Abstract:
Soil water and heat are important physical aspects of soil. Their presence and
transmission considerably impact on plant growth and performance as well as on
soil organic matter decomposition. Both soil water and heat depend on soil pore
geometry that can be altered by tillage application. The purpose of this study was
to differentiate the effects of conventional tillage (CT) and no-tillage (NT) on water
and heat movement in Japanese Andisols during November to January, which is the
transitional period from autumn to winter. Water movement in the soil was
analyzed through changes in moisture content and hydraulic conductivity. Heat
movement was analyzed considering the temperature variability. Soil hardness and
soil moisture characteristics were determined to identify the factors that
contribute for tillage impacts on soil. Mini disk infiltrometer at three different
suction heads (-0.5, -3, and -6 cm) was used to measure field infiltration and
unsaturated hydraulic conductivity. Falling head method was used for saturated
hydraulic conductivity determination, whereas hanging water column and
pressure plate methods were used for determining soil moisture characteristics.
Soil hardness was measured using cone penetrometer. Moisture sensors (Ech20
5TE and TDT sensors) buried at 2.5 cm (corresponding to surface soil), 7.5 cm, 20
cm and 40 cm depths were used to measure and record volumetric moisture
content and soil temperature simultaneously. Two sample t-test (p<0.05) was used
to determine statistical significance between the two sites. The soil hardness was
significantly low in CT site up to the tillage depth (20-30 cm), and higher in CT than
NT below that level. Possible formation of a hard pan below the tillage depth due to
long-term migration and deposition of finer soil particles and the use of heavy
machinery might be the reason for this result. Field unsaturated hydraulic
conductivity was significantly higher in CT site than NT in November and January.
Saturated hydraulic conductivity was also higher in CT than in NT up to tillage
depth. Conversely, moisture retention and moisture content of surface soil (at 2.5
cm depth) were significantly lower in CT. Surface soil temperature was notably
lower in CT than in NT as a result of enhanced soil surface area of CT, facilitating
the dissipation of heat. These results emphasize that water and heat movement in
soil were affected by tillage. Further investigations are needed to determine the
most appropriate tillage system considering cropping systems.
