6 research outputs found
Modelling soil P dynamics and P cycling in soils amended with organic waste
The reprioritization of the circular economy in agricultural sector worldwide leads to an increase of the recycled fertilisers production and use. To develop sustainable strategies for soil phosphorus (P) management using recycled P fertilizers, an understanding of their effect on soil P dynamics is required. This study investigates the impact of various dairy processing sludge (DPS) based recycled P fertilisers on soil P build up and availability. The experiments were conducted at incubation, pot, and field scale. A novel isotope pool dilution technique was used to quantify the labile P pool reserves as well as the rate of soil P turnover between the available (soluble) soil P and the labile (rapidly exchangeable) P.The incubation study was designed using soils with different P fertilisation history and enabled a description of a model of biotic and abiotic soil P cycling in the soils depending on the initial status. The pattern of the soil P build up and turnover between the available and labile P pools were investigated in the soil that received recycled DPS-based fertiliser or mineral fertilisers and the differences in the build-up mechanism was described. Chemically treated DPS-based products demonstrated high potential to replace conventional P fertilisers, however they showed slower rates of available and exchangeable P build up compared to chemical fertilizers, suggesting the need for higher application rates or earlier application times. Thermally treated products exhibited poor agronomic performance as P fertilizers.The long term changes in soil P dynamics in soil amended with the recycled P fertilisers was further assessed in a long-term pot study where soil was subjected to a P build up and drawdown cycles. The findings revealed that during the period of high P demand, available P levels fell below the baseline values but recovered as crop growth and P demand decreased. The recovery time differed depending on soil P status and DPS amendment.Finally, a field-scale study was conducted to describe temporal changes in available, exchangeable, and Mehlich3 P pools in P-deficient grassland soil amended with DPS-derived hydrochar and struvite. The results showed that struvite increased available, exchangeable, and Mehlich3 P levels, reaching optimal values for crop production within a month. Hydrochar exhibited slower P release, with P levels remaining low during the dormant period. These findings contribute to the understanding of soil P dynamics and provide insights into the sustainable use of DPS and its derived products as P fertilizers. The results emphasize the need for tailored nutrient management approaches and regulations that account for the slower P turnover rates associated with recycled fertilizers and cautious approach to thermally produced fertilisers application.</p
Temporal changes in labile soil phosphorus pools in grassland receiving P recycled from dairy processing sludge
Replacing chemical fertilisers with recycled products will require new advice for phosphorus (P) use.. Emerging P fertilisers derived from dairy processing sludge (DPS) include products such as struvite and hydrochar. A field study monitored temporal changes in available, exchangeable, and Mehlich3 P pools in a P deficient grassland amended with DPS-derived hydrochar and struvite. Herbage P content and yields were compared with data from plots amended with a mineral P fertiliser. Regardless of fertiliser used, there was no statistical difference in dry matter yield. However, herbage P content varied depending on the fertiliser type. The optimal P content in herbage for cattle feed (0.3–0.4 %) was reached using struvite and mineral fertiliser. Application of struvites increased available, exchangeable, and Mehlich3 P, raising the available P levels to the agronomic optimal value for crop production (>5 mg L-1) within one month. In hydrochar amended plots, the optimal level of P was reached 4 months after fertilisation, at the end of the growing season. During the low growth or dormancy period, soil P levels decreased and remained low regardless of the treatment. In the struvite amended plots, available and exchangeable P pools recovered at the beginning of the second season. This effect was not observed in mineral fertiliser and hydrochar amended plots. A single application of struvite can replace mineral fertilisers supplying crops with P for more than one season. This needs to be reflected in the advice for growers to avoid excessive P application and legacy P deposition. </p
Contrasting phosphorus build‑up and drawdown dynamics in soils receiving dairy processing sludge and mineral fertilisers
Sustainable utilisation of waste from the food industry is required to transition to a circular economy. The dairy industry relies on high phosphorus (P) inputs and produces large quantities of P-rich dairy processing sludge (DPS). Recycling DPS into P fertilisers provides an opportunity to decrease the reliance on chemical P fertilisers. However, current soil nutrient management planning (NMP) is based on chemical P and does not account for recycled alternatives. A pot trial using a novel isotope pool dilution technique was used to describe build-up and drawdown cycles of P in soils fertilised with DPS. Changes in available, exchangeable, and Mehlich3 P (M3-P) pools were recorded over 36 weeks of grass growth. Results demonstrated that in the period of high P demand (12 weeks), these P pools were depleted. As crop growth and demand decreased, available P recovered through mobilisation of P from exchangeable P and M3-P reserves. DPS allowed available P to recover and build up to agronomic target levels after 24 weeks. Using DPS, build-up of available and exchangeable P was slower but P use efficiency was higher at stages of slow growth. Dairy waste created a more stable P pool which could be utilised by crops over a growing season indicating that NMP needs to account for this in the decision support for growers. Isotope studies revealed that extractive agronomic tests do not capture drawdown in P reserves.</p
Contrasting phosphorus build‑up and drawdown dynamics in soils receiving dairy processing sludge and mineral fertilisers
Sustainable utilisation of waste from the food industry is required to transition to a circular economy. The dairy industry relies on high phosphorus (P) inputs and produces large quantities of P-rich dairy processing sludge (DPS). Recycling DPS into P fertilisers provides an opportunity to decrease the reliance on chemical P fertilisers. However, current soil nutrient management planning (NMP) is based on chemical P and does not account for recycled alternatives. A pot trial using a novel isotope pool dilution technique was used to describe build-up and drawdown cycles of P in soils fertilised with DPS. Changes in available, exchangeable, and Mehlich3 P (M3-P) pools were recorded over 36 weeks of grass growth. Results demonstrated that in the period of high P demand (12 weeks), these P pools were depleted. As crop growth and demand decreased, available P recovered through mobilisation of P from exchangeable P and M3-P reserves. DPS allowed available P to recover and build up to agronomic target levels after 24 weeks. Using DPS, build-up of available and exchangeable P was slower but P use efficiency was higher at stages of slow growth. Dairy waste created a more stable P pool which could be utilised by crops over a growing season indicating that NMP needs to account for this in the decision support for growers. Isotope studies revealed that extractive agronomic tests do not capture drawdown in P reserves.</p
Changes in phosphorus turnover when soils under long-term P management are amended with bio-based fertiliser
Understanding available phosphorus (P) turnover could improve sustainable P management. An isotope tracing 33P was used to measure daily P turnover rates and exchangeable P (E) in P deficient, balanced, and excess P soils from a long-term P site. Turnover under P deficient conditions was characterised by the lowest P flux predominantly from the available into the exchangeable P pools (P efflux). The P efflux in the P deficient soil was 3.7 ± 0.6 mg P/L day− 1 and the inverse flux (P influx) was 1.6 ± 0.4 mg P/L day− 1 . Turnover rates were more than twofold higher under P balanced and surplus conditions, exhibiting an equilibrium between influx and efflux rates. The contribution of abiotic processes to P turnover was predominant in the excess P soil, whereas biotic processes dominated turnover rates under P deficient conditions. Changes in P turnover were measured following application of single superphosphate (SSP) and dairy processing sludge (DPS). Both fertiliser types increased P turnover rates and availability across all soils. After SSP application, E values plateaued between 238 and 297 mg P/L regardless of initial P status. Slower P release from DPS was evidenced by a wider range of E values (97–160 mg P/L) with slower turnover. </p
A comparative study of thermally and chemically treated dairy waste: Impacts on soil phosphorus turnover and availability using 33P isotope dilution
Dairy processing sludge (DPS) and DPS-derived secondary products such as struvite, biochar, hydrochar and ash (collectively known as SRUBIAS) are emerging as alternatives to fertilizers produced from mined rock phosphate. However, little is known about how these products affect soil P availability and daily P turnover rates.. A lack of such information prevents precision nutrient management planning using these products out on farms. This study used a novel isotope dilution technique (IPD) with 33P as a tracer to compare P turnover in soils amended with chemically (alum-treated DPS and struvite) and thermally (biochar, hydrochar, ash) treated DPS. Results showed that thermally treated products exhibited poor agronomic performance as P fertilizers, potentially inhibiting P availability when applied to soils. For example, a P deficient soil amended with hydrochar treatment at the highest application rates did not record a build-up of available P to agronomic target values. In ash and biochar treated P deficient soils, available P increased but only with very high application rates of 150 and 80 mg P kg −1. The application of these products as fertilizers could have negative implications for both environmental and agronomic goals. Conversely, chemically treated fertilisers demonstrated better agronomic performance. The same agronomic target value was reached with application rates of only 20 mg P kg −1 soil for DPS and 50 mg P kg −1 soil for struvite. However, the techniques deployed revealed that these products exhibited slower rates of available and exchangeable P build-up when compared with chemical fertilisers. This suggests that these bio-based alternatives require higher application rates or earlier application times compared to conventional chemical fertilizers. Regulations providing advice on P use in agricultural soils need to account for slower P turnover in soils receiving recycled fertilizers. The IPD technique is transferrable to all wastes to examine their performance as fertilizers.</p