 95, 352-364, 2003.
With permission.
