Science Reconsiders the Value of Land Application
New guide offers additional management practices to ensure farm productivity in the northeastern United States
- By Ellen Z. Harrison
- Oct 01, 2007
The Guidelines for Application
of Sewage Biosolids to
Agricultural Lands in the
Northeastern U. S.offers
the best science available
and seeks to protect the
land resource base, emphasizing agricultural
productivity in perpetuity. Scientists from Cornell,
Rutgers, the University of Massachusetts,
Penn State, and the University of New Hampshire
developed the document, which is an
updated version of a 1985 document, Criteria
and Recommendations for Land Application
of Sewage Sludge in the Northeast.
More than 20 years later, new scientific evidence
and regulatory policy have emerged, and
the use of sewage biosolids on agricultural soils
has expanded. The multistate research committee
of faculty from land grant universities
convened in 2000 to reconsider the topic. Guidelines was published by Rutgers University
It’s a matter of soil
The range of soil conditions, farming practices,
and demographic factors in the Northeast led
the scientists to conclude that the Code of Federal
Regulations Section 40 Part 503 may not
be adequately protective under all agricultural
use scenarios in this region. The purpose of the
new guidelines is to inform potential users of
sewage biosolids (including landowners, farmers,
and their advisers) of situations
in which additional management
practices beyond current regulations
can be implemented to promote sustained
farmland productivity and to
better protect public health and the
Soil conditions, farming systems,
and the population density of the
Northeast dictate a cautionary
approach to land spreading of
sewage biosolids. Relatively acidic,
shallow, low-organic matter soils are
common. The chemistry and
hydrology of these soils contrast
sharply with the deep, high-organic
matter mollisols of the Corn Belt
in the Midwest or the calcareous
aridisols of the West, for example.
Northeast soils have been shown to
have lower heavy metal sorption
capacities than do soils with higher
pH or more organic matter. This situation
places the Northeast in a
position of having some soils that
are less suitable for biosolids application.
Dairy farming is the primary agricultural
system in most Northeast states. On many
dairy farms, applications of farm manure supply
more nutrients than required for on-farm
crop production (due to feed importation),
resulting in the potential for excess nutrients
polluting groundwater and surface waters. The
addition of sewage biosolids in such systems
may exacerbate this
Certain elements in
(such as sulfur and
the potential to
result in copper deficiency
in cattle (as
well as sheep and
goats) if there are
Fruit and vegetable
and both are sensitive
commodities with regard to public perception.
A decision to land-apply sewage
biosolids on a fruit or vegetable crop can directly
affect a farmer’s livelihood, because some
supermarket chains, food processors, and
wholesalers do not accept produce from farms
where sewage biosolids have been used.
A summary of the guideline recommendations
follows, with fuller explanation and
references available on the Internet at http://hdl.handle.net/1813/7934.
|RECOMMENDED MAXIMUM SOIL
TRACE ELEMENT CONCENTRATIONS
FOR THE NORTHEAST UNITED STATES
||Recommended maximum soil concentration (mg/kg)1
||Sand & laomy sand
||Sandy loam to silt loam
||Silt to Clay
|1 The values in this table represent total elemental concentrations. The recommendations apply to soils maintained
at pH of 6 or greater.
|2 This is the plant health Ecological Soil Screening Level established by the U.S. Environmental Protection Agency.
|3 Limit to prevent phytotoxicity to less than 10 percent yield reduction. Higher concentrations can be tolerated in
calcareous soils with pH greater than 7.
These guidelines refer to bulk application of
both “exceptional quality” (EQ) and non-EQ
1. Any farm considering the application of
sewage biosolids should construct a farm-scale
nutrient balance to ensure a demonstrated need
for the additional nutrients.
2. Apply the highest quality sewage
biosolids available. Suggested maximum concentrations
(expressed as parts per million,
ppm) are 18 ppm arsenic, 8 ppm cadmium,
160 ppm chromium, 1,100 ppm copper, 180
ppm lead, 3 ppm mercury, 33 ppm molybdenum,
70 ppm nickel, 15 ppm selenium, and
1,500 ppm zinc, on a dry weight basis. These
are approximately the 95th percentile values
for several different data sets representing
northeastern U.S. sewage biosolids as of 2005.
These are not risk-based values or regulatory
limits but rather provide reference points to
determine general quality of the material.
3. Apply material that has consistent quality.
Nitrogen concentrations in sewage biosolids
from one wastewater treatment plant can be
highly variable, making accurate calculation of
appropriate agronomic application rates difficult.
Some wastewater treatment plants produce
sewage biosolids with relatively low trace
element concentrations in comparison to other
facilities. The best strategy is to choose sewage
biosolids from facilities that have consistent
nutrient and trace element concentrations and
also low trace element concentrations. For trace
elements, a rolling average, including at least
four analyses per year, is recommended for
sewage biosolids from each wastewater treatment
plant source. Seasonal and operational
variations need to be taken into account.
4. Maximum recommended, cumulative
soil trace-element concentration limits for sites
to which sewage biosolids are applied are
intended to address and protect the agricultural
productivity under soil conditions and for farming
practices and demographics, some of which
are unique to the Northeast (see table).
5. Farmers should test soils before application
and again when it is estimated that the
soil trace element concentrations have reached
approximately one half of the recommended
maximum soil concentration.
6. The potential for induced copper deficiency
in ruminant animals due to molybdenum,
iron, cadmium, and sulfur in sewage
biosolids requires careful consideration of livestock
7. Alkaline-stabilized sewage biosolids
should not be applied at rates greater than
the soil liming requirements, and the nutrients
present in the product (nitrogen, phosphorus)
must be accounted for.
8. Wherever possible, sewage biosolids
should be incorporated (injected into, mixed
into, or turned under the surface) in the soil
within 24 hours of application. When stockpiling
material, caution is advised to minimize
odor and leaching problems.
9. Care is needed to spread sewage biosolids
uniformly and avoid creating “hot spots” in a
field where the material is over-applied locally.
10. Soil pH of 6 or above should be maintained
as long as the land to which sewage
biosolids have been applied is used for crop
11. Use of sewage biosolids on soils used
to grow vegetable or fruit crops is not recommended.
12. Farmers should keep records of the
source, quantity, and quality of materials
applied. Records should be kept of when, how,
and by whom sewage biosolids are applied,
as well as any concerns (such as odors) noted
13. Farmers using sewage biosolids may
wish to obtain written assurance from the supplier
that any sewage biosolids being land
applied are of appropriate quality (pollutants,
pathogen reduction, vector attraction reduction)
and have been properly treated and that
the application procedures meet federal and
The table contains the recommended maximum
soil elemental concentrations because
these can be measured at any point and are
what the plants respond to. Although only a
portion of the total trace elements in the soil
are bioavailable, the research on which these
recommendations are based was developed primarily
using total trace element data, and thus
the relative bioavailability already was accounted
for in these data.
Based on the typical concentrations of various
trace elements in sewage biosolids, copper
is frequently the element that would first
reach recommended maximum soil concentrations
and thus limit cumulative application.
Molybdenum may be the limiting element
in some situations.
If sewage biosolids containing 548 mg copper/
kg of sewage biosolids (which is approximately
the median copper concentration for
sewage biosolids in the Northeast) are used,
the guidelines suggest that the total quantities
of sewage biosolids that could be applied
(before reaching the recommended maximum)
range from approximately 79 dry tons/acre for
a coarse textured soil to 186 tons for fine textured
soils. These quantities drop to between
40 and 93 tons/acre, respectively, if the sewage
biosolids applied have a higher copper concentration
of 1100 mg/kg (which is approximately
the 95th percentile concentration for
copper in the Northeast).
This article originally appeared in the issue of .