Repeated applications of farm dairy effluent treated with poly-ferric sulphate did not adversely affect soil phosphorus availability, P fractions and pasture response — a 4-year field plot study

Abstract

Abstract Purpose Land application of farm dairy effluent (FDE) can cause phosphorus contamination of freshwater due to its high nutrient content especially phosphorus (P) in the animal dung. A novel FDE treatment technology has been developed that uses poly-ferric sulphate (PFS) to treat the FDE and recycle water for washing farmyard and reduce the risk of water pollution from P leaching from through the soil. It is important that the application of PFS-treated FDE (TE) does not cause any adverse impacts on soil fertility or plant growth when the TE is applied to the soil. Materials and methods A multi-year field plot study was conducted to determine the effect of repeat applications of FDE and PFS-treated FDE (TE) on soil P availability, P fractionations, plant yield and nutrient uptake. Eight applications of untreated FDE, TE and water as control were applied to replicated soil plots over the period of 4 years. The soil samples were collected on 1 December 2020, and nine pasture samples were harvested during the 2021–2022 dairy milking season. Measurements included soil chemical properties, soil phosphorous fractionations, plant biomass and plant phosphorus and nitrogen uptake. Results and discussion The results indicated that the majority of soil fertility indices and soil P fractions had no significant difference between the FDE and TE applications, with the exception of labile P which was significantly higher in the TE (122.7 mg kg−1) than in the FDE treatments (103.0 mg kg−1) at 0–10-cm soil depth and was also significantly higher in the TE (114.6 mg kg−1) than in the FDE treatments (74.0 mg kg−1) at 10–20-cm soil depth. Similarly, plant P uptakes and dry matter yields were also the same between the TE and FDE treatments with the average of being 54.4 kg P ha−1 and 12.8 t ha−1, respectively. Conclusions Repeated applications of PFS-treated FDE had no adverse effect on soil P availability or plant growth when compared to untreated FDE application and had the potential to benefit soil fertility compared to control.