The Compatibility of Biosolids Land Application with Nutrient Management Regulations


Nutrient Management Regulations

The Natural Resources Conservation Service (NRCS) Conservation Practice Standard for Nutrient Management, Code 590[i], is defined as: “Managing the amount (rate), source, placement (method of application), and timing of plant nutrients and soil amendments.”  The purposes of this National Standard are:

  • To minimize agricultural nonpoint source pollution of surface and groundwater resources.
  • To properly utilize manure or organic byproducts as a plant nutrient source.
  • To protect air quality by reducing odors, nitrogen emissions and the formation of atmospheric particulates.

This Standard applies to animal manure, biosolids, commercial fertilizers, and other materials used to provide plant nutrients.  Both Class B biosolids and Exceptional Quality biosolids products, which are marketed as a fertilizer or soil amendment, are managed in accordance with this Standard.  Pennsylvania’s Nutrient Management Law, Act 38, and Nutrient Management Regulations are at least as stringent as the NRCS Standard. 


Nutrient Management Regulations have many of the same restrictions for manure as Class B biosolids land application regulations.  These include setbacks from waterways, sinkholes, and wetlands, soil analysis, loading at agronomic rates, etc.  In a telephone conversation with Frank X. Schneider, Director, Nutrient and Odor Management Programs, State Conservation Commission, he indicated the Exceptional Quality biosolids products would be treated the same as fertilizer.


Compliance with Nutrient Management Regulations is important to farm operations.  Farmers must be in compliance with Code 590, in addition to Soil Conservation Standards, in order to qualify for NRCS funding for manure storage or other farm improvements.  Nutrient Management Regulations for agriculture strictly limit the amount of Nitrogen (N) and Phosphorus (P) that may be applied to farm fields.  Traditional biosolids products usually have more phosphorus than needed when the crop nitrogen demand is met so this can be problematic.  Farmers want to be sure that what goes in or on their fields is available to the crops, otherwise the yield will be reduced. 


Monitoring P application is a crucial part of nutrient management.  Phosphorus is one of many elements essential to life for both plants and animals and is usually non-toxic even in high concentrations.  However, excessive levels of P are the primary contributing factor to the over-growth of green algae in aquatic freshwater systems (a process known as eutrophication).  The key to slowing or preventing this process is by controlling the P levels of agricultural soil and the soil erosion in the areas surrounding a fresh water ecosystem. 


In the past, fertilizer and biosolids were land applied at a loading rate adequate to meet the crop demand for N.  Excess N was much more likely to leach than P.  Phosphorus was assumed to be associated with soil particles, therefore, efforts to control P loss were focused on erosion control.  However, research at Penn State University showed how agricultural practices impact P loss even after soil conservation Best Management Practices (BMPs) are in place.


Although Total P transport by erosion was less in no-till fields, the Soluble P transported in erosion was greater than on a conventionally tilled wheat field.  This was because fertilizer, biosolids and manure were surface applied in the no-till fields, rather than injected or incorporated in conventional tillage, which resulted in a buildup of P on the upper surface of the soil.  This buildup was more vulnerable and subject to runoff erosion.  As a result, NRCS is accepting fertilizer and manure injection using minimal disturbance equipment as a part of a no-till operation.


A common reaction of environmental regulators is to simply prohibit additional P sources on soils that contain enough P for crop growth.  This critical crop level would be 60 mg/kg with the Mehlich-3 soil test.  However, Penn State research showed that between 200 mg/kg and 400 mg/kg is the environmental critical level.  As a result, fields in this range must be evaluated to determine the factors that would influence nutrient losses.



The Phosphorus Index

PA has developed a phosphorus risk assessment methodology, called the Phosphorus Index (P Index), to determine how much, if any, phosphorus may be applied to a field.  The P Index is used as a tool by Nutrient Management Planners to determine how much P may be applied to a field.  The index quantifies and rates the risk to water quality from P sources and P transport mechanisms. 


In order to determine if a full risk assessment for phosphorus is required, a Nutrient Management Planner must first complete the Part A screening tool.  If the answer to any of the following questions is yes, Part B must be completed:

  • Is the field in a special protection watershed? 
  • Is there a significant farm management change?
  • Is the soil test greater than 200 ppm phosphorus?
  • Is the distance to surface water less than 250 feet?


Part B of the P Index then assigns numerical values to both the source of P and transport factors. Source of P factors include the concentration of P in the soil, the pounds of P applied as a fertilizer, manure or biosolids, the method and timing of application, and the Phosphorus Source Coefficient (PSC).  The PSC is based on a laboratory water extraction procedure that determines whether the manure or biosolids is likely to leach P.


The biosolids application methods are rated for their risk of leaching P to the watershed.  Starting at lowest risk to highest risk, they include:

  • Placed or injected two inches or more deep
  • Incorporated less than one week following application
  • Incorporated greater than one week or not incorporated April-October
  • Incorporated greater than one week or not incorporated November-March


Transport factors assessed by the P Index include:

  • The soil loss calculated in the Soil Conservation Plan must be less than 2 tons/acre/year
  • The runoff potential is based on drainage class; i.e. excessively well drained to very poorly drained, with poorly drained soils presenting the highest risk of runoff
  • Subsurface drainage; if there are tile drains or a direct outlet to receiving water
  • Contributing distance to surface water, ranges from greater than 500 ft. to less than 100 ft.  The closer the field is to surface water, the higher the risk


All these factors are assigned numerical values.  The greater the risk of nutrient loss, the higher the number.


TABLE 1. P management based on results of P Index

P Index Rating

Nutrient Application Guidance

Low: 59 or less

Nitrogen based management

Medium: 60-79

Nitrogen based management

High: 80-99

Phosphorus limited to crop removal

Zero Threshold: 100 or greater

No additional phosphorus applied


Nutrient Management Planners try to minimize the P Index rating.  There is not a lot that can be done under transport factors such as location of surface water, slope, soil classification, soil erodibility.  But planners could modify how a field is managed to reduce the P Index rating. 





Storage and timing – Wastewater treatment plants should be designed to store biosolids so that it is available close to the time the crops need it.  For example, large aerobic or anaerobic digesters could provide storage during most of the winter and mid-summer.  Also, dewatering equipment could be designed with the capacity to dewater the stored liquid fairly quickly.  Field storage on the farm is also feasible provided the dewatered product is 20%TS or greater.

Produce biosolids with a low Phosphorus Source Coefficient (PSC) - Heat dried biosolids, lime stabilized biosolids and composted biosolids have a lower PSC than the book value of 0.4. Biosolids produced at plants with biological P removal have the highest PSC.

Reduce potential for nutrient loss through erosion using proper placement and rate of application – Land appliers could incorporate biosolids into the soil provided the soil conservation plan allows this practice.  Injection of a high solids liquid biosolids could also lower nutrient loss.  By placing biosolids into the root zone, any readily available nutrients will be used by the crop and will be less likely to leach.

Suitability for no-till and minimum-till cropping systems - Many farms are converting to no-till to save time plowing, conserve moisture and to improve soil health.  It is also a means of reducing erosion and complying with a Soil Conservation Plan. The only tillage allowed in no-till fields is subsurface injection of fertilizer or manure. 

Government subsidies – NRCS provides farmers reimbursement for injection of liquid fertilizer or manure rather than for the practice of surface application.  There are also subsidies for use of Enhanced Efficiency Fertilizer.  Maybe in the future, the slow release nature of biosolids based fertilizers would be recognized and rewarded similarly.

Slow release N and P - Since the N and P are primarily in organic form, they are not all plant available or leachable when applied in the spring.  We rely on soil microorganism to break down organic forms of nutrients to plant available forms. This occurs gradually over the course of the growing season as the growing crop’s demand for nutrients increases, thereby reducing the risk of nutrient losses.

Custom blend a fertilizer- Depending on the source of the biosolids, the P loading may exceed demand when the loading to meet the crops nitrogen demand is applied.  It is possible to increase the nitrogen and potassium concentrations and custom blend a fertilizer for a farmer’s needs.  




Beegle, D.  2015, “Phosphorus Behavior and Management”, Managing Manure Nutrients Workshop, Penn State University


Minerals Education Coalition. 2013. Phosphate rock.


Natural Resources Conservation Service, 2012 “Nutrient Management Standards” (Code 590)


Penn State University, 2007 “The Pennsylvania Phosphorus Index Version 2” College of Agricultural Sciences, Agricultural Research and Cooperative Extension


Soil Association (United Kingdom). 2010. A rock and a hard Place: Peak phosphorus and the threat to food security.


USDA 2015 “Soil Health Bucket- Guides and Reference”


ESEPA 1994 “A Plain English Guide to the EPA Part 503 Biosolids Rule” Office of Wastewater Management


USEPA, USDA, 2000 “Guide to Field Storage of Biosolids”


Water Environment Federation 2014 “Phosphorus in Biosolids Fact Sheet”

[i] Note the date of the last revision was January 2012





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