Pulp mill sludges as a solution for reducing the risk of mineral nitrogen leaching from agriculture

Authors

• Sari Kinnula University of Helsinki https://orcid.org/0000-0002-3264-9803
• Sanna Kanerva University of Helsinki https://orcid.org/0000-0002-2307-4892
• Helena Soinne Natural Resources Institute Finland https://orcid.org/0000-0002-7965-6496
• Marjaana Toivonen Finnish Environment Institute https://orcid.org/0000-0002-9215-8643
• Juuso Joona University of Helsinki https://orcid.org/0000-0003-4681-0300
• Antti Tuulos Lantmännen Agro Oy, Finland
• Tuure Parviainen Volare Oy, Finland
• Ossi Kinnunen Soilfood Oy, Finland
• Jukka Kivelä University of Helsinki

DOI: https://doi.org/10.23986/afsci.142012

Keywords:

primary sludge, secondary sludge, soil amendment, recycled fertiliser, nutrient recycling, nitrogen leaching

Abstract

Nitrogen (N) from agricultural systems contributes to the eutrophication of waterbodies through leaching. Incorporating organic material with a high carbon-to-nitrogen (C/N) ratio, such as mixed pulp mill sludges (PMSs), into the soil in autumn could reduce the amount of leachable N. This study tested the potential of composted and lime-stabilised mixed PMSs (CPMS and LPMS) in reducing the concentration of mineral N in the soil, and thus the risk of N leaching from arable land in the boreal region using a two-year field experiment. To better understand the mechanisms of the PMSs for influencing mineral N concentration in soil, the impact of PMSs with different quality on the reactions of N in the soil was investigated in a laboratory incubation study. In the field experiment, nitrate-N (NO₃^--N) concentration was lower with PMSs compared to mineral fertilisation and the control during the first autumn and the following spring after PMS application. The undersowing of Italian ryegrass reduced the NO₃^--N concentration in the soil during the first autumn. In the incubation experiment, PMSs reduced the soil ammonium-N (NH₄⁺-N) concentration at the beginning of the experiment and the soil NO₃^--N concentration throughout the experiment compared to a mineral fertiliser treatment and an organic fertiliser. Increased soil respiration in PMS-treated soils indicated increase in microbial activity, and thus immobilisation of soil NO₃^--N and NH₄⁺-N due to PMSs addition. These results suggest that PMSs have the potential to reduce N leaching from agricultural soils. However, the immobilisation of N must be considered when planning the nutrient requirements of the following crops.