Spatial variability in soil water under adjacent mature oil palm and rubber plantations: application of a new dielectric method in evaluating soil water
Hermawan, B., Suhartoyo, H., Anandyawati, Sukisno, Gonggo, B., Hasanudin and Agustian, I.
Many people have commonly addressed that oil palm plantations release much more
water from the ground by evapotranspiration compared to other crops. The current research
evaluated the spatial variability in soil water content under adjacent oil palm and rubber
plantations established in 2005 and 1995, respectively. We collected ten pairs of soil electrical
impedance data (Z, in kΩ) from the oil palm and rubber sites using a newly-developed
electrical impedance meter, then converted to soil water content (θ, in g.g-1) using the equation
of θ = 0.45.Z-0.2. The impedance measurements took place at 0-10 and 10-20 soil depths to
allow the comparisons of actual soil wetness between the two crops at the rooting zones. At the
same time, we also collected disturbed soil samples from the measurement points for the
laboratory determination of soil water using the standard gravimetric method. Results showed
that soils under oil palm plantation were consistently more wet than under rubber in all pairs of
measurements. At the 0-10 cm depth, the average soil water content at the time of
measurements was 0.04 g.g-1 higher for oil palm than for rubber. The field water content
ranged from 0.310 to 0.384 and 0.268 to 0.318 g.g-1 for oil palm and rubber, respectively. The
standard deviations of samples were about 0.02 g.g-1 for both crops indicating the statistical
confidence that the oil palm site contained more water than the rubber site. Similar trends were
found at the 10-20 cm soil depth suggesting the consistent benefit of the oil palm plantation in
preserving soil water in the 0-20 cm rooting zone. Results in soil water variability gained from
the dielectric method were similar to those obtained using the standard gravimetric method.
Keywords
Electrical impedance, oil palm, rubber, soil water
INTERNATIONAL JOURNAL OF AGRICULTURAL TECHNOLOGY
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