Differing Phosphorus Crop Availability of Aluminium and Calcium Precipitated Dairy Processing Sludge Potential Recycled Alternatives to Mineral Phosphorus Fertiliser

The European dairy industry generates large volumes of wastewater from milk and food processing. Removal phosphorus (P) by complexing with metal (e.g., aluminium, calcium) cations in P rich sludge is a potential source for agricultural reuse recycling. However, there significant knowledge gap concerning the plant availability this complexed comparison to conventional mineral fertiliser. current absence information on bioavailability processing (DPS) limits ability farmers nutrient management advisors incorporate it correctly into fertiliser programmes. present study examined most common types sludge—(1) aluminium-precipitated (“Al-DPS”) (2) calcium-precipitated lime-stabilised (“Ca-DPS”) at field scale assess grassland versus over growing season. experimental design was randomised complete block five replications. Crop yield uptake were assessed 4 harvests. initial soil test low level treatments super phosphate 15, 30, 40, 50 60 kg ha?1, two applied 40 ha?1 (comparison made same application rate) zero control single beginning Results showed positive slope relationship between response rate indicating suitability site assessment. Al- Ca-DPS varied greatly treatments. replacement value based 1st harvest 16% increased 109 31% cumulatively four harvests Ca-DPS, respectively. Al concentration Al-DPS did not limit bioavailability, but can be associated its high Ca content that lead formation soluble Ca-P compounds alkaline pH conditions Ca/P ratio. These findings show quite different depending treatment process. Consequently, critical have as well total available ensure meets crop requirements without creating environmental risk application.