The previous sections show the rapeseed production, the rapeseed processing to obtain oil and the use of the cake meal obtained from the seed processing. This information can be
used to develop a cropping model that comprises the introduction of rapeseed to the current agricultural rotation based on wheat and barley (WBBB, where W stands for wheat and B for barley). The proposed rotation would preserve the 3 years of barley after one year of wheat in each field portion adding on year rapeseed prior to wheat (RWBBB). The introduction of rapeseed increases the two next following crop yields by 10% (wheat) and 3% (barley) for normal weather conditions. Additionally to the introduction of rapeseed to the rotation, the processing of the seed into oil and cake meal would allow its use as straight vegetable oil to fuel the exploitation tractor.

The proposed model for small-scale biofuel self consumption exploitations is graphically represented in Fig. 4, where the basis model, the rapeseed processing and the fate of the different products obtained are shown.

In order to design this model some hypotheses have to be made. First of all, small-scale producers are considered. The mean farmer is supposed to work an arable land of about 100 ha. The proposal involves using approximately 10% of the arable land for self-supply. In the studied area, as a dry Mediterranean zone, irrigated lands are nearly inexistent, being the traditional sowed crops wheat and barley. It is proposed to cultivate rapeseed as a dry crop in order to avoid putting pressure on water resources. Secondly, the system of crop-rotation jointly with direct seeding is going to be applied. Thus, rapeseed can be seeded in the same land one out of five years. Only the seeds are extracted whereas the rest of the plant is crushed while gathering the seed and left on the fields to be rot. Doing so, the soil recovers part of the nutrients contained in the straw from the plant, thus avoiding the use of some amount of fertilizer. Finally, the farmers bring the harvest to the farmer’s cooperative, which is located near their lands and where there is an industrial press for extracting the oil of the rapeseed harvest.

Important institutions such as the Food and Agriculture Organization (FAO) of the United Nations support good agricultural practices to mitigate negative impacts, in particular on carbon, soil and water resources. Among such practices we find no tillage and direct seeding, retention of soil cover, multiple cropping, appropriate crop choice and crop rotations. There are mainly three systems of harvest namely traditional seeding, minimum cultivation and direct seeding that nowadays coexist in the studied area, being direct
seeding the chosen one for its lower impact, better carbon retention in soil and reduced fuel consumption.

General assumptions are made in this model. For example, the press is assumed to extract in average 80-85% of the total oil content from the seeds. This means that after pressing, seeds are converted in a 35% of oil and a 65% of meal cake. Additionally, according to a survey answered by farmers in the Anoia area (EUETII-UPC, 2010), the average yield of the rapeseed harvest in this area is a minimum of about 2300 kg of rapeseed/ha.

Supposing a direct harvesting system of cultivation, the fuel consumption would be about 7000 l per 100 ha. As explained, the production of rapeseed SVO is supposed to be 875 l per ha. Therefore, dedicating 10% of the arable land to cultivating rapeseed is enough for self fuel supply. Also there is a small excess of SVO that could be sold for other needs. Vegetable oils can be also used in the production of additives that are useful for various industrial purposes as pointed out by (Hancsok et al., 2008). The 15000 kg of rapeseed cake per 10 ha would be used to feed the animals in this area as calculated in section 5.