Advantages of Biosolids in Improving Crop Nutrition

Biosolids can play a key role in providing cheap organic fertilizer for agriculture, yet a significant portion of municipal sludge that is not reused as biosolids are disposed of in landfills. Failure to recognize the advantages of biosolids as a natural soil enhancer not only translates to wasted resources but has resulted in the filling up of limited landfill space.

In many countries, the recovery of biosolids from sewage sludge is considered a sustainable method of recycling human waste. The rich nutrients used for agriculture is one of the main advantages of biosolids. Governments from across that globe have enacted legislation that has helped step up efforts in developing technology to effectively extract vital nutrients from wastewater. This resulted in various technological advancements in sewage treatment and biosolids management.

The use of biosolids in land application and composting can reduce soil erosion and improve water quality. Soil particles can be better bonded with organic matter from biosolids which results in improved soil properties, texture and water-holding capacity. This enhances root growth and increases the drought resistance of crops.

Growing plants can also benefit from the slow release of organic nutrients from biosolids. Since these organic nutrients are less water-soluble, it is less likely to leach into groundwater or be carried away by streams and other surface waters. Surface-applied biosolids are less likely to pollute compared to chemical fertilizers.

Here are a few of the important compounds found in biosolids that can play a key role in crop production:


Nitrogen (N) is essential in plant growth and increasing crop yield. Plants deficient in nitrogen experience stunted growth and yellowish leaves. Most nitrogen in soils are contained in humus forms making it difficult for plants to access. Organic compounds present in biosolids increase the available nitrogen for plant use. The stabilization process in the treatment of biosolids such as digestion and composting also contributes to the increase in nitrogen. In biosolids that are a result of anaerobic digestion and dewatering, about 80 percent of total nitrogen is in the organic form. Biosolids can supply around 10% of the nitrogen for use in agriculture. It is an organic compound that is slowly released as the soil warms and stays persistent throughout the crop growth cycle.


Phosphorus (P) helps plants store and transfer energy that is a result of photosynthesis in its growth and reproductive processes. Biosolids contain high levels of phosphorus because humans and animals do not need significant amounts of this nutrient and the excess is often excreted. It can also come from residues from laundry detergents since manufacturers usually add this compound to enhance the product’s cleaning ability. Examples of crops benefit from the phosphate provided by biosolids are corn, cereals and oilseed rapes. Phosphates from biosolids can augment the phosphate soil index as necessary to ensure that the standard application yield is met.


Sulphur is an essential element of all plant proteins as well as some plant hormones. Plants utilize it in the production certain oils and volatile compounds found in the onion and garlic family. Most water sources do not deliver enough sulphur to ensure normal plant development. Biosolids supply both rapidly available S (from oxidation of sulphides) and slow-release S (from decomposition of biosolids organic matter). It is estimated that biosolids can supply 15 – 40 % of the plant available form (sulphate-S) in the first year following biosolids application.


Magnesium has a wide range of roles in many plant functions. It is vital in the photosynthesis process since it is a building block of Chlorophyll, which makes leaves appear green. Factors such as soil acidity, cold temperatures, dry soil conditions and presence of high levels of potassium and calcium can lessen the availability of magnesium. Biosolids provide substantial amounts of magnesium to improve soil fertility.


Calcium is responsible for proper plant cell wall formation and neutralizes cell acids. Lack of this nutrient results in withered or distorted plants. To reduce foul odours in the sewage sludge treatment process, some biosolids are stabilized with alkaline materials (calcium oxide or calcium hydroxide). When the biosolids are applied to the land, the excess alkaline helps neutralize soil acidity. However, caution should be taken when applying them to acid-loving crops such as blueberries and some nursery crops (rhododendrons and maples).

Trace elements

These are nutrients found in small quantities that are just as important in improving the quality of the soil. Compounds like boron, copper, molybdenum, zinc, iron, sodium, manganese, and aluminium can be extracted from biosolids.

The improved soil structure from application of biosolid nutrients have resulted in robust root systems and maximum nutrient uptake by crops. Their slow-release of vital nutrients has allowed crops to be adequately nourished throughout its development. Studies have shown the doubling of yields after biosolids were used as fertilizer.

Because of the availability of biosolids, many farmers are no longer dependent on costly chemical fertilizers that must be re-applied each year. Biosolids can cost considerably less to apply than traditional synthetic fertilizers.

If you are a farmer in the Niagara Region and are interested in considering biosolids as a potential application to your fields, please call us on 1 (877) 479-1388.


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© Thomas Nutrient Solutions, 2014