Project title:
Agronomic, Economical, and Environmental Impact of Land Applying Biosolids
Binder,
D., Sander, D. Frank, K., Shires, W., Cassman, K., Dobermann, A.
Duration: 1996
- 1999
Funding: City
of Lincoln
Collaborators:
Lancaster County Extension, Public Works and Utilities Dept. of the City of Lincoln
Contact:
Darren
Binder
University
of Nebraska-Lincoln
Department
of Agronomy and Horticulture
Lincoln,
68583-0915
(phone:
402-472-1503)
Project
description:
Application of biosolids to agricultural land has been gaining popularity over the last 30 years. One third of the biosolids produced in 1993 were land applied compared to 20% in 1972. Land application is considered to be beneficial to the municipality generating the biosolids as well as the participating agricultural producer. The municipality benefits because land application is an environmentally acceptable and cost effective means of managing the biosolids. The agricultural producer benefits by receiving nutrients, generally at a lower cost than conventional fertilizer.
In Nebraska, 90% of the biosolids are land applied. Since 1992, anaerobically digested biosolids from Lincoln’s Theresa Street Wastewater Treatment facility have been land applied. On average nearly 32,000 tones (6400 dry tones) per year of dewatered anaerobically digested biosolids from this facility have been supplied exclusively to agricultural producers in Lancaster County Nebraska.
Farmers need information on the nutrient value and the expected crop response in order to make decisions on biosolids use. More reliable predictions, especially for local soil and climatic conditions, of the nitrogen supplying capacity of biosolids are required in order to minimize the environmental impact of biosolids. While N mineralization has been widely studied, especially in laboratory incubations, there are relatively few field studies relating N availability predictions to crop growth. There are even fewer studies that attempt to determine the residual value of biosolids. We conducted a 4-year field experiment to
1. Determine the optimal single application rate of Lincoln's biosolids for irrigated corn and dryland sorghum for soil and climatic conditions of eastern Nebraska.
2. Quantify the nitrogen (N) value of biosolids in terms of N use efficiency and N fertilizer equivalency.
3. Determine the residual value of biosolids in terms of crop yield response.
4. Evaluate the environmental hazards associated with the land application of biosolids.
Key
results:
·
Biosolids increased corn
grain yield by 2.3 to 4.8 Mg ha-1 over a control with no
application. Sorghum yield response to biosolids was not as consistent as that
of irrigated corn, but grain yield was doubled in two years and nearly tripled
in 1999 from biosolids application.
·
Plant N accumulation
increased up to rates of 75 Mg ha-1 biosolids in corn and up to 100
Mg ha-1 in sorghum. At very high rates of biosolids, the extra N
taken up did not consistently increase grain yield due to climatic and other
factors limiting growth.
·
Optimal biosolids rates for
achieving maximum relative yield on Sharpsburg Silty Clay Loam were about 62
Mg ha-1 for corn (441 kg organic N ha-1) and 36 Mg
ha-1 for typical sorghum years (= 257 kg organic N ha-1).
This refers to yield response in the year of application only and assumes a)
that application is not repeated within four years and b) no mineral N
fertilizer is applied.
·
On average, the total amount of
N taken up by corn increased by 1.1 kg N ha-1 for every Mg of
biosolids applied. This is equivalent to an average yield increase of 14 kg
corn ha-1 for every Mg of biosolids or a grain yield increase of
approximately 3500 kg ha-1 at the biosolids rate required to
maximize corn yield. The increase in total N uptake resulted in an increase of
26 kg sorghum ha-1 per Mg of biosolids or approximately 2500 kg ha-1
at the biosolids rate required to maximize sorghum yield.
·
There were no differences in
the internal N use efficiency (grain yield per unit N taken up by the plant)
between N from biosolids or N from mineral fertilizer.
·
Agronomic N use efficiency
(AEN, grain yield increase per unit applied N) decreased with increasing
biosolids rate in corn, but was similar to that from inorganic N fertilizer
applied to corn. In sorghum, AEN from biosolids was lower than that of mineral
fertilizer at similar N rates. For example, the AEN from biosolids N was 10 kg
kg-1 as compared to 21 kg kg-1 from inorganic N
fertilizer.
·
First-year recovery
efficiency of N in the plant (REN, increase in N uptake per unit applied N) of
biosolids N was 39 to 45% compared to 37 to
9% for fertilizer N at similar rates of N for corn. In the subsequent years
after application of biosolids, additional N was recovered. For example, corn
recovered a total of 43% in the first year, 58% in two years, and 76% in three
years of the N applied in the 25 Mg ha-1 biosolids rate. This
suggests that N losses into the environment by leaching, denitrification, or
ammonia volatilization are small at moderate rates of biosolids application.
·
First-year recovery
efficiency of biosolids N by sorghum was lower (30%) than that of fertilizer N
(48%).
·
Relative grain increase over an no-biosolids control
over the whole four-year period of this study was similar for corn and sorghum
when biosolids were applied at the rate required to maximize yield in the first
year. On average, relative yield increase due to a one-time application of
biosolids was 33% in the year of application, 21% in the second year, 14% in
the third year and 9% in the fourth year.
·
In order to get a similar
yield increase with inorganic N fertilizer for the first year, approximately $77
worth of N fertilizer at $0.33 per kg N, was required for corn and $42 worth of
N fertilizer was required for sorghum.
·
Over a four-year period,
biosolids resulted in yield equivalent to $137 and $76 ha-1 worth of
N fertilizer for corn and sorghum respectively when the biosolids were
applied at a rate that maximized yield in the first year.
· At the irrigated site nearly a third of the accumulated nitrate, 200 kg N ha-1, leached to the 120 cm soil depth in less than one year after biosolids were applied when biosolids were applied at double the recommended rate. None of the nitrate remained in the 150 cm soil profile after four growing seasons. At the dryland site approximately 25% of the accumulated nitrate, 60 kg N ha-1, leached to the 120 cm soil depth in less than one year after biosolids application at a rate over twice the recommended. None of the nitrate remained in the 150 cm soil profile after four growing seasons.
· At or below the recommended biosolids rate (<62 Mg ha-1 in corn and <36 Mg ha-1 in sorghum) very little nitrate accumulated and was leached downward. Nitrate accumulation was minimal at the dryland sorghum site even when biosolids were applied at rates 29% greater than recommended.
· More phosphorus (P) and metals are applied than crops utilize when biosolids are applied to supply enough N for crops. Soil Bray-P levels were built up to near 300 mg kg-1 when 80 Mg ha-1 (dry basis) of biosolids were applied over a 16 year period. This is nearly 20 times the critical level (15 mg kg-1) at which P is not limiting for most row crops.
· The potential for soil P build-up is much lower with a single or less frequent applications of biosolids. Recommended biosolids rates of about 30 to 60 Mg ha-1 contains approximately 150 to 300 kg P ha-1. At the low recommended biosolids rate an average corn or sorghum crop could remove nearly all of the applied P after 5 years.
·
Concentrations of Cd, Cu, Pb, Ni, and Zn in surface and
subsurface soils were slightly higher than on average great plains soils when
nearly 80 Mg ha-1 (dry basis) of biosolids was applied over a 16
year period. However, none of these elements posed a hazard because soil levels
remained far below of even the most stringent international soil standards. It
seems highly unlikely that metals would accumulate significantly from a single
application of the City of Lincoln’s biosolids in the recommended range of
30-60 Mg ha-1.
Preliminary
recommendations for biosolids application on Sharpsburg Silty Clay Loam in
Lancaster County are:
· Apply biosolids at rates of about 30 to 60 Mg ha-1 once every four to five years. In years succeeding the application, supplementary side dressings of mineral N may be required to sustain high yields and maximize profits
·
For optimal performance, actual
biosolids rates should be adjusted depending on the cropping system, soil
nitrate level, soil organic matter content, yield goal, and biosolids
composition.
·
Soil nitrate status should be
monitored frequently, preferably each year, to adjust the application rate and
avoid hazardous build-up and leaching of nitrate, particularly in irrigated
agriculture.
·
Strategies for optimizing biosolids application in the
proximity of larger towns such as Lincoln must consider long-term effects on
soil P and possible hazards for eutrophication of surface waters. Soils should be monitored every 4 to 5 years for P and
biosolids application should not be repeated more than every four to five
years, except if lower amounts are applied each year.
·
Occasional quality control should be done to ensure
that heavy metals concentrations in the biosolids remain low.
Publications:
Binder, D.L., A. Dobermann, D.H. Sander, and K.G. Cassman. 2002. Biosolids as nitrogen source for irrigated maize and dryland sorghum. Soil Sci. Soc. Am. J. 66:531-543. [View and Download PDF of full paper]
Binder, D.L., A. Dobermann, D.H. Sander, and K.G. Cassman. 2001. Potential benefits of land-applying biosolids in eastern Nebraska. In Biosolids 2001: Building public support. WEF, San Diego (CD Rom). [View full paper]
Binder, D.L., A. Dobermann, D.H. Sander, K.G. Cassman, K.D. Frank, and W.L. Shires. 2000. Agronomic, economical, and environmental impact of land applying biosolids. Terminal report 1996-1999. University of Nebraska-Lincoln, Lincoln, NE. [View and Download PDF of full paper]