The use of agri-food industrial wastewater for grassland irrigation

The objective of this study was to determine the influence of 20-year sprinkler irrigation of permanent grassland with potato starch and brewery wastewater on the botanical composition of sward, and the yield and nutritional value of hay. The experiment was carried out in Kupiski-Jednaczewo, near Łomża, NE Poland (approximately 600 ha). Potato starch and brewery effluents were mixed at a ratio of 1:0.4. Wastewater was applied in autumn and after the first harvest, at an annual dose of 200-300 mm. The analyzed wastewater contained on average (mg dm-3): N – 223, P – 48, K – 285, Ca – 80, Mg – 46 and Na – 68. The floristic composition of meadow sward was determined before the first harvest in 1998, 2003, 2008, 2013 and 2018, while the yield was determined on trial plots. Five major floristic types of grassland communities were identified based on the percentage of dominant species (above 20% share of the sward). Herbage samples were collected for botanical-gravimetric and chemical analyses. Soil samples were collected in 1991 and 2018. Chemical analyses of soil and plant material were performed by standard methods. The following floristic types of grassland communities developed: Alopecurus pratensis (Ap), Arrhenatherum elatius (Ae), Dactylis glomerata + Festuca rubra (Dg+Fr), and Poa pratensis + Dactylis glomerata (Pp+Dg), Phalaris arundinacea + Glyceria maxima (Pha+Gm), and the Festuca rubra + Anthoxanthum odoratum (Fr+Ao) community in the control treatment (non-irrigated grassland). The content of P, K, Fe, Cu, Mn and Zn increased, whereas the content of Ca, Mg and Na, and pH levels decreased in the analyzed soils. Regardless of the floristic type of sward, the yield of grassland irrigated with wastewater was significantly (1.6 to 2.8-fold) higher than the yield of non-irrigated grassland. Hay harvested from wastewater-irrigated meadows met the nutrient requirements of animals in terms of crude fiber, ash and fat, excluding total protein.