The effect of long-term wastewater irrigation on the botanical composition of meadow sward, yield and nutritional value of hay

The aim of this study was to determine the effect of 20-year-long irrigation of permanent grasslands with potato starch and brewery wastewater on the botanical composition of sward, yield and nutritional value of hay. The experiment was conducted in the center for wastewater treatment and use in Mątwica-Kupiski (668 ha), which has been equipped with facilities for flood irrigation with wastewater since 1965. Potato starch and brewery effluents were mixed in a storage reservoir at a ratio of 1:0.4. Meadow sward was irrigated with wastewater in autumn and after the first harvest, at an annual dose of 200 – 300 mm. On average, wastewater contained (mg dm-3): N – 223, P – 48, K – 285, Ca – 80, Mg – 46, Na – 68. Before the first harvest in 1998, 2003, 2008, 2013 and 2018, the floristic composition of meadow sward was determined on an 11-degree scale by the Klapp method. Yield was determined in trial plots. Based on the percentage of dominant species (above 20% share of the sward), several floristic types of grassland communities were identified. Herbage samples were collected for detailed botanical and chemical analyses according to the floristic composition of the identified grassland communities. Chemical analyses of plant material were performed by standard methods. Longterm irrigation of meadow sward with wastewater contributed to the development of agronomically important plant communities, except for the Agropyron repens community in the western part of the research site. The yield of grassland irrigated with wastewater, regardless of a floristic type, was 2- to 3-fold higher than the yield of non-irrigated grassland. Hay harveste in wastewater-irrigated meadows met the crude fiber, ash and fat requirements of animals. The total protein content of hay remained within the recommended limits for high-quality fodder, except for the Alopecurus pratensis + Agropyron repens community.