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Trends in Power and Machinery
J. agric. Engng Res. (2000) 76, 237}247 doi:10.1006/jaer.2000.0574, available online at http://www.idealibrary.com on
KEYNOTE PAPER
Trends in Power and Machinery Heinz Dieter Kutzbach Hohenheim University, Department of Agricultural Engineering (440), Garbenstrasse 9, D-70599 Stuttgart, Germany; e-mail: [email protected] (Keynote address for the scientixc session on Power and Machinery, presented at AgEng 2000, 2}7 July 2000)
The economic situation and the future supply of food for the growing world population require the productivity of power and machinery to increase further. Moreover, legislation and demands in the areas such as environmental protection, maintenance of product quality and facilitation of work are factors that will exert a decisive in#uence on future developments. In the foreseeable future, the trend towards larger, more powerful machines will remain undiminished. Mobile machines are becoming even more complex due to the combination of work steps and because subsequent processing has been taken over by these machines. The percentage of self-propelled machines will grow further. Self-propelled machines are also being developed for those kinds of work that are still carried out by tractors and implements today. Nevertheless, the development of new sensors for the control of additional machine functions makes operation easier. Despite high vehicle mass, further developments in tyres and tracks avoid harmful soil compaction. In the future, continuously variable, power-splitting hydrostatic transmissions with electric control will lead to further increase in the productivity of agricultural tractors and simplify their operation. Electric power-splitting transmissions will gain in importance as an alternative to hydrostatic transmissions. Automatic vehicle control, especially through high-precision global positioning systems (GPS), will allow new working procedures such as onland ploughing to be carried out. In addition, the driver's work load will be reduced further, and productivity will increase due to higher driving speed and extended work time during twilight periods. Only after numerous safety questions have been solved will autonomous, unmanned vehicles be employed. At "rst, their use will be restricted to simple work such as tillage. 2000 Silsoe Research Institute
1. Introduction The beginning of the new millennium is a special occasion for a preview of future developments. In this contribution, an attempt is made to predict some important future aspects of power and machinery on the basis of previous developments. It is assumed that the development will be evolutionary and progressive in small steps. In such a preview, it is impossible to foresee pioneering inventions which simplify the entire process in a revolutionary way. In the distant future, there may be "elds without farmers, where autonomous machines plant, cultivate and harvest individual plants. Additionally, industrial farming methods without soil are conceivable with cultures in substrates in a controlled environment (e.g. 0021-8634/00/070237#11 $35.00/0
greenhouses). Fruit and vegetable cultivation with its high-quality products is leading the way into the development of new methods and machines. In arable farming, progress will be slower. However, this development is not only determined by the knowledge, skills and experience of agricultural engineers, but also by economic, ecological and agricultural-policy requirements under which this development takes place (Fig. 1). Environmental factors which will have an in#uence on power and machinery include not only environmentally sound farming methods, but also possibly the greenhouse e!ect. Growing CO concentrations and a slightly higher annual mean temperature due to the greenhouse e!ect might cause the spectrum of the cultivated crops to shift and thus, lead to additional demands on agricultural
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2000 Silsoe Research Institute
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Fig. 1. Power and machinery under the pressure of diwerent requirements; EU, European Union
engineering. Legislators and international standards also in#uence future developments in a di!erent, sometimes in an unpredictable way. Necessary increases in productivity, which are important for limiting costs, are achieved not only through the design of better and larger machines to provide for higher technical performance. Improved machine management and longer e!ective time of use, as well as enhanced application of information technologies for automatization may also result in productivity improvements. These two aspects will be discussed in other contributions.
2. Conditions for future development The future development of agriculture and consequently, the development of power and machinery will be determined in particular by the previous and future decisions in agricultural policy. The 1992 agricultural reform has already led to lower product prices. This development is continuing as a result of Agenda 2000. Price and quantity guarantees are being restricted further, while direct income subsidies in the form of area- and animal-
Fig. 2. Increase in average farm size in some European Union countries EEC10, European Economic Community (10 nations); EEC12, European Economic Community (12 nations); UK, United Kingdom; F, France; FRG, Federal Republic of Germany; E, Spain; GR, Greece
related compensation payments are being expanded. Therefore, farmers' sales proceeds have diminished significantly, while costs of means and machinery have increased considerably. This development will continue. Only in the long term can greater demand and higher price levels in important world agricultural markets be expected as a consequence of the growing world population and increasing incomes in many developing countries (Reisch, 1998). For these reasons, productivity increases will remain very important within the next 10}20 years (Kutzbach, 1999). Hence, structural change towards larger farms will also continue (Fig. 2). To an increasing extent, farm land is cultivated by a smaller number of larger operations. The area percentage of farms with a size of over 100 ha varies greatly between individual European countries (Table 1). It ranges from 2)9% in Greece to 65% in the
Table 1 Farm structure and mechanization costs in European countries (1993)
Country Denmark Germany Greece Spain France Italy Netherlands United Kingdom
Total no. of farms, 1000s
Average farm size, ha
Farms over 100 ha % of no.
% of area
74 606 819 1384 801 2488 120 244
37 28 4 18 35 6 17 67
5)8 2)7 0)1 3)1 7)6 0)6 0)8 15)9
19)2 38)0 2)9 50)7 34)3 21)7 7)2 65)2
Mech. costs, % of total production 22)0 33)5 23)0 18)5 23)5 22)0
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UK. Multi-farm machinery use, which allows better exploitation of machine capacity and lower capital tie-up, is particularly important for cost reduction (Kutzbach, 1997). Decreasing numbers of farms, along with the multi-farm machinery use cause the number of machines sold per year to diminish further (Fig. 3). This reduction particularly a!ects those machines that have been in the market for a long time such as tractors and combines. This decrease in unit numbers will continue in the years to come. It requires that the manufacturers be very #exible in production and even take the special wishes of every single customer into account.
3. Future buyers and users of agricultural machinery In the future, customers' wishes and demands will continue to encompass a wide range. Demands by the private contractors in the industrialized countries are particularly high. They ask for special machinery (generally self-propelled machines) with very high performance, very simple operation, automatic setting, as well as equipment for #eet management and invoicing. Requirements include precision farming and the cultivation of virtual "elds, as well as the possibility to use public roads without time-consuming machine preparation. For large farms with consolidated "elds, road journeys do not have such high priority. In other respects, their demands are the same as those of private contractors. Depending on the farm size, full-time farmers require machinery with medium to high performance while making lower demands on electronic equipment and information technology. Tractors and implements will retain their importance on these farms. New machines for part-time farms (generally in the lower performance range) should be easy to operate, robust and inexpensive. Agricultural machinery for developing countries must, in particular, "t into the cost frame of the individual
Fig. 3. Sales of agricultural equipment in Western Europe
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country. Therefore, machine performance is lower and their equipment is smaller and simpler than that in the industrialized countries. However, these machines are exposed to higher mechanical load due to heavy duty service and because stones and roots as well as inappropriate use may result in heavy strain. Hence, new machines must be developed for those countries. By transferring their knowledge, agricultural engineers from industrialized countries can make a signi"cant contribution towards this goal. This technology transfer is a great challenge for all parties involved. A successful solution to this problem, which is extraordinarily important for the future supply of food for the world population, can only be found in those countries where the onset of industrialization causes a shortage of farm workers. Even though a wide spectrum of agricultural machinery will remain necessary in the future, the following sections focus on the future development of agricultural machinery which has to meet very high demands.
4. Innovations for higher capacity In order to increase productivity and to allow scheduled work to be carried out on time, the output of agricultural tractors and machines has risen steadily during the recent decades (Fig. 4 ). For tractors, the increase in mean engine power is shown, while for combines and forage harvesters maximum engine power is indicated, in addition to the estimate of Busse (1981) for combines, that was considered to be too high at that time. Nonetheless, the engine power of combines is not expected to grow any more slowly in the future. Engine power will probably increase even faster so that combines will reach a maximum engine power of 350 kW in 2010. Similar growth in engine power is also expected for other machines. Conforming to this development, the grain throughput of combines has also grown (Fig. 4 ). For sugar beet harvesting the percentage of the area harvested with six-row machines in Germany is shown. With reference to technical aspects, use of wider working elements are the simplest way to increase performance. This includes, for example, larger cutting width of mowers, widening of the application booms of plantprotection implements, etc. If space is limited, as is the case with combines, for example, new or improved threshing and separating systems (such as axial threshing units or rotating separators instead of the walker (Fig. 5), multiple-drum threshing units and additional air steps in the cleaning system) allow higher performance to be achieved. Other challenges for the future work of agricultural engineers comprise, for example, single-seed drilling of grain, better seed insertion by drills, reduction of, or
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Fig. 4. Increase in capacity indices: (a) maximal power of com) ~ including the estimate of Busse (1981) ~ and of bines ( forage harvesters ; (b) , average farm tractor power of sales in Germany; (c) , average increase in combine grain throughput (Braunhardt, 1999); and (d) , area share harvested with six row sugar beet harvester
automatic reaction to, the in#uence of the properties of mineral fertilizer on the spread pattern and automatic implement coupling without manual intervention. Higher output can also be achieved with the aid of new techniques such as the stripper header for combines developed at Silsoe or improved conditioning during the hay harvest. In addition to higher technical performance, the reduction of driving, setup and non-productive time can lead to a higher output. Foldable grain and maize headers as well as automatic sharpening of forage harvester chopping knives during transport journeys, for example, also allow higher performance to be achieved. Machine management requires special attention. Careful scheduling of machinery use may achieve a signi"cant increase in output, combined with cost reduction and higher productivity. In the future, modern telecommunication technology with position establishment through global positioning systems (GPS) will have increasing importance in this "eld.
Fig. 5. New John Deere STS combine with rotary separator
Thanks to their optimal technical adaptation to their tasks, self-propelled machines enable set-up time to be reduced. In addition, adjusted working speed along with better arrangement of the operating elements provide a better view of the working width. This allows work to be carried out better and faster while reducing the driver's work load. Therefore, the range of self-propelled machines available will continue to grow. In addition to the traditional self-propelled machines such as combines and forage harvesters, the following machines are currently being o!ered as self-propelled versions: sugar beet and potato harvesters, swath mowers, balers and plantprotection sprayers. In the future, this range will be extended to comprise self-propelled fertilizer spreaders, drills, as well as cultivation and sowing combinations. To increase the transport performance of agricultural tractors, their driving speed is already being increased further. In tractors with higher driving speeds, front-axle suspension has established itself as a means of increasing ride safety and comfort. In the future, kinematics will be improved further (Freimann & Brenninger, 1998) and other self-propelled machines will be equipped with front-axle suspension. Rear-axle suspension will also be introduced, at least for faster vehicles (Renius, 1999). As in other vehicles, the continuously variable, powersplitting hydrostatic transmission leads to considerably higher productivity of agricultural tractors, in addition to simpler operation. Meanwhile, these transmissions are o!ered by three manufacturers. Other companies will follow suit. On light soils and under very heterogeneous soil and crop conditions, a continuously variable transmission was found to achieve a 25% higher forward speed during ploughing and 16% higher throughput during chopping (Demmel et al., 1999). Load-limit sensing control systems, which adapt the forward speed and the engine speed to the individual conditions far better than a driver could while operating a vehicle manually, are of great importance for this increase in output. In the future, this automatic adjustment of the forward speed will also be required for other machines. If yields are pre-calculated for yield mapping, the necessary preconditions for automatic speed adaptation are ful"lled (Schneider et al., 1996). The relatively high e$ciency of 84% was important for the success of the continuously variable hydrostatic transmissions (Renius, 1994). Nevertheless, attempts must be made to achieve better values in the future. Mechanical chain converters and electric transmissions are being developed as alternatives to hydrostatic transmissions. Thanks to the di!erent technical measures such as the control of the clamping load of the discs, the e$ciency of the mechanical chain converter has improved (Sauer, 1996). Due to recent new developments, the use of electric transmissions in agricultural machines
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Table 2 Advantages and disadvantages of continuous variable electric transmissions Advantages
Disadvantages
Simple, robust structure Low-noise level High start-up torque Uniform power train Stepless acceleration/ retardation Simple control and engine/ transmission management Fast availability of max. power
High costs Complex electronic control Power e$ciency Water cooling of electrical motors Final drive with high gear ratio
and tractors seem to o!er great potential for the future (Table 2). Power-splitting electric transmissions and further improvement to components enable higher e$ciency to be achieved (Barucki et al., 1999). If higher quantities cause costs to diminish further, electric drive systems for agricultural machines and tractors will gain in importance.
5. Higher productivity through fewer or combined work steps Productivity increases particularly if labour-intensive work steps can be replaced. This particularly applies to
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direct drilling, which does not require ploughing. While the area capacity of ploughing is low, it accounts for approximately 20}25% of the annual fuel consumption in plant production. If the soil is not turned by the plough, it can lead to better soil structure and reduces erosion. Meanwhile, many studies have shown that comparable yields can be achieved (KoK ller, 1998). However, direct drilling requires well-balanced crop rotation, e$cient weed control and plant protection, adjustable fertilizer levels as well as direct drills which allow trouble-free insertion of the seeds through the mulch cover. Thanks to its economic and ecological advantages, direct drilling will also gain wider acceptance in Europe. In North and South America as well as in Australia, direct drilling is common. Soil cultivation can be simpli"ed if sowing is combined with the harvest. With the combination of a drill at the rear end of a six-row sugar beet harvester, good winter wheat yields have been achieved (Nawroth et al., 1998). For sowing of intercrops after the grain harvest, a combination of direct drill with the cutter bar of a combine is being developed (Fig. 6). Thanks to the curved, slightly pitched shares, the draught power requirements are low. The straw layer does not impede seed insertion. The straw is deposited again from the combine after sowing. Two further examples will show that the combination of work steps allows part of the subsequent work to be done in the "eld immediately afterwards. This increases
Fig. 6. Combine header equipped with seeder for seeding during grain harvest (photo: Ho( nscher)
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Fig. 7. Self-propelled carrot harvester with washing and packing units (Kleisinger, 1994)
the real net output of the farm and improves its economic situation (Welschof, 1997). One example is bundled carrots which are packed on the "eld so that they are ready for sale (Fig. 7). The machine consists of a basic vehicle with hydrostatic allwheel drive and all-wheel steering (Kleisinger, 1994). A lifter with belt pulling mechanism mounted at the front end places the carrots on a washing belt. The carrots with leaves are conveyed to a washer with water conditioning. Subsequently, they are bundled up by three workers and tied automatically. Another worker packs them into the market boxes on the platform and stacks them on pallets. Another example is a mobile machine for the potato harvest and for direct processing of potato starch for the industrial use (Bernhardt et al., 1998). This machine consists of a one-row potato harvester, which, instead of the sorting belts, features a group of brush rollers for the dry cleaning of the potatoes and functional groups for crushing and de-watering instead of the hopper (Fig. 8). A pair of cracker rollers from a forage harvester with a succeeding grinding roller crushes the potatoes, while a decanter is used for de-watering. The largest part of the water contained in the potatoes remains in the "eld, together with the substances solved in the water (minerals, proteins).
6. Technical developments for environmental protection Avoidance of soil compaction is necessary for sustainable agriculture because soil compaction is di$cult to correct and it leads to possible soil erosion and lower yield. Increasing machine output together with larger grain tanks or hoppers leads to a higher total mass and an increasing engine power (Fig. 9). Even though in the wet 1998 harvest season, large six-row sugar beet harvesters proved superior to smaller one-row machines, their total mass of over 40 t is near the upper limit. To increase productivity further, agricultural engineers must work on the following solutions: (a) development of better wheel or track systems for higher total mass with good steerability; (b) removal of the hopper from the harvester, with the hoppers having their own drives to follow the harvester automatically or automatically driving to the "eld's edge for unloading; (c) operation of two or more small machines by one driver, with driverless machines automatically following the manned machine (Iida et al., 1998); and (d) automatic operation of unmanned, autonomous machines with high precise navigation for time-consuming
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Fig. 8. Potato harvester with mobile starch extraction for industrial use (Bernhardt et al., 1998)
"eld work (Nagasaka et al., 1998)*ploughing of a rice paddy (including the headland) by a driverless tractor having already been demonstrated in trials (Matsuo et al., 1998). In recent years, technical developments for diminishing soil compaction have included wide and super-wide tyres as well as rubber tracks. Crab steer setting of the tyres, adjustment of the track width and an odd number of tyres, allow ruts to be avoided and cause the surface to be rolled over evenly with a positive e!ect (Fig. 10).
Fig. 9. Engine power against total weight for combines, forage harvesters and sugar beet harvesters
Rubber tracks have excellent traction characteristics. Turning processes and pressure distribution under the track need improvement. Half-tracks, which have been presented for agricultural tractors and combines, can at least improve the turning processes. A wide-tyre chassis
Fig. 10. Complete tyre footprint overlay of harvested area (photo: Stoll)
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with multiple axles and individual steering is another alternative. In order to avoid plough pan formation and deeper soil compaction, onland ploughing will considerably gain in importance in Europe also. Automatic steering systems, which signi"cantly facilitate onland ploughing for the driver, support this development. Protection of the environment through the reduction of herbicide application requires a return to mechanical weed control. Agricultural engineers are working on the following solutions: (a) mechanical inter-row cultivation with di!erent tools and subsequent separation of the soil from the weed plants, which are deposited as mulch afterwards (Fig. 11) (Meyer & Bertram, 1998); (b) image-analytical recognition of weed plants and mechanical hoeing with controlled tools or spatially and strictly limited application of herbicides (Wi{erodt et al., 1999) and (c) thermal treatment of weeds through #aming or the use of hot water on tree rows, near fences, on railway embankments, etc. (Kurfess & Kleisinger, 1999). In the long run, the position of nursery plants will be registered individually with the aid of highly precise, real-time kinetic global positioning systems (RTKGPS) during planting. This will open up new challenges for fertilizing, weed control, irrigation and the harvest. Demand-oriented fertilizing, which is currently being discussed with regard to precision farming, is gaining in importance for environmental protection through reduced nitrate leaching into the subsoil and the groundwater. However, nutrient maps are necessary if there is a requirement for drawing up application maps based on yield maps. Control equipment which can react directly on the current needs of the crops is more e$cient. This
Fig. 12. Nitrogen-sensor for fertilizer broadcaster control system
requires the development of other sensors for the establishment of the water and nutrient supply. Thus, the necessary treatment can be carried out on the move without yield maps as an intermediate step. The control sensor for the nitrogen fertilization of healthy crops is already being o!ered (Fig. 12). In the future, sensors and machines will be developed that are required to limit the application of fertilizers and plant protection products to the application target. This will not only make a contribution towards environmental protection, but it will also be advantageous under quality aspects, which will gain in importance in the future.
7. Maintenance of product quality In the future, customers will be willing to pay more for high-quality products. Particularly for smaller farms, these niches provide interesting perspectives if the products are marketed directly. As a consequence, agricultural machines will have to meet special requirements with regard to the maintenance of the product quality. This applies particularly to fruits and vegetables, but to a smaller extent also to "eld crops. General factors that in#uence product quality are variety, location, climate and production method. In addition, the harvesting machine in particular in#uences the quality of the product. More speci"cally the harvesting machine can cause mechanical strain on the product (shock, shear and friction). This may lead, for example, to reduced germination ability of grain, broken grain kernels and damage to potato tubers. In particular, potatoes need very gentle treatment by means of low drop heights during the harvest (Fig. 13).
8. Developments for the bene5t of drivers
Fig. 11. Weihenstephan separating hoe for mechanical weeding (Meyer & Bertram, 1998)
Ergonomic design of work places on agricultural machinery reduces a driver's work load. It takes longer before the driver becomes tired. This increases the willingness to work and the worktime. In the past 20 years, the introduction of cabs, "rst on tractors, then on
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Fig. 13. Two-row potato harvester with v-shaped conveyer belts for careful potato handling (Peters, 1999)
combines led to steady improvement to the work place on agricultural machines. This development is continuing. It is not limited to the actual work place, but it includes the entire design and control positions of agricultural machinery. The introduction of the multi-functional lever for the operation of the cutter bar of a combine, with the aid of electric keys in combination with the speed control lever
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brought about the development of the joystick; this also allows for easier operation of important functions on a tractor. The joystick replaces several hand levers and switches and it can be installed in the arm rest. Electric control enables the hydraulic valves, which cause annoying #ow noises, to be installed in a position where pipe arrangement and function are optimal (Fig. 14). While operating continuously variable transmissions, the joystick serves to adjust the acceleration. This allows speed to be altered in a more sensitive way than with the aid of a speed control lever. In the future, electric operation will also increasingly establish itself on other self-propelled machines and for other operating functions. Upon request, the operator will be able to call up routines, such as the turning routine with implement operation, engine/transmission and implement management according to di!erent strategies. Machine-setting routines, allow for example, the threshing and separating of elements of a combine to be adjusted to the grain variety and the harvest conditions. In addition to automatic speed setting, automatic vehicle control is a prerequisite for the automation of farm machines. Over decades, numerous studies and developments focused on automatic vehicle control. So far, only the mechanical sensing of maize and sugar beet rows has proven itself in practice. Today, virtually all forage
Fig. 14. Tractor driving cab with joystick using electronic control of hydraulic valves situated away from driving cab (photo: Fendt)
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Fig. 15. Automatic steering systems of farm machines: (a) mechanical sensing bars; (b) ultrasonic sensors; (c) laser beam reyection; (d) machine vision; (e) real-time kinematic global positioning system and ( f ) laser optic navigation
harvesters are equipped with this automatic control system. Recently, two other systems have been presented (Fig. 15): scanning the edge of the uncut grain crop using the re#ection of a fanned laser beam (laser pilot) for combine control and the scanning of hay swaths with the aid of several ultra-sound sensors. Image-analytical registration of plant rows is currently still at the developmental stage (Seufert et al., 1998), while the use of high-precision global positioning systems (RTKGPS) for automatic vehicle control enables vehicles to follow virtual, calculated guide lines and hence goes far beyond guidance along real lines (Stoll, 1999). Turning processes at the "eld edge, for example, can be initiated and carried out automatically. Subsequently, the vehicle is positioned at the beginning of the next row. In the future, such systems will make a contribution towards a very signi"cant increase in productivity. For safety reasons, the driver cannot be dispensed with in the near future. In the long run, however, driverless, autonomous vehicles will determine the character of intensive agriculture.
are exhibiting a growing trend towards self-propelled, specialist machines. Tractors are used particularly for soil cultivation and transport. Continuously variable transmissions and suspended axles enable high performance to be achieved while performing these tasks. Electric transmissions may be considered as an alternative to hydrostatic transmissions. New machines and farming methods must be developed to increase farm incomes by means of higher real net output direct from the farm. While working on these developments, agricultural engineers must meet the following requirements: protection of the environment through reduced emissions of pollutants, maintenance and improvement of product quality and further facilitation for the driver's work through better working conditions, simpler machine operation, automatic vehicle control and the automation of recurrent work processes. Looking further into the future, driverless, autonomous machines will signi"cantly alter the character of agricultural machinery. References
9. Conclusions Globalization and international agricultural and trade policy will keep up cost pressure on agriculture. This will cause structural changes towards fewer, but larger, farms to continue. These farms need even larger and more e$cient machines. The combination of work steps, the operation of several machines by one driver and the replacement of time-consuming work steps are expected to increase productivity further. Current developments
Barucki T; Kis J; Rudik R (1999). Modelling of diesel}electric drives for traction and auxiliaries of agricultural machinery. Proceedings International Conference on Agricultural Engineering, Braunschweig, pp 87}92. VDI-Verlag, DuK sseldorf Bernhardt G; Firus S; Kaiser M (1998). Direkte Karto!elstaK rke-Gewinnungauf dem Feld*Stand der technischen und verfahrenstechnischen Forschung. [Direct processing to potato starch in the "eld*status of technical research.] Internationale Tagung &Sto%iche Nutzung nachwachsender Rohsto!e,' Chemnitz, pp 1}10 Braunhardt K (1999). Combine development in a global environment. Proceedings International Conference on
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Agricultural Engineering, Braunschweig, pp 317}322. VDIVerlag, DuK sseldorf Busse W (1981). Mechanisierung der Getreideernte*Revolution fuK r die Kornkammern der Welt. [Mechanization of grain harvest*revolution for world granaries.] VDI-Berichte No. 407, pp 19}26 Demmel M; Attenberger G; Dischinger G; Auernhammer H; Settele H P (1999). Examinations at a tractor with continuously variable transmission during heavy pull-type and pto-type work. Proceedings International Conference on Agricultural Engineering, Braunschweig, pp 81}86. VDIVerlag, DuK sseldorf Freimann R; Brenninger M (1998). Systematic re#ections on suspended tractor front-axles. Proceedings International Conference on Agricultural Engineering, Braunschweig, pp 25}30. VDI-Verlag, DuK sseldorf Iida M; Umeda M; Suguri M (1998). Automatic follow-up vehicle system for agriculture. ASAE Paper No. 98-3112 Kleisinger S (1994). Erntetechnik fuK r WurzelgemuK se und Porree. [Harvest technology of root crops and leek.] GemuK se No. 8, pp 445}449 KoK ller K H (1998). Drilling and precision seedling. In: Yearbook Agricultural Engineering, No. 10, pp 93}96. Landwirtschaftsverlag, MuK nster Kurfess W; Kleisinger S (1999). Weeds in hot water. Resource, 6(8), 13}14 Kutzbach H D (1997). Contractors: new machines to increase e$ciency of the various "eld operations. A critical analysis. Proceedings of the 8th Meeting Club of Bologna, No. 8, pp 17}37 Kutzbach H D (1999). Capacity increase in crop harvesting. Conference Abstracts of International Conference of Agricultural Engineering (ICAE), Peking, pp 15}22 Matsuo Y; Yukumoto O; Noguchi N (1998). Navigation systems and work performance of tillage robot. ASAE Paper No. 98-3192 Meyer J; Bertram A (1998). Strategies for optimizing the physical weed control in organic and integrated farming. Conference Abstracts AgEng 98A-113, Oslo, pp 761}762 Nagasaka Y; Otani R; Shigeta K; Taniwaki K (1998). Autonomous rice transplanting system with GPS and FOG. Conference Abstracts AgEng 98A-043, Oslo, pp 633}634 Nawroth P; Auernhammer H; Demmel M; Estler M (1998). Test of a harvest-seeding-system for winter wheat in a 6-row sugar
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beet harvester. Conference Abstracts AgEng 98A-118, Oslo, pp 771}772 Peters R (1999). Potato harvesting. In: Yearbook Agricultural Engineering, No. 11, pp 133}137. Landwirtschaftsverlag, MuK nster Reisch E (1998). Europas Zukunft als Standort landwirtschaftlicher Produktion unter dem Ein#u{ der Globalisierung. [Europe's future as location of agricultural production under the in#uence of globalisation.] KTBLArbeitspapier No. 254, pp 7}26. Landwirtschaftsverlag, MuK nster-Hiltrup Renius K T (1999). Agricultural tractor development. In: Yearbook Agricultural Engineering, No. 11, pp 39}44. Landwirtschaftsverlag, MuK nster Renius K T (1994). Trends in tractor design with particular reference to Europe. Journal of Agricultural Engineering Research, 57(1), 3}22 Sauer G (1996). Grundlagen und Betriebsverhalten eines Zugketten-Umschlingungsgetriebes. [Fundamentals and operating behaviour of a continuously variable chain drive.] Fortschritt Berichte VDI, Reihe 12, Bd.293, VDI Verlag, DuK sseldorf Schneider H; Reitz R; Wacker P; Kutzbach H D (1996). Automatische Maschineneinstellung. [Automatic combine adjustment.] Landtechnik, 51(4), 202}203 Seufert H; Knechtges H; Keicher R; Schaal A (1998). Automatic vehicle guidance in row crops using digital image processing. Proceedings International Conference Agricultural Engineering, Braunschweig, pp 87}92. VDI-Verlag, DuK sseldorf Statistische JahrbuK cher (1998). Statistische JahrbuK cher uK ber ErnaK hrung, Landwirtschaft und Forsten. [Statistical Yearbook on food, agriculture and forest.], Vol. 1950}1998. Landwirtschaftsverlag, MuK nster Stoll A (1999). Automatische Lenkung mit DGPS. [Automatic steering with DGPS.] Agrartechnische Forschung, 5(2), 91}100 Welschof G (1997). Neue Agrartechnik*Kapital fuK r unsere Zukunft. [New agricultural engineering*funds for our future.] KTBL-Arbeitspapier 240, Darmstadt, pp 214}221 Wi*erodt E; Grimm J; Kemper M; Kielhorn A; Kleine-Hartlage H; Nardmann M; Naescher J; Trautz D (1999). Controlled hoe for weed control within the row of plants. Proceedings International Conference of Agricultural Engineering, pp 155}160. VDI-Verlag, DuK sseldorf
KEYNOTE PAPER
Trends in Power and Machinery Heinz Dieter Kutzbach Hohenheim University, Department of Agricultural Engineering (440), Garbenstrasse 9, D-70599 Stuttgart, Germany; e-mail: [email protected] (Keynote address for the scientixc session on Power and Machinery, presented at AgEng 2000, 2}7 July 2000)
The economic situation and the future supply of food for the growing world population require the productivity of power and machinery to increase further. Moreover, legislation and demands in the areas such as environmental protection, maintenance of product quality and facilitation of work are factors that will exert a decisive in#uence on future developments. In the foreseeable future, the trend towards larger, more powerful machines will remain undiminished. Mobile machines are becoming even more complex due to the combination of work steps and because subsequent processing has been taken over by these machines. The percentage of self-propelled machines will grow further. Self-propelled machines are also being developed for those kinds of work that are still carried out by tractors and implements today. Nevertheless, the development of new sensors for the control of additional machine functions makes operation easier. Despite high vehicle mass, further developments in tyres and tracks avoid harmful soil compaction. In the future, continuously variable, power-splitting hydrostatic transmissions with electric control will lead to further increase in the productivity of agricultural tractors and simplify their operation. Electric power-splitting transmissions will gain in importance as an alternative to hydrostatic transmissions. Automatic vehicle control, especially through high-precision global positioning systems (GPS), will allow new working procedures such as onland ploughing to be carried out. In addition, the driver's work load will be reduced further, and productivity will increase due to higher driving speed and extended work time during twilight periods. Only after numerous safety questions have been solved will autonomous, unmanned vehicles be employed. At "rst, their use will be restricted to simple work such as tillage. 2000 Silsoe Research Institute
1. Introduction The beginning of the new millennium is a special occasion for a preview of future developments. In this contribution, an attempt is made to predict some important future aspects of power and machinery on the basis of previous developments. It is assumed that the development will be evolutionary and progressive in small steps. In such a preview, it is impossible to foresee pioneering inventions which simplify the entire process in a revolutionary way. In the distant future, there may be "elds without farmers, where autonomous machines plant, cultivate and harvest individual plants. Additionally, industrial farming methods without soil are conceivable with cultures in substrates in a controlled environment (e.g. 0021-8634/00/070237#11 $35.00/0
greenhouses). Fruit and vegetable cultivation with its high-quality products is leading the way into the development of new methods and machines. In arable farming, progress will be slower. However, this development is not only determined by the knowledge, skills and experience of agricultural engineers, but also by economic, ecological and agricultural-policy requirements under which this development takes place (Fig. 1). Environmental factors which will have an in#uence on power and machinery include not only environmentally sound farming methods, but also possibly the greenhouse e!ect. Growing CO concentrations and a slightly higher annual mean temperature due to the greenhouse e!ect might cause the spectrum of the cultivated crops to shift and thus, lead to additional demands on agricultural
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2000 Silsoe Research Institute
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Fig. 1. Power and machinery under the pressure of diwerent requirements; EU, European Union
engineering. Legislators and international standards also in#uence future developments in a di!erent, sometimes in an unpredictable way. Necessary increases in productivity, which are important for limiting costs, are achieved not only through the design of better and larger machines to provide for higher technical performance. Improved machine management and longer e!ective time of use, as well as enhanced application of information technologies for automatization may also result in productivity improvements. These two aspects will be discussed in other contributions.
2. Conditions for future development The future development of agriculture and consequently, the development of power and machinery will be determined in particular by the previous and future decisions in agricultural policy. The 1992 agricultural reform has already led to lower product prices. This development is continuing as a result of Agenda 2000. Price and quantity guarantees are being restricted further, while direct income subsidies in the form of area- and animal-
Fig. 2. Increase in average farm size in some European Union countries EEC10, European Economic Community (10 nations); EEC12, European Economic Community (12 nations); UK, United Kingdom; F, France; FRG, Federal Republic of Germany; E, Spain; GR, Greece
related compensation payments are being expanded. Therefore, farmers' sales proceeds have diminished significantly, while costs of means and machinery have increased considerably. This development will continue. Only in the long term can greater demand and higher price levels in important world agricultural markets be expected as a consequence of the growing world population and increasing incomes in many developing countries (Reisch, 1998). For these reasons, productivity increases will remain very important within the next 10}20 years (Kutzbach, 1999). Hence, structural change towards larger farms will also continue (Fig. 2). To an increasing extent, farm land is cultivated by a smaller number of larger operations. The area percentage of farms with a size of over 100 ha varies greatly between individual European countries (Table 1). It ranges from 2)9% in Greece to 65% in the
Table 1 Farm structure and mechanization costs in European countries (1993)
Country Denmark Germany Greece Spain France Italy Netherlands United Kingdom
Total no. of farms, 1000s
Average farm size, ha
Farms over 100 ha % of no.
% of area
74 606 819 1384 801 2488 120 244
37 28 4 18 35 6 17 67
5)8 2)7 0)1 3)1 7)6 0)6 0)8 15)9
19)2 38)0 2)9 50)7 34)3 21)7 7)2 65)2
Mech. costs, % of total production 22)0 33)5 23)0 18)5 23)5 22)0
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UK. Multi-farm machinery use, which allows better exploitation of machine capacity and lower capital tie-up, is particularly important for cost reduction (Kutzbach, 1997). Decreasing numbers of farms, along with the multi-farm machinery use cause the number of machines sold per year to diminish further (Fig. 3). This reduction particularly a!ects those machines that have been in the market for a long time such as tractors and combines. This decrease in unit numbers will continue in the years to come. It requires that the manufacturers be very #exible in production and even take the special wishes of every single customer into account.
3. Future buyers and users of agricultural machinery In the future, customers' wishes and demands will continue to encompass a wide range. Demands by the private contractors in the industrialized countries are particularly high. They ask for special machinery (generally self-propelled machines) with very high performance, very simple operation, automatic setting, as well as equipment for #eet management and invoicing. Requirements include precision farming and the cultivation of virtual "elds, as well as the possibility to use public roads without time-consuming machine preparation. For large farms with consolidated "elds, road journeys do not have such high priority. In other respects, their demands are the same as those of private contractors. Depending on the farm size, full-time farmers require machinery with medium to high performance while making lower demands on electronic equipment and information technology. Tractors and implements will retain their importance on these farms. New machines for part-time farms (generally in the lower performance range) should be easy to operate, robust and inexpensive. Agricultural machinery for developing countries must, in particular, "t into the cost frame of the individual
Fig. 3. Sales of agricultural equipment in Western Europe
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country. Therefore, machine performance is lower and their equipment is smaller and simpler than that in the industrialized countries. However, these machines are exposed to higher mechanical load due to heavy duty service and because stones and roots as well as inappropriate use may result in heavy strain. Hence, new machines must be developed for those countries. By transferring their knowledge, agricultural engineers from industrialized countries can make a signi"cant contribution towards this goal. This technology transfer is a great challenge for all parties involved. A successful solution to this problem, which is extraordinarily important for the future supply of food for the world population, can only be found in those countries where the onset of industrialization causes a shortage of farm workers. Even though a wide spectrum of agricultural machinery will remain necessary in the future, the following sections focus on the future development of agricultural machinery which has to meet very high demands.
4. Innovations for higher capacity In order to increase productivity and to allow scheduled work to be carried out on time, the output of agricultural tractors and machines has risen steadily during the recent decades (Fig. 4 ). For tractors, the increase in mean engine power is shown, while for combines and forage harvesters maximum engine power is indicated, in addition to the estimate of Busse (1981) for combines, that was considered to be too high at that time. Nonetheless, the engine power of combines is not expected to grow any more slowly in the future. Engine power will probably increase even faster so that combines will reach a maximum engine power of 350 kW in 2010. Similar growth in engine power is also expected for other machines. Conforming to this development, the grain throughput of combines has also grown (Fig. 4 ). For sugar beet harvesting the percentage of the area harvested with six-row machines in Germany is shown. With reference to technical aspects, use of wider working elements are the simplest way to increase performance. This includes, for example, larger cutting width of mowers, widening of the application booms of plantprotection implements, etc. If space is limited, as is the case with combines, for example, new or improved threshing and separating systems (such as axial threshing units or rotating separators instead of the walker (Fig. 5), multiple-drum threshing units and additional air steps in the cleaning system) allow higher performance to be achieved. Other challenges for the future work of agricultural engineers comprise, for example, single-seed drilling of grain, better seed insertion by drills, reduction of, or
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Fig. 4. Increase in capacity indices: (a) maximal power of com) ~ including the estimate of Busse (1981) ~ and of bines ( forage harvesters ; (b) , average farm tractor power of sales in Germany; (c) , average increase in combine grain throughput (Braunhardt, 1999); and (d) , area share harvested with six row sugar beet harvester
automatic reaction to, the in#uence of the properties of mineral fertilizer on the spread pattern and automatic implement coupling without manual intervention. Higher output can also be achieved with the aid of new techniques such as the stripper header for combines developed at Silsoe or improved conditioning during the hay harvest. In addition to higher technical performance, the reduction of driving, setup and non-productive time can lead to a higher output. Foldable grain and maize headers as well as automatic sharpening of forage harvester chopping knives during transport journeys, for example, also allow higher performance to be achieved. Machine management requires special attention. Careful scheduling of machinery use may achieve a signi"cant increase in output, combined with cost reduction and higher productivity. In the future, modern telecommunication technology with position establishment through global positioning systems (GPS) will have increasing importance in this "eld.
Fig. 5. New John Deere STS combine with rotary separator
Thanks to their optimal technical adaptation to their tasks, self-propelled machines enable set-up time to be reduced. In addition, adjusted working speed along with better arrangement of the operating elements provide a better view of the working width. This allows work to be carried out better and faster while reducing the driver's work load. Therefore, the range of self-propelled machines available will continue to grow. In addition to the traditional self-propelled machines such as combines and forage harvesters, the following machines are currently being o!ered as self-propelled versions: sugar beet and potato harvesters, swath mowers, balers and plantprotection sprayers. In the future, this range will be extended to comprise self-propelled fertilizer spreaders, drills, as well as cultivation and sowing combinations. To increase the transport performance of agricultural tractors, their driving speed is already being increased further. In tractors with higher driving speeds, front-axle suspension has established itself as a means of increasing ride safety and comfort. In the future, kinematics will be improved further (Freimann & Brenninger, 1998) and other self-propelled machines will be equipped with front-axle suspension. Rear-axle suspension will also be introduced, at least for faster vehicles (Renius, 1999). As in other vehicles, the continuously variable, powersplitting hydrostatic transmission leads to considerably higher productivity of agricultural tractors, in addition to simpler operation. Meanwhile, these transmissions are o!ered by three manufacturers. Other companies will follow suit. On light soils and under very heterogeneous soil and crop conditions, a continuously variable transmission was found to achieve a 25% higher forward speed during ploughing and 16% higher throughput during chopping (Demmel et al., 1999). Load-limit sensing control systems, which adapt the forward speed and the engine speed to the individual conditions far better than a driver could while operating a vehicle manually, are of great importance for this increase in output. In the future, this automatic adjustment of the forward speed will also be required for other machines. If yields are pre-calculated for yield mapping, the necessary preconditions for automatic speed adaptation are ful"lled (Schneider et al., 1996). The relatively high e$ciency of 84% was important for the success of the continuously variable hydrostatic transmissions (Renius, 1994). Nevertheless, attempts must be made to achieve better values in the future. Mechanical chain converters and electric transmissions are being developed as alternatives to hydrostatic transmissions. Thanks to the di!erent technical measures such as the control of the clamping load of the discs, the e$ciency of the mechanical chain converter has improved (Sauer, 1996). Due to recent new developments, the use of electric transmissions in agricultural machines
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Table 2 Advantages and disadvantages of continuous variable electric transmissions Advantages
Disadvantages
Simple, robust structure Low-noise level High start-up torque Uniform power train Stepless acceleration/ retardation Simple control and engine/ transmission management Fast availability of max. power
High costs Complex electronic control Power e$ciency Water cooling of electrical motors Final drive with high gear ratio
and tractors seem to o!er great potential for the future (Table 2). Power-splitting electric transmissions and further improvement to components enable higher e$ciency to be achieved (Barucki et al., 1999). If higher quantities cause costs to diminish further, electric drive systems for agricultural machines and tractors will gain in importance.
5. Higher productivity through fewer or combined work steps Productivity increases particularly if labour-intensive work steps can be replaced. This particularly applies to
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direct drilling, which does not require ploughing. While the area capacity of ploughing is low, it accounts for approximately 20}25% of the annual fuel consumption in plant production. If the soil is not turned by the plough, it can lead to better soil structure and reduces erosion. Meanwhile, many studies have shown that comparable yields can be achieved (KoK ller, 1998). However, direct drilling requires well-balanced crop rotation, e$cient weed control and plant protection, adjustable fertilizer levels as well as direct drills which allow trouble-free insertion of the seeds through the mulch cover. Thanks to its economic and ecological advantages, direct drilling will also gain wider acceptance in Europe. In North and South America as well as in Australia, direct drilling is common. Soil cultivation can be simpli"ed if sowing is combined with the harvest. With the combination of a drill at the rear end of a six-row sugar beet harvester, good winter wheat yields have been achieved (Nawroth et al., 1998). For sowing of intercrops after the grain harvest, a combination of direct drill with the cutter bar of a combine is being developed (Fig. 6). Thanks to the curved, slightly pitched shares, the draught power requirements are low. The straw layer does not impede seed insertion. The straw is deposited again from the combine after sowing. Two further examples will show that the combination of work steps allows part of the subsequent work to be done in the "eld immediately afterwards. This increases
Fig. 6. Combine header equipped with seeder for seeding during grain harvest (photo: Ho( nscher)
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Fig. 7. Self-propelled carrot harvester with washing and packing units (Kleisinger, 1994)
the real net output of the farm and improves its economic situation (Welschof, 1997). One example is bundled carrots which are packed on the "eld so that they are ready for sale (Fig. 7). The machine consists of a basic vehicle with hydrostatic allwheel drive and all-wheel steering (Kleisinger, 1994). A lifter with belt pulling mechanism mounted at the front end places the carrots on a washing belt. The carrots with leaves are conveyed to a washer with water conditioning. Subsequently, they are bundled up by three workers and tied automatically. Another worker packs them into the market boxes on the platform and stacks them on pallets. Another example is a mobile machine for the potato harvest and for direct processing of potato starch for the industrial use (Bernhardt et al., 1998). This machine consists of a one-row potato harvester, which, instead of the sorting belts, features a group of brush rollers for the dry cleaning of the potatoes and functional groups for crushing and de-watering instead of the hopper (Fig. 8). A pair of cracker rollers from a forage harvester with a succeeding grinding roller crushes the potatoes, while a decanter is used for de-watering. The largest part of the water contained in the potatoes remains in the "eld, together with the substances solved in the water (minerals, proteins).
6. Technical developments for environmental protection Avoidance of soil compaction is necessary for sustainable agriculture because soil compaction is di$cult to correct and it leads to possible soil erosion and lower yield. Increasing machine output together with larger grain tanks or hoppers leads to a higher total mass and an increasing engine power (Fig. 9). Even though in the wet 1998 harvest season, large six-row sugar beet harvesters proved superior to smaller one-row machines, their total mass of over 40 t is near the upper limit. To increase productivity further, agricultural engineers must work on the following solutions: (a) development of better wheel or track systems for higher total mass with good steerability; (b) removal of the hopper from the harvester, with the hoppers having their own drives to follow the harvester automatically or automatically driving to the "eld's edge for unloading; (c) operation of two or more small machines by one driver, with driverless machines automatically following the manned machine (Iida et al., 1998); and (d) automatic operation of unmanned, autonomous machines with high precise navigation for time-consuming
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Fig. 8. Potato harvester with mobile starch extraction for industrial use (Bernhardt et al., 1998)
"eld work (Nagasaka et al., 1998)*ploughing of a rice paddy (including the headland) by a driverless tractor having already been demonstrated in trials (Matsuo et al., 1998). In recent years, technical developments for diminishing soil compaction have included wide and super-wide tyres as well as rubber tracks. Crab steer setting of the tyres, adjustment of the track width and an odd number of tyres, allow ruts to be avoided and cause the surface to be rolled over evenly with a positive e!ect (Fig. 10).
Fig. 9. Engine power against total weight for combines, forage harvesters and sugar beet harvesters
Rubber tracks have excellent traction characteristics. Turning processes and pressure distribution under the track need improvement. Half-tracks, which have been presented for agricultural tractors and combines, can at least improve the turning processes. A wide-tyre chassis
Fig. 10. Complete tyre footprint overlay of harvested area (photo: Stoll)
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with multiple axles and individual steering is another alternative. In order to avoid plough pan formation and deeper soil compaction, onland ploughing will considerably gain in importance in Europe also. Automatic steering systems, which signi"cantly facilitate onland ploughing for the driver, support this development. Protection of the environment through the reduction of herbicide application requires a return to mechanical weed control. Agricultural engineers are working on the following solutions: (a) mechanical inter-row cultivation with di!erent tools and subsequent separation of the soil from the weed plants, which are deposited as mulch afterwards (Fig. 11) (Meyer & Bertram, 1998); (b) image-analytical recognition of weed plants and mechanical hoeing with controlled tools or spatially and strictly limited application of herbicides (Wi{erodt et al., 1999) and (c) thermal treatment of weeds through #aming or the use of hot water on tree rows, near fences, on railway embankments, etc. (Kurfess & Kleisinger, 1999). In the long run, the position of nursery plants will be registered individually with the aid of highly precise, real-time kinetic global positioning systems (RTKGPS) during planting. This will open up new challenges for fertilizing, weed control, irrigation and the harvest. Demand-oriented fertilizing, which is currently being discussed with regard to precision farming, is gaining in importance for environmental protection through reduced nitrate leaching into the subsoil and the groundwater. However, nutrient maps are necessary if there is a requirement for drawing up application maps based on yield maps. Control equipment which can react directly on the current needs of the crops is more e$cient. This
Fig. 12. Nitrogen-sensor for fertilizer broadcaster control system
requires the development of other sensors for the establishment of the water and nutrient supply. Thus, the necessary treatment can be carried out on the move without yield maps as an intermediate step. The control sensor for the nitrogen fertilization of healthy crops is already being o!ered (Fig. 12). In the future, sensors and machines will be developed that are required to limit the application of fertilizers and plant protection products to the application target. This will not only make a contribution towards environmental protection, but it will also be advantageous under quality aspects, which will gain in importance in the future.
7. Maintenance of product quality In the future, customers will be willing to pay more for high-quality products. Particularly for smaller farms, these niches provide interesting perspectives if the products are marketed directly. As a consequence, agricultural machines will have to meet special requirements with regard to the maintenance of the product quality. This applies particularly to fruits and vegetables, but to a smaller extent also to "eld crops. General factors that in#uence product quality are variety, location, climate and production method. In addition, the harvesting machine in particular in#uences the quality of the product. More speci"cally the harvesting machine can cause mechanical strain on the product (shock, shear and friction). This may lead, for example, to reduced germination ability of grain, broken grain kernels and damage to potato tubers. In particular, potatoes need very gentle treatment by means of low drop heights during the harvest (Fig. 13).
8. Developments for the bene5t of drivers
Fig. 11. Weihenstephan separating hoe for mechanical weeding (Meyer & Bertram, 1998)
Ergonomic design of work places on agricultural machinery reduces a driver's work load. It takes longer before the driver becomes tired. This increases the willingness to work and the worktime. In the past 20 years, the introduction of cabs, "rst on tractors, then on
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Fig. 13. Two-row potato harvester with v-shaped conveyer belts for careful potato handling (Peters, 1999)
combines led to steady improvement to the work place on agricultural machines. This development is continuing. It is not limited to the actual work place, but it includes the entire design and control positions of agricultural machinery. The introduction of the multi-functional lever for the operation of the cutter bar of a combine, with the aid of electric keys in combination with the speed control lever
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brought about the development of the joystick; this also allows for easier operation of important functions on a tractor. The joystick replaces several hand levers and switches and it can be installed in the arm rest. Electric control enables the hydraulic valves, which cause annoying #ow noises, to be installed in a position where pipe arrangement and function are optimal (Fig. 14). While operating continuously variable transmissions, the joystick serves to adjust the acceleration. This allows speed to be altered in a more sensitive way than with the aid of a speed control lever. In the future, electric operation will also increasingly establish itself on other self-propelled machines and for other operating functions. Upon request, the operator will be able to call up routines, such as the turning routine with implement operation, engine/transmission and implement management according to di!erent strategies. Machine-setting routines, allow for example, the threshing and separating of elements of a combine to be adjusted to the grain variety and the harvest conditions. In addition to automatic speed setting, automatic vehicle control is a prerequisite for the automation of farm machines. Over decades, numerous studies and developments focused on automatic vehicle control. So far, only the mechanical sensing of maize and sugar beet rows has proven itself in practice. Today, virtually all forage
Fig. 14. Tractor driving cab with joystick using electronic control of hydraulic valves situated away from driving cab (photo: Fendt)
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Fig. 15. Automatic steering systems of farm machines: (a) mechanical sensing bars; (b) ultrasonic sensors; (c) laser beam reyection; (d) machine vision; (e) real-time kinematic global positioning system and ( f ) laser optic navigation
harvesters are equipped with this automatic control system. Recently, two other systems have been presented (Fig. 15): scanning the edge of the uncut grain crop using the re#ection of a fanned laser beam (laser pilot) for combine control and the scanning of hay swaths with the aid of several ultra-sound sensors. Image-analytical registration of plant rows is currently still at the developmental stage (Seufert et al., 1998), while the use of high-precision global positioning systems (RTKGPS) for automatic vehicle control enables vehicles to follow virtual, calculated guide lines and hence goes far beyond guidance along real lines (Stoll, 1999). Turning processes at the "eld edge, for example, can be initiated and carried out automatically. Subsequently, the vehicle is positioned at the beginning of the next row. In the future, such systems will make a contribution towards a very signi"cant increase in productivity. For safety reasons, the driver cannot be dispensed with in the near future. In the long run, however, driverless, autonomous vehicles will determine the character of intensive agriculture.
are exhibiting a growing trend towards self-propelled, specialist machines. Tractors are used particularly for soil cultivation and transport. Continuously variable transmissions and suspended axles enable high performance to be achieved while performing these tasks. Electric transmissions may be considered as an alternative to hydrostatic transmissions. New machines and farming methods must be developed to increase farm incomes by means of higher real net output direct from the farm. While working on these developments, agricultural engineers must meet the following requirements: protection of the environment through reduced emissions of pollutants, maintenance and improvement of product quality and further facilitation for the driver's work through better working conditions, simpler machine operation, automatic vehicle control and the automation of recurrent work processes. Looking further into the future, driverless, autonomous machines will signi"cantly alter the character of agricultural machinery. References
9. Conclusions Globalization and international agricultural and trade policy will keep up cost pressure on agriculture. This will cause structural changes towards fewer, but larger, farms to continue. These farms need even larger and more e$cient machines. The combination of work steps, the operation of several machines by one driver and the replacement of time-consuming work steps are expected to increase productivity further. Current developments
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