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

中文翻译：

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铝和钙沉淀的乳制品加工污泥潜在的磷作物可再生替代品的磷作物利用率不同

欧洲乳业从牛奶和乳制品加工过程中产生大量废水。通过与富磷污泥中的金属（例如铝，钙）阳离子络合去除磷（P）是农业再利用和磷回收的潜在磷源。但是，与常规矿物P肥料相比，关于这种复合P的植物利用率存在很大的知识空白。当前缺乏关于乳品加工污泥（DPS）的植物P生物利用度的信息，限制了农民和营养管理顾问将其正确纳入肥料计划的能力。本研究检查了最常见的乳制品污泥类型：（1）铝沉淀污泥（“ Al-DPS”）和2）钙沉淀石灰稳定的污泥（“ Ca-DPS”），以评估磷的有效性在生长季节中，在草地上施用磷与矿物P肥料相比。实验设计是具有五个重复的随机完整块。评估了4次收获的作物产量和磷吸收量。最初的土壤测试P为低水平，实验处理为15、30、40、50和60 kg P ha的过磷酸钙^-1，以40 kg P ha ^-1施加两种乳制品污泥（与以相同施用量的矿物P进行比较），在生长季节开始时以单次施用方式施用了零磷对照。结果表明，磷吸收响应与矿物质磷施用量之间的关系呈显着的正斜率，表明该实验点对磷有效性的评估是否合适。Al-和Ca-DPS的P生物利用度在不同处理之间差异很大。相对于铝和钙DPS的四次收获，基于第一次收获的磷肥替代价值分别为50％和16％，分别累积至109％和31％。Al-DPS中的Al浓度不会限制P的生物利用度，但Ca-DPS的低P的生物利用度可能与其高Ca含量有关，这可能导致在碱性pH条件下以高Ca /形成低可溶性Ca-P化合物。 P比。这些发现表明，根据处理过程的不同，乳制品污泥中磷的利用率可能存在很大差异。因此，至关重要的是要提供磷的有效性信息以及可用的磷总量，以确保施用量满足作物需求，而又不会因过量施用而造成环境风险。