rations that include duckweed. If the duckweed is to be fed to pigs (and especially to sows), the addition of extra starch will not be needed, which means the financial benefits of duckweed as feed would be greater in the pig sector. Economy Based on the measures carried out at the ECOFERM in Uddel and the experiences gained during the project, a model has been made with which the economic effects have been worked out for a virtual farm with 1,200 pink veal calves. This is described in Chapter 4. At the ECOFERM in the model, 3 hectares of grassland were replaced with duckweed. The ECOFERM was compared with a fictitious farm that did not replace grassland. It is assumed that the duckweed is cultivated in tunnel greenhouses. This would appear to be the least expensive way of producing duckweed inside, which is necessary in order to be able to gain as much as possible from heat and CO2 from the calves. An additional advantage of the tunnel greenhouses is that the wind does accumulate the duckweed at the sides of the pond, allowing the entire water surface to be productive. A significant disadvantage of the use of the tunnel greenhouses are the high investment costs. The fertiliser products generated in the ECOFERM are deployed in roughage cultivation, including that of duckweed. This saves costs on chemical fertiliser. Moreover, it saves costs for removal of the surplus of manure from the farm, which in The Netherlands amounts to 15 euros per tonne of manure. The details of the various aspects of the fictitious companies described above have been worked out, and the effects of business measures on business operations have been calculated. This concerns the effects on diet, the production of duckweed, minerals and fertilizer, the amount of agricultural land, energy, and greenhouse gas emissions. An economic comparison has also been included. For the sake of convenience, it was assumed that the production of duckweed takes place for six months of the year, and that in the remaining six months of the year no duckweed is available. In reality, the growing season for duckweed in the ECOFERM was about 8 months, but production levels were lower during several months in spring and autumn. Separating the manure into different fractions enables ECOFERM to save on its costs for manure disposal. A greater volume of animal manure products can be used in the ECOFERM. Because of the great need for nitrogen by duckweed, a significantly larger amount of nitrogen − and therefore urine or liquid fraction − can be used than is the case with corn or grass. Additionally, there is a modest benefit from saving costs for the purchasing of artificial fertilizers in ECOFERM. No environmental standards have yet been set down for the fertilisation of duckweed. Due to the fact that the cultivation takes place in closed ponds, it is not necessary to set these standards. After all, nitrate leaching is not possible in this type of cultivation. Duckweed with a production of 25 tons of dry solids per hectare and 43% of raw protein has a major requirement of nitrogen and 125 Pagina 132
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