Impact of Dairy Pond Sludge Application on Phosphorus Fractions in Paddock Soil Woo Taek Hong & Dharmappa Hagare & Zuhaib Siddiqui & Sai Kiran Natarajan & Julian Fyfe Received: 9 December 2019 /Accepted: 13 March 2020 # Springer Nature Switzerland AG 2020 Abstract Waste stabilization ponds (WSP) used to treat dairy shed effluent hold significant loads of recoverable nutrients in the sludge. Land application of this pond sludge over grazing paddocks is a potential alternative to chemical fertilizer. Desludging of WSPs can further enhance the nutrient removal efficiency of the WSP and thereby improve the water quality of the WSP effluent and limit accumulation of phosphorus (P) in WSPs. The aim of this study was to investigate the changes in the nutrient content of soil after land applica- tion of pond sludge (PS) collected from WSP over graz- ing paddocks. In particular, P fractions (e.g. labile P as H 2 O-P and NaHCO 3 -P, and stable P as NaOH-P and HCl-P) were analysed in pond sludge applied soil col- lected from grazed paddocks. It was found that the appli- cation of PS significantly changed the composition of phosphorus in the soil compared with a control paddock that was not treated with PS. The inorganic P in the paddocks treated with pond sludge was 605 mg/kg, which was significantly higher than 67 mg/kg observed in the control paddock. Similarly, the soil treated with pond sludge exhibited increased P fractions of 245%, 36%, 47% and 3000% in terms of H 2 O-P, NaHCO 3 -P, NaOH-P and HCl-P, respectively, compared with the control paddock. The results of labile and stable P frac- tions in the soil samples show that PS could be a viable alternative to other forms of commercial fertilizers and a sustainable source of P for the dairy grazing paddocks. Keywords Plant available phosphorus . Labile P . Stable P . Sequential fractionation Abbreviations DSE Dairy shed effluent H 2 O-P Water extractable phosphorus NaHCO 3 - P Sodium bicarbonate extractable phosphorus NaOH-P Sodium hydroxide extractable phosphorus HCl-P Hydrochloric acid extractable phosphorus 1 Introduction Australian dairy farming has been undergoing a process of intensification since the 1980s, with milk yield and production per hectare having increased the overall number of farms decreased (Fyfe et al. 2016). The process of milking dairy herds generates significant volumes of nutrient-rich effluent as the manure depos- ited by the herd in the dairy sheds is hydraulically flushed to maintain a clean and hygienic environment. As dairy farming continues to intensify, this effluent stream grows, demanding more effective strategies to prevent pollution of waterways and promote productiv- ity gains (Dairy Australia Limited 2014). The manage- ment of effluent nutrients at the farm level, including the Water Air Soil Pollut (2020) 231:181 https://doi.org/10.1007/s11270-020-04537-7 W. T. Hong (*) : D. Hagare : Z. Siddiqui : S. K. Natarajan : J. Fyfe School of Engineering, Western Sydney University, Penrith, NSW 2751, Australia e-mail: wt.hong76@gmail.com