122 The density of the duckweed can be determined using reflection or leaf measurements. A harvesting machine linked to these parameters and to the model could then determine when the duckweed needs to be harvested. Finally, there are also ways of improving the fertilisation of the duckweed. More effective separation of the digestate or the use of very clean urine reduces the supply of organic materials, resulting in less oxygen that needs to be pumped into the water. The supply of nutrients should be automated, as is the case in the horticulture sector. This leads to fewer fluctuations in the concentration of nutrients. Optimal cultivation of duckweed based on experiences at ECOFERM ➸ Water temperature 26 °C • Range of 20 to 30°C gives high rate of growth • Heating using animal heat • Spray cooling when temperatures are high ➸ 13 hours’ light saturation per day • Maximise light transmission through greenhouse roof or cultivate outdoors • Artificial lighting ➸ Completely and homogenously covered water surface • 400 to 100 gram duckweed/m2, depending on duckweed species • Paddle wheel for homogenous flow • No “dead” corners • Automatic harvest based on leaf density • Elimination of wind influences ➸ Oxygen-rich cultivation water • No organic contamination • Aeration based on oxygen % ➸ Optimal fermentation based on digestate • No organic contamination • EC 1 to 1.5 • pH 6 to 7 • Adjustments based on nutrient intake by the duckweed • Homogenous distribution using substrate unit • Increase CO2 content • Effect on crop growth up to 1500 ppm Research into the cultivation of duckweed Further research is needed for optimizing duckweed production and integrating this new activity on the farm. This involves: • The effect of light intensity on the growth of duckweed; • The possibilities for genetic improvement of duckweed; • The effect of harvest management on the density and the homogeneity of the layer of duckweed; • The technical and economic viability of a practical cultivation system; • Integration of the ECOFERM concept in the agricultural sector. Duckweed as feed for calves What are the characteristics of cultivated duckweed as a feedstuff, and how does it fit in with the diets of pink veal calves? This is the subject Pagina 129
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