A tractor operated straw chopping cum tilling cum mixing machine was developed at ICAR–Central Institute of Agricultural Engineering (CIAE), Bhopal. The paddy (c.v. Kranti) crop was grown over an area of 0.30 ha during the main crop season of the year 2021–2022. The machine was evaluated on the combine operated paddy harvested field and experiment was performed on three different days with five days interval. Observation was recorded at first, fifth and tenth days after harvesting of crop and the moisture content of straw was taken into consideration which was corresponding to said three days (M1 = 35 ± 3.4, M2 = 24 ± 2.2, and M3 = 17 ± 2.6% w.b) and the soil moisture content corresponding to respective days (16.8 ± 2.1%, 14.67 ± 1.8% and 13.43 ± 1.4%). The soil type was Black cotton soil (12.8 ± 1.1% sand, 32.5 ± 3.4% silt, and 54.4 ± 4.6% clay) and straw residue were also measured before the experiment. The bulk density of the soil was 1.5 ± 0.06 g cm−3 and the straw load was found 7–7.5 t ha−1 after the harvesting of crop.
Selection of cutting blade for developed machine
Selection of blade was done on the basis of minimum cutting torque predicted by the torque sensor. Different blades were arranged over the flange for the action of rotary impact cutter blades in vertical axis aligned shown in Fig. 1 (a) SMS serrated, (b) cutter bar serrated and (c) SMS plain blade. After the selection of blade, a straw chopper cum mixer machine was fabricated and integrated with the selected blade and required speed of chopping blades.
Types of blades for chopping unit (a) SMS serrated (b) cutter bar and (c) SMS plain.
Design of power transmission
Cutting and mixing units were operated by the tractor PTO power. Initially the power was transmitting with the gear box having transmission ratio 1:1. Rotational speed of chopping blades was selected based on the minimum cutting torque optimized in the laboratory. The optimum rotational speeds of cutting and mixing unit were 810 and 270 rpm, respectively based on minimum cutting torque. The gearbox and pulleys were selected to achieve the required rotational speed of chopping unit.
Brief description of the straw chopper cum mixer machine
The developed machine was consisted of two distinct units: a mixing unit with a rotary tiller and chopping unit having rotary impact cutter blades (Fig. 2). At first the chopping of straw is performed thereafter tilling and mixing operations are performed by mixing unit. The chopping unit consisted a pair of shafts having two flanges on each shaft. Four straw management system (SMS) serrated blades were installed on the periphery of a single flange. The blades were mounted on the flanges and rotated with the help of shafts. In this machine a novel counter-rotating mechanism was provided to chop straw using rotary impact cutter blades.
CAD model of straw chopper (a) side (b) Isometric (c) power flow in cut section (d) Arrangements of blades on flange.
The chopping unit has both a horizontal and vertical arrangement to reduce the size of chopped straw. After passing the chopped straw from the chopping unit, the straw was further reduced in size by the mixing unit. The machine was powered through tractor PTO and the detailed transmission system is shown in Fig. 3. Detailed specifications of developed machine are presented in Table 1.
Schematic view of power transmission system.
Experimental layout and treatments
After the development of the machine its performance was evaluated in terms of mixing index, pulverization index or mean weight diameter, effective field capacity, straw length, fuel consumption and bulk density of soil in field condition. The experiments were performed with two independent parameters i.e., forward speed of the machine (F1, F2 and F3), and moisture content of straw (M1, M2 and M3) (Table 2). Determined moisture content were corresponding to three different days after harvesting (0, 5 and 10 DAH). The SMS serrated blade was selected for chopping unit as it required minimum cutting torque. The rotational speed of rotary blade and the width of cut were fixed at 810 rpm and 910 mm respectively. The bulk density of soil was 1560 g cc−1 before operation of the machine. Soil moisture content on the 0, 5 and 10 days were observed as 16.8, 14.67 and 13.43%.
Performance evaluation of straw chopper cum mixer machine
The experiments were showed to study the effect of forward speed and moisture content of straw on machine parameters i.e., mixing index, mean weight diameter, effective field capacity, straw length, fuel consumption and bulk density of soil. The data was analyzed using full factorial design in Design expert-13 software. The post hoc analysis was also performed to compare the means at different level by tukey’s (b) method at 5% level of significance using SPSS Statistics 20.0 software (SPSS Inc., Chicago, USA).
Mixing Index (MI)
Mixing operation refers to the procedure of incorporating straw into the soil. The mixing index, was calculated using the formula mentioned in Eq. (1). Mixing index represents how thoroughly the straw had been mixed with the soil. In order to determine mixing index, the collected straw samples were weighing before and after the operation of the machine (Fig. 4)16.
$${\text{Mixing}}\;{\text{Index}}\;({\text{MI}}),\% = \frac{{({\text{W}}_{1} – {\text{W}}_{2} )}}{{{\text{W}}_{1} }}$$
(1)
whereas: MI is the Mixing Index, %, \({W}_{1}\) is the Initial weight of straw, g, \({W}_{2}\) is the Final weight of straw, g.
Mixing index measurement (a) before (b) after field operation.
Mean weight diameter (MWD)
The soil breaks into small aggregates resulting from the action of tillage forces. The mean weight diameter (MWD) of the soil clods were determines by the Eq. (2). The pulverization index was quantified by measuring the mean weight diameter (MWD) of the soil clod using sieve shaker analysis method28. Greater pulverization was indicated by smaller MWD of soil clod.
$${\text{MWD}} = \frac{1}{{{\text{W}}_{{\text{T}}} }}\mathop \sum \limits_{{{\text{i}} = 0}}^{{\text{n}}} {{\overline{\text{d}}_{{\text{i}}} {\text{X}}_{{\text{i}}} }}$$
(2)
where, \(\overline{{d }_{i}}\) is the Average diameter of i & (i + 1)th sieve and \({d}_{i}< {d}_{i+1}\), mm, \({X}_{i}\) is the Soil mass sustained on the ith sieve, g, \({W}_{T}\) is the Total mass, \({W}_{T}= \sum_{i=0}^{n}{X}_{i}\).
Bulk density (BD)
The strength of a soil can be determined based on its dry bulk density. It is defined as the mass of soil after oven drying of soil per unit volume and determined by the Eq. (3). Using a conventional core cutter with established dimensions (diameter = 100 mm and height = 80 mm), bulk density was determined28.
$${\text{Bulk}}\;{\text{density}} = \frac{{\text{M}}}{{\text{V}}} \times 100,{\text{g}}\,{\text{cc}}^{ – 1}$$
(3)
\(\text{M}\) is the dry weight of soil, g, \(\text{V}\) is the Volume of soil cc.
Fuel consumption (FC)
The amount of fuel consumed by the tractor while operating in the field was determined with the help of measuring cylinder. Initially the tank was full before the operation. The tank was refilled after the operation with measured quantity of fuel28. The fuel consumption was calculated using Eq. (4).
$${\text{Fuel}}\;{\text{consumption}}\left( {{\text{l}}\,{\text{h}}^{ – 1} } \right) = \frac{{{\text{Quantity}}\;{\text{of}}\;{\text{fuel}}\;{\text{refilled}}\;{\text{after}}\;{\text{the}}\;{\text{operation}}\;({\text{l}}) }}{{{\text{duration}}\;{\text{of}}\;{\text{operation}}\;({\text{h}})}}$$
(4)
Effective field capacity (EFC)
Effective field capacity (EFC) of the machine was calculated by recording the time require to cover per unit area, including the time spent in lifting and lowering of the equipment and turning of the tractor28.
Straw length
Size of cut is the term used to describe the size of chopped straw. The size of straw was measured for the sample collected from one square meter area at three locations.
Cost economics
The cost economics of a machine were calculated by considering the cost of construction materials, labor, and overhead charges. The cost of a developed machine was determined by considering both fixed and variable costs29.
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