Optimizing Field Performance of Axial Flow Rotary Combine With Single Rotor and Snap Roll Header for Maize Harvesting

To study the effect of operational factors on combine performance, a maize combine with snap roll header was tested at feed rates levels of 69.94 Mg h, 85.48 Mg h, 124.33 Mg h and moisture content levels of 24.45%, 26.03%, 28.90% respectively. Pre harvest losses increased from 1 to 4% as the maize crop were sun dried from a grain moisture level of 28.90% to 24.45% because the ear shank became weak with decrease in moisture content. The shelling efficiency varied from 96.81% to 98.13%, cleaning efficiency varied from 95.20% to 95.80%, minimum grain damage obtained was 2.1% and minimum total loss obtained was 9.96%. The optimum values of feed rate and moisture content (w.b.) were 85.48 Mg h (forward speed of 1.10 km h) and 26.03%, respectively. The corresponding data obtained for shelling efficiency, cleaning efficiency, grain damage and total loss by combine were 98.13%, 95.80%, 2.10% and 10.23%, respectively. The energy involved in maize harvesting for maize dehusker cum sheller and maize combine with snap roll header were 2152.26 and 2633.25 MJ ha, respectively. The Solar energy is crucial for gaining optimum moisture for maize harvesting and reducing losses. Maize with low global warming potential is a viable energy crop and leftover corn stover is also a viable alternative to fossil fuels which can be used for bioethanol, silage production and also as domestic fuel in rural, hilly areas. However optimum harvesting stage is crucial to minimize energy involved during maize harvesting, grain storage and alternative uses.


Introduction
Maize is cultivated on nearly 178 million ha globally in about 160 countries and contributes approximately 50% (1,170 million metric tonnes (MT)) to the global grain production. In India, maize constitutes about 9% of the total volume of cereals produced and is the third most important food grain after rice and wheat. Advance estimates for total production in India stands at 9.3 million MT in trade year 2015, growing at almost 6% in the past 5 years. Policies around price correction and initiatives to improve quality can be key drivers of corn exports from India in the coming years. Mechanized harvesting and postharvest management can also provide additional yield benefits (Anonymous, 2016a). Maize is the predominant raw material (together with sugar cane) for the production of bioethanol, the most common and widespread biofuel, and at the same time the predominant raw material for biogas production, with the highest yields in Europe. A maize grain harvester consists of maize head, conveying, threshing, separation, cleaning units and a grain tank. This same maize grain harvester can not only simplify the harvesting procedure, improve production efficiency, but also reduce grain loss. Maize harvesting is one of the most important filed operations of maize production. Due to the accelerated development in the maize industry, mechanized maize harvesting is widely accepted and used by farmers in the world. According to the harvesting methods, maize harvesters could be classified into two types, one is maize-for-grain harvesters which include pickers and grain harvesters, while the other one is whole plant harvesters which include forage harvesters and combined grain-stover harvesters (Yang et al., 2016). At present, maize harvesting in the United States, Germany, Ukraine, Russia and other western countries apply direct threshing because of the planting pattern of one crop a year and low grain content during harvest period (Hou, 2006;Ji et al., 2006;Zhu & Chen, 2010;Yan et al., 2007). Maize is considered to be a promising option for diversifying agriculture in upland area of India. India stands fifth in terms of production accounting for 2% of the total world maize production.
Presently, it ranks as the third most important grain crop in India after wheat and paddy. The area and production of maize in India during 2012 and 2013 were 8.67 million ha and 22.26 million tonnes, respectively (Anonymous, 2016a). The mechanization of sowing and harvesting operation play a key role in increasing land under maize crop. The remaining corn stover can be used for production of bioetahnol fuel using rakes, rectangular and round baler (Sokhansanj & Turhollow, 2002), corn stover collector attachement with combine (Singh et al., 2015), manual collection method or using harvester loader machines. A study revealed that maximum higher heating value that was observed by corn stover and switchgrass was 21.51 and 21.53 MJ kg -1 at 270 °C and a 120-min residence time and showed consistent proximate, ultimate, and energy properties after torrefaction,. The van Krevelen diagram drawn for corn stover and switchgrass torrefied at 270 °C indicated that H/C and O/C values are closer to coals like Illinois Basis and Powder River Basin (Jaya Shankar, 2015).
The purpose of mechanized maize harvesting is to replace manual labour to harvest maize from fields on time with minimum time loss while maintaining high quality. The harvesting method and equipment depend upon planting pattern, agronomy and climate conditions. The entire harvesting operation may be divided into gathering, snapping, husking, cutting, threshing, separation and cleaning. Reducing human drudgery and energy, increasing productivity, improving timeliness of agricultural operations and reducing peak labour demands are among the most advantages of mechanized maize harvesting. Factors affecting harvester efficiency and yield losses include combine adjustments, field space, kernel moisture levels and lodging. The harvesting operation is also considered critical, if delayed huge grain loss is resulted (Bector & Singh, 1999).
Harvesting and threshing of grain crops are two major farm operations requiring considerable energy (Baruah & Panesar, 2005). For most varieties, the losses increases rapidly as the grain moisture dropped below 25%. Ear drop losses were summed up to 85 to 95% of all losses before or during the harvesting operation. The factors affecting losses are maize variety, cylinder speed, concave clearance, type of roll. Straight-fluted rolls are more aggressive than spiral-lugged rolls. Stripper plates located above the rolls prevent maize ears from directly contacting the rolls. They can be divided into quadrangular, five ribs and six-rowed etc. according to their cross-sectional shape. The maize head of straight-fluted snapping rolls is reliable with high efficient, small losses but leads to a high mixture of stalks and husks in harvested grain (Brass, 1970). The test results showed that the concave clearance at the front place should be about 10 mm less than the average diameter of maize ears, and that it should be equal to the core diameter at the rear place (Petkevičius et al., 2008). The key feature of the longitudinal axial flow threshing device is that the maize ears are fed axially into the threshing cylinder, and the maize ears are moving in axial and tangential direction along the cylinder. It performs the threshing and separation functions and the time of threshing and separating is longer, as well as the device has lower threshing losses and grain damage. Damage in the axial device was half of that in the tangential threshing roller (Wacker, 1990). Test results shows that the complementary angle of friction which is the angle between grain and helix lamina should be larger than the helix angle of the feeding section, and the friction angle between grain and leading lathing should be larger than the helix angle of threshing and separation section (Yang & Yan, 2008). The high demand for energy worldwide and fossil fuel reserves depletion have generated increasing interest in renewable biofuel sources (Lynd et al., 2005). The use of bioethanol produced from lignocellulosic material can reduce our dependence on fossil fuels (Balat, 2011). The solid residues after LHW pretreatment of corn stover is suitable to be used as substrate for ethanol production, and the fed-batch S-SSF is one effective process for obtaining higher ethanol concentration and ethanol yield. The optimum feeding process in fed-batch S-SSF of the solid residues was that 6.1% of semi-weighted solid residues at pre-hydrolysis time of 6 h were added into the system (Li et al., 2014). Maize crop cultivation is energy efficient and it can generate energy benefits (Konieczna et al., 2021). Moisture plays an important role during maize harvesting on seed quality and harvest losses. Below 18% shattering losses will drastically increase beyond permissible limits. On the other end, corn typically has a soft pericarp at 28% moisture content and beyond. Harvesting and threshing at maize grain moisture content equal to or greater than 28% will lead to cracks and breaks in the pericarp which is not desirable by maize seed growers. Generally, around 21-22% the pericarp is much more durable and can withstand impacts better and it is easier to thresh as moisture content lowers. From a harvest loss view, the 28% moisture content valuewill allow harvesting sooner, less chance for stalk lodging and ears dropping on the ground. The maximum total combine losses with header ear losses as largest portion are reported in the severely lodged corn (Paulsen et al., 2014). Harvesting corn when grain moisture levels are high can result in excessive drying costs, kernel damage and harvest loss from improper threshing. The gradual increase of mechanical damage to seeds, as moisture content increased at harvest, has contributed to the reduction of seed physiological potential and to the increased occurrence of fungi during storage (Ferreiraet al., 2013). Allowing corn to stay in the field too long can result in excess harvest loss from stalk lodging, ear drop or kernel shattering. Pre harvest ear losses and machine gathering losses increase as the season advances. The stalks become dry and brittle and tend to lodge as a result of adverse weather conditions and the ears break off easier. High forward speeds and poor centering of the snapping unit on the row increase ear losses, especially when the stalks are lodged. The most important plant properties influencing mechanical damage are kernel detachment force, kernel strength, initial and final kernel thickness (kernel deformation), and cob strength. Low kernel damage is associated with low detachment force, high kernel strength, low kernel deformation, low cob strength. By changing plant characteristics, such as reducing detachment force and increasing kernel strength, it should be possible to reduce kernel damage during combining. Field losses are influenced by the type of harvester, machine adjustments, forward speed, date of harvesting, moisture content, varietal differences, amount of lodging and other factors. An optimal harvest depends not only on the condition of the crop but also on the proper maintenance and adjustment of harvest and grain handling and drying equipment.
Maize harvesting in India is done by either manual picking of cobs or threshing using conventional thresher or maize dehusker cum shelleror by maize combines. In the manual harvesting method, the crop is first pre dried to a moisture content of about 20-25%. This is done through thepre drying of maize in the field.Maize is left inside the field as such, due to action of heat from the sun which is responsible for drying maize to amoisture content of 20% from 35%. After pre drying, only ears are pulled from the stalk of the plant without the involvement of tool. The average duration of manual harvesting varies from 120 to 200 man-hours (15-25 man-days) per hectare. Shelling the ears, that is, removal of the husks covering the ears may be done by hand or by a machine at the time of harvest. If this is done by hand, it requires about 130 man-hours (about 16 man-days) per hectare. The conventional thresher is used to separate the grains from the cobs or both dehusking and threshing can be done at the same time using maize dehusker cum sheller. The output of such machine is generally around 2500 kg h -1 for sheller and 2000-2500 kg h -1 for dehusker cum sheller. The threshing performance is good with these threshers but they involve more labour cost and time. To reduce labour cost and time of operation farmers are also using self-propelled combine harvester with snap roll header for maize harvesting nowadays. It is a single machine which does all the harvesting operation simultaneously, i.e., gathering of maize ears, dehusking, threshing and cleaning. This combine harvester uses a header arrangement in front of the machine which does the operation of separating the ears from the plant and also it gathers the ears and conveys it to the threshing cylinder. Threshing cylinder is a rotating drum with a concave around it and due to the shearing and rubbing action husk is removed and cobs are shelled. The separated grains are cleaned before sending them to the grain tank, this is done through the cleaning mechanism, which uses chaffer and cleaning sieves to separate trash from the grains. The clean grain goes to the grain tank and the trash is discharged at the back of the combine, clean grains in the tank are loaded into a trailer through an auger mechanism. Use of the combines has increased in the past due to increase in production through hybrid varieties and mechanization in India. However various parameters like, forward speed, feed rate, moisture content of crop affect the performance of combine harvesters along with quality of harvested maize grains needs to be studied which plays a major role in its storage and germination. Thus considering all these points present study was conducted to optimize the performance of maize combine harvester (picker sheller) with snap roll header in field for harvesting of maize crop to find the optimum operational and crop parameters. The study was also done to find out drying behavior and costs of harvested maize grain and to compare economics of combine with snap roll header with traditional method (manual picking and threshing with maize dehusker cum sheller) in Indian conditions.

Experimental Site
Maize was planted at theresearch farm of the Farm Machinery and Power Engineering Department during 2013, 2014 and 2015 planting season. The climate of the area is semi-arid, with an average rainfall of 700 mm (75-80% of which occursfrom July to September), minimum temperature of 0-4 ºC in January, maximum temperature of 41-45 ºC inJune, and relative humidity of 67-83% throughout the year. The soil (0-15 cm) of the experimental field was sandy loam in texture.

Crop and Combine Harvester Information
Combine header and combine was check for all repair and maintenance. Before operating thecombine harvester in the field total grain yield was recorded in the field by collecting samples from different locations. The pre-harvest losses were negligible. Maize varieties PMH-2, Pioneer-1844, DKC-9108 were taken for the present study. Maize crop was sown at recommended spacing of 0.60 m by 0.20 m in experimental plots. The mean stalk height, girth, weightand grain yieldvaried between2. 00-2.29 m, 49.23-60.30 mm, 9.58-11.52  Each snapping blade had four blades fitted at right angle to each other ( Figure 6). Stop watch was used to measure forward speed of the combine. Measuring tape was used to measure the dimensions of the field. A cloth was used to collect the samples from different locations of the field for different losses. Weighing balance was used to measure the weight of threshed grain, unthreshed grain and straw of maize crop. Oven was also used to measure moisture content of the maize grain. jas.ccsenet.

Equipm
The weigh dimension . The used for harvesting the grains while the non-productive time consisted of the turning time, repair and adjustment time and other time losses. The area covered divided by the total time gave the effective field capacity. The grain losses were determined based on the grain yield recorded during harvesting operation. Shattering loss refers to the ears and grains fallen on the ground during harvesting. Rack and shoe losses were measured from the material discharged by the machine. Samples were collected from 3.0 m by 3.6 m size plots from the field at different locations afterthe combine harvester operation. Total machine loss refers to the summation of header, rack and shoe losses. The quality of maize grain was determined in terms of broken grains percentage and cleaning efficiency, which was determined by taking three samples of grain from the grain tank of the combine harvester, each weighing 200 g. These samples were taken at successive time intervals depending on the size of the field. Foreign matter were manually sorted and weighed to calculate percentage (%) broken grains and cleaning efficiency. The effective field capacity of combine was calculated using theexpression provided by Kepner et al. (1978): where, C is effective field capacity, ha h -1 ; S is speed of travel, km h -1 ; W is rated width of implement, m; E f is Field efficiency, in percent.
where, T o is theoretical time per hectare (per acre); T e is effective operating time = T o × 100/K; K is percent of implement width actually utilized; T h is time lost per acre due to interruptions that are not proportional to area. At least part of T h usually tends to be proportional to T e ; T a is time lost per acre due to interruptions that tend to be proportional to area.

Estimation of Fuel Consumption
Before starting the test, the engine's fuel tank was completely filled. The quantity of fuel required to fill the tank after harvesting the test field was measured using 1litregraduated cylinder. Thus, the fuel consumed during the test was determined.
where, F is the fuel consumption in l ha -1 ; A is the area harvested in ha; L is the quantity of fuel required tofill the tank after harvesting the test field in l.

Pre-harvest Losses
Pre-harvest losses are those caused by shattering and lodging, and loss of dry matter due to birds, wildlife, weather and other natural causes. Pre-harvest losses are important but are not related to machine performance. Large pre-harvest losses indicate a genetic weakness in some varieties and a need for further breeding work to develop plants less susceptible to lodging and with stronger bonds between the ears and the stalks. Pre-harvest losses increase as the season progresses. This can go much higher in adverse crop years or when harvest is delayed. The combine header width multiplied by the distance stepped off represents 1/100 acre. To measure pre-harvest losses, required distance was stepped off in standing corn.The length of corn rows for this 1/100 acre varies with row width and number of rows covered by corn head (Table 2). For header width of 3.6 m it was calculated as 11 m. All the loose and lodged ears in these rows were counted and gathered to calculate the pre-harvest losses. The pre-harvest losses were calculated as follows: Pre-harvest losses, (%) = Weight of grains from naturally fallen cobs (kg) Total grain yield (kg) × 100% 2.9.2 Header and separation loss (L s+h ) The loose kernels and cobs on ground behind the combine were collected in 1/100 acre area. For header width of 3.6 m it was calculated as 11 m. This represented the total header plus separation loss (L s+h ).  For measuring header lossesdata for fallen cobs and kernels in front of machine where the separator had not yet passed. The combine was backed off by distance equal to length of combine. Loose kernels, broken and whole cobswere gathered from this front area (w × l). These were gathered to calculate the header losses. The header ear losses were calculated as: Header ear loss, (%) =

Weight of grains [loose and from fallen cobs (kg)
Total grain yield (kg) × 100% (9) 2.9.4 Separation Kernel Loss (L s ) These were obtained by subtracting header rear lossfrom header and separation losswhich could be expressed mathematically as: where, L s is Separation loss, %; L h is Header rear losses, %; L s+h is header and separation losses, %.

Cylinder Loss (L c ) and Shelling Efficiency (η sh )
For measuring cylinder loss and shelling efficiency kernels still attached to the threshed cobs were collected from 1/100acre area and weighed. The small kernels at the butt and tip end of cobs were not taken.Shelling efficiency is defined as the mass of the kernels actually shelled to the total mass of kernels on the earbefore shelling.The expression used for calculating shelling efficiency was given by Al-Jalil (1978) as: Shelling efficiency, (%) = 1 - where, L is shelling loss (weight of unshelled kernels attached to the cob), kg; W is mass of shelled kernels, kg.
Samples weighing 200 g for cleaning and broken kernels were collected from the grain tank of the combine after the operation. These samples were then cleaned to get the trash content, broken grains and clean grains for calculating grain damage (G d ) and cleaning efficiency (η c ).

Data Analysis
All data varying from shelling efficiency, cleaning efficiency and losses obtained from the experiment wereanalyzed using factorial experiment in completely randomized design with CPCS1 software (p < 0.05).

Energetics and Economics
A complete inventory of all inputs (machine, fuel, human labor), after which the energy value of each input was determined through published conversion coefficients derived only from peer-reviewedliterature, expressed in MJ ha -1 . Fuel consumption and time required per hectare was measured for both machines in each harvesting season, with average values extrapolated for energy calculation. The energy required for drying maize crop at different stages of moisture content with maize combine and that of whole maize harvesting process was calculated for both machines. The economics of maize crop harvesting was also calculated for both machines. jas.ccsenet.   Figure 11. Effect of feed rate (MOG) and moisture content on different losses These prediction equations can be used for evaluating the performance of maize combine at different moisture contents and feed rates.

Economic Analysis
The economic analysis of maize combine with snap roll header was done using the traditional method. Using the conventional method, 8 to 10 persons pick cobs from one acre area between 8 and 10 h. The cobs are transported to the threshing unit where they would be threshed using maize dehusker cum sheller ( Figure 12). This machine comprises of an axial spike tooth type threshing cylinder with a suitable concave and a thrower mechanism to eject empty stalk and husk. Grains fall on the cleaning sieves for cleaning. The thresher can thresh the dehusked maize cobs having moisture content in the range of 12-24% successfully. This machine saves one extra operation   The increase in cost of drying at 28.90% and 26.03% moisture contents were 28.57% and 16.67% higher when compared with 24.45% moisture content. However, the higher cost of drying in 26.03% moisture content was compensated as contained in Tables 4 and 5 by lesser grain damage (2.10%), lower cylinder losses (1.87%), lower separation losses (2.18%) and higher shelling efficiency (98.13%) and cleaning efficiency (95.80%) during mechanical harvesting. The added advantage of higher moisture is in bioethanol production and silage production. In general, high-moisture silages have higher concentrations of soluble N and NH 3 -N than drier silages because of the overall more robust fermentation in the former. Higher than normal levels of soluble N and NH 3 -N in wet legume silages are usually a result of proteolytic activity from clostridia. Similarly moisture content between 15-40% was considered good for bioethanol production from maize, switchgrass, wheat, fiber sorghum and sugarcane residues (Kung et al., 2018;Hattori & Morita, 2010).

Energy Calculation for Axial Flow Rotary Combine With Single Rotor and Snap Roll Maize Header and Maize Dehusker Cum Sheller
The energy calculations were done based on energy equivalents for machinery, fuel and human labour taken for mean of various reviews (Table 9). The total energy requirements were 2152.26 and 2633.25 MJ ha -1 for maize harvesting with conventional method (CT) and maize combine with snap roll header (MCH). It is clear from Table 2 that the energy required in maize combine with snap roll header was 22.35% approximately higher than conventional method. Again the higher energy requirement was compensated by lower human labourrequirement and higher field capacity in case of maize combine harvester with snap roll header. Both factors make it feasible to use the maize combine harvester for commercial harvesting which fetches more profit to owners. If theoptimized parameters for the harvester were used the owners can get more harvesting rates and more working hours.

Discussion
One hundred percent of the acreages in large corn producing nations (United States and Argentina) sow and harvest maize mechanically ( Figure 13). China has increased its mechanical harvesting from 16% in 2010 to 33% in 2013. With increase in mechanical harvesting, large maize producing nations have experienced increase in yields. In India, the mechanical sowing and harvesting penetration has only been 5 to 7%. Farm losses (due to poor harvesting practice or lack of timely labour) can potentially be controlled through mechanization. Increase in thrust on promotion and adoption of mechanical harvesting could potentially assist in improving productivity and control farm losses. Overall mechanization of maize crop harvesting can reduce maize cultivation costs especially labour costs and provide a good employment opportunity for rural youth to run these machines on custom hiring basis and thus can raise their economic status. Also rural youth can open workshops after taking technical training on these machines for repair and maintenance of these machines which is another employment aspect for them. The usage of maize grain after harvesting as desired by purchaser is also a key driver for determining optimum moisture stage. Figure 13. Distribution of global corn production Source: https://www.statista.com/statistics/254294/distribution-of-global-corn-production-by-country-2012 Farmer prefer harvesting at higher moisture content as purchasers prefer this moisture as they sell it for beer so that farmer could get it a rate of 950 to1000 Rs. qtl. -1 and if harvested after drying as desired by seed producers then they get ita rate of 1000 to1300 Rs. qtl. -1 . But harvesting at optimum conditions can fetch them a good profit. Overall use of mechanical harvester can be beneficial in recovering more grain yield and increasing area under maize cultivation. But from seed production and storage point of view the optimum conditions for maize combine harvester and maize crop play a crucial role which was worked out in present study. The drying time and costs were also calculated after mechanized harvesting of maize crop with mechanical harvester with snap roll header. Keeping in view the weather conditions and moisture level of maize crop, present research gives a decision criteria to help maize growers for selection of optimized parameters for mechanical harvesting of maize crop with snap roll header with minimum field losses. Alongwith this Biofuel compared with fossil fuels is considered to be more effective. For example with oil, coal and natural gas to produce 1 MJ of electricity; non-renewable energy consumption is projected to be between 1.7 and 4.2 MJ whereas biomass values range from 0.1 to 0.4 MJ. In the case of thermal energy, prices are 1.1 and 1.5 for fossil fuels and only 0.01-0.15 for biomass. Although the energy is considered to be CO 2 neutral, in fact there is actually a burden on greenhouse gas emissions due to the process of cultivation and harvesting. However, this charge does not exceed the total emissions of fossil fuels which results in being up to 90% reduced (Ingenito et al., 2012). The biomass produced can be used heating as raw material for thermochemical processes such as pyrolysis and gasification for the