SIMULATION OF DRAFT FORCE FOR THREE TYPES OF PLOW USING RESPONSE SURFACE METHOD UNDER VARIOUS FIELD CONDITIONS

In this study a mathematical models were developed to simulate draft force for three types of plows (moldboard, chisel and disk plow). The study was carried out in the experimental field of Agricultural Machinery Department at University of Basrah, which had silty clay soil texture. Independent parameters included three levels of tillage depth (0.15, 0.20 and 0.25m), three forward speeds (0.54, 0.83 and 1.53 m/s) and two levels of cone index (550 and 980 kPa). Response Surface Method (RSM) was utilized to produce models and to analyze results. Acquired results were used to extract accurate model for draft force. The draft force increased by 114% when tillage depth increased from 15 to 25 cm. Increasing forward speed from 0.54 to 1.53 m/s led to increased draft force by 80%. The cone index had positive effect on draft force by 42% when increased cone index from 550 kPa to 980 kPa. The most influential factor in draft force is the tillage depth, followed by the forward speed and cone index. The highest draft requirements were recorded for moldboard plow, followed by chisel and disk plow. Models validation was acceptable ( R-Squared = 0.97) and the draft force could be predicted with reliability of about 95%. Keyword: modeling, response surface method, draft force, moldboard, chisel and disk plow. ةيقارعلا ةيعارزلا مولعلا ةلجم 8104 6 45 ( 6 6) 0081 0010 يكلاملا ثيراحملا نم عاونا ثلاثل بحسلا ةوق ةاكاحم تساب لامع ةيحطسلا ةباجتسلاا ةقيرط ةفمتخم ةيمقح فورظ دنع يكلاملا ردنب رجع ملاس سردم ةيعا رزلا تلالااو نئاكملا مسق ةرصبلا ةعماج / ةعا رزلا ةيمك / ملا صمختس بحسلا ةوق ةاكاحمل ةيضاير جذامن ريوطت مت ةسا ردلا هذى يف .)يصرقلا ،رافحلا ،بلاقلا يحرطملا( ثيراحملا نم عاونأ ةثلاثل ،ةرصبلا ةعماج يف ةيعا رزلا تلالآا مسقل عباتلا لقحلا يف براجتلا تيرجأ تناك تنمضت .ةينيرغ ةينيط ةجسن تاذ لقحلا ةبرت ( ةثا رحلا قامعأ نم تايوتسم ةثلاث ةسا ردلا 0.15 ، 0.20 ، 0.25 ( ةيمامأ تاعرس ثلاث ،)م 0.54 ، 0..3 و ، 1.53 م ( طورخملا رشؤم نم نايوتسمو ،)ةيناث / 550 ، 0.0 .)لاكساب وميك تسا تممع ةقيرط ةيحطسلا ةباجتسلاا جذامنلا ءاشنلإ تسا ايمقح ةمصحتسملا جئاتنلا .تانايبلا ليمحتلو تممع لا تريظا .بحسلا ةوقل قيقد جذومن جا رختسلا بحسلا ةوق ةدايز جئاتن ةبسنب 114 ز دنع ٪ ي دا ة نم ةثا رحلا قمع 15 مس ىلإ 25 نم ةيماملأا ةعرسلا ةدايز تدا امك .مس 0.54 ةيناث/رتم ىلإ 1.53 ةبسنب بحسلا ةوق ةدايز ىلإ ةيناث /رتم .0 ةبسنب بحسلا ةوق ىمع يباجيإ ريثأت طورخملا رشؤمل ناك .٪ 42 امدنع ٪ نم طورخملا رشؤم عفترا 550 ىلإ لاكساب وميك 0.0 ا .لاكساب وميك ةثا رحلا قمع وى بحسلا ةوق يف اً ريثأت رثكلأا لماعل و ةيماملأا ةعرسلا ويمت مث بلاقلا يحرطملا ثا رحملا يف بحس تابمطتم ىمعأ ليجست مت .طورخملا رشؤم و رافحلا ويمي مث ( ةيلاع ةيقوثوم بحسلا ةوقب ؤبنتلا جذامن تريظا .يلاوتلا ىمع يصرقلا R-Squared = 0.97 ةوقب ؤبنتلا نكميو ) بحسلا ةيقادصمب 05 .٪ ،ةجذمنلا :ةيحاتفملا تاممكلا ،ةيحطسلا ةباجتسلاا ةقيرط يصرقلا ،رافحلا ،بلاقلا يحرطملا ،بحسلا ةوق *Received:29/4/2018, Accepted:10/7/2018 Iraqi Journal of Agricultural Sciences –8104:49(6):0081-0010 Almaliki

it is important to prepare information about the ability of the tractor and the implement and the accessible tractor load. Accordingly, draft force requirements vary with the implement size, soil type, speed and depth of operation. Therefore, to have an effective tractorimplement matching, there is a necessity to fulfill actual field efficiencies and draft requirements along with other indices of tractive performance (2, 13, 21 and 23). Draft force is considered as a pertinent measure of tractive performance parameters (12). Almaliki (6) revealed that the most influential factor in drawbar pull of moldboard plow is the tillage depth, followed by the forward speed and cone index. Mathematical models of soil-tool interaction established on empirical and semi-empirical models may be support tool for designers and researchers in the domain of tillage implements (15). Shafaei, et al. (28) studied the effect of forward speed and tillage depth on draft force of chisel plow using adaptive neural fuzzy inference system. Then compare their model with mathematical model suggested by American Society of Agricultural and Biological Engineers (ASABE) to select the best model. The variation of energy requirements and fuel consumption for primary ploughing related to parameters such as soil type and its conditions, depth and width of cut, tool shape and geometry, manner of tool movement, previous treatments and crops, ground cover, tillage system and operation speed (8 and 18). Several techniques have been used for predicting draft force, and they are analytical, empirical, and numerical methods (3, 4, 5, 7, 19, 20, 22 and 25). Al-Suhaibani et al. (9) assessed the effects of tillage depth and forward speed on draft of moldboard, disk and chisel plows on sandy loam soil, the results demonstrated significant effects of forward speed and tillage depth on draft force for all the studied implements. The moldboard and chisel plow had highest draft force. Appropriate selection of implements and tractors for a specific field situation to diminish energy inputs for crop yield can be determined from these performance parameters. Many researchers believed the increasing of overall energy efficiency for tractor and implements and correct matching of tractor and agricultural machinery can be effective in decreasing fuel consumption (8, 16 and 27). The objective of this research is to predict premium model which represent the draft force using three types of implements under different field conditions. For more accurate, the Response Surface Method (RSM) will be utilized to model and analyze the collected data using Design-Expert Software 8.0.6. MATERIALS AND METHODS Experiment Site: Experiments were carried out at the experimental field of Agricultural Machinery Department at University of Basrah located in (19ʹʹ 30´ 33 N 54ʹʹ 47´ 44 E, Basrah province, Iraq). The soil at the experimental site has silty clay texture (49% silt, 20% sand, and 31% clay).

Moisture content and bulk density
For measuring moisture content and bulk density, several soil samples from depth levels of 0.15, 0.20 m and 0.25 m at different parts of the field were collected using a cylindrical core sampler. Collected samples were immediately put in plastic bags to conserve moisture during transferring to the laboratory. Samples were weighted before and after drying in oven at 105˚C. Moisture content and bulk density were calculated from equations 1and 2 respectively.

Data logging system
The draft force of the plows (chisel, disk and moldboard) for each experiment of the treatments was also registered based on the RNAM system (26). The drawbar load cell is an S shaped (Model H3-C3-3.0t-6B-D55 from Zemic with capacity of 30 kN). It is mounted between two tractors. The first one is a as puller CASE JX75T and the other one is Massey Ferguson (MF 285) as auxiliary. The auxiliary tractor pulls the implement-mounted tractor with the latter in neutral gear but with the implement in the operating position.
Recorded force data were considered as rolling resistance force of the auxiliary tractor wheels. An instrumentation package was developed by Almaliki, (8) which used for measuring draft force of implements. This package included the data logging system and the transducers. The data logging system consisted of an Arduino electronic board and portable computer (laptop) linked via a USB port. Data were sampled at 50 ms intervals.

RESULTS AND DISCUSSION
In this research, a total of 162 tests were carried out for producing acceptable models of draft force, for three type of implements. After averaging treatments, for opting more roboust and more dependable models, a assortment of several polynomial models were analyzed by using Design Expert software. In order to optimize and diminsh the amount of candidate regressors, a stepwise regression algorithm, as a most widely used variable selection technique (17), was then utilized, resulting in the reduced models (Table 3). Table 3. Summary of statistics of reduced quadratic models ANOVA table (Table 4) was accomplished utlizing Design Expert software to determine the level of significance effects of the plow type, cone index, tillage depth, and the forward speed on draft force. The results ilustrated that significant effect of the type of plow, cone index, tillage depth, and the forward speed on dradraft force. Moreover the ANOVA table exposed a significant effect between interactions of these parameters at various probability value (lower than 0.05).  This is due to the increased magnitude of the cultivated soil by plow with increasing tillage depth that posteriorly results in increasing of draft force. one more cause is that increasing of plowing depth would produce an increase of soil tear, volume and mass, so that more energy is need to shear the soil. Moreover, increment the soil mass gathered around the plow causes the sidelong stress on the plow, consequently the friction between runner and furrow surface increases. These results are in agreement with the findings of other researchers (1,15 and 25). The results demonstrated that requirements of draft force at tillage depth 25cm were recorded 18.27, 15..47 and 12.07 kN for moldboard, chisel and disk plow, respectively. This is in assent with the findings of the Al-Suhaibani et al. (9). They reported that moldboard and chisel plow had highest draft force from disk plow in sandy loam soil. The effect of forward speed on draft force was positive. Increasing forward speed from 0.53 to 1.53 m/s led to increased draft force by 80%. This goes back to increment of acceleration of cutting soil particles. Also the disk plow had lowest draft force with increasing forward speed by 8.24 kN followed by chisel plow (10.87 kN) and moldboard plow (11.79 kN) at forward speed 1.53 m/s. The effect of cone index on draft requirement was apparent. Draft force increased by 42% when the cone index increased from 550 to 980 kPa. This attributed to considering cone index as indicator for soil strength. Raising cone index of soil, cohesion and friction of soil particles will be increased. This lead to need more energy for cutting soil by plow which reflects on draft requirement. The requirements of energy for draft force were highest for moldboard plow from the other plows. It was recorded 8.55 kN at cone index 980 kPa while chisel and disk plow recorded 6.87 kN and 4.34 kN, respectively. The results are disagreament to finding by Arvidsson et al. (10) .They found the draft force of the chisel plow to be higher than moldboard plow and referred that to the differences in implement geometry and mode of soil break-up. Results showed that the interaction between depth of tillage and forward speed had the biggest effect on draft force from cone index for all types of studied plows. where draft force recorded 20.21 kN at tillage depth 25 cm and forward speed 1.53 m/s. consequently, the most influential factor in draft force is the tillage depth, followed by the forward speed and cone index.

Figure 1 (A-F). (A) Interaction between Type of plow -Depth; (B) Type of plow-Forward speed; (C) Type of plow-Cone index; (D) Depth-Cone index;(E) Depth-Forward speed and Cone index-Forward speed for the draft force
The correlation between measured and predicted values of draft force under different field conditions is shown in Figure 2. The small variation between the predicted and experimental values promoted the reliability of this model in predicting the draft force. Figure  3 explained the most compatible power transformation (lambda) for responses by the Box-Cox diagram that results the least residual sum of squares in the transformed model for draft force. It can Also be noted, the internally studentized residuals vs run number ( Figure 4) and internally studentized residuals ( Figure 5) of the models vs predicted values, are in the proper range.The results illustrated the developed models by using RSM are significantly eligible to predict draft force for three types of plow (moldboard, chisel and disk plow) under various field conditions (three levels of tillage depth (0.15, 0.20 and 0.25m), three forward speeds (0.54, 0.83 and 1.53 m/s) and two levels of cone index (550 and 980 kPa). ANOVA table exposed a considerable increment in draft force for all the three tillage implements with an increase in tillage depth, forward speed and cone index. Moreover the results showed a significant effect between interactions of these parameters at various probability values (lower than 0.05). Also the obtained results demonstrated that the most influential factor in draft force is the tillage depth, followed by the forward speed and cone index. The moldboard plow showed greatest draft requirement, followed by chisel and disk plow at the same depth, forward speed and cone index. The small variation between the predicted and experimental values promoted the reliability of this model in predicting the draft force.