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4. Discussion
The ISUM methodology provides additional measured points in the
inter-row areas that shows micro-topographical information that is
missing from SUM estimates of soil displacement (
Rodrigo-Comino
et al., 2018a
). ISUM improves accuracy, has lower costs, and is easier to
apply and faster than photogrammetric methods (
Remke et al., 2018
).
The SUM technique only considers the midpoint of the inter-row areas
which leads to large errors in previous soil erosion studies on vineyards
that used the SUM method. Soil depletion rates have been severely
underestimated by SUM, for example, by −14.2% and −37.8% at 1-
and 86-day tillage vineyards in one study, respectively (
Rodrigo-
Comino et al., 2018b
).
We confirmed that the ridges determined the soil erosion rates along
Fig. 8.
The lost soil according to primary topsoil level at planting date and secondary topsoil level.
Table 1
The estimated lost soil rate using ArcGIS software.
ArcGIS
Area (m
2
) BD (g cm
−3
) Volume (m
3
) Mass
Mg 25 yr
−1
Mg yr
−1
a (0–45)
225
0.91
21.19
19.07
0.76
b (45–90)
225
0.91
33.03
29.73
1.19
c (90–135)
225
0.91
29.52
26.57
1.06
d (135–185)
250
0.91
33.29
29.96
1.20
abcd (0–185) 925
0.91
117.04
105.34
4.21
F. Bayat, et al.
Catena 183 (2019) 104176
7
the hillslope. Some researchers have argued that due to non-uniform
infiltration patterns created by the furrow and ridge topography severe
surface runoff and soil erosion in the interrow areas resulted (
Ruidisch
et al., 2013
;
Arnhold et al., 2013
). Others stated that low infiltration
rates on the ridge focused water flow into the furrows resulting in
runoff and soil loss (
Saffigna et al., 1976
;
Leistra and Boesten, 2010
).
This study demonstrated that the production of persimmon results
in high erosion rates. Long-term soil erosion studies are very rare. Most
of the research is carried out for some years or even seasons, or un-
derneath rainfall simulators. Information on long-term measurements
will shed light on the soil erosion processes and rates and allow in-
formed decisions about the best management practices to control soil
erosion. This is why long-term soil erosion measurements are so re-
levant and necessary for the advancement of science. In Mediterranean
ecosystems, more research on long-term soil erosion is needed in per-
ennial crops. For example,
Vanwalleghem et al. (2011)
conducted a
study that measured and modeled soil erosion in olive orchards over a
250-year period and related erosion to changes in management prac-
tices and yields as documented in historical sources. At three study sites
in Spain, the height of relic tree mounds was measured in olive orchards
dated at between 153 and 291 years old to determine soil profile
truncation. The measured average of soil erosion was between 29 and
47 Mg ha
−1
year
−1
. Those results are similar to what we measured in
the persimmon plantations and give credit to both types of research.
This data also confirms the non-sustainability of agricultural erosion in
the Mediterranean, in both traditional systems such as olive and new
ones such as persimmon.
The tree needs a long time to develop their canopy cover and protect
the soil surface, while annual crops close their canopy a few weeks after
planting (
Morgan, 2009
). During the immature phase of tree crops,
there may be insufficient soil cover to protect the soil against erosion
such as
Cerdà et al. (2017)
and
Rodrigo-Comino et al. (2018c)
found in
vineyards by means of rainfall simulation experiments and ISUM,
respectively.
Alagna et al. (2017)
also found changes in the soil hy-
draulic conductivity after the vine plantation.
The average soil erosion in the EU's semi-natural areas, agricultural
and forests lands is 2.46 Mg ha
−1
yr
−1
(
Panagos et al., 2015
). The re-
search carried out here demonstrated that the new persimmon planta-
tions enhanced soil erosion by one order of magnitude.
Biddoccu et al.
(2018)
evaluated long-term soil erosion in a 44-year-old sloping vine-
yard in Italy using a botanical benchmark and estimated annual soil
erosion as 15.7Mgha
−1
yr
−1
. They stated that runoff, tillage practices,
and the high slope gradient had a significant effect on the high soil
depletion rates.
Rubio-Delgado et al. (2018)
investigated soil erosion in
Mediterranean dehesas using the inflection point of holm oaks and es-
timated mean soil loss of 26.7 Mg ha
−1
y
−1
. They claimed that soil
erosion showed a slightly negative trend in relation to tree age, similar
to what
Rodrigo-Comino et al. (2018b)
found in vineyards. Besides that,
they stated that exposure of tree or shrub roots represents a clear in-
dicator of soil loss in the surrounding area and can be used as botanical
evidence to estimate soil erosion with preference given to roots that are
some distance from the tree's trunk because the root collar is affected by
dislocation due to vertical elongation.
Steinhoff-Knopp and Burkhard
(2018)
conducted a survey to determine soil erosion by water over
17 years on 465 ha of cropland in Northern Germany. Their findings
showed that mean soil loss for all fields was relatively small at
0.85 Mg ha
−1
yr
−1
and the highest rate for a single field was
7.02 Mg ha
−1
yr
−1
. They found that soil loss was highly varied in terms
of time and place and the highest soil loss on a single field was
53.07 Mg ha
−1
yr
−1
, which is the same as we found for the average in
the persimmon plantations in the Valencia region. Compared with other
plantations and countries, as shown in this brief review, persimmon has
one of the highest soil loss rates. However, is in the same order of
magnitude as other crops, which is a clear demonstration that soil
erosion is a Europe-wide problem that needs action.
Non-sustainable agricultural management has increased erosion
rates in the Mediterranean region (
Cerdà et al., 2016
;
Jianjun et al.,
1997
). Unfortunately, there is a misconception among some farmers in
the area that their farm should be kept “clean” and “tidy” (
Cerdà et al.,
2018a, 2018b
). The reason that orchard land is often left without any
living (cover crops) or non-living (mulch and litter) soil cover is many
farmers prefer to adopt frequent tillage passes to control weeds that
compete with crops for growth requirements and to facilitate sub-
sequent operations. This strategy to keep the soil free of weeds results in
high erosion rates, as was shown by
Keesstra et al. (2019)
in glyphosate-
treated citrus plantations. There is a need to fight against the high
Table 2
The estimated lost soil rate using three software.
Software
Area (m
2
)
BD (g cm
−3
)
Volume (m
3
)
Mass
Mg 25 yr
−1
Mg yr
−1
SolidWorks
925
0.91
128.97
116.07
4.64
MATLAB
925
0.91
129.53
116.58
4.66
ArcGIS
925
0.91
143.66
129.29
5.17
Fig. 9.
The amount of lost topsoil according to primary topsoil level at sowing date.
F. Bayat, et al.
Catena 183 (2019) 104176
8
erosion rates in orchards to achieve the land degradation neutrality
challenge (
Keesstra et al., 2018
).
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