Soil transformation with sewage sludge

Sewage Sludge: Is This Waste a Hidden Treasure for Your Soil?

Mira Elwood in Climate & Environment August 2025 • 4 min read.

"Uncover the surprising long-term effects of using sewage sludge in agriculture and how it could revolutionize sustainable farming practices."

The concept of transforming waste into resources is rapidly gaining traction, particularly in agriculture. One promising avenue involves repurposing plant nutrients from waste materials, integrating them back into agricultural practices for sustainable food production. This approach not only addresses waste management but also enriches the soil, fostering healthier crop yields and reducing reliance on synthetic fertilizers.

A recent study delves into the prolonged impact of directly applying sewage sludge (SS) to land, examining its influence on soil fertility. Conducted across two Swedish farms, the field experiments spanned three decades. Initiated in 1981, the research scrutinized three different SS application rates alongside varying levels of mineral fertilization. The experimental design incorporated a factorial approach with four replicates, providing a robust framework for analysis.

The findings from these experiments offer valuable insights into the advantages and limitations of using sewage sludge as a soil amendment. The study sheds light on the intricate dynamics between SS application, soil composition, crop yield, and environmental impact. By understanding these relationships, farmers and policymakers can make informed decisions about adopting sustainable agricultural practices that promote both productivity and ecological well-being.

What Are the Long-Term Benefits of Using Sewage Sludge?

Over the course of the study, consistent application of SS at one site showed a tendency to boost crop yield over time. Although this effect was most noticeable for spring barley, its impact was only significant when plant nutrients were not a limiting factor. Researchers concluded that improvements in soil structure played a crucial role in enhancing fertility after SS application. This was evidenced by a reduction in soil bulk density and an increase in soil carbon concentration.

After three decades, the soil organic carbon stocks to a depth of 0.40 meters varied by up to 17 Mg ha⁻¹ between treatments. Carbon balance calculations revealed that the retention of carbon derived from SS ranged from 18% to 20% in the analyzed soil layers across both sites. Additionally, soluble phosphorus (P) levels increased with the rate of sludge application, although it only accounted for approximately 2% of the anticipated residual P based on P-balance calculations.

Here are the key impacts observed from the use of Sewage Sludge (SS) in the field experiment:

Improved Soil Structure: Lower soil bulk density and higher carbon concentration.
Carbon Retention: 18-20% retention of carbon derived from SS in analyzed soil layers.
Increased Soluble Phosphorus (P): Higher P levels with increased sludge application.
Low Nitrogen Use Efficiency: Only 3-8% nitrogen use efficiency.
Heavy Metal Accumulation: Moderate accumulation of copper, zinc, and mercury in the soil.

Nitrogen fertilizer value was notably low, with a mere 3-8% nitrogen use efficiency. While heavy metals like copper, zinc, and mercury exhibited moderate accumulation in the soil, their elevated levels were not detected in crops, even at the highest SS dosage. These findings suggest that SS is a valuable asset for enhancing soil fertility in terms of soil organic matter and structure, but its efficiency in nutrient cycling is limited within the study's timeframe.

Is Sewage Sludge a Viable Solution for Sustainable Farming?

While sewage sludge offers notable benefits for soil structure and organic matter content, it is not without its limitations. The study reveals a low efficiency in nutrient cycling, particularly for nitrogen and phosphorus. Additionally, the accumulation of heavy metals, although not detected in crops, remains a concern for long-term soil health. Therefore, the use of sewage sludge should be carefully managed and monitored to maximize its benefits while minimizing potential environmental risks. Further research is needed to optimize application methods and address the nutrient cycling inefficiencies to fully harness the potential of sewage sludge in sustainable agriculture.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1007/s10705-018-9952-4, Alternate LINK

Title: Soil Fertility Effects Of Repeated Application Of Sewage Sludge In Two 30-Year-Old Field Experiments

Subject: Soil Science

Journal: Nutrient Cycling in Agroecosystems

Publisher: Springer Science and Business Media LLC

Authors: Gunnar Börjesson, Thomas Kätterer

Published: 2018-09-24

Everything You Need To Know

What are the key long-term benefits observed from using Sewage Sludge in agriculture, based on the field experiments?

Over the long term, consistent application of Sewage Sludge at one site showed a tendency to increase crop yield, especially for spring barley when plant nutrients were not limited. This is largely due to improvements in soil structure, specifically a reduction in soil bulk density and an increase in soil carbon concentration. After three decades, soil organic carbon stocks varied significantly between treatments, with Sewage Sludge contributing to carbon retention in the soil.

Is Sewage Sludge truly a sustainable solution for agriculture, considering both its benefits and limitations highlighted in the research?

Yes, Sewage Sludge can be a viable solution for sustainable farming, offering benefits such as improved soil structure and increased organic matter content. However, it has limitations, including low nutrient cycling efficiency, particularly for nitrogen, and potential accumulation of heavy metals in the soil, though these were not detected in crops. Therefore, its use must be carefully managed to maximize benefits and minimize environmental risks. Optimizing application methods and addressing nutrient cycling inefficiencies are essential for fully harnessing the potential of Sewage Sludge in sustainable agriculture.

How efficient is the nitrogen utilization when Sewage Sludge is applied to agricultural land, according to the study's findings?

The study found that the nitrogen fertilizer value from Sewage Sludge was notably low, with only 3-8% nitrogen use efficiency. This indicates that while Sewage Sludge does contain nitrogen, plants are not efficiently utilizing it within the timeframe of the study. This is an area needing improvement for Sewage Sludge to be a more effective fertilizer.

Does the application of Sewage Sludge lead to heavy metal contamination in the soil or uptake by crops, based on the research?

The use of Sewage Sludge led to a moderate accumulation of heavy metals like copper, zinc, and mercury in the soil. However, these elevated levels were not detected in crops, even at the highest Sewage Sludge dosage. This suggests that while there is a risk of heavy metal accumulation, the crops are not absorbing these metals at levels that would cause immediate concern. Continuous monitoring of heavy metal levels is recommended when using Sewage Sludge.

How effectively does Sewage Sludge contribute to increasing available phosphorus levels in the soil, according to the study results?

While Sewage Sludge application did increase soluble phosphorus levels, it only accounted for approximately 2% of the anticipated residual phosphorus based on phosphorus balance calculations. This low percentage indicates that most of the phosphorus in the Sewage Sludge is not readily available for plant uptake, suggesting a limitation in the phosphorus cycling efficiency within the soil. Further research is needed to enhance the availability of phosphorus from Sewage Sludge.