Tractor fuel consumption in tillage as a function of soil texture, water content and plot size

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Agricultural Segment: 3(2) AGS/1580, 2012

In the field of the Higher Institute of Agronomy (Tunisia), we studied the average fuel consumption in tillage based on certain physical parameters using a tractor Kubota L3430. The technical itinerary of tillage is formed by a passage of two disks plow with 85 cm of width. We studied the impact of the soil clay percentage on fuel consumption in l/ha and l/h using a plot with a sandy texture (0.5% clay), another with a loam sandy texture (10.9% clay) and a plot with a sandy loam texture (17.7% clay). Indeed, consumption is 12.7, 17.7 and 29 l/ha and 2.3, 3.3 and 5 l/h respectively. We also studied the effect of soil water content on fuel consumption. Tillage was performed after a few rainy days with a good amount of water (date 1). We repeated the test after 27 days with a lower water content (date 2) while the third part of the test was performed after 42 days when the soil becomes much drier (date 3). Indeed, for an average water content of 12.4, 7.3 and 4.6%, consumption is respectively 20.9, 22.2 and 17 l/ha and 3.9, and 4.6 3.5 l/h. In order to evaluate the effect of the plot size on fuel consumption, the test was conducted on three plots with a size of 64, 32 and 24 m in a sandy-medium loam soil. Indeed, the increase in size causes a decrease in fuel consumption.

Abrougui Khaoula*, Chehaibi Sayed

Department of Horticultural Systems Engineering,
Higher Institute of Agronomy, 4042 Chott-Mariem,
Tunisia.
Tel: +216 73 32 75 44 / +216 22 38 10 27
Fax: +216 73 32 75 91
E-mail: khaoula_abr@yahoo.fr

Introduction
The intensification of agriculture is mainly characterized by increased mechanization in tillage operations (Vitlox and Loyen, 2002). Fuel prices may in the future be an increasing load in the farms economy (Védie and al., 2009). In long term, energy will be rare and become increasingly expensive (Chervet and al., 2007), decreasing oil resources and climatic change require asking for energy save (Gerber, 2008). According to (Hoogmoed, 1994), one of the fundamental objectives of modern agriculture is to optimize fuel consumption for motorized tillage operations, especially plowing. According to studies conducted by (Bochu and al., 2008), fuel consumption for a conventional cereal crop is about 80-90 l / ha: 25 l / ha (20 to 30) for plowing, 35 l / ha for other farming activities (stubble, seeding, fertilization, pesticide treatments ...) and 20 to 30 l / ha for harvest (combine harvester + straw). Plowing is one of the main tillage operations consuming fuel (Vitlox, 1998). A good choice of the tractor parameters (transmission report, advancement speed, etc.) reduces energy consumption by 25% (Ismail and al., 1981). Performances of the tractor-tool set in tillage depend on soil physical characteristics (density, texture, moisture) which vary with the soil type (Lyles and Woodruff, 1990) and (Abrougui and Chehaibi, 2009). Although economical aspect is not the only factor in choice of material and that we should also consider the technical and human conditions as wear, performances, time and working conditions, etc. (Abrougui and Chehaibi, 2012). It is important to not neglect the costs analysis associated with the use of agricultural machinery (Miserque and al., 1992). The objective of this work is to study the tractor fuel consumption in the context of the economy of energy during the execution of tillage operations: plowing and plow back. This objective will be achieved through the variation of certain soil parameters such as texture, water content and the plot size.

Materials and Methods

Presentation of Essays
Five plots of different textures were used for experiments in the Higher Institute of Agronomy (Tunisia). Plowing is performed by a two-disk plow and the plow back is practiced by two passages of offset harrow with a respectively width of 0.85 and 1.20 m. Statistical treatment of all measurements made for fuel consumption was based on the method of variance analysis.

Measured Parameters

Soil texture
Three plots of 400 m² each one, were used to compare the impact of soil texture on fuel consumption. The first has a sandy texture, the second consists in a loam sandy soil and a sandy loam soil represents the third plot. Particle size analysis by sedimentation is based on Stokes law. Each plot was divided into three blocks for three repetitions. The statistical treatment of measurements was based on the method of variance analysis.

Water content
The test was conducted on a parcel with (50 x 12) m ² of area and formed by a sandy loam soil. .Tillage is performed on three dates spaced of average 20 days which corresponds to three different soil moistures (H1, H2, and H3) with three repetitions for each measurement date. The weighing method was adopted for determining soil water content: samples were taken with an auger at 10, 20 and 30 cm of depth at the same hole. We weigh the humid sample then we put it in stove at a temperature of 105°C for 24 h. Water content will be determined by the expression: W = Ph-Ps/Ps × 100

P _h is the wet weight of soil sample (g), P _s the dry weight of soil sample (g) and W is the water content (%).

The Plot size
The test was conducted on a parcel divided into three plots with different lengths of 64, 32 and 24 m from a sandy-medium loam soil in order to evaluate the effect of the size plot on fuel consumption. Each plot was divided into three blocks for three repetitions. The statistical treatment of measurements was based on the method of variance analysis.

Fuel consumption
First step: fill up before starting. In this case, we set the tank filler cap to avoid trapping an air bubble (tractor slightly inclined if necessary). For a total filling, we don’t hesitate to shake the tractor and start it, before completing. Second step: note the start time. Third step: realizing the planned work, noting any move times and stop phases. Fourth step: note the finish time of the site, before refilling the tank with a graduated test tube with the precautions listed above (Fig 1). The volume needed to filling is the volume consumed during tillage (Lerat, 2007). With these elements, we can estimate the average hourly consumption (l/h), but also the consumption by volume of the realized work (l/ha). Tractor performances were determined for each operation (Nielsen and Sorensen, 1993) and (Miserque and al., 1992).

Results and discussion

Texture
Soil texture is a qualitative classification tool used in both the field and laboratory to determine classes for agricultural soils based on their physical texture. The classes are distinguished in the field by the 'textural feel' which can be further clarified by separating the relative proportions of sand, silt and clay using grading sieves: The Particle Size Distribution (PSD). The class is then used to determine crop suitability and to approximate the soils responses to environmental and management conditions. Plot 1 is represented by a sandy soil; plots 2 and 3 are formed by a loam sandy soil and sandy loam soil with however, the second plot which encloses more clay. Examination of results (Fig 2) shows that tractor fuel consumption is closely related to soil texture and more specifically to the clay rate. Indeed, for a loam sandy soil containing an average of 17.7% clay, consumption per hectare is elevated to 29 l. For sandy loam soil (10.9% clay), consumption is 17.7 l / ha, whereas at the first plot (0.5% clay), consumption is 12.7 l / ha. The hourly consumption has the same look as the consumption per hectare. This can be explained by the fact that the presence of a high clay percentage in soil led to a greater working depth and thereafter a high worked section, this has been materialized by an important traction effort leading to a high consumption. It is clear that consumption in l / ha product of the hourly consumption by the site time increases with the increase in the site time and inversely. In fact, agricultural tractors are one of the machines in agricultural productions which have great importance. It is obvious in order to increase efficiency of agricultural products; it is needed to increase the machine working efficiency. For example (Taylor, 1980) estimated that in the US for each 1% improvement in traction efficiency, 75-80 million gallons of fuel could be saved annually. Duo to the limitation of non renewable fossil energy sources it is essential to optimize fuel consumption. Statistical analyses of the data show highly significant effect at (P < 0.05) of soil texture, precisely the clay rate on fuel consumption in tillage (Table 1). The comparison showed that average consumption measured per hectare and per hour at 0.5% clay, significantly differs from the others and texture containing more clay is indicated by the highest means.

Water content
Field operations needed to culture crops pose a major fuel demand. Farmers can save significant money and energy if they use field operation plans that provide adequate crop care with minimal fuel consumption. Fuel requirements for all field operations vary somewhat by location and date of operation. Tillage fuel requirements are especially difficult to predict. Moisture content, soil type and depth of operation also directly affect fuel consumption. Obtained results show that tractor fuel consumption is affected by soil water content. For wet soil, consumption per hectare is low, but for dry soil, fuel consumption depends on the working depth of the tool. Indeed, for water content values of 12.4 and 7.3% respectively consumption is 20.9 and 22.2. But for a lower water content value of 4.6%, fuel consumption decreases and corresponds to 17 l / ha. Indeed, when the soil becomes drier, the effort required for tractor increases. The effort control of the tractor hydraulic lift intervenes for lifting the tool. The working depth is reduced, which causes a decrease in fuel consumption. Regarding the hourly consumption, results show its increase with decreasing water content in soil. Indeed, at an average of 12.4, 7.3 and 4.6% we recorded a respective consumption of 3.9, 4.6 and 3.5 l / h, at date 1, date 2 and date 3. Soil resistance to penetration is 120 daN / cm² at 5 cm of depth and 260 daN / cm² at a depth of 15 cm when the soil is very dry. Advancement speed also increases and causes a decrease in the site time and depth and inversely, which explains the decrease of hourly consumption at date 3. Statistical analyses (Table 2) shows a highly significant effect at (P < 0.05) of soil water content on fuel consumption. The averages comparison showed that consumption measured per hectare and per hour at 12.4%, significantly differs from the others values and the higher water content is indicated by good means.

The Plot size
There are many parameters in a tillage operation that can affect fuel consumption of a tractor, such as type and soil structure, climate, relative humidity, tractor type (two or four wheel drive), tractor size, the tractor implement relationship and the worked plot size. So, tractor fuel consumption in different methods is not constant and varies from one to another (Nielsen and Sorensen, 1993). Results indicate that the consumption evolution in l / ha depending on the plot size is practically linear (Fig 3). Indeed, the increase in size is followed by a decrease in fuel consumption. Consumption is 17.7, 22.5 and 30.2 l / ha respectively for large (64 m), intermediate (32 m) and small plot (24 m). This is due to the difference between the hourly consumption calculated for the different sizes with executed site time for the three plots. For the small plot, a significant time was lost by tractor in pounds and maneuvers. Indeed, we recorded site times of 5.3, 5.7 and 6.5 h / ha respectively for the three sizes. Regarding hourly consumption, the look is identical to that of consumption per hectare. The small plot is indicated by the highest means and the largest one by reduced means. Consumption is 3.3, 3.5 and 4.6 l / h respectively for large, intermediate and small plot. Statistical analyses show significant effect of the tilled plot size on fuel consumption (Table 3). The comparison of means showed that there is no significant difference between the measured consumption per hour for large and intermediate size. But consumption differs significantly from those measured for the small plot that is indicated by the highest means.

Conclusion
The experimental study conducted to optimize fuel consumption based on soil physical parameters, leads to the following results: the plowing execution for a sandy soil with 0.45% of clay, produces poor fuel consumption. Indeed, we recorded a consumption of 12.8 liters per hectare against 29.5 liters for loam sandy soil containing 18% of clay. Tillage with a suitable water content of about 15%, improves fuel economy, promotes the plow penetration in soil and reduces the sliding losses. The consumption evolution based on the plot size is practically linear. In fact, fuel consumption decreases when tilled plot size increases due to reduced time wastes in pounds.. Otherwise, fuel economy could be achieved by several ways: reducing tillage (Bourarach, 1989). Indeed, plowing appears to be a very expensive item: With its suppression a margin of potential progress appears to improve the energy balance of biological farming systems (Gerber, 2008); choose the tractor really needed; maintain its equipment, use a good fuel quality; choose the type of tools suitable for practiced cultures (Anken and al., 1999) find a suitable adequacy between tools and traction machines and have a good driving ability.

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