Temporal changes in labile soil phosphorus pools in grassland receiving P recycled from dairy processing sludge

Olha Khomenko, Owen Fenton, J. J. Leahy, Karen Daly

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish
Article number100110
JournalSoil Security
Volume13
DOIs
Publication statusPublished - Dec 2023

Keywords

  • Availability
  • Dairy processing waste
  • Exchangeable phosphorus
  • Hydrochar
  • Phosphorus use efficiency
  • Struvite

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