Performance Evaluation of design and operational parameters of Conventional Combine Harvester for Basmati Rice (Oryza Sativa)


 Among all the food grains, Basmati rice (Oryza sativa) has significant export potential. At present, majority of harvesting and threshing of basmati is accomplished manually because of high quality of grain. Manual harvesting and threshing operation is quite costly and mostly done by hired labour, threshing cost and family labour. Labour in harvesting has become scarce due to industrialization. The commercially available machines for paddy harvesting and threshing are not suitable for basmati varieties because of relatively delicate nature. There is no data available regarding design and operational parameters for harvesting basmati with conventional combine harvester. Therefore, this study has been planned to study the effect of selected design and operational parameters of threshing mechanism of conventional combine harvester for basmati crop and to compare the performance with prevalent practice. Field evaluation of experiment was carried out to assess the influence of independent design variable i.e., arrangement of spikes (AS) and independent operational parameters namely concave clearance (CC) and cylinder speed (CS). The study was aimed to quantify various combining losses viz., extent of grain damage (visible and invisible), unthreshed and clean grain losses in straw walker at different arrangement of spikes, concave clearance and cylinder speed. Initial testing of conventional combine harvester on PUSA Basmati-1121 to reduce the visible as well invisible losses had been carried out at PAU Regional Research Station, Gurdaspur (Punjab) during the year 2017.

(1) Arrangement of spikes 44, 68 and 136 spikes were investigated and found that 44 spikes gives minimized losses in terms of grain loss (visible and invisible loss).
(3) Cylinder speed 560, 640 and 720 rpm were investigated and found that 560 rpm gives minimized losses in terms of grain loss (visible and invisible loss).
(4) AS1CC3CS1 (44 spikes, 17-13 mm and 560 rpm, 2017) was better combination as it minimized the visible loss to 3.50 %, it also minimized the invisible loss to 17.33 %. The average yield of basmati was 4500 kg/ha (Anonymous 2018-19). The time of sowing basmati is 15-30 June. Seedlings of basmati are ready for transplanting after 25 to 30 days. Ground water depletion decreases with the arrival of monsoon in the month of July, so it is bene cial to sow basmati crop. There is always an option of going for the wheat-basmati rice rotation. Basmati should be harvested as soon as it matures. Delayed harvesting will cause over-ripening and shattering of grains (Anonymous 2015). In Punjab, the total basmati area was 7,63,000 ha (Anonymous 2018-19). The production of PUSA Basmati-1121 is maximum i.e., 20.47 million metric tonnes. Basmati is an important export commodity among the food grains exported from India. During the past few years, basmati export has been growing steadily from 0.771 million metric tonnes in 2003 to an estimated 4.41 million metric tonnes in 2018-19. India's exports will be 5 to 6 million metric tonnes by 2020. Almost 132 countries have been importing basmati from India every year. Iran and Saudi Arabia are leading destinations, accounting 50-55% of Basmati rice exports from India (Anonymous 2018-19).
Harvesting and threshing of paddy has been done in three ways, namely manual harvesting and threshing; manual harvesting and threshing with thresher; and harvesting with combine. There are mainly three forces acting on a plant while reaping the plant for cutting. These forces are impact of reel, couple of cutting resistance and impact as forces and weight of the ear and its forced acceleration multiplied by the mass component on the opposite to the forced direction (Biggs and Stewart 1954). Lamp and Bushele (1960) de ned threshing as the process of freeing the seed from its attachment and this occurs whenever the applied forces on kernels exceed the sum of forces restraining it on the ear-head. Four general methods for obtaining the threshing force namely mechanical rubbing, impact or impulsive threshing, mechanical stripping and non-impulsive threshing were enumerated. Action of drum in threshing was explained by Whitney et al (1966). At the very beginning of feeding the straw, the drum beats down the ears with its teeth. The drum then grips the straw and while pulling it through the packer compresses the ears together with straw, separating the grain from them and nally the drum ejects the straw.
Main advantage of combine harvester is that it can harvest and thresh the crop in a single operation.
Thus, combines have helped in timely harvesting and threshing. Combine harvesting saves time, labour and cost apart from weather risks. However, major problem in combine-harvested basmati crop is higher percentage of ssured grain as gain is long leading to reduced rice recovery during milling. Most of the combine harvesters currently used in India employ rasp-bar or spike-tooth type tangential threshing drums and straw walker. This conventional tangential threshing unit threshes mostly by impact (Kutzbach and Quick 1999).
Traditional combines have very less cylinder to concave clearance (around 25 mm at inlet and 10 mm at concave outlet). Particularly in spike tooth type threshing cylinders having counter spikes, it is further reduced to 7 mm (Singh 1999). This in turn results in aggressive threshing action. This aggressive threshing action leads to higher percentage of visible and invisible grain damage particularly in paddy.
The invisible grain damage caused during threshing gets re ected as reduced recovery of whole grain during milling operation.
At present, majority of harvesting and threshing of basmati is accomplished manually because of high quality of grain. Manual harvesting of basmati is a labour intensive operation requiring about approximately 180 man-h/ha. Some times during the peak periods of harvesting and threshing, nonavailability of labour delays the operation of harvesting which causes progressive decrease in yield of next crop i.e., wheat due to late sowing (Garg and Madan 1989). Manual harvesting and threshing operation is also quite costly and mostly done by hired labour, threshing cost and family labour which generally costs about Rs. 4704 per hectare (Ahuja et al 2007). Labour in harvesting has become scarce due to industrialization. Commercially available machines for paddy harvesting and threshing are not suitable for basmati varieties because of relatively delicate nature (Sinha et al 2014).
Another option is axial ow combines, in which crop advances through the threshing mechanism in a direction parallel to the axis of rotor rather than perpendicular as in case of conventional threshing cylinder. The rotor threshes the grain by a combination of rubbing, impact and centrifugal action as the crop passes repeatedly. Generally, it takes more than three drum rotations in case of axial threshing system (i.e. 1080 degrees) before the crop is ejected out of the threshing cylinder as compared to 120 to 150 degrees in tangential cylinder. The repeated passes in the threshing system in case of axial system provide more retention time but gentle threshing action. Since the retention time as well as cylinder to concave clearance are more in axial threshing drum in comparison to that in tangential threshing drums thus the threshing is less aggressive. Another major advantage of axial ow combines over conventional combines is in terms of separation loss (DePauw et al 1977). However, the cost of axial attachment may deter combine operators. On the other hand, operation in controlled conditions has resulted a nonsigni cant difference in grain loss in case of commercially available machines. Moreover, there are machine constraints in case of axial ow combines, as they are not available for custom hiring.

Location
The experimental studies were carried out at PAU Regional Research Station, Gurdaspur (Punjab) during November-December, 2017.

Conventional combine harvester
The self-propelled conventional combine harvester was used to study the effect of selected design and operational parameters of threshing mechanism of conventional combine harvester for basmati crop.
Brief speci cations of the machine are given in the Table-1.

Dependent variables
The study was related to optimize the machine and crop parameters for mechanical harvesting of PUSA Basmati-1121. Therefore, visible grain damage, invisible grain damage and threshing e ciency was included in this study.

Independent variables
Different parameters that affect the performance of combine have been considered in the present study were arrangement of spikes, concave clearance and cylinder speed.

Range of independent variables
Three levels of arrangement of spikes viz., AS1 (44 spikes), AS2 (68 spikes) and AS3 (136 spikes), three levels of concave clearance viz., CC1 (13 mm at entry and 9 mm at rear), CC2 (15 mm at entry and 11 mm at rear) and CC3 (17 mm at entry and 13 mm at rear) and three levels of cylinder speed CS1 (560 rpm), CS2 (640 rpm) and CS3 (720 rpm) were selected for the study. Spikes were arranged on the threshing drum in the form of helical arrangement. Cylinder speed was varied by changing the pulleys, measured by tachometer in rpm. Forward speed of 1.5 km/h was maintained throughout the experiment. Different outlets for enumerating losses were cylinder outlet, tank outlet, header outlet, straw walker and sieve outlet.

Equipment for collecting samples and enumerating losses
Two cylindrical rollers were specially fabricated for collecting the sieve and straw walker losses. A 10 m long and 1.5 m wide cloth was rolled on the cylindrical rollers to collect the sample of 10 m length during the harvesting. The cylindrical rollers were attached to the combine in such a way that they freely move on their axis during the operation of harvesting. For the measurement of the invisible grain damage, internal cracks in grains were determined with the help of an illuminated purity board.
Evaluation procedure Preliminary eld evaluation of experimental prototype was carried out at Regional Research Station, Gurdaspur (Punjab). The conventional combine harvester was operated for harvesting PUSA Basmati-1121 as shown in Fig. 1. Preliminary eld testing of prototype could be operated at a forward speed of 1.5 km/h. Test setup was able to cover 20 m in one minute. A eld more than 100 m long and 40 m wide was selected for evaluation of test setup. It was assumed that ten metre run is su cient for turning of combine harvester.
Field evaluation of the experimental setup for the year 2017 was carried out using randomized block design. There were three treatments for basmati rice i.e., arrangement of spikes (AS), cylinder speed (CS) and concave clearance (CC) and each treatment had three levels forming 27 (3 × 3 × 3) treatment combinations in the complete experiment. Each treatment was replicated thrice to make total number of trial runs equal to 81 (27 × 3). Sequence of trial runs/ experiments was selected by condition randomization. Arrangement of spikes in the form of helix was major operation. After that different cylinder speed at different helical arrangement of spikes and concave clearance was studied. Then effect of concave clearance over different helical pattern of spikes and at different cylinder speed was observed. These different treatments were tried to gure out the visible loss, invisible loss and threshing e ciency respectively.
Three samples of grains approximately 250 g each were taken at each experimental setup. The losses were measured at variable cylinder speeds for different arrangement of spikes and concave clearance.
The experiment was carried out and the whole procedure was repeated by varying the peripheral speed.
There were three independent factors taken for the study i.e., arrangement of spikes, concave clearance and cylinder speed. Their effect was measured on dependent factors i.e., visible loss, invisible loss and threshing e ciency. Different helical arrangement of spikes forming helix was taken for the study, various level of concave clearance and cylinder speeds were also taken for the experimental purpose. A 50 g sample was taken for each experiment where broken grains were separated and weighed, so in this way we enumerate visible grain loss. With the help of illuminated purity board, internal cracks of the grain were determined for enumerating invisible grain loss. Unthreshed grains in the ear heads tell the effectiveness of threshing. Ratio of unthreshed grains to the threshed grains gives us the threshing e ciency. Different combination of independent factors were tried to gure out the best combination at which less loss (visible as well as invisible loss) and more pro tability in terms of farmers bene t.
The data observed from various treatments was analyzed in terms of arrangement of spikes, cylinder speed and concave clearance and their effect was measured on each other for enumerating visible loss, invisible loss and threshing e ciency. The statistical analysis of the data was done by using Statistical Package for Social Sciences (SPSS, Version 22.0). Analysis was done considering the main effects and two factor interactions. Means were computed and tested at 5% level of signi cance.
In Design Expert 11, Response surface methodology (RSM) was very useful for the modeling and analysis of problems in which the response was in uenced by several variables and the objective was to optimize this response. In Response surface methodology (RSM), tests were performed using different combinations of levels of the experiments according to the predetermined design, and an appropriate data was tted to the data by the method of least squares. Three-dimensional plots provide a useful visual aid for checking the adequacy of the model and for examining the response surface and location of the optimum. Response surface methodology (RSM) was reported to be an e cient tool for optimizing a process when the independent variables have the joint effect on the responses Response surface methodology (RSM) also predict the equation in terms of coded factors about the response for given levels of each factor. By default, the high levels of the factors were coded as + 1 and the low levels were coded as -1. The coded equation was useful for identifying the relative impact of the factors by comparing the factor coe cients. It also provide the overall desirability plot and contour plots.

Results And Discussion
Field evaluation of experiment was carried out to assess the in uence of independent design variable i.e., arrangement of spikes (AS) and independent operational parameters namely concave clearance (CC) and cylinder speed (CS). The study was aimed to quantify various combining losses viz., extent of grain damage (visible and invisible), unthreshed and clean grain losses in straw outlet at different arrangement of spikes, concave clearance and cylinder speed.
Initial testing of conventional combine harvester on PUSA Basmati-1121 Initial testing of conventional combine harvester on PUSA Basmati-1121 to reduce the visible as well as invisible losses had been carried out at PAU Regional Research Station, Gurdaspur (Punjab) during the year 2017. Conventional combine harvester was operated at different arrangement of spikes, concave clearance and cylinder speed. The arrangement of spikes was kept at 44 spikes (AS1), 68 spikes (AS2) and 136 spikes (AS3) respectively. The concave clearance was kept at 13 mm at entry and 9 mm at the exit (CC1), 15 mm at entry and 11 mm at the exit (CC2) and 17 mm at entry and 13 mm at the exit (CC3) for conducting the experiments. The cylinder speed was kept at 560 rpm (CS1), 640 rpm (CS2) and 720 rpm (CS3). Generally, as per the practice 68 spikes (AS2), 640 rpm (CS2) and 15 mm at entry and 11 mm at the exit (CC2) was used by the manufacturer. Conventional combine harvester was generally operated in 2nd, low gear. The area for harvesting PUSA Basmati-1121 was 8 ha.
Evaluation of experimental setup on PUSA Basmati-1121 (Location: Regional Research Station, Gurdaspur, Punjab), 2017 Field evaluation of the experimental setup was carried out on PUSA Basmati-1121 during the year 2017.
Harvesting and collection of the samples during eld evaluation was carried out at Regional Research Station, Gurdaspur (Punjab). Subsequent analysis of small samples was carried out to assess the grain damage (both visible and invisible) and threshing e ciency. The effect of independent design parameters viz., arrangement of spikes (AS) and independent operational parameters namely concave clearance (CC) and cylinder speed (CS) on dependent variables viz., visible loss, invisible loss and threshing e ciency and results obtained have been discussed.

Effect Of Independent Variables On Broken Grains (visible Loss):
The data on fraction of broken grains (tank loss) as affected by arrangement of spikes, concave clearance and threshing e ciency was recorded. The changes in study variables were carried out in tangential cylinder of conventional combine harvester. Design parameter and operational parameter was varied in tangential cylinder. Arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) for percent visible loss gives signi cant result as all the three factors contribute to the measurement of visible loss.
The interaction between AS and CC gives signi cant results in terms of visible loss, interaction between AS and CS gives non-signi cant results in terms of visible loss and interaction between CC and CS gives non-signi cant results in terms of visible loss. Statistical analysis revealed that interactions were signi cant for AS and CC as shown in Table 2. three levels of concave clearance CC1 (13 mm at entry and 9 mm at rear), CC2 (15 mm at entry and 11 mm at rear) and CC3 (17 mm at entry and 13 mm at rear) and three levels of cylinder speed CS1 (560 rpm), CS2 (640 rpm) and CS3 (720 rpm). Here, effect of arrangement of spikes AS1 (44 spikes) was taken into account and it was observed that visible loss increase with increase in cylinder speed, CS1 (560 rpm) gives minimized loss in terms of grain loss as compared to CS2 (640 rpm) and CS3 (720 rpm), CC3 (17 mm at entry and 13 mm at rear) gives minimum visible loss as compared to CC1 (13 mm at entry and 9 mm at rear) and CC2 (15 mm at entry and 11 mm at rear) as shown in Fig. 2. Further, it was concluded that percentage of broken grains range between 3.50 to 4.53% with helical arrangement of spikes (44 spikes) and variation in cylinder speed and concave clearance as compared to conventional combines where it has been reported to a maximum loss upto 8.1% (Manes et al, 2002).

Effect Of Independent Variables On Fissured Grains (invisible Loss):
The data on fraction of ssured grains (tank loss) as affected by arrangement of spikes, concave clearance and threshing e ciency was recorded. The changes in study variables were carried out in tangential cylinder of conventional combine harvester. Design variable and operational parameter was varied in tangential cylinder. Arrangement of spikes (AS) for percent invisible loss gives signi cant result, concave clearance (CC) for percent invisible loss gives signi cant result and cylinder speed (CS) for percent invisible loss also gives signi cant result as all the three factors contribute to the measurement of invisible loss. The interaction between AS and CC gives non-signi cant results in terms of invisible loss, interaction between AS and CS gives non-signi cant results in terms of invisible loss and interaction between CC and CS gives non-signi cant results in terms of invisible loss. Statistical analysis revealed that interactions were non-signi cant as shown in Table 3. Effect of variation in invisible loss on three levels of arrangement of spikes was studied at three levels of cylinder speed and concave clearance on percentage of cracked grains. The mean percent ssured grains collected at different arrangement of spikes AS1 (44 spikes), AS2 (68 spikes) and AS3 (136 spikes) on three levels of concave clearance CC1 (13 mm at entry and 9 mm at exit), CC2 (15 mm at entry and 11 mm at exit) and CC3 (17 mm at entry and 13 mm at exit) and three levels of cylinder speed CS1 (560 rpm), CS2 (640 rpm) and CS3 (720 rpm). Here, effect of arrangement of spikes AS1 (44 spikes) was taken into account and it was observed that invisible loss increases with increase in cylinder speed, CS1 (560 rpm) gives minimized loss in terms of grain loss as compared to CS2 (640 rpm) and CS3 (720 rpm), CC3 (17 mm at entry and 13 mm at exit) gives minimum invisible loss as compared to CC1 (13 mm at entry and 9 mm at exit) and CC2 (15 mm at entry and 11 mm at exit) as shown in Fig. 3. Further, it was concluded that percentage of ssured grains range between 17.33 to 24.67% with helical arrangement of spikes (44 spikes) and variation in cylinder speed and concave clearance as compared to conventional combines where it has been reported to a maximum loss upto 28% (Singh et al, 2001).

Effect Of Independent Variables On Threshing E ciency:
It was observed that threshing was complete for all the treatment combinations. Therefore, any treatment can be considered optimum as far as threshing e ciency is concerned.   Effect of cylinder on grain loss of conventional combine harvester: The data on fraction of grains (broken or cracked) in cylinder loss as affected by arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) was recorded. The changes in study variables were carried out in tangential cylinder of conventional combine harvester. Design variable and operational parameter was varied in tangential cylinder. Arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) gives signi cant result, as all the three factors contribute to the measurement of visible loss, invisible loss and threshing e ciency similar to the tank loss. So, corresponding to the different arrangement of spikes, concave clearance and cylinder speed the range of broken grains, cracked grains and threshing e ciency was enumerated.
Effect of variation in visible loss on three levels of arrangement of spikes was studied at three levels of cylinder speed and concave clearance on percentage of broken grains. The mean percent broken grains collected at different arrangement of spikes AS1 (44 spikes), AS2 (68 spikes) and AS3 (136 spikes) on three levels of concave clearance CC1 (13 mm at entry and 9 mm at exit), CC2 (15 mm at entry and 11 mm at exit) and CC3 (17 mm at entry and 13 mm at exit) and three levels of cylinder speed CS1 (560 rpm), CS2 (640 rpm) and CS3 (720 rpm). Here, effect of arrangement of spikes AS1 (44 spikes) was taken into account and it was observed that visible loss increases with increase in cylinder speed, CS1 (560 rpm) gives minimized loss in terms of grain loss as compared to CS2 (640 rpm) and CS3 (720 rpm), CC3 (17 mm at entry and 13 mm at rear) gives minimum visible loss as compared to CC1 (13 mm at entry and 9 mm at rear) and CC2 (15 mm at entry and 11 mm at rear) as shown in Fig. 4. Further, it was concluded that percentage of broken grains range between 2.59 to 3.64% with helical arrangement of spikes (44 spikes) and variation in cylinder speed and concave clearance as compared to conventional combines where it has been reported to a maximum loss upto 8.1% (Manes et al, 2002).
Effect of variation in invisible loss on three levels of arrangement of spikes was studied at three levels of cylinder speed and concave clearance on percentage of broken grains. The mean percent ssured grains collected at different arrangement of spikes AS1 (44 spikes), AS2 (68 spikes) and AS3 (136 spikes) on three levels of concave clearance CC1 (13 mm at entry and 9 mm at exit), CC2 (15 mm at entry and 11 mm at exit) and CC3 (17 mm at entry and 13 mm at exit) and three levels of cylinder speed CS1 (560 rpm), CS2 (640 rpm) and CS3 (720 rpm).
Here, effect of arrangement of spikes AS1 (44 spikes) was taken into account and it was observed that invisible loss increases with increase in cylinder speed, CS1 (560 rpm) gives minimized loss in terms of grain loss as compared to CS2 (640 rpm) and CS3 (720 rpm), CC3 (17 mm at entry and 13 mm at exit) gives minimum invisible loss as compared to CC1 (13 mm at entry and 9 mm at exit) and CC2 (15 mm at entry and 11 mm at exit). Further, it was concluded that percentage of ssured grains range between 13.33 to 20.67% with helical arrangement of spikes (44 spikes) and variation in cylinder speed and concave clearance as compared to conventional combines where it has been reported to a maximum loss upto 28% (Singh et al, 2001).
Threshing e ciency was almost complete i.e., it comes in the range of 98 to more than 99% as per BIS code.
Effect of sieve and straw walker loss of conventional combine harvester: Straw walker loss including threshed grain which ranges between 0.21 to 1.14%, unthreshed grain which range between 0.00 to 0.09% and broken grain which ranges between 0.00 to 0.02%. So, major loss in straw walker loss was threshed grain which was collected in a 10 m long cloth for 20 s. Unthreshed and broken grain percentage was negligible and hence neglected.
Sieve loss including threshed grain which ranges between 0.34 to 1.34%, unthreshed grain which ranges between 0.00 to 0.06% and broken grain which ranges between 0.00 to 0.01%. So, major loss in sieve loss was threshed grain collected in a 10 m long cloth for 20 s. Unthreshed and broken grain percentage was negligible and hence neglected.

Optimization Of Design Variable And Operational Parameters, 2017
The response surface and contour plots were generated for different interaction of any two independent variables, while In contour plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is cylinder speed (CS), X 1 = AS (arrangement of spikes) and X 2 = CC (Concave clearance). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which visible loss was minimum i.e., 3.42%. The range of visible loss was between 3.42 to 5.74% as shown in Fig. 6.
In contour plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor was concave clearance (CC), X 1 = AS (arrangement of spikes) and X 2 = CS (cylinder speed). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which visible loss was minimum i.e., 3.42%. The range of visible loss was between 3.42 to 5.74% as shown in Fig. 7.
In contour plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is arrangement of spikes (AS), X 1 = CC (concave clearance) and X 2 = CS (cylinder speed). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which visible loss was minimum i.e., 3.42%. The range of visible loss was between 3.42 to 5.74% as shown in Fig. 8.
In response surface plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is cylinder speed (CS), X 1 = AS (arrangement of spikes) and X 2 = CC (concave clearance). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which visible loss was minimum i.e., 3.42%. The range of visible loss was between 3.42 to 5.74% as shown in Fig. 9.
In response surface plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is concave clearance (CC), X 1 = AS (arrangement of spikes) and X 2 = CS (cylinder speed). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which visible loss was minimum i.e., 3.42%. The range of visible loss was between 3.42 to 5.74% as shown in Fig. 10.
In response surface plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is arrangement of spikes (AS), X 1 = CC (concave clearance) and X 2 = CS (cylinder speed). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which visible loss was minimum i.e., 3.42%. The range of visible loss was between 3.42 to 5.74% as shown in Fig. 11. In contour plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is cylinder speed (CS), X 1 = AS (Arrangement of spikes) and X 2 = CC (Concave clearance). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which invisible loss was minimum i.e., 18%. The range of invisible loss was between 18 to 32% as shown in Fig. 12.
In contour plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is concave clearance (CC), X 1 = AS (arrangement of spikes) and X 2 = CS (cylinder speed). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which invisible loss was minimum i.e., 18. The range of invisible loss was between 18 to 32% as shown in Fig. 13.
In contour plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is arrangement of spikes (AS), X 1 = CC (concave clearance) and X 2 = CS (cylinder speed). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which invisible loss is minimum i.e., 18%. The range of invisible loss was between 18 to 32% as shown in Fig. 14.
In response surface plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is cylinder speed (CS), X 1 = AS (Arrangement of spikes) and X 2 = CC (Concave clearance). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which invisible loss was minimum i.e., 18%. The range of invisible loss was between 18 to 32% as shown in Fig. 15.
In response surface plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is concave clearance (CC), X 1 = AS (arrangement of spikes) and X 2 = CS (cylinder speed). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which invisible loss was minimum i.e., 18%. The range of invisible loss was between 18 to 32% as shown in Fig. 16.
In response surface plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is arrangement of spikes (AS), X 1 = CC (concave clearance) and X 2 = CS (cylinder speed). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which invisible loss is minimum i.e., 18%. The range of invisible loss was between 18 to 32% as shown in In contour plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is cylinder speed (CS), X 1 = AS (Arrangement of spikes) and X 2 = CC (Concave clearance). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which threshing e ciency was minimum i.e., 98.706%. The range of threshing e ciency was between 98.706 to 99.971% as shown in Fig. 18.
In contour plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is concave clearance (CC), X 1 = AS (arrangement of spikes) and X 2 = CS (cylinder speed). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which threshing e ciency was minimum i.e., 98.706%. The range of threshing e ciency was between 98.706 to 99.971% as shown in Fig. 19.
In contour plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is arrangement of spikes (AS), X 1 = CC (concave clearance) and X 2 = CS (cylinder speed). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which threshing e ciency was minimum i.e., 98.706%. The range of threshing e ciency was between 98.706 to 99.971% as shown in Fig. 20.
In response surface plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is cylinder speed (CS), X 1 = AS (Arrangement of spikes) and X 2 = CC (Concave clearance). Low axis was taken as 1 and high axis was taken as 3 with a combination of AS = 1 (44 spikes), CC = 3 (17 mm at entry and 13 mm at exit) and CS = 1 (560 rpm) at which threshing e ciency was minimum i.e., 98.706%. The range of threshing e ciency was between 98.706 to 99.971% as shown in Fig. 21.
In response surface plots, there were three factors viz., arrangement of spikes (AS), concave clearance (CC) and cylinder speed (CS) with actual factor is concave clearance (CC), X 1 = AS (arrangement of We wish to con rm that this is not applicable in this study.

Consent for publication:
We wish to con rm that this is not applicable in this study.
3. Availability of data and material:    Standing crop of PUSA Basmati-1121 and conventional combine harvester in operation