C - Lublin

The mean difference (MD) and the root mean square difference (RMSD) were
calculated for evaluating the accuracy of the estimated soil water retention curves
and the closeness between the measured and calculated water retention curves,
respectively, according to Tietje and Tapkenhinrichs (1993). The jack-knifing
method was used for verification: soil water retention curves, measured at 3
sampling times were utilised to determine the parameters C and α, characteristic
for the tillage treatment analysed. One set of pF-curves (consisting of 9 curves: 3
depths x 3 replicates), corresponding to one measurement period was out of the
fitting procedure in all of the cases to be used for the independent verification of
the estimated pF-curves. Thus, 5x4 fitting procedures were performed: “5” refers to
the number of the tillage treatments (NT, P, L, LP and LD), while “4” to the
combination of the sampling times.
The nomination used was MM_TT, where MM referred to the tillage
treatment, whereas TT – to the number of the month, the pF-data of which was
taken out of the non-linear estimation and used for the verification.
In case of ploughing treatment, the estimation procedure was repeated separately
for each sampled soil layer for evaluating the possibilities to reduce the estimation
error. Consequently, 4x3 fitting procedures were done, where “3” refers to the
number of soil layers the samples were taken from (5-10, 15-20 and 40-45 cm),
while “4” to the combination of the sampling times.
RESULTS AND DISCUSSION
The MD and RMSD values, calculated for different tillage treatments varied
between –0.004 ÷ 0.038 m 3 /m 3 and 0.021 ÷ 0.048 m 3 /m 3 , respectively (Table 1).
Tietje and Tapkenhinrichs (1993) present results of soil pedotransfer function
evaluation of 13 authors. They report 5 authors with 100% evident applicability.
MD and RMSD values according to these authors vary between –0.053 to 0.013
m 3 /m 3 and 0.033 to 0.075 m 3 /m 3 , respectively. Nemes (2002), comparing the soil
water content dynamics, simulated with measured and estimated pF-curves
concluded, that pF-curve estimations, producing RMSD up to 0.07 m 3 /m 3 is
satisfactory for soil water content modelling. Similar Concerning these results, we
can conclude, that the estimation method, proposed by Sobczuk and Walczak
(1996) gave good results for the presented dataset.
The statistical evaluation of the pF-curve estimation for 3 different soil layers
of the ploughing treatment is given in Table 2. In general, slight improvement of
the estimation of the pF-curves was obtained, when handling soil layers separately.
Estimation accuracy, however, did not increase as much as we expected, probably
because ploughing homogenises the upper 20-23 cm of the soil or because more
measured data is required for the calculation of the parameters (α and C).
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