Use of summer harvested common reed (Phragmites australis) as nutrient source for organic crop production in Sweden

Increasing nutrient levels in lakes contribute to environmental problems such as overgrowth and eutrophication. Decreasing soil nutrient levels in organic farming systems result in reduced plant growth. During July and August, nutrient concentration in aboveground parts of the widely distributed aquatic plant common reed (Phragmites australis) is relatively high. The purpose of this work was to identify and analyse technical and logistic systems useful in removing reed biomass from the lake and using it as nutrient supply in organic crop production. The area studied for reed harvest was limited to the “Kållandsundet” drainage basin in Sweden. 160 ha are scheduled for harvesting each year. One strategy studied was to chop the harvested material and spread it directly on farmland. Another was to compost the material before spreading, and a third was to use the harvested biomass as raw material in biogas production and spread the by-product (sludge) on farmland. The energy balances for the three systems were calculated to −0.35, −0.43 and +4.05 MJ kg−1 harvested dry matter, respectively. The biogas strategy produces both large amounts of energy in the gas and nutrients in a form easily available to agricultural plants. The economics of the system are sensitive to changes in income provided by the gas produced and in the cost of the chopping operation. The alternative of chopping and spreading the reed directly as green manure does not require large investments or complicated processing plants, but produces no useful energy and the risks for nitrogen leakage are higher than for the biogas alternative. The compost alternative has the least favourable characteristics among the three strategies studied. The operations at the compost plant are costly and no useful energy is produced. For all three alternatives, the total economics are highly improved if the positive effects of nutrient removal from the lake are included in the calculations.