外文原文.pdf

Biosystems Engineering (2002) 81(3), 281286 doi:10.1006/bioe.2001.0011, available online at on PM*Power and Machinery Seed Loss when Cutting a Standing Crop of Oilseed Rape with Two Types of Combine Harvester Header R. N. Hobson; D. M. Bruce Biomaterials Group, Silsoe Research Institute, Wrest Park, Silsoe, Beds. MK45 4HS, England; e-mail of corresponding author: norris.hobsonbbsrc.ac.uk (Received 8 July 2000, accepted in revised form 9 October 2001) Oilseed rape has the potential to expand as an industrial crop. However, as oilseed rape matures, seed loss occurs by dehiscence of the seed from the pods prior to harvest and also as a result of crop disturbance by machinery during harvest. Seed loss of 600 kgha?, 25% of the recorded yield, is not uncommon. This directly increases the price for industrial users and can also reduce oil purity because volunteer plants in subsequent oilseed rape crops may have a di!erent oil fatty acid prole. Oilseed rape plants also persist as weeds in subsequent crops. An experiment was carried out to identify the cause of, and quantify contributions to, seed loss from two di!erent designs of header tted to the combine harvester; a standard header and a header with a conveyor tted behind the cutterbar, claimed to assist crop #ow into the auger. Seed loss was measured using traysplaced in the ripening crop prior toharvest. Seedshed before harvest, 11 kgha?, was low as a result of the relatively settled weather conditions. There was a signicant di!erence between losses from the two types of header. The loss from each side knife was the same, but because of the di!ering header widths, translated into losses of 18)4 and 34)6 kgha? for the conveyor-assisted and standard headers, respectively, showing the advantage of using a wider header in reducing this loss. Excluding shedding loss and side knife losses, seed loss from the conveyor-assisted header was 59 kgh? against 104 kgh? with the standard header. Loss caused only by the cutterbar of the conveyor-assisted header, 27 kgha?, was less than half that of the standard header cutterbar, showing the e!ectiveness of the combination of forward positioning of the cutterbar and conveyor- assistance. At 2001 costs, the conveyor-assisted header would recover its additional purchase price in ve years if used to harvest 171 ha of oilseed rape per year.? 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. All rights reserved 1. Introduction Oilseed rape (Brassica napus) is an important non- cereal, combinable break crop, the oil from which is used mainly for food production (NIAB, 1992). Industrial ap- plications have also been developed for the oil; high erucic acid rape is grown for industrial lubricants (Cook- sley, 1993), rapeseed oil is convertible to bio-diesel (rape methylester) (McDonnellet al., 1995) and forms the basis of a bio-degradable lubricant for underwater drilling (Coghlan, 1997). Several countries, in particular France and Austria, are actively promoting bio-diesel mainly as it is a renewable resource and also because it is seen as delivering benets of lower emissions over standard die- sel, and therefore, nds favour in city centres and in environmentally sensitive areas such as the Norfolk Broads, England (Grimshaw, 1994). Oilseed rape is a plant that can be easily genetically engineered to change the composition of the oil, so in the next few years, rapeseed could become an alternative and less expensive source of oil containing ricinoleic, petroselinic, stearic and lauric acids and jojoba wax, raw materials for plasticizers, pharmaceuticals, printing inks, cosmetics, detergents, lubricants and polymers (Murphy, 1993). The seed-bearing pods of this indeterminate plant be- come fragile and easily split open as the seed reaches maturity, making plants with mature pods very suscep- tible to seed loss as a result of bad weather. As harvesting must be done at seed maturity for maximum oil content, seed loss is also caused by disturbance of the plants 1537-5110/02/$35.00/0281? 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. All rights reserved Fig. 1. Schematic of conveyor-assisted header: (a), reel; (b), auger; (c), conveyor; (d) cutterbar during harvesting operations (Ogilvy et al., 1992; Price et al., 1996). In ideal conditions, seed loss can be as low as 25% of yield, but a loss of 2025% has been recorded in weather conditions that were normal (Price et al., 1996) and loss can be as high as 50% in extreme cases (Mac- Leod, 1981). In autumn-sown varieties of oilseed rape, the extra plant height and longer period of seed ripening make harvesting generally more di$cult than with a spring sown crop. Price et al. (1996) found that, in a single crop of winter oilseed rape harvested at the optimum time, 11% of the seed was lost compared with lessthan 3% in a spring-sowncrop, thoughthe harvested yield of the winter rape, 2)76 tha?, still exceeded that of the spring rape, 2)57 tha?. There are two methods of harvest in common use. In the UK, about half of the crop is direct cut, i.e. the standing plants are cut by combine in a single harvest operation, usually after chemical desiccation, although some of the crop is direct cut after a period of natural ripening typically several weeks longer than when desic- cation,is used. This avoids the cost of desiccation and the disturbance to the crop caused by vehicles but leaves the crop vulnerable to damage, particularly by wind or hail. The alternative to direct cutting is a two-stage harvest, involving swathing of the crop at an early stage of ripen- ing. According to Ogilvy (1989), swathing should take place when the seed colour in the bottom pods is dark brown, middle pods redbrown with some green and the top pods green and just turning brown, and the swath will be ready for harvesting after a ripening and drying period of 714 days. As seed loss tends to be higher during direct cutting of oilseed rape than in the swathing method, several devices have been promoted which are claimed to reduce seed loss. One of these is a header that includes a conveyor between the cutterbar and auger (Fig. 1). This device assists the #ow of crop away from the cutterbar; so cut plants are not crushed by the auger until they are su$- ciently far behind the cutterbar for shed seed to be more likely to fall on to the bed of the header, rather than be lost. Also, there is likely to be less need to use the reel to pull the crop onto the header in which case disturbance to the top of uncut plants would be reduced. No reports of the performance of this type of device were found in the literature, so an experiment was carried out to quantify the loss from this type of header in autumn- sown oilseed rape and compare it with the loss from a standard header. Other approaches, not tested here, include reducing the auger speed and the use of an extended (static) table, i.e. a section is inserted into the bed of the header to move the cutterbar fartherin front of the auger. 2. Materials and methods 2.1. Harvesting equipment Each of the two types of header was available on only one make of combine harvester, a conveyor-assisted(CA) header of 6)1 m width was tted to combine harvester A and a standard header 3)6 m wide tted to combine harvester B. The standard header was typical of devices in common use. Both headers had side knives; the standard header had an electrically operated side knife tted retrospectively, whilst the CA header had mechan- ically driven side knives tted as original equipment. The main components of the CA header, shown in Fig. 1, are; (a), reel; (b), auger; (c), auger; (d), conveyor; (e), cutterbar. 2.2. Experimental layout The work was carried out on a commercial farm in Bedfordshire, UK, in a crop of winter oilseed rape, cul- tivar Capricorn. The crop was desiccated on 21 July 1994 using Reglone applied with Dessicoat, and direct com- bine harvested on 6 August. There was a period of rela- tively good weather between desiccation and harvest, when the crop was most vulnerable to shedding, although there was a period of heavy rain 4 days prior to harvest. Seed loss caused by the operation to apply desiccant was not measured, but loss from the desiccated crop was measured. A uniform area of crop was chosen R. N. HOBSON; D. M. BRUCE282 Fig. 2. Trayfor catching seed640 mmlong by 66 mm wide witha *V+ section, made ofsheet aluminium;the tray was inserted between, and held upright by, the rape stems for the experiment and its edges squared up by cutting. Working to a cut edge, a series of parallel runs was made through the crop. Alternate runs were made by combine harvesters A and B, each tted with its particular header. Six runs were carried out by each machine. As counting seeds on, or collecting seeds from, the soil surface is unreliable and very time consuming, a tech- nique developed at Silsoe Research Institute (Price et al., 1996) was used. This technique employed trays placed in the standing crop to catch samples of seed falling from the crop itself and from the combine harvester. Trays (Fig. 2) with a narrow D. M. BRUCE284 0 20 40 60 80 100 120 140 160 SheddingConveyor assistedStandard Seed loss, kg ha _1 Fig. 3. Measured seed loss shed from standing crop, and caused by three elements of two headers; losses are not adjusted for header width; six replicate observations were made; bars, $1 standard error of the mean;, shedding losses;, side knife losses;, cutterbar losses;, centre losses;, total losses loss from the CA header is likely to be a result of (a) increased distance of the cutterbar from the auger, which allows more loose seed to be collected rather than falling on the ground, (b) more e!ective transport of crop into the auger by the conveyor, allowing room for the next crop to be harvested and, (c) less need for the reel to be used to pull the cut crop onto the header, because the crop is actively fed into the auger, thereby reducing the damage from contact with the reel. While the crop harvested here was relatively short, it was well suited to direct cutting. The di!erence in cutterbar losses may be expected to increase in taller, more tangled crops, which the CA header would be able to harvest with less need for contact with the reel. Although the measured seed loss from the centre sec- tion of the CA header was lower than that from the standard one, the di!erence was not great enough to be signicant (P0)26). The ratio of header width to width of centre opening was very similar for the two headers so the nominal degree of crushing of the cut crop arriving at the centre was similar for each. Increasing the distance of the cutterbar from the auger would be expected to reduce seed loss from the centre section, but the present results do not demonstrate this. For the CA header, the centre loss was 21% higher than the cutterbar loss, which sug- gests that further study of the machine/crop interaction in the centre region would be benecial. Excluding shedding and side knife losses, the CA header lost 58)9 kgha? compared with 103)9 kgha? for the standard header, a saving of 45 kgha?. Further work is needed (a) to elucidate how the con- veyor-assisted header achieves lower seed loss so that its action could be further improved; (b) to compare the performance of the conveyor-assisted device with that of the simpler device of an extended table and to investigate whether slower auger speeds reduce seed loss; (c) to study the causes of centre loss; (d) to evaluate header perfor- mance in a range of oilseed rape crops, because crops vary widely in susceptibility to losses depending on stage and evenness of ripeness, canopy structure, cultivar and weather preceding harvest; and (e) to investigate and quantify the benets from using a CA in the mainstream cereal crops and other alternative crops. 4. Economic evaluation Although the crop used for the experiment was parti- cularly suitable for direct cutting, in that the overall loss was low compared with previously measured losses, use of a header with the CA design rather than the standard design of header saved 45 kgha? of seed, worth C5)85 ha? to the producer at a market price of seed of C130 t? (March 2001). The di!erence in list price for a CA header of width 6)10 m compared with a standard header of the same width from the same manufacturer is C5680,or around C5000 after discount.Assuming that the extra cost of the header is depreciated over 5 years and that the savings found in this crop were consistently achieved, then the header would have to harvest 171 ha y?of oilseed rape to justify the increased purchaseprice. The payback would be improved by any saving in loss on other combinable crops, or reduction in spraying costs as a result of fewer volunteer rape plants in subsequent crops. 5. Conclusions The 6)1 m wide conveyor-assisted (CA) header produ- ced signicantly lower loss than the 3)6 m wide standard header; total header loss from the CA header of 88)3 kgha?(4)0%ofharvestedseedyieldof 2200 kgha?) was 59% of that from the standard header at 149)5 kgha? (6)8%). Eliminating side knife loss (which was the same for each side knife and only di!ered between headers because the headers were of di!erent widths) and pre-harvest shedding loss, the loss from the CA header was 59 kgha?, 57% of the 104 kgha? from the standard header. Cutterbar loss was reduced from 58 kgha? for the standard to 27 kgha? for the CA header. Centre loss was not signicantly a!ected. Shed- ding loss at 11 kgha?, 0)5% of the harvested yield was small in comparison to the overall loss caused by har- vesting. The highest component of the loss from the CA header was the centre loss. Assuming that a 6)1 m CA header was operated in oilseed rape alone, it would need 285SEED LOSS OF OILSEED RAPE to harvest more than 171 hayr? over 5 years to recoup its extra initial cost, compared with a standard header of the same width. Further work is needed to understand precisely how losses occur in order to improve the design and cost/performance ratio of headers. References Coghlan A (1997). A perfect recipe for the North Sea. New Scientist, 19 April Cooksley J (1993). Correct oil selection will become ever more vital. Arable Farming, December 3134 GrimshawP (1994).Investmentboost for bio-fuel.Crops, 12(11) MacLeod J (1981). Oilseed Rape Book. A manual for Growers, Farmers and Advisors. Cambridge Agricultural Publishing, Cambridge, pp 107119 McDonnell K P; Ward S M; Timoney D J (1995). Hot water degummed rapeseed oil as a fuel for diesel engines. Journal of Agricultural Engineering Research, 60, 714 Murph