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| The rights of the farmer must be respected with regard to timing, method and rate of application of the sewage biosolid. |
By Michael Payne, Biosolids Utilization Specialist, Crop Technology Branch, Ontario Ministry of Agriculture Food and Rural Affairs; Mark Janiec, Terratec Environmental Ltd.; Marius Marsh, MOE; Janice Patterson, Robert Stone, and Larry Schut, OMAFRA
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| The rights of the farmer must be respected with regard to timing, method and rate of application of the sewage biosolid. |
Utilization of sewage biosolids on agricultural land as a crop nutrient input is a common practice in Ontario. The material provides nutrients for plant growth and is a source of organic matter for the soil. Sewage biosolids can reduce fertilizer costs and improve the tilth of the soil.
The establishment of municipal sewer use by-laws, as well as improvements in municipal sewage treatment systems, have increased the quality and as a result the quantity of sewage biosolids available for agricultural use. Agricultural land application also benefits municipalities by reducing costs associated with the disposal of this material in landfill sites or by incineration.
Sewage biosolids result from the decomposition and settling of solids at a sewage treatment plant. This material usually contains about 0.1% - 0.3% total nitrogen, and considerable amounts of organic matter and elemental phosphorous. Other nutrients such as magnesium, zinc, copper and boron are also present. Since the influent materials that enter a sewage treatment plant may vary considerably, chemical analysis of the resulting biosolids is required to determine the nutrient and heavy metal content, and calculate an application rate.
Before sewage biosolids can be used for land application, they must satisfy the criteria outlined in the joint Ontario Ministry of Agriculture Food and Rural Affairs/Ministry of Environment (OMAFRA-MOE) publication Guidelines for the Utilization of Biosolids and Other Wastes on Agricultural Land. Only stabilized sewage biosolids with low metal concentrations are suitable for land application.
Sewage biosolids must be stabilized before land application. Stabilization is a process that involves reducing bacteria and other pathogenic organisms. It is accomplished by a process of sewage digestion or other acceptable methods such as lime stabilization. The digestion process reduces the number and types of pathogens (viruses, bacteria, fungi and parasites), reduces the volume of material, and stabilizes organic matter, reducing the potential for odours.
Sewage biosolids must meet the guideline quality criteria before being land applied. If the material does not meet the provincial guideline criteria, it must be disposed of at a licensed landfill or incinerated.
Sewage biosolids that meet the requirements and the criteria as set out in the guidelines may only be applied on agricultural land that meets certain site criteria. Those criteria are also specified in the guidelines. Land application of sewage biosolids must be carried out under a Certificate of Approval issued by the Ontario Ministry of the Environment (MOE).
Limits to Land Application
1. Nutrients.
The guidelines limit sewage biosolid application to fields with a soil test of less than 60 parts per million (ppm) of available phosphorous in the top 15 cm, as measured by the Olsen sodium bicarbonate extraction method.
Soils with a pH of less than 6.0 should not receive sewage biosolids unless the material contains enough lime to raise the soil pH to or above 6.0. Another option is to lime the field to raise the soil pH above 6.0.
2. Heavy Metals.
The major factor in determining the acceptability of sewage biosolids for land application is the presence and concentration of heavy metals. There are 11 heavy metals in sewage biosolids of concern to agriculture. These are: arsenic, cadmium, chromium, cobalt, copper, lead, mercury, molybdenum, nickel, selenium, and zinc.
Sewage biosolid quality and application rate is determined by the amount of available nitrogen, and the quantities of metals.
Therefore, limiting the amount of nitrogen supplied by the material for the crop to be grown, in turn, limits the amount of heavy metals applied to the soil. For anaerobically digested sewage biosolids, minimum ammonium plus nitrate nitrogen to metal ratios have been developed as quality standards to ensure that heavy metals are limited (Table 1, column IV).
Aerobic sewage biosolids are low in ammonium plus nitrate nitrogen and for this reason is limited by total metal concentrations rather than a nitrogen/metal ratio (Table 2).
3. Physical Limitations.
The maximum depth of a fluid sewage biosolid that can be surface applied at any one time is 1.3 cm. This depth is equivalent to an application rate of 130 m3/ha. Additional applications may be carried out only when the preceding application has dried. If fluid sewage biosolids are injected immediately into the soil, then greater volumes may be applied, but not greater than 135 kg/ha of ammonium + nitrate nitrogen.
Winter application of sewage biosolids on frozen or snow-covered ground is not recommended.
Sewage biosolids may only be applied to mineral soils. Mineral soils are defined as having less than 17% organic carbon by weight.
Site characteristics determine separation distances and the timing of sewage biosolid applications. Separation distances are the set back distances from environmentally sensitive or conflicting use areas. They are buffer areas where biosolids spreading is not permitted. The distances are determined in part by soil texture, slope, drainage, application methods, and neighbouring land use. These limitations are further outlined in the Guidelines for the Utilization of Biosolids and Other Wastes on Agricultural Lands.
4. Other Limitations.
Waiting periods developed for specific crops and livestock species are outlined in Table 3. Access to fields is limited for a period of time after sewage biosolid application to protect human and livestock health. The waiting periods are necessary to further reduce the number of pathogenic organisms (viruses, bacteria, fungi and parasites) that remain in sewage biosolids after stabilization. It is the responsibility of the farmer to enforce the appropriate waiting periods between sewage biosolid spreading and cropping, pasturing or human access. (See Table 4 for more cropping limitations.)
Application/Spreading
Spread sewage biosolids only when the soil is dry enough to minimize soil compaction. Spreading when soil is wet may result in rutted fields and reduced crop productivity. Using flotation tires on spreading vehicles can increase the number of days when sewage biosolids may be spread, but it does not eliminate the possibility of soil compaction.
Injection of fluid sewage biosolids into the soil using a self-propelled or drag hose system can greatly reduce the chance of run-off, odours, and nitrogen loss. Another method of application is surface spreading or broadcasting by means of a splash plate using a self-propelled or drag hose system. Applying the material by spray irrigation (irrigation gun) decreases the potential for soil compaction, but greatly increases the potential for odour complaints, run-off, and nitrogen loss. Also, if wind conditions are not favourable, there is increased potential for wind-drift and over spray onto surrounding land uses.
The nitrogen in sewage biosolids is used most effectively when the material is applied in the spring, either by injection or surface spreading with incorporation into the soil within 24-48 hours. Delaying incorporation will result in nitrogen loss to the atmosphere. In these cases, adjust supplemental fertilizer rates to compensate for the loss of nitrogen.
The importance of uniform application of sewage biosolids cannot be over emphasized. Higher than recommended application rates may result in:
Equally important to uniform application is applying fertilizer to separation areas such as the field edges, where sewage biosolids cannot be applied. These separation areas must be fertilized to provide for more even crop growth. For more information on separation distances see the guidelines.
Application Rates
The application rate of sewage biosolids is based on the nitrogen fertilizer recommendations in the most recent editions of either OMAFRA Publication 296, Field Crop Recommendations, Publication 360, Fruit Production Recommendations, Publication 363, Vegetable Production Recommendations, and Publication 384, Recommendations for Turfgrass Management. The rate of available nitrogen (ammonium and nitrate nitrogen) permitted to be supplied by sewage biosolids is limited to 135 kg N/ha every fiveyears. For commercial sod production, this amount may be applied every four years.
Depending on the nitrogen fertilizer recommendations, oneapplication of 135 kg N/ha from sewage biosolids may be made in one year. However, sewage biosolids cannot be applied to that site until the remainder of the five year period has lapsed. If the amount of applied sewage biosolid nitrogen is less than 135 kg/ha sewage, biosolids may be applied to the site again as long as the total rate does not exceed 135 kg N/ha for the five year period.
The nitrogen content of sewage biosolids is reported in milligrams/litre or parts per million (ppm) of ammonium plus nitrate nitrogen. This is an approximate measure of nitrogen, which is readily available to plants.
Sewage biosolids contain large amounts of plant available phosphorous. This phosphorous is estimated to be about 40% as available as that of commercial fertilizer.
Responsibilities
The generator of the biosolids is responsible for:
The hauler/spreader must apply the sewage biosolid uniformly on land at the approved rate, and using the method required by the farmer. The rates of actual nitrogen applied (kg/ha) and/or sewage biosolid applied (m3/ha) must not exceed those specified by MOE.
The hauler/spreader must maintain all required separation distances and comply with other site requirements as specified on the Certificate of Approval. A report outlining the nutrients applied must be provided to the farmer after completing the sewage biosolid application to any field.
The rights of the farmer must be respected with regard to timing, method and rate of application of the sewage biosolid.
Farmers, the sewage biosolid hauler/spreader and the generator should work together to develop a nutrient management program for maximum utilization of land applied sewage biosolids. Farmers have the right and the responsibility to insist on program flexibility. The sewage biosolid application rates must be adjusted to suit the nitrogen and phosphorous requirements of the crop, as long as the adjusted rate does not exceed that specified in the Certificate of Approval. The farmers have the right to instruct the applicator to discontinue sewage biosolid spreading at any time if soil compaction or environmental damage is likely or if timing interferes with soil and crop practices on the farm.
Farmers have the responsibility to enforce the appropriate waiting periods between sewage biosolid spreading and cropping, pasturing or human access.
For further information, contact: mpayne@omafra.gov.on.ca.
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