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The road to pure plant oil in diesel engines?

Growing and harvesting rapeseed

This chapter briefly describes the technical, economic and environment-related aspects of cultivating rapeseed. Detailed background information can be found in Appendix D.
Rapeseed farming provides a considerable contribution to the total environmental impact in the well-to-wheel (WTW) chain of PPO, with its greenhouse gas emissions, acidification and fertilised substances in the form of using fertiliser and diesel (for agricultural vehicles). At the same time, there is also considerable uncertainty of the farming-related environmental impact per unit of rapeseed. This uncertainty is mainly related to the harvest per hectare of rapeseed, but there are also other – often difficult to quantify – uncertainties. The fuel consumption of agricultural machinery often varies between fields, due to aspects such as differences in soil condition and structure. For example, if one farmer ploughs his fields just after it has rained, or another farmer ploughs in a dry period. This means that it is not possible to give more than an indication or a range of aspects such as environmental impact and costs.

The following chapter therefore contains a best-case scenario and a worst-case scenario, to indicate how the environmental impact boundaries relating to rapeseed farming can vary.
These scenarios are used throughout this report.
This chapter also looks at the reference situation: the farmer’s cultivation schedule if he/she did not cultivate rapeseed.

Technology, growth and results

Cultivation methods Rapeseed

This study assumes the cultivation of winter rapeseed. Firstly because this forms the raw material for the initiatives in Oltamt and De Peel. Secondly, because it is the most popular crop for producing PPO and most of the biodiesel in Germany and France. See also [Broek, 2003]. In other words, it seems to be the most representative crop. Winter rapeseed also produces a greater harvest of seed and oil per hectare, and the farmer can generate a higher income than with summer rapeseed.

Winter rapeseed is a crop that is typically used in crop rotation schemes in combination with grains, primarily winter wheat and winter barley. See, for example [Moens, 2003], [Brouwer, 2004]. Winter rapeseed is sown at the end of August and germinates in the autumn. The crop remains in the ground during the winter, grows further from February onwards, and is harvested around July. The grains that are grown in the same rotation are sown in the autumn or winter and harvested at the end of July or August. Rapeseed is therefore sown almost immediately after the grain harvest.

The straw, stubbles and underground crop residues that remain after the rapeseed harvesting (around July) are generally ploughed back into the soil. Straw is rarely sold, see also [Velthof, 2000] and [Jansen, 2004]. In theory it is possible to use the straw in horse stables, but this rarely happens in practice. The material has good characteristics for this application, because it is not eaten by the horses and has high moisture absorbing capacities.
However, wheat straw is generally preferred because, in contrast to rapeseed straw, it is very flexible and soft, and after use it can be sold as fertiliser to mushroom farmers.
Rapeseed straw is also more expensive than wheat straw.
Ploughing back the crop residue means that the nutrients absorbed by the crops are returned to the soil. Nitrogen is the only exception here. As the crops disintegrate , the nitrogen present in the crop residue is released as nitrate and is largely rinsed away or converted into molecular, gaseous nitrogen. Only the nitrate that is released during the growing season of the next crop is effectively used. This then contributes to a higher mineral nitrogen content in the soil, and makes it possible to limit the use of fertiliser for the next crop. Since the residue of the harvested rapeseed crop is in the ground or ploughed back into the soil from August, and wheat or barley do not germinate (and thus absorb nitrogen) until the following February, a large part of the nitrogen in the rapeseed residue is lost.

Green manure

In accordance with various studies, and the general practice in Germany, this study assumes that cultivating rapeseed is an alternative for having fallow fields. In the Netherlands fallow fields generally mean green fields, or cultivating a so-called‘green manure’. This has several uses, e.g.

• Reducing the spreading and stiffening of the soil top layer;
• Reducing the growth of weeds by covering the soil;
• Capturing mineral nitrogen in the soil after harvesting the main crop, to prevent nitrate being rinsed away during the winter and spring months;
• Maintaining the humus level in the soil.

With green fallowing the plants are sown in the spring (before 31 May) and the crop may not be harvested before 31 August. Even making hay and storage in silos (for further application as animal fodder) are not allowed until this date. The crop is either killed by spraying in the autumn and then ploughed back into the soil, or remains in the fields during the winter and is killed by spraying and ploughed back during the spring. Since this study assumes that crops are rotated with grains – that are sown in autumn or winter – ploughing back in the autumn is the only part that is relevant to this study.

The most popular green fallow crops are wild radish, yellow mustard and Italian hempnettle grass. There are few real differences between these crops as far as harvesting and nitrogen absorption are concerned. Due to the subsidy deadline set for sowing green fallow, this study assumes that wild radish is used, which can be sown in May. Italian hemp-nettle grass and yellow mustard need to be sown later in the year.

Crop area and results

The rapeseed yield in the Netherlands over the past few years has totalled around 3.5 ton/ha per ± 0.5 ton/ha of fresh seed. This was limited to several hundreds of thousand hectare, primarily located in Groningen (Oltamt). France and Germany grow considerably more rapeseed: each of these countries has a rapeseed crop area of around 1.2 million hectare. Cultivating rapeseed here generally focuses on selling to the foodstuff industry. Of this total area, Germany uses around 310,000 ha (around 30%) for the biodiesel industry. Both countries use very little of the crop for PPO production.
Germany currently achieves regular harvests of 4 - 4.5 ton/ha. Only in the good years, such as this past year, are farmers able to achieve results of 5 ton/ha or more. These higher results are primarily due to applying newer, so-called hybrid types (see, for example, the UFOP website : http://www.ufop.de, and the DSV website: http://www.dsv-saaten.de).
However, the results can vary per farmer. Recent experience has shown that the results in the same year and in the same region can vary from 3.7 ton/ha to 5 ton/ha6 .

Oil results

The seeds obtained from rapeseed can contain 40-45% oil [Bernelot Moens, 2003], [Van der Mheen, 2003]. The literature provides little information about influences on harvesting measures with respect to the oil content. [Van der Mheen, 2003] includes a brief overview of information taken from a number of practical tests. In order to obtain the final oil results, the oil contents need to be coupled to the seed results.
It now appears that a high oil content is usually negatively correlated to a high seed result [Van der Mheen, 2003].

Best case and worst case

Due to the wide range of results per hectare found in practice, this study chose to define a worst case and a best case, thus showing the effect of the results on the total environmental impact and costs. The following assumptions are made per case:

The worst case can be seen as respresentative for rapeseed harvests such as those produced, until recently, in the Netherlands and for bad rapeseed years. The best case is representative of above-average high yields. The average of 4 ton rapeseed per hectare is equal to the agricultural practice in Germany (see footnotes in previous subsections).

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