OPTIMIZATION OF OPERATING PARAMETERS OF THE THRESHING UNIT AT SPELT WHEAT HARVESTING

Liudvikas Špokas, Dainius Steponavičius
Department of Agricultural Machinery, Lithuanian University of Agriculture, Kaunas-Akademija, Lithuania

ABSTRACT

Spelt wheat is the crop suitable for ecological farms, because it is disease-resistant, winter-hardy, less demanding for the soil and fertilizers and its seeds do not need dressing. The Schwabenspeltz is the best variety resistant to lodging.

Tests carried out in 2002-2003 defined the biometrical characteristics of the spelt wheat Schwabenspelz. Different meteorological weather conditions in both years had no significant influence to the biometrical characteristics of the plants. Combine harvesting of this spelt wheat variety at medium grain moisture content (15.8%) brought about the following: the ears broken by the reel amounted to 1.6%, the naked grain in the grain tank did not exceed 10%, the hulled grain equaled to 83%, the ear fractions made approximately 5% and the impurities did not exceed 2%. The hulls comprised approximately 35% of the overall grain mass.

Optimal adjustment of the threshing unit operating parameters has been substantiated by the laboratory tests. When the spelt wheat of medium moisture content was threshed the permissible load of the drum rasp bars of 1 m length was 3.3 kg·(m·s)^-1, and that for the dry wheat (12% grain moisture content) was 4.2 kg·(m·s)^-1. The load of the threshing unit has been limited by the permissible unseparated grain amount (20%), which falls with straw on the straw walkers. Damage of the naked spelt wheat grain did not exceed permissible 2%, less than 15% chaff and straw pieces were found in the materials separated through concave when the drum rasp bars load was not less than 2.5 kg·(m·s)^-1 of the crop of the spelt wheat at the medium moisture the optimum clearance between the drum and the concave was set to 14-8 mm, the peripheral velocity of the drum reached 31.4 m·s^-1. For the dry grain the appropriate setting were 16-6 mm and 28.3 m·s^-1, respectively.

Key words: Spelt wheat, threshing losses, grain damage, adjustment of threshing units.

INTRODUCTION

Spelt wheat (Triticum Spelta L.) is one of the oldest plants the grain of which has been used for food [6]. Spelt wheat was grown already 6000 years B.C. in the Middle East [26]. Belea [5] and Dorofejev [11] stated that the place of origin of the spelt wheat is the territory of Iran. According to other authors [14, 26] the spelt wheat was grown in Iran and Southeastern Europe. Siegel [20] reported that in 1850 spelt wheat was grown in Württemberg land on the area of 200 thousand ha, and wheat was grown on the area of 12 thousand ha. Later the spelt wheat areas were reduced because more fertile and productive wheat varieties were developed. The reduction of the area of the spelt wheat crop was stopped not only because of lower yields but also owing to greater costs of production as well as grain and hull separation.

In the nineties of the last century the demand for the wholesome food increased and the growing area of the spelt wheat increased [20]. Now spelt wheat in Germany is grown on the area of 30 thousand hectares, in Ohio in the USA it is 12 thousand ha [22], in Austria – 2.8 thousand ha, and in Hungary – 700 ha [13].

Spelt wheat is the plant of ecological farms. Its roots are widely spread. When there is no nitrogen and enough moisture the spelt wheat yield is greater than the winter wheat yield. Spelt wheat is less sensitive to the meteorological conditions and to the lack of fertilizers and microelements [4, 15]. It can be grown on the hilly fields. Grain does not need dressing before planting because hulls protect them from pests and diseases [19].

The yield of spelt wheat is approximately 1.4 t·ha^-1 less than that of winter wheat despite the fact that there are more grains in their ears, but the mass of 1000 grains is less since hull makes up 37.1% of all the grain mass [17]. In Italy the yield of spelt wheat variety Altgold Rotkorn was 3.09 t·ha^-1, the mass of 1000 grains was 34.3 g [25]. Balanced fertilization of spelt wheat and application of the growth regulators contributed to the yield increase up to 5.5 t·ha^-1, and the yield of Rouquin variety was 7.5 t·ha^-1 [1].

The nutritional characteristics of spelt wheat were better than those of wheat. Souci et al. [21] has determined that in 100 grams of the spelt wheat grains there were about 12 g of green proteins, 2.4 g of fat, and 67.7 g of plant hydrates. Baumgärtel-Blaschke [3] has stated that 100 g of grains accumulated 1.27 MJ of energy and 8.8 mg of iron that can easily be assimilated by the human body.

The ecological agriculture becomes more popular and quickly expands in Lithuania and other Baltic republics because the demand for ecological products grows. Since 1993 to 2005 the number of ecological farms in Lithuania increased from 9 to 1800 [4]. Since 2000 the growing of different varieties of the spelt wheat has been investigated in Lithuanian Agricultural University. It has been shown that many varieties of spelt wheat are apt to lodging, their ears are fragile thus during harvest the grain losses exceed the permissible level by 2%. The best variety resistant to lodging is the spelt wheat Schwabenspelz.

Cubadda and Marconi [8] have stated that the growing and harvesting of spelt wheat has not been widely investigated. The agricultural engineers testing the spelt wheat found that ears are broken during the threshing and only a small part of the grain has been threshed and dehulled [4]. Oplinger et al. [18] has recommended to leave the cut wet spelt wheat in the windrows but in the Baltic States it would be rather dangerous because of the bad weather conditions. Cuendet [9] has stated to adjust the threshing unit in such a way that more ears could be broken. But then it would be much more difficult to separate the broken and rough ears from the straw than the grain. Due to this the grain losses would increase.

Research object is to state the moisture dynamics of the grain and straw of the spelt wheat, also to substantiate the optimal operating adjustment parameters of the combine threshing unit.

MATERIALS AND METHODS

In 2002 and 2003 the tests were carried out in the fields of the experimental station and in the laboratory of the Department of Agricultural Machinery of Lithuanian Agricultural University. Biometrical characteristics, the moisture change of grain and straw of Schwabenspelz spelt wheat variety were determined during their maturation period.

Research scope. The influence of the feed rate of spelt wheat, the revolution of the drum, and the clearance between drum and concave on the grain separation through the concave, threshed materials composition and the number of broken grains was defined during laboratory tests.

Measuring of biometrical characteristics of Schwabenspelz spelt wheat. The stems of the plant were taken in five replications on the experimental plots of 0.25 m² area. The stem height and ear length were measured and their average values were calculated. Every ear was threshed, the grains were counted, weighed and the average grain mass in the ear was estimated. Five samples of 1000 grains were taken from all the grain mass, they were weighed and the mass of 1000 grains was calculated. Grain and straw samples were dried at the temperature of 105°C till they reached constant mass, and their average moisture content was calculated. The mass of straw, grain and 1000 grains was calculated at the moisture content reached 14%.

Estimation of the change in the grain and straw moisture content. Every day at 2 p.m. five samples of grain were taken from spelt wheat threshed ears. The stems were cut into pieces of 10 mm length. They were mixed and five samples were taken to determine the moisture content. In the laboratory the samples were weighed, dried at the temperature of 105°C till they reached constant mass content, then once again were weighed and the average moisture of the grain and stems was calculated.

Grain losses during harvesting, their damage and the grain composition in the combine grain tank. The grain losses during crop harvesting, threshing, separating and cleaning were defined in the Department of Agricultural Machinery of Lithuanian Agricultural University. The methodology was presented [23]. To state the damage of the naked grain five samples of 50 g each were taken, the damaged grains were separated, weighed and the average percent damage of the grain was calculated. Five 150 g mass samples were taken to estimate the composition of the grain and the chaff mix in combine grain tank, or the grain that was separated through the concave and passed through the grate bar. These samples were divided into four groups: the naked grain, hulled grain, ear pieces (with more than 3 grains), and chaff with straw pieces. Each sample group was weighed and the composition of grain and separated materials was established.

Technical data of combine-harvester E 514 and that of laboratory test bench. During the field tests spelt wheat was harvested with the combine-harvester E 514, the width of its cutter bar was 4.8 m, the drum diameter was 0.6 m. the width was 1.2 m, the concave wrap angle was 115°, the sieves area was 3.45 m², the surface area of the straw walkers was 3.45 m², and the motor power was 85 kW. The threshing unit of the laboratory test bench (fig. 1) included: the drum, the diameter of which was 0.6 m, the width was 1.2 m, two parts of 146° concave wrap angle, the area of front part of concave was 0.33 m², that of the main part was 0.65 m², and the area of grate-bar was 0.26 m².

In the laboratory spelt wheat was delivered to the threshing unit by the conveyor belt of 30 m length at the speed of 1 m·s^-1 (fig. 1). The separated materials trough the front part 8 of the concave, the main concave 7 and the grate-bars 6 was collected into the separate boxes 6, 10, and 11. The separated material was weighed, cleaned and the grains were also weighed. The straw and the grain (the mass that enters the straw walkers) were collected into the separate container 12. The grain and the ear pieces were collected from the straw and weighed. The grain separation through the front part of the concave, the main part of concave, the grate-bar, and the part of the grain on the straw walkers was calculated.

The test data has been evaluated by the statistic computer programs ANOVA and STAT_ENG. Student and Fisher tests were used for the comparison of the average values. Confidence intervals (±) of data average values equal to 0.95 were calculated for the probability level. Change of the grain separation through the comparative area of 0.1·m² of the both parts of the concave and the grain amount in straw on the straw walkers were approximated by the equations. The change of the grain separation through the grate-bars was not statistically significant thus the data was not proved by equations.

RESULTS

Weather conditions during the maturing period and yield harvesting. Meteorological conditions in July and August of 2002 were good for the spelt wheat harvesting. The average air temperature in July was 20.6°C, in August it was 20.4°C, but the soil lacked moisture because in July the precipitation level was equal to 53.5 mm, in August it was 13.8 mm. The full maturity spelt wheat variety crop was harvested on 26^th of July.

In July of 2003 the average air temperature was 20.1°C, in August it was 17.1°C, and the precipitation level was equal to 118.2 mm and 53.4 mm, accordingly. The crop reached its maturity later than in 2002, and it was harvested on 4^th of August. Due to high precipitation levels at the end of July and the beginning of August, the wheat harvesting could be started only on 15^th of August (as it was in 2005).

Biometrical characteristics. Since 2001 the Department of Plant Growing and Stockbreeding of Lithuanian Agricultural University has been testing the growing of 15 varieties of spelt wheat. The tests have demonstrated that the hardiest is Schwabenspelz variety.

Different meteorological weather conditions in 2002 and 2003 had no significant influence to the biometrical characteristics of the plants (tab. 1). The ears of spelt wheat were long (109.1±1.4 mm – 2002) and dropping down. The mass of 1000 grains with hulls was 51.0±1.0 g (2002) and 52.5±2.4 g (2003), but the hulls of these grains made up 35±2.1% of the total grain mass.

The dynamics of the moisture content of spelt wheat straw and grain in the maturation period. The dynamics of the moisture content of grain and straw was started to watch when the grain moisture was still more than 30% (fig. 2). Transit precipitation of up to 3 mm had no influence to the moisture content reduction of spelt wheat grains (on 11^th and 12^th of July, 2002 and on 25^th of July, 2003). But rainy weather slowed or increased the reduction of the straw moisture. At good weather conditions the grain moisture was reduced by 5% every day that of the straw was reduced by about 2%. When the grain moisture reached the limit of 10% its change became insignificant.

Grain losses of spelt wheat during harvesting and grain composition in the grain tank. In 2002 and 2003 spelt wheat was harvested by the combine-harvester E 514 in the experimental field. The crop density was uneven thus at the constant speed of the combine operation the feed rate of the crop was not equal. The clearance between the drum and the concave (threshing slot) and the revolution of the drum was changed during the tests. It was stated that the greatest influence to the grain losses during the harvesting had the reel impact on ears (tab. 2) since the spelt wheat ears are delicate and drooping down. The grain losses due to the reel impact varied from 0.3% to 1.6%. When there was no dew spelt wheat should be harvested early in the morning or at evening, then the ears would be less delicate. Grain losses during threshing did not exceed the permissible limit of 0.1%, when the peripheral speed of the drum was 31.4 m·s^-1, and the concave clearance was 19-8 mm. The field tests did not prove the reliable relationship between the threshing grain losses and the clearance between the drum and concave, because of inconstant feed rate of spelt wheat crops of various moisture contents was delivered during the experiments. When the average moisture content (U₁ = 15%) of spelt wheat was harvested the optimum drum peripheral velocity was 31.4 m·s^-1, and when dry crop of (U₁ = 11.4%) of spelt wheat was harvested the velocity was 28.3 m·s^-1.

The total harvesting grain losses of spelt wheat did not exceed the permissible 2% limit when the combine-harvester operation speed was 3 km·h^-1, peripheral speed of the drum was 31.4 m·s^-1, the concave clearance was 19-8 mm. The inspection of the materials composition in the grain tank showed that when the drum rasp bars move at the speed of 31.4 m·s^-1, the amount of naked grain did not exceed 10%, the hulled grain comprised from 76% to 85%, ear pieces with 3 to 6 grains comprised from 4% to 12%, and chaff in the grain tank did not exceed the permissible 2% limit (tab. 3).

• to determine the impact of the feed rate of spelt wheat on the grain damage, separation through the concave and the amount of grain in the straw on the straw walkers;

• to substantiate the optimum operating parameters of the threshing units for not more than 20% of the grain could be found in the straw on the straw walkers, the damage of the naked grains was not greater than 3%, and through the concave passed not more than 15% of the chaff and straw pieces.

The impact of the feed rate of spelt wheat on the threshing unit throughput and grain damage. The most important indices of the operation of the threshing unit are grain separation through the concave, separated materials composition and the grain damage. The feed rate of spelt wheat has some impact on the change of these indices the flow is limited by the permissible grain amount (20%) that is found on the straw walkers. Laboratory tests (fig. 3) showed that increasing the feed rate from 0.8 to 4.2 kg·(s·m)^-1 of spelt wheat with the average moisture content of (U₁ = 12.2%; U₂ = 28.6%) delivered to the threshing unit, grain separation through the front part of the concave decreased by 1.16 times, through the main concave it was reduced by 1.37 times, thus the amount of grain on the straw walkers increased from 3.2% to 25.5%. The grain amount that passed through the grate-bar increased insignificantly but the statistically reliable relationship was not defined. The permissible part of the grain in the straw (20%) was increased, when the feed rate of spelt wheat was more than 3.3 kg·(s·m)^-1.

The inspection of the composition of the separated materials through the concave showed that the part (T) of the chaff and straw passed through the grate-bar was reduced from 78.0% to 38.3% when the feed rate of spelt wheat was increased to 4.2 kg·(s·m)^-1. This change can be calculated from equation:

T = 6.0 m² – 41.1 m + 107.2; R² = 0.96; (0.8 < m < 4.2)   (1)

where m is the feed rate of spelt wheat, kg·(s·m)^-1.

When the feed rate of spelt wheat was more than 2.5 kg·(s·m)^-1 the chaff and straw pieces under the concave made up 12% and varied in the limits of the data error. In order to reduce the chaff and straw pieces load onto the cleaning shoe the not less than 2.5 kg·(s·m)^-1 of the average moisture content wheat and not greater than 3.3 kg·(s·m)^-1 feed rate should be used for the delivery into the threshing unit, for not more than 20% of the threshed grain was left in straw on the straw walkers.

The threshing unit threshed about 20% of grain while the rest remained in the ears. When the optimum feed rate of 3.3 kg·(s·m)^-1 of spelt wheat flow was delivered into the threshing unit 1.1% of the naked grain were damaged, the hulled grain remained sound as they were protected by hulls. The area of the front part of the concave of the threshing unit is two times less than the main part of the concave thus more grain leaves it but this does not show the intensity of the separation of chaff and grain. Calculation of the separation through the comparative 0.1·m² areas of both concaves showed that grain separation was more intensive through 0.1·m² area of the front part of concave if compared with the same area of the main part of concave (fig. 4). In 2003 drier crop of (U₁ = 11.9%) of spelt wheat was threshed (fig. 5). Grain separation through 0.1·m² area of the front part of the concave was 1.3 times more intensive (m = 3.3 kg·(s·m)^-1) if compared with the average moisture of spelt wheat threshing (fig. 4). The permissible grain part in the straw (20%) was exceeded when 4.5 kg·(s·m)^-1 of dry spelt wheat were delivered into the threshing unit. The percentage of chaff and straw pieces (T) passed through the grate-bars changed:

T = 0.77 m² – 15.5 m + 85.5; R² = 0.97; (0.8 < m < 5.0)   (2)

The inspection of the separated materials composition under front part of the concave and main part of concave showed that increasing the feed rate of the spelt wheat from 0.8 to 5.0 kg·(s·m)^-1, the amount of the naked grain was reduced almost twice, that of ear pieces increased about 15%, the reduction of chaff and small straw was insignificant and comprised about 15% of all the separated materials (tab. 4). When dry spelt wheat is threshed the feed rate should be 2.5 kg·(s·m)^-1 that less naked grain and ear pieces could be found in the separated materials. In order to increase the feed rate of spelt wheat into the threshing unit the grain separation through the front part of the concave should be intensified by reducing the concave clearance and or maximizing the revolution speed of the drum.

The impact of the concave clearance to the throughput of the threshing unit and grain damage. In the newest combine-harvesters in order to increase the throughput of the threshing unit is set equal clearance between the drum and concave [12], that more grain could be threshed over the front part of the concave and less grain with straw would occur on the straw walkers. Tests proved (fig. 6) that the change of the concave clearance from 14-8 to 10-10 mm, the grain separation through 0.1·m² area of concave increased approximately by 1.5 times, the part of the grain on the straw of the straw walkers almost did not change but the grain damage in the front part of the concave increased about 1.25 times (more than 3% of the naked grain was damaged) (fig. 7). The optimum concave clearance when dry spelt wheat was threshed was 16-6 mm. While defining the optimum concave clearance one should estimate the separated materials composition under both concaves (tab. 5). When the concave clearance was increased the amount of the naked grain, straw pieces and chaff increased. The optimum clearance was 16-6 mm as only 12% grain in straw on the straw walkers was noticed.

The influence of the drum peripheral velocity on the throughput of threshing unit and grain damage. During the tests when the optimum feed rate of spelt wheat was 3.3 kg·(s·m)^-1, the peripheral velocity of rasp bars of the threshing drum has changed from 25.1 m·s^-1 to 37.7 m·s^-1 (fig. 8). It has been defined that the grain separation through the front part of concave increased about 80% (up to 13.8%·(0.1·m²)^-1) and through the main concave did not change at all. The permissible part of the grain (20%) on straw walkers was exceeded when peripheral velocity of the drum (rasp bars speed) was less than 28.3 m·s^-1, thus the velocity should be greater than 29 m·s^-1. The peripheral velocity of the drum is connected with the straw damage because of its breaking. The increase of the velocity means that more straw pieces and chaff passed through the grate-bar (fig. 9). While threshing spelt wheat the thick grate-bar or sieve should be installed under the back beater that less straw and chaff could pass through it.

The impact of drum rasp bar moving at faster speed in relation to the feed rate of the mass is greater so more grain is damaged (fig. 10). Grain pieces latest pass the crop layer that moves over surface the concave while being beaten by the rasp bars thus on straw walkers could be found more damaged grain than in the separated materials under the concave. The test results showed that when threshing of the average moisture spelt wheat the peripheral velocity of the drum should be not greater than 31.4 m·s^-1.

Tests were fulfilled when the concave clearance was 10-10 mm and 16-6 mm. It was proved that the reduction gap between the drum rasp bars and concave allowed to minimize the peripheral velocity of the drum up to 25 m·s^-1, when the optimum feed rate of the spelt wheat was 3.3 kg·(s·m)^-1. When the feed rate of crop was increased up to 4.2 kg·(s·m)^-1, the drum peripheral velocity should be not less than 29 m·s^-1, but not exceed 31.4 m·s^-1, in order not to brake the permissible limit of 20% of grain in straw on the straw walker.

SUMMARY AND CONCLUSIONS

The tests proved that the best variety of spelt wheat resistant to lodging is Schwabenspelz. This wheat variety was resistant to the changes of temperature and lack of moisture content. Different meteorological weather conditions in both years (2002 and 2003) had no significant influence to the biometrical characteristics of the plants. The mass of 1000 grains with hulls was 52.5±2.4 g (2003), but the hulls of these grains made up 35±2.1% of the total grain mass. The results of biometrical characteristics analysis corresponded with the data given by Müller [17] and Stallknecht et al. [22].

In 2002 and 2003 when spelt wheat was harvested in experimental field with combine-harvester E514 the total grain losses changed from 1.02% to 2.26%. The greatest were the harvesting losses (1.60%) since the drooping down ears were sensitive to the mechanical impact of the reel. After the estimation of the grain composition in the grain tank of the combine it was determined that naked grain comprised 8.6±1.2%, ear pieces (with more than 3 grains) comprised 6.7±1.3%, chaff comprised 1.3±0.7%, and grain with hulls comprised 84.0±1.8%. Test results substantiated the conclusion of Hein [13] that during the threshing spelt wheat grain were not hulled.

Laboratory tests showed that the optimum feed rate of the average moisture crop mass of spelt wheat Schwabenspelz was 3.3 kg·(s·m)^-1 to the drum rasp bars of one meter length as the grain in straw on the straw walkers did not exceed the permissible limit of 20%, only 1.1±0.4% of naked grain were damaged. Grain separation at the beginning of the concave was more intensive than through the main concave. When dry crop of (11.8%) of spelt wheat was threshed the grain separation through the concave and grate-bar was still more intensive thus the permissible feed rate of the mass increased to 4.2 kg·(s·m)^-1. It was limited by the permissible grain part in straw on the straw walkers (20%). Analogous results were achieved while threshing the wheat Zentos [24]. Test results correspond with conclusions of Anil et al. [2] and Büermann [7] who have stated that the feed rate of the crop has the greatest impact on the grain separation intensity trough the concave.

In order to increase the feed rate of spelt wheat into the threshing unit the grain separation through the front part of concave should be made more intensive. Tests showed that the reduction of the concave clearance from 14-8 mm to 10-10 mm increased the grain separation through 0.1·m² area of the concave at first but the grain damage also maximized. This corresponds the conclusions of the research made by Kornacki [16], Dreszer and Gieroba [10] etc., who pointed out that the grain damage, was influenced by the speed of drum, the clearance between the drum and concave, and the moisture content of the crop. After the testing of the impact of various concave clearances on the grain separation and grain damage the conclusion has been made that when harvesting dry spelt wheat the optimum clearance was 16-6 mm, when harvesting average moisture spelt wheat the clearance should be 14-8 mm, as the grain part in straw on straw walkers did not exceed the permissible limit of 20%.

The most intensive grain separation at the beginning of the concave was when the peripheral velocity of the drum was 37.7 m·s^-1, then only 9.3% of the grain occurred with the straw on straw walker. But thrice as much naked grain were damaged if compared with the velocity of 28 m·s^-1. Chaff and straw pieces separated through the grate-bars equaled to 60.6% and that trough the concave – 18%. Thus the optimum velocity of the drum was from 28.3 m·s^-1 to 31.4 m·s^-1.

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Accepted for print: 07.09.2006

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