عنوان مقاله [English]
The Effect of Different Tillage Instruments on Some Soil Physical Characteristics and Soil Translocation
Tillage is defined as disturbing the soil and changing soil physical condition of seedbed and root zone and making it suitable for cultivation. Soil physical characteristics like soil moisture and temperature conduction, bulk density, porosity and particle size are changed in the following of soil tillage. Tillage also increases water infiltration rate and plays an important role in soil moisture protection and decreasing flood hazards in arid and semi-arid regions. Molboard plough is currently implemented for tillage in different parts of Iran including Chaharmahal va Bakhtiari province. There are evidences which show Moldboard plough triggers physical soil characteristics deterioration and soil tillage erosion. Tillage translocation coefficient, as a component of tillage erosion, is defined as the amount of soil transition for 1 m width of tillage instrument. Comparing the impacts of available tillage instruments on physical soil characteristics, soil transition and their efficiency with of Moldboard plough may encourage field managers to substitute other instruments with Moldboard plough. This research aimed to: 1) study the impacts of the currently available tillage instruments (Moldboard, Disk and Chisel plough) on some prominent physical soil characteristics and 2) compare soil translocation coefficients of the mentioned tillage instruments.
Materials and Methods
This research was executed in Research-Training Field of Shahrekord University, Shahrekord county, Chaharmahal va Bakhtiari Province, Iran. A split plot experimental design with complete randomize block was considered with 3 major treatments of tillage instruments (Molboard, Disk and Chisel plough), minor treatments of slope (0, 3, 6 and 8%) and tillage speeds (2, 5, and 8 km h-1) and 3 replications. The conventional tillage depth of 25 cm was adjusted for all three tillage instruments. Standard protocols were applied and soil electrical conductivity (EC), pH, calcium carbonate equivalent (CCE), organic matter and soil texture components were measured before tillage application and soil field capacity (FC), mean weight diameter (MWD) of aggregates, geometric mean diameter (GMD) of aggregates, aeration porosity (Fa), bulk density (ρb) and water stable aggregates (WSA) were measured using standard protocols after tillage implementations. Colored gypsum cylinders were used as indicators for detecting soil translocation. The transition distance of the colored gypsum cylinders of each layer of tillage depth (0-9, 9-18 and 18-25 cm) was measured using tape meter or ruler and mean transition for each layer were calculated. In the next step the depth weight soil translocation was calculated for each tillage instrument.
Results and Discussions Chemical analysis of soil samples showed that soils were non-saline, soil OM content was less than 1% and CCE of soil samples was relatively high. Physical soil analysis of soil samples before tillage implementation indicated that there was not any restriction for plant root development and aeration as ρb was relatively low and aeration porosity was 10% <, respectively. Analysis of variance (ANOVA) indicated that the effects of tillage type on MWD and ρb were significant (P < 0.05). Comparing the means of MWD and ρb induced by tillage instruments (Duncan method) revealed significantly higher values of MWD and lower values of ρb for soils which were treated by MB plough, the results were corresponded to the finding of other researchers. There were not significant differences between MWD and ρb of soils which were treated by disk and chisel plough. The results also showed that tillage instruments did not impact on physical characteristics like FC, WSA, GMD and FA. Non-significant impact of MB plough on soil moisture condition also was reported by other researchers in the northwest of Iran. The ANOVA was calculated for soil translocation and showed that the effects of tillage instruments were significant (P < 0.05) for all three layers of soil depth. Mean soil translocation of surficial layer of tillage depth (0-9 cm) was significantly higher than of other layers of tillage depth. Despite other researchers' findings, our research indicated that the slope levels were not significant for soil translocation. This research also revealed that tillage speed significantly (P < 0.05) impacted on soil translocation which was corresponded to findings of other researches in different parts of the world. Interaction of slope-speed and tillage type-speed were significant (P < 0.05) which could be due to accelerated impacts of speed on soil translocation in steep areas. Amount of coefficient of translocation for MB plough was 141 kg m-1 per application. This value was about one third of soil translocation which was reported by others from Belgium (545 kg m-1 y-1) or Denmark (456 kg m-1 y-1) and very closed to the finding of Spanish researchers (164 kg m-1 per application). The coefficient of translocation for disk and chisel plough were 114 and 93 kg m-1 per application, respectively. According to researchers from Portugal, the coefficients of translocation for disk and chisel plough were in ranges of 0-333 kg m-1 and 18-770 kg m-1 per application, respectively. The magnitude of soil translocation coefficients for tillage instruments were in order of MB plough > disk plough > chisel plough.
Keywords: Aggregate mean weight diameter, Bulk density, Soil coefficient of translocation