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生物工程（2002）81期（3），281-86页。doi:10.1006/bioe.2001.0011，在 网站上的机械和能量这块可以在线阅读。用两种不同类型机头的联合收割机收割油菜时的种子损失霍布森和布鲁斯先生著Silsoe研究所材料组，英格兰MK45.beds，silsoe，瑞斯特公园；作者的电子邮箱：norris.hobsonbbsrc.ac.uk。（2000年7月8日完成，经过修改后2001年10月9 正式发行）油菜是一种有潜力扩大的经济作物。然后，随着油菜的成熟，有一部分油菜籽会在收割之前从裂开的豆荚上脱落，也有一部分是在收割时由于机器的碰撞而脱落，因此每公顷损失600公斤（相当于产量记录的百分之二十五）并不少见。这直接对用户增加了价格，也减少了油的纯度，这是因为在随后的自播油菜中可能含有不同的油脂肪酸，掉下去的油菜籽长出来也可能会成为随后庄稼的杂草。为了加以量化地证明安装在联合收割机的两种不同的收割头造成的种子损失的原因而进行了一个实验，结果表明一个标准的切割头和一个在切割器后面有运输机的切割头能协助作物流入螺旋内。在收割之前通过在成熟的作物下面放一个托盘来测量损失的油菜籽，在天气情况相对稳定时每公顷损失11公斤的油菜籽还属于比较少的，但在收割时两种不同类型的收割机头之间却存在着很大的差别。虽然每边的刀片造成的损失是一样的，但是由于头部宽度不一样，标准的切割头和带有运输机的切割头造成的损失分别是34.6/公顷和18.4/公顷，这表明了在减少损失时用宽的切割头的优势。包括自然脱落和由于刀片碰撞造成的脱落在内，带有运输机的切割头造成的油菜籽损失是59kg/公顷而标准切割头造成的损失是104kg/公顷。仅仅由带有运输机的切割头切割器造成的损失是27kg/公顷，比标准切割头切割器造成的损失的一半还要少，这表明了将切割器的前段定位和辅助运输机结合在一起的好处。在2001年，带有运输机的切割头如果被用在收割中，每年收割171公顷油菜就能在五年内恢复其潜在的购买价格。1.介绍油菜（甘蓝型油菜）一个重要的临时真正打破组合的作物，它的油主要是用在食品生产当中（植物研究所，1992），在工业应用中也一直在用。种植的高芥子酸油菜是用来做工业润滑油的（Cooksley ， 1993年），油菜籽可以转化为生物柴油（油菜甲酯）（麦克唐奈等，1995年）和形成水下钻探用的可降解生物润滑油（科格伦，1997年）。许多国家，尤其是法国和澳大利亚，正在推行生物柴油，主要是因为它是一种可再生资源，还因为它的排放量比标准的柴油要少，因此在城市中心和环境敏感地区如诺福克湖区和英格兰使用它是最好的（格里姆肖， 1994年）。油菜是一种很容易通过基因工程来改变其油的组成成分的植物，因此在接下来的几年中，油菜籽可能成为一种替代物和一种含有蓖麻油、岩芹酸、硬脂酸、月桂酸氨基酸、荷荷芭蜡、可塑剂的原材料、医药品、印刷油墨、化妆品、清洁剂、润滑剂和聚合物的廉价资源（墨菲， 1993年）。从不成熟的植物的豆荚中掉下来的油菜籽变得易碎，当其成熟后也很容易裂开，在天气不好的情况下成熟植物的豆荚也很容易裂开导致损失油菜籽。当大部分油菜籽都成熟必须收割的时候，由于收割机器的碰撞也会导致种子的损失（奥格尔维等，1992年；皮李斯特等，1996年）。在理想的情况下，最低的油菜籽损失可以使产量的百分之二到百分之五，但是根据记录在正常的天气情况下损失率是百分之二十到百分之二十五（普艾斯等，1996年），在极端的情况下，损失率可高达百分之五十（麦克劳德，1981年）。在秋季播种的多种油菜品种中，由于额外的株高和较长的成熟种子使得收割起来比春天播种的油菜要难得多。普艾斯等（1996）发现在冬季油菜单一作物的最佳收获时间时，油菜籽损失率是百分之十一，比春播作物少百分之三，虽然冬季油菜的产量是2.76吨/公顷，但仍然超过了春季油菜的2.57吨/公顷。有两种常用的收获方法，在英国大约有一半的作物是直接收割，没收割的作物被一个联合收割机收割，然后经过化学脱水，虽然有些作物在经过一段时间成熟以后直接收割，但通常比脱水的时间要长几个星期，这可以避免干燥的费用和交通工具对作物造成的损失，但却让剩下的作物更容易受到尤其是风和冰雹的袭击。另一种收割方法是分为两步，包括在成熟的早期阶段包扎作物。根据奥格尔维（1989年）的观点，包扎作物应该在豆荚底部的油菜籽颜色呈棕黑色，中间的油菜籽呈红色并伴有一些绿色，上面的油菜籽呈绿色并且刚刚变成棕色的时候进行，收割以及干燥需要7到14天的时间，因此要为此做好准备。由于在直接收割油菜中油菜籽的损失要比采用包扎的方法收割大得多，因此许多声称要减少油菜籽损失的设备正在被推行。其中一个就是在收割机机头的切割器和螺丝钻之间含有一个运输机（图1）。这个设备可以让作物远离切割器，只要作物离切割器足够远就可以避免油菜籽在收割时被螺丝转压碎，因此掉落的油菜籽也很可能调入切割头的槽中而不是丢失了。此外用卷轴来将作物推到切割头上去以减少没有被收割到的作物也不太可能用到。在文献中还没有发现有关于这种设备的报道，因此就做了一个实验来量化地证明在收购秋季播种的油菜时的损失，并与用标准切割机进行切割时的损失作对比。其它方法，不是在此测试，包括减少螺旋速度和使用延长（静态）表，即在切割机头的槽中插入一个截面用来在螺丝转之前推动切割器，使其移动得更远一点。带有辅助运输机的机头示意图：（a）卷轴，（b）螺丝转，（c）运输机，（d）切割器2材料和方法： 2.1收割设备：这两种类型的收割机头只有在联合收割机中才可以用，带有辅助运输机（CA）的宽度为6.1米的机头很适合用在联合收割机A中，宽度为3.6的机头很适合用在联合收割机B中。标准机头在常用的设备很典型、常见。两种机头都有刀片，标准机头在两边安装了合适的电动刀片，而CA机头在两边安装了机械驱动刀片作为原始设备。CA机头的主要构成如图1所示，分别是：（a）卷轴，（b）螺丝转，（c）运输机，（d）切割器。2.2实验规划： 这项实验是在英国贝德福德郡的一个培育冬季油菜的商业农场里进行的。在1994年7月21日用敌草快对作物进行脱水，然后在8月6日用联合收割机直接收割。在脱水和收割之间要有一段时间的相对较好的天气，当作物的种子最容易脱落的时候，虽然在收割之前有4天的大雨。使用干燥机后由于机器碰撞造成的种子损失没有被测量，但脱水作物的损失能被测量。一个同一作物的地方被选定为试验场地，其边缘被弄成正方形，根据切割边缘展开工作，按照作物进行一系列的并行处理。联合收割机A和B交替运行，每一种都和它独特的机头相搭配。每个收割机处理了六行。随着统计种子的增加，或者采用了研究所（普艾斯等，1996年）发明的技术而收集到的种子，土壤表面是不可靠的而且也非常耗时。这种技术受雇于放在未收割的作物下面的用来收集从作物和联合收割机上掉下的种子的托盘。用超薄铝片材料制成的带有狭窄V型切面的托盘（图2）能足够苗条地插入相邻油菜茎和所有种子都能掉进托盘里的相对有限的空间里，因为两边都比较陡峭。每个托盘长640毫米，宽66毫米，还带有一个两边由40度角形成的倾斜坡度。 图2：接收种子的托盘-长640毫米，宽66毫米，带有一个“V”型侧面，由超薄铝片材料制成，托盘用来插在直立的油菜之间。托盘被放在4-8组，每个托盘都相互平行而且和机器工作的方向也平行，在每个托盘和离工作的机器尾部大概1米之间由一个约100毫米的缺口。在每次试验中机器通过卷轴与庄稼之间的最小磨合这样正常的方式来收割庄稼。在机头而不是切割机剩下的部分已经通过托盘完成庄稼的收割，联合收割机将停止工作，以防止种子从联合收割机后面调入托盘中，也防止轮胎压碎托盘。一旦联合收割机撤回之后，托盘将被取出，托盘里面的油菜籽会被收集起来，然后会被脱干水分，让种子的水分含量大概为百分之八的基本湿度，最后油菜籽会被过滤器按重量分开。2.3站立着的植物的脱落损失：成熟植物的脱落损失发生在收割之前，当豆荚成熟之后就变得非常脆弱，任何扰乱都会引起油菜籽的脱落，这种损失假定是均匀分布的。在开始收割的前一周，托盘会被放置在油菜下面已经选好的适合做实验的地方，在放置的时候要小心不要碰到油菜，在放置托盘前没有明显的会脱落的豆荚和菜籽。在收割前夕移走托盘，托盘里面的菜籽将留着供以后分析。2.4切割机机头造成的损失：选择三个不同的地方来收集菜籽是因为它们代表在作物和机头零部件之间的亲密接触中不同根源造成的菜籽损失。2.4.1两边的刀片造成的损失：油菜作物通常有许多分支而且还纠缠在一起，就这需要在收割的时候将在机头两边的庄稼割掉而不是将其分开，用于谷物加工，否则将会撕裂作物和增加损失。两边的刀片，实际上是垂直在每个机头末尾前面的切割器，切割直立的庄稼。由于切割时力量很大，有些菜籽脱落了，一部分或者整个豆荚都没切割了，菜籽和豆荚掉到地上狭窄的地带中，因此两边刀片造成的损失是集中的而且是掉在跟切割机机头宽度相等的间距里。以前的实验（普艾斯，1996年）已经指出刀片造成的损失可以假设为均匀分布在刀片中心底下300毫米宽的地方，虽然损失的菜籽集中在在侧面的刀片下面的中心处，被放在刀片外面的托盘接住，因此托盘不会落掉任何因为切割器而造成的损失。因为只有一半的菜籽会被作为试验样本，所以在计算损失时必须进行调整。除此之外，由于两种切割机机头的宽度不一样，所以会用适当的乘数来表示在试验田的平均损失。可导致托盘里绝大多数菜籽转变的对实验田来说可能意味着损失的可预知的转变因素将会在附录A中解释。2.4.2由切割器造成的损失：尽管切割器造成的损失表明该损失是由于切割器的往复运动造成的，在收割油菜的时候茎肯定会颤动，联合收割机的卷轴和豆荚接触时也会造成油菜籽的损失，而且在切割器后面的螺丝钻也会将纠缠在一起的庄稼分开。假设掉在切割器前面的地上的油菜籽均匀分布在它的宽度范围内。2.4.3中心损失：在机头中心来自两边末尾的沉重的植物会导致一会菜籽脱落，有的掉到切割器前面好远，这一损失称为中心损失。中心损失会加到超过切割器中心空地而造成的损失上去，并因此可以减去后者。根据以往对分布的测量（普艾斯，1996年），中心损失是在超过收割机中心空地的宽度的范围外取样的，并表示这是试验田的平均损失，乘以机头的中心宽度系数（附录A）。在这两种机头中使用的机头宽度和中心空地宽度飞比率非常相似，CA机头和标准机头分别的比率为3.7：1和3.8：1。3结果：试验田总的收获产量是2.2吨/公顷，与收获的产量相比，脱落的油菜籽是11.0kg/公顷（相当于总产量的0.5%），由于收割前天气比较稳定，因此在这种特殊的作物里相对来说还不是很严重。在比较机器中切割器和侧面刀片造成的损失时，选取了托盘中大量的菜籽进行数据分析，从而避免了由于机头宽度等造成的任何因素的影响。为了获得中心损失的数据，要减去切割器造成的损失，但用来测量中心损失的托盘的数目跟用来测量切割器造成的损失的托盘数目并不一样，在这种情况下，数据是在对平均托盘的分析上得出来的。表一显示了数据和分析结构的差异性，图3显示了用附录A中详细的可预知的因素而计算出来的每公顷损失的千克数。表格一：损失油菜籽的数据分析带有辅助运输机机头造成的损失标准机头造成的损失相差的损失标准误差的差别可能性侧面刀刀（g；kg/公顷）6.3318.47.0134.60.681.370.631切割器（g；kg/公顷）0.9026.61.941.941.040.3340.011中心（g/托盘；kg/公倾）0.53432.30.74346.40.2090.1750.175图三：（kg/公顷） 脱落 带有辅助运输机 标准图三：测量由自然脱落的、两种机头的三个要素造成以及不符合机头宽度而造成的种子损失，对六种情况进行了观察：彩条，+/-1，标准误差均值； 自然脱落；侧面刀片造成的损失； 切割器造成的损失；中心损失； 总的损失。把包括自然脱落在内的所有损失加在一起，CA机头的总损失是88.3kg/公顷，标准机头的总损失则是149.5kg/公顷。然后这些数据并不是在对机头的公平比较基础上得出来的，因为刀片造成的损失原则上与机头的切割宽度是下个户独立的。通过表格一中在刀片下面的四个托盘中大量收集的种子分析，从而验证了这一说法。CA机头造成的损失是6.33g而标准机头造成的损失是7.01g，差别还不是很大（概率为0.631）。在试验田的实验结果中，CA机头和标准机头的刀片造成的损失分别为18.4kg/公顷和34.6kg/公顷。这就突出了在收割油菜时用宽一点的切割机头的好处了。CA机头中切割器造成的损失（p=0.011）比标准机头造成的损失要小得多，见表格1。带有运输机的切割头将切割器造成的损失减少到标准机头的切割器造成的损失46%。CA机头之所以能够减少的损失，很可能是由于增加了切割器和螺丝钻之间的距离的结果（a），因为这样就使得许多脱落的种子被收集起来了而不是掉到地上。（b）通过运输机可以更有效地将作物输送到螺丝钻中，给即将要收割的作物腾出空间，（c）这样就不再需要用卷轴将割下的作物运送到机头上去，因为作物被卷进螺旋钻中，因而减少与卷筒的接触所造成的损失。因为这里的作物收割时间相对较短，所以非常适合直接切割。各种切割器造成的损失的差异可能要比预期的要大，纠缠在一起的作物也更多，而CA机头却能够在收割中减少与卷轴的接触。虽然在CA机头下面的中心部分中测量到的种子损失要低于比标准机头，但是其中的差别还不够大，不足以显示其重要性（p=0.26）。两种机头的机头宽度与空心空地宽度的比率比较相似，因此到达空心空地的支离破碎的作物的数量也差不多。增加切割器与螺丝钻之间的距离可能会减少中心损失，但是目前的结果还不足以证明。对CA机头来说，中心损失比切割器造成的损失要高21%，表明进一步研究机器和作物在中心地区的互动会有好处的。除自然脱落和刀片造成的损失外，CA机头造成的损失是58.9kg/公顷，标准机头造成的损失是103.9kg/公顷，每公顷节省了45kg。需要（a）进一步的研究来阐明带有辅助运输机的机头是如何达到减少种子损失的，以便对其进行更好的改造；（b）将带有辅助运输机的设备的性能和带有一个扩充表格的简单设备的性能进行比较，对螺丝钻的转速慢一点时能否减少种子损失研究；（c）找到造成中央损失的原因；（d）在油菜作物的一定范围内对机头的性能进行评估，因为在一大片范围内研究造成的损失需要不同的阶段和均匀度的成熟、冠层结构、以及收割之前的天气情况；调查和在收割谷物类作物和其他作物时使用CA时的量化好处。4经济性评估：虽然在在试验中用到的作物尤其适合直接收割，但是总的损失比之前衡量的要低，用带有CA设计的机头比标准设计的机头每公顷要节约45kg菜籽，对生产者而言每公顷价值5.85英镑，市场价格则是每吨130英镑（2001年3月）。宽度为6.10的CA机头和同一个制造商生产的相同宽度的标准机头相比价格却不一样，5680英镑或者打完折之后5000英镑左右。假设机头的额外价格贬值超过5年，在这种作物中节省的储蓄也完全实现，那么这种机头得收割171公顷的油菜才能证明其额外增加的购买价格。投资回报率将在收割机收割其他作物时节省了损失，或者在收购油菜之后由于长出来的自播植物较少而减少了喷洒费用时才能得到提高。5结论：61米宽的带有辅助运输机的机头比3.6米宽的标准机头节省的损失要少得多，CA机头造成的全部损失是每公顷88.3kg（相当于每公顷收获2200kg时的4.0%），是标准机头造成的损失每公顷149.5kg的59%（相当于每公顷收获2200kg时的6.8%）。消除刀片造成的损失（每边刀片造成的损失是一样，只是在各种机头宽度不同时才不一样）和收割前的自动脱落损失，CA机头的造成的损失为每公顷59kg，是准机头造成的损失104kg/公顷的57%。标准机头和CA机头的切割器造成的损失分别减少到58kg/公顷、27kg/公顷，中心损失受到的影响不是很大。自动脱离的损失是每公顷11kg，和在收割过程造成的损失相比，这0.5%的损失还算比较小。CA机头造成的损失中最高的部分是中心损失，假设6.1米宽的CA机头在油菜地中单独收割，和一个同样宽度的标准收割机相比它将需要每年收割超过171公顷，连续工作5年才能收回刚开始的额外成本。因此需要进行 更进一步的工作去准确地了解损失是如何发生的，以便于提高设计水平和机器的成本/效能比率。 参考文献：Coghlan A（1997年），海的完美食谱，科学家，1997年4月。Cooksley J（1993年），确选择石油至关重要，可开垦农场，12期31-34页。Grimshaw P （1994年），投资推动生物燃料，作物12期11页MacLeod J （1981年），油菜图书，种植者手册，农民和顾问。剑桥农业出版社，剑桥第107-119。McDonnell K P; Ward S M; Timoney D J (1995年)，热水脱胶菜籽油作为燃料的柴油发动机，农业工程研究所杂志，60期，7-14页。Murphy D (1993年)，油菜作物产业的设计者，农艺师，2期，6-8页。NIAB (1992年)，油菜品种多样性，第九号农民传单，NIAB，剑桥。Ogilvy S E (1989年)，时间对冬季油菜包扎质量的影响， 生物工程和保护油菜和其他芸苔科植物方面的应用，vol.23，101-107页。Ogilvy S E; Milford G F J; Evans E J; Freer J B S (1992年)，收割前对油菜处理后对其产量和质量的影响，HGCA油菜研究所，OS7。Price J S; Neale M A; Hobson R N; Bruce D M (1996)，商业收割中油菜损失的种子，农业工程研究所期刊，65期，183-191页。附录A：从每个托盘中收集到的种子计算每公顷损失的种子数托盘面积=0.0422平方米，所以在大多数情况下，kg/公顷=236.7g，g是指每个托盘中收集的种子的重量。四种具体损失的计算方法：1. 自动脱落造成的损失时kg/公顷=236.7g，g是指自然脱落时每个以g为单位的托盘中的平均重量。2. 侧面刀片造成的损失时kg/公顷=236.7300g/h，g是指刀片造成的损失时每个以g为单位的托盘中的平均重量，h是指机头宽度的毫米长度，CA切割机是6100毫米，标准切割机是3600毫米，丢失的种子在以300毫米为半径的范围内。3. 切割器造成的损失时kg/公顷=236.7g，g是指由于切割器造成的掉在以g为单位的托盘中的种子的平均重量。4. 中心损失时kg/公顷=236)7(g1-g2)h1/h2，g1是指中心损失时掉在以g为单位的托盘里的种子重量，h1是谷仓的宽度的毫米长度，CA机头切割机是1560毫米，标准机头切割机是950毫米。Biosystems Engineering (2002) 81(3), 281286doi:10.1006/bioe.2001.0011, available online at onPM*Power and MachinerySeed Loss when Cutting a Standing Crop of Oilseed Rape with Two Types ofCombine Harvester HeaderR. N. Hobson; D. M. BruceBiomaterials 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 lossoccurs by dehiscence of the seed from the pods prior to harvest and also as a result of crop disturbance bymachinery during harvest. Seed loss of 600 kgha?, 25% of the recorded yield, is not uncommon. This directlyincreases the price for industrial users and can also reduce oil purity because volunteer plants in subsequentoilseed rape crops may have a di!erent oil fatty acid prole. Oilseed rape plants also persist as weeds insubsequent crops. An experiment was carried out to identify the cause of, and quantify contributions to, seedloss from two di!erent designs of header tted to the combine harvester; a standard header and a header witha conveyor tted behind the cutterbar, claimed to assist crop #ow into the auger. Seed loss was measured usingtraysplaced in the ripening crop prior toharvest. Seedshed before harvest, 11 kgha?, was low as a result of therelatively settled weather conditions. There was a signicant di!erence between losses from the two types ofheader. The loss from each side knife was the same, but because of the di!ering header widths, translated intolosses of 18)4 and 34)6 kgha? for the conveyor-assisted and standard headers, respectively, showing theadvantage of using a wider header in reducing this loss. Excluding shedding loss and side knife losses, seed lossfrom the conveyor-assisted header was 59 kgh? against 104 kgh? with the standard header. Loss causedonly by the cutterbar of the conveyor-assisted header, 27 kgha?, was less than half that of the standard headercutterbar, 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 yearsif used to harvest 171 ha of oilseed rape per year.? 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. Allrights reserved1. IntroductionOilseed rape (Brassica napus) is an important non-cereal, combinable break crop, the oil from which is usedmainly for food production (NIAB, 1992). Industrial ap-plications have also been developed for the oil; higherucic acid rape is grown for industrial lubricants (Cook-sley, 1993), rapeseed oil is convertible to bio-diesel (rapemethylester) (McDonnellet al., 1995) and forms the basisof a bio-degradable lubricant for underwater drilling(Coghlan, 1997). Several countries, in particular Franceand Austria, are actively promoting bio-diesel mainly asit is a renewable resource and also because it is seen asdelivering benets of lower emissions over standard die-sel, and therefore, nds favour in city centres and inenvironmentally sensitive areas such as the NorfolkBroads, England (Grimshaw, 1994). Oilseed rape isa plant that can be easily genetically engineered tochange the composition of the oil, so in the next fewyears, rapeseed could become an alternative and lessexpensive source of oil containing ricinoleic, petroselinic,stearic and lauric acids and jojoba wax, raw materials forplasticizers, 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 reachesmaturity, making plants with mature pods very suscep-tible to seed loss as a result of bad weather. As harvestingmust be done at seed maturity for maximum oil content,seed loss is also caused by disturbance of the plants1537-5110/02/$35.00/0281? 2002 Silsoe Research Institute. Published byElsevier Science Ltd. All rights reservedFig. 1. Schematic of conveyor-assisted header: (a), reel; (b),auger; (c), conveyor; (d) cutterbarduring harvesting operations (Ogilvy et al., 1992; Priceet al., 1996). In ideal conditions, seed loss can be as low as25% of yield, but a loss of 2025% has been recorded inweather conditions that were normal (Price et al., 1996)and loss can be as high as 50% in extreme cases (Mac-Leod, 1981). In autumn-sown varieties of oilseed rape,the extra plant height and longer period of seed ripeningmake harvesting generally more di$cult than witha spring sown crop. Price et al. (1996) found that, ina single crop of winter oilseed rape harvested at theoptimum time, 11% of the seed was lost compared withlessthan 3% in a spring-sowncrop, thoughthe harvestedyield of the winter rape, 2)76 tha?, still exceeded that ofthe spring rape, 2)57 tha?.There are two methods of harvest in common use. Inthe UK, about half of the crop is direct cut, i.e. thestanding plants are cut by combine in a single harvestoperation, usually after chemical desiccation, althoughsome of the crop is direct cut after a period of naturalripening typically several weeks longer than when desic-cation,is used. This avoids the cost of desiccation and thedisturbance to the crop caused by vehicles but leaves thecrop 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 takeplace when the seed colour in the bottom pods is darkbrown, middle pods redbrown with some green and thetop pods green and just turning brown, and the swathwill be ready for harvesting after a ripening and dryingperiod of 714 days.As seed loss tends to be higher during direct cutting ofoilseed rape than in the swathing method, several deviceshave been promoted which are claimed to reduce seedloss. One of these is a header that includes a conveyorbetween the cutterbar and auger (Fig. 1). This deviceassists the #ow of crop away from the cutterbar; so cutplants are not crushed by the auger until they are su$-ciently far behind the cutterbar for shed seed to be morelikely to fall on to the bed of the header, rather than belost. Also, there is likely to be less need to use the reel topull the crop onto the header in which case disturbanceto the top of uncut plants would be reduced. No reportsof the performance of this type of device were foundin the literature, so an experiment was carried out toquantify the loss from this type of header in autumn-sown oilseed rape and compare it with the loss froma standard header. Other approaches, not tested here,include reducing the auger speed and the use of anextended (static) table, i.e. a section is inserted into thebed of the header to move the cutterbar fartherin front ofthe auger.2. Materials and methods2.1. Harvesting equipmentEach of the two types of header was available on onlyone make of combine harvester, a conveyor-assisted(CA)header of 6)1 m width was tted to combine harvesterA and a standard header 3)6 m wide tted to combineharvester B. The standard header was typical of devicesin common use. Both headers had side knives; thestandard header had an electrically operated side knifetted 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 layoutThe work was carried out on a commercial farm inBedfordshire, UK, in a crop of winter oilseed rape, cul-tivar Capricorn. The crop was desiccated on 21 July 1994using 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 toharvest. Seed loss caused by the operation to applydesiccant was not measured, but loss from the desiccatedcrop was measured. A uniform area of crop was chosenR. N. HOBSON; D. M. BRUCE282Fig. 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 stemsfor the experiment and its edges squared up by cutting.Working to a cut edge, a series of parallel runs wasmade through the crop. Alternate runs were madeby combine harvesters A and B, each tted with itsparticular header. Six runs were carried out by eachmachine.As counting seeds on, or collecting seeds from, the soilsurface is unreliable and very time consuming, a tech-nique developed at Silsoe Research Institute (Priceet al., 1996) was used. This technique employed traysplaced in the standing crop to catch samples of seedfalling from the crop itself and from the combineharvester. Trays (Fig. 2) with a narrow &V sectionmadeof sheet aluminium were slim enough to be insertedinto the limited space available between adjacent rapestems and, because of their steep sides, retained anyseed falling into them. Each tray was 640 mm long by66 mm wide with an included angle between the slopingsides of 403.The trays were placed in groups of 48, arrangedparallel to each other and to the direction of travel ofthe machine, with a gap of about 100mm between eachand approximately 1m into the crop from the endtowards which the machine was working. During eachrun, the machines harvested the crop in the normalmanner with gentle engagement of the reel with thecrop canopy. After the header but not the rest ofthe combine harvester had passed over the trays andnished cutting the crop strip, the combine harvesterwas halted to avoid the e%ux from the rear of thecombine harvester falling into the trays, and alsoto prevent its tyres crushing the trays. Once the combineharvester had withdrawn, the trays were extracted andtheir contents bagged for later drying so that the moist-ure content of the seed was approximately 8% wetbasis moisture, after which the seed was separated bysieving, and weighed.2.3. Shedding loss from the standing cropShedding loss occurs in the ripening crop prior toharvest, caused by any disturbance to the fragile pods asthey become ripe. This loss was assumed to be evenlydistributed.A week before harvest was due to commence, trayswere placed in the standing crop in the areas which hadbeen chosen as a suitable site for the harvest trials, takingcare not to disturb the crop. There had been no notice-able splitting of pods or shedding of seed prior to theinsertion of the trays. Immediately prior to harvest, thesetrays were removed from the crop and their contentscollected for later analysis.2.4. Header lossesThree positions for loss collection were chosen becausethey represented distinct sources of seed loss caused byan active contact between the crop and the componentsof the header.2.4.1. Side knife lossCrops of oilseed rape are usually highly branched andentangled. This makes it necessary during harvesting, todivide the crop at the side of the header by cutting ratherthan by a crop divider, used for cereals, that would tearthe crop and increase the loss. Side knives, in e!ectverticalcutterbars locatedat the front edge of each end ofthe header, cut through the standing crop. Owing to theirnecessarilyvigorous cutting action, someseed is shedandwhole pods and pieces of the pods are cut o!. The seedand pods fall onto the ground in a narrow band. Sideknife loss is, therefore, a concentrated loss and occurswith a spacing equal to the cutting width of the header.Previous experiments (Price et al., 1996) have shown that283SEED LOSS OF OILSEED RAPETable 1Analysis of seed loss dataLoss fromconveyor-assistedheader*Loss fromstandardheader*Diwerence inlossStandarderror ofdiwerenceProbabilityg6)337)010)681)370)631Side knifekgha?18)434)620)4-Cutterbarg0)901)941)040)3340)011kg ha?26)657)5Centreg per tray0)5340)7430)2090)1750)260kg ha?32)346)4*Six replicates.-Side knife loss from the standard header adjusted to correspond to the width of CA header.the loss from the side knife can be assumed to be uni-formly spread over a 300 mm width centred beneath theside knife. Although this loss is centred beneath the sideknife, it is measured by trays placed immediately outsidethe line of the side knife so that the trays do not collectany cutterbar loss. As only half of the loss distribution issampled, adjustments have to be made in calculating theloss. In addition, as the two headers had di!erent cuttingwidths, appropriate multipliers were used to express themean loss over the experimental plot. The conversionfactors calculated to convert seed mass collected in traysto mean loss for the plot are explained in Appendix A.2.4.2. Cutterbar lossAlthough the term cutterbar loss implies that thesource of this loss is solely the reciprocating cutterbar,which necessarily vibrates the stems as they are cut, lossmay also be caused by any contact of the combine har-vesters reel with pods, and by the auger behind thecutterbar tearing apart the entangled crop. Seed fallingonto the ground in front of the cutterbar was assumed tobe evenly distributed across its width.2.4.3. Centre lossThe crushing together at the centre of the header ofplants arriving from both ends causes some seed to bereleased, some of which is lost over the front of thecutterbar. This loss, termed centre loss, is superimposedupon cutterbar loss over the width of the centre opening,and can therefore be calculated by deducting the latter.Based on the previous measurements of its distribution(Price et al., 1996), the centre loss was sampled over thewidth of the centre opening of the machine and, toexpress it as a mean plot loss, multiplied by the ratio ofwidth of centre opening to header width (Appendix A). Inthe two headers used, the ratio of header width to widthof centre opening is very similar, 3)7:1 and 3)8:1 for theCA and standard headers, respectively.3. ResultsThe harvested yield from the plot as a whole was 2)2tha?. Compared with harvested yield, shedding loss at11)0 kgha? (0)5% of harvested yield), was relativelyunimportant in this particular crop, helped by settledweather before harvest.To compare the cutterbar and the side knife lossesbetween machines, data were analysed at the level ofmass of seed collected in the trays because this avoidedthe use of any scaling factors for header width, etc. Toobtain the centre losses, the cutterbar losses had to besubtracted, but the number of trays used to measurecentre loss was not the same as the number used forcutterbar loss, so the data in this case were compared onthe basis of mass/tray. Table 1 shows the data and theresults of the analysis of variance. Figure 3 shows thelosses in kg ha? calculated using scaling detailed inAppendix A.Adding all the losses including the shedding loss to-gether, the total for the CA header was 88)3 kgha? andfor the standard header was 149)5 kgha?. However,these values are not a fair basis for comparison of theheaders because the side knife loss is, in principle, inde-pendent of the cutting width of the header. This is con-rmed by analysis in Table 1 of the mass of seed collectedin the four trays beneath each side knife, 6)33 g from theCA header and 7)01 g from the standard one, which werenot signicantly di!erent (probability, P0)631). Whenexpressed on a plot basis, side knife losses from the CAheader and standard header were 18)4 and 34)6 kgha?respectively, which highlight the benet of using a widerheader in reducing the loss from this source.The cutterbar loss from the CA header was signi-cantly less (P0)011) than the loss from the standardheader, as shown in Table 1. The conveyor-assistedheaderreduced the loss from the cutterbarto 46% of thatfrom the cutterbar of the standard header. The reducedR. N. HOBSON; D. M. BRUCE284020406080100120140160 SheddingConveyor assistedStandardSeed loss, kg ha_1Fig. 3. Measured seed loss shed from standing crop, and causedby three elements of two headers; losses are not adjusted forheader width; six replicate observations were made; bars, $1standard error of the mean;, shedding losses;, side knifelosses;, cutterbar losses;, centre losses;, total lossesloss from the CA header is likely to be a result of (a)increased distance of the cutterbar from the auger, whichallows more loose seed to be collected rather than fallingon the ground, (b) more e!ective transport of crop intothe auger by the conveyor, allowing room for the nextcrop to be harvested and, (c) less need for the reel to beused to pull the cut crop onto the header, becausethe crop is actively fed into the auger, thereby reducingthe damage from contact with the reel. While the cropharvested here was relatively short, it was well suited todirect cutting. The di!erence in cutterbar losses may beexpected to increase in taller, more tangled crops, whichthe CA header would be able to harvest with less need forcontact with the reel.Although the measured seed loss from the centre sec-tion of the CA header was lower than that from thestandard one, the di!erence was not great enough to besignicant (P0)26). The ratio of header width to widthof centre opening was very similar for the two headers sothe nominal degree of crushing of the cut crop arriving atthe centre was similar for each. Increasing the distance ofthe cutterbar from the auger would be expected to reduceseed loss from the centre section, but the present resultsdo not demonstrate this. For the CA header, the centreloss was 21% higher than the cutterbar loss, which sug-gests that further study of the machine/crop interactionin the centre region would be benecial.Excluding shedding and side knife losses, the CAheader 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 itsaction could be further improved; (b) to compare theperformance of the conveyor-assisted device with that ofthe simpler device of an extended table and to investigatewhether slower auger speeds reduce seed loss; (c) to studythe causes of centre loss; (d) to evaluate header perfor-mance in a range of oilseed rape crops, because cropsvary widely in susceptibility to losses depending on stageand evenness of ripeness, canopy structure, cultivar andweather preceding harvest; and (e) to investigate andquantify the benets from using a CA in the mainstreamcereal crops and other alternative crops.4. Economic evaluationAlthough the crop used for the experiment was parti-cularly suitable for direct cutting, in that the overall losswas low compared with previously measured losses, useof a header with the CA design rather than the standarddesign of header saved 45 kgha? of seed, worthC5)85 ha? to the producer at a market price of seed ofC130 t? (March 2001). The di!erence in list price fora CA header of width 6)10 m compared with a standardheader of the same width from the same manufacturer isC5680,or around C5000 after discount.Assuming that theextra cost of the header is depreciated over 5 years andthat the savings found in this crop were consistentlyachieved, then the header would have to harvest 171 hay?of oilseed rape to justify the increased purchaseprice.The payback would be improved by any saving in loss onother combinable crops, or reduction in spraying costs asa result of fewer volunteer rape plants in subsequentcrops.5. ConclusionsThe 6)1 m wide conveyor-assisted (CA) header produ-ced signicantly lower loss than the 3)6 m wide standardheader; total header loss from the CA header of88)3 kgha?(4)0%ofharvestedseedyieldof2200 kgha?) was 59% of that from the standard headerat 149)5 kgha? (6)8%). Eliminating sid