=Paper=
{{Paper
|id=Vol-1498/HAICTA_2015_paper90
|storemode=property
|title=Soil Parameters Assessment by Remote Sensing
|pdfUrl=https://ceur-ws.org/Vol-1498/HAICTA_2015_paper90.pdf
|volume=Vol-1498
|dblpUrl=https://dblp.org/rec/conf/haicta/GemtosCCAGF15
}}
==Soil Parameters Assessment by Remote Sensing==
https://ceur-ws.org/Vol-1498/HAICTA_2015_paper90.pdf
Soil Parameters Assessment by Remote Sensing
Theofanis A. Gemtos1, Christos Cavalaris2, Christos Caramoutis2, Dimitris
Anagnostopoulos2, Stavros Giouvanidis2, Spyros Fountas2
1
Laboratory of Farm Mechanisation, University of Thessaly, Fytoko Street, N. Ionia, 38446
Mangesia, Greece, +30.2421093228, gemtos@agr.uth.gr
2
Laboratory of Farm Mechanisation, University of Thessaly, Fytoko Street, N. Ionia, 38446
Mangesia, Greece
Abstract. In this paper, remote sensing measurements like apparent electrical
conductivity (ECa.) are used to assess soil compaction. In an experiment
comparing five tillage treatments and their effect to energy crops soil
penetration resistance (SPR) was measured at the same time as ECa. ECa
measurements were carried out using EM-38with dipoles at 1m apart and SPR
by an electronic penetrometer. The negative correlation between the two
parameters for all measurements resulted in R2= 0.73. Taking the
measurements for each treatment in conventional tillage plots R2 = 0.53, chisel
plough tillage 0.61, rotary tiller 0.69, disk harrow 0.55, strip-till 0.35 and no
till 0.81.
Keywords: soil compaction, tillage, soil apparent electrical conductivity, soil
penetration resistance
1 Introduction
Soil compaction is a major problem of soil degradation affecting soil fertility and
crop yields. Soil compaction is caused in the present day agriculture mainly by heavy
farm machinery. Several factors affect compaction by machinery like soil water
content, machinery weight, machinery tyres (width, type and inflation pressure).
Compaction is not homogeneous in all parts of the field because it depends on the
traffic of each part. The compaction caused is alleviated by soil tillage. Soil deep
loosening causes breaking of the soil causing the restoration of large pores and
facilitates the soil functioning. Tillage practices employing deep loosening and soil
inversion like conventional tillage using ploughing or minimum tillage that causes
soil loosening at different depths without soil inversion can lead to higher or lower
soil disturbance and loosening. Soil tillage is an energy and labour consuming
practice and the intensity depends on the soil compaction. It would be of interest to
find ways to assess soil compaction in order to apply variable rate tillage depth and
reduce energy consumption.
Soil compaction is measured by instruments like penetrometers measuring soil
penetration resistance (SPR) at different depths, by measuring dry bulk density at
layers of different depths and by measuring water infiltration rate. Penetrometers are
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usually following the ASABE standardisation (ASABE 2014). The penetrometer has
a cone with base diameter of 12.83 mm and cone angle of 30o. It is inserted at stable
speed up to a depth usually of 50 cm. Undisturbed soil cores are taken at different
depths and the dry weight of the unit of volume is estimated. Water infiltration is
measured by metallic tubes filled with water and the rate of water infiltrated by the
soil is measured. All methods are time and labour consuming and are difficult to be
applied. An alternative method proposed in the literature to estimate soil compaction
is the measurement of soil apparent electrical conductivity (ECa). This is a method
that can measure soil properties on the go. This is a fast and low cost method. The
sensors are based on electrical and electromagnetic, measurements (Adumchuk et
al.2004). Electrical resistivity and electromagnetic induction (EM) was used to
assess the soil apparent electrical conductivity (ECa). The ECa measures
conductance through not only the soil solution, but also through the solid soil
particles and via exchangeable cations that exist at the solid–liquid interface of clay
minerals.(Colvin and Lesch 2003). This property is directly connected to soil
properties like texture, water content, organic matter, salinity, ions in the soil and
temperature. There are formulae to correct measurements to a basis of 25o C (Ma et
al. 2011). If we exclude saline soils from the measurements and take measurements
near field capacity most measured conductivity is due to soil texture. Electric
resistivity instruments use flat, vertical disks to apply a voltage and measure the soil
resistance by measuring the current in other similar disks (Figure 1). The distance
between the disks defines the depth of the measurement. In Electromagnetic
induction sensors (Figure 2) coils induce and measure the electricity. An EM
transmitter coil located at one end of the instrument induces circular eddy-current
loops in the soil. The magnitude of these loops is directly proportional to the ECa of
the soil in the vicinity of that loop. A second coil measures the produced current
which is the result of soil properties (e.g., clay content, water content, organic matter,
ions). Instrument construction (distance between the dipoles), orientation and
distance from the soil when measurements are taken define the depth the soil the
measurements present.
Fig. 1. Electrical resistivity instrument Fig. 2. Electromagnetic induction (EM)
(VERIS) instrument.
The two instruments were used in many applications in precision agriculture
combined with GPS. They provide a fast and relatively cheap way to produce maps
which are presenting the variability of the field and they are correlated to yield.
Many researchers have reported this connection (Kitchen et al. 2005).
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The two instruments were used to assess soil compaction. Siqueira et al. (2010)
have studied the correlation between ECa and SPR. They found negative correlation
between SPR amd ECa measured by an inductance instrument EM38. The best
correlation coefficient of r= - 0.695 was found between the Vertical position of the
EM38 and the SPR at 0.30 to 0.40 m depth interval. They explain the negative
correlation by the water content of the soil. High water content gives high ECa and
low SPR. Jabro et al.(2006) have studied the relationship between SPR and ECa
measured by a VERIS electrical resistivity instrument. They found very low negative
correlation between the two.
During the last three years experiments studying soil tillage systems under
different crop rotations were carried out in the University of Thessaly Farm at
Velestino, Central Greece. During the experiment soil compaction was measured
using a soil penetrometer and soil apparent electrical conductivity using an EM38.
The results of these experiments are presented in the present paper.
2 Material and Methods
The tillage treatments were:
1. Conventional tillage (CT) using ploughing at 25-30 cm and 2-3 passes of a disk
harrow at 7-9 cm or a light cultivator at 6-8 cm for seedbed preparation.
2. Reduced tillage (HC) using a heavy cultivator at a depth of 20-25 cm at 30-35
cm and 2 passes of a disk harrow or a light cultivator for seedbed preparation.
3. Reduced tillage (RC) with one pass of a rotary cultivator at 10-15 cm for
primary tillage, and a second pass with rotary cultivator or one or two passes of
a disk harrow or a light cultivator before planting.
4. Reduced tillage (DH) Primary and secondary tillage with a disk harrow at 6-8
cm for the winter crops and strip tillage for spring crops. For winter crops one
or two passes for residue management and weed destruction and one or two
passes for seedbed preparation before planting the crop. A strip tillage machine
developed in the laboratory (lit) of farm mechanisation was used for spring
crops.
5. No-tillage (NT). Direct planting using a no till pneumatic drilling for winter
crops and a planting machine for spring row crops.. The plots were split in two
parts. In one part all residues were removed and added to the other plot. That
way one plot had double mulching material.
The following soil properties were measured: 1. Soil penetration resistance by
using a Bush penetrometer with a 12.8 mm base diameter and 30o angle. The
instrument was able to record soil penetration resistance every 1 cm depth. The
measurements were made in each experimental plot. Five measurements were made
and the mean values for each depth were used 2. Soil apparent electrical conductivity
by using an EM 38. Measurements were made by moving the instrument along the
plot. Two modes of operation was used. The horizontal (H) measuring the ECa at 0-
75 m depth and the vertical (V) measuring the ECa at 0-1.5 m depth. As the
Horizontal mode is more sensitive to the surface layers of the soil the Horizontal
mode was used for the present measurements. Three groups of measurements were
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taken. From 25/6/2011 till 6/7/2011 five measurements were taken, from 25/2/2013
till 2/4/2013 six measurements were taken and from 21/6/2013 till 26/7/2013 twelve
measurements were taken. Date analysis were made using Excel 2013 and SPSS.
3 Results and Discussion
Figure 3a shows the correlations of all data. An exponential curve is fitted with a
high correlation coefficient of 0.73. Figure 3b shows the same data with a linear
curve fitted with R2 = 0.69. Figures 4 show the curve fitting of the tillage treatments
of the experiment. In all cases the correlation is negative i.e that higher ECa is
connected to lower SPR. The basic soil parameter that can explain this is the effect of
soil water content has in the two measured parameters. ECa is larger with higher
water content as electrons are moving freely through water and SPR is lower with
higher water content. The same conclusions were drawn by Siqueira et al. (2010).
Fig. 3. a) Power regression model between SPR and ECa for all data taken and b) Linear
regression model between SPR and ECa for all data.
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Fig. 4. Curve fitting for conventional tillage (CT), Heavy cultivator tillage (HCT), rotary
cultivator tillage (RT), no-tillage (NT), disk harrow tillage (DT) and strip tillage (ST)
treatments.
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Table 1. Models connecting ECa and SPR
Tillage treatment Regression curve R2
All field data −0 , 6972 0,73
EC a = 26565 × SPR
Conventional tillage 0,53
EC a = 27192 × SPR −0, 758
Heavy cultivator 0,61
EC a = 30070 × SPR −0, 719
Rotary cultivator EC a = −1604 × ln(SPR) + 8069,2 0,74
Disk Harrow 0,55
EC a = 29275 × SPR.−0, 712
Strip tillage EC a = −707,1× ln(SPR) + 4309,8 0,35
No Till EC a = −2559 × ln(SPR) + 11829 0,81
Table 1 shows the regression curves fitted to the data and the respective
correlation coefficients. Strip tillage presents the lower correlation coefficient. This
effect was expected as strip tillage is not homogeneous in all the area of the plot. Soil
loosening is taking place only on the rows i.e. every 0.75 m while the rest of the soil
remains undisturbed. Conventional and disk harrow treatments have the lower
coefficients. But generally the other coefficients indicate high correlation and that
RCa is a possible indicator of soil compaction.
If the results will be verified and the measurement of ECa at different depths can
be achieved through the adjustment of the distance between the dipoles then the
method can be used to assess soil compaction at different soil depths. This can be the
basis to develop a variable rate (depth) tillage (soil disturbance) system or precision
tillage system that can contribute to the reduction of energy consumption for tillage
and help at improving energy productivity in agriculture.
4 Conclusions
From the results presented in this paper it can be concluded that:
• Different tillage treatments cause different residual compaction to the soil.
• ECa is negatively correlated to soil compaction measured by soil penetration
resistance.
• ECa can be used to predict soil compaction at least under the conditions of
the present experiment
• Correlation coefficients were higher in no till, heavy and rotary cultivator.
Low correlation was found in stripe tillage and disc harrow due to the lower
homogeneity of the tillage.
Acknowledgement. The present project was funded by the Greek Ministry of
Education and EU, by the programme of Life Long Learning through the THALIS
programme.
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