Runoff from Pasture and Cultivated Land Amended with Biosolids and Fertilizer

Crop and Soil Environmental News, September 1997

Greg Evanylo,
Nutrient and Waste Management
& Blake Ross,
Biological Systems Engineer

Introduction

Approximately 25,000 acres of farm land are permitted for the application of biosolids (sewage sludge) in Virginia. A large portion of this land is pasture and hayland, which receive surface applications with no incorporation of the biosolids. Concern about the runoff of potentially water-impacting nutrients (N, P), heavy metals (Cd, Cu, Pb, and Zn), and bacteria exists among local government officials and citizens of Virginia, who often request that land-applied biosolids be incorporated. However, incorporation of biosolids also removes protective vegetation and may increase runoff and erosion potential. Demonstration of the protection afforded surface water through regulations is necessary to promote the judicious recycling of this natural resource.

Rainfall simulation is the artificial duplication of a natural rainstorm. Rainfall simulators are used to study the relationship of rainfall to erosion, infiltration, and water quality, as well as to evaluate the effectiveness of Best Management Practices (BMP's) for non-point pollution control. Since rainfall simulators allow controlled rainstorms to be applied when and where they are desired, they can overcome the problems associated with uncertainty and variability of natural rainfall. Therefore, the rainfall simulator can also be used to visually demonstrate BMP effectiveness while water quality data are being collected. Relative BMP effectiveness is particularly evident if the area under rainfall simulation is subdivided into two or more adjacent plots implementing practices of varying degrees of effectiveness.

Objective

A study was conducted to determine the impact of surface-applied, unincorporated and incorporated biosolids and fertilizer on rainfall simulator-generated runoff of N, P, Zn, Cu, Cd, Pb, sediment and E.Coli bacteria.

Methodology

A pasture site on an Appling sandy loam soil of Mr. J.R. Smith (Bumpass, Louisa County, Virginia) was utilized for the demonstration. Four plots 25 feet wide by 55 feet long were arranged side-by-side and oriented with their length down an 11% slope. The four treatments were: 1) surface-applied to pasture, unincorporated biosolids, 2) surface-applied to plowed pasture and disc-incorporated biosolids, 3) surface-applied to pasture, unincorporated commercial fertilizer, and 4) surface-applied to plowed pasture and disc-incorporated commercial fertilizer. Biosolids (Chesterfield anaerobically-digested sludge) were surface-applied at the agronomic rate (i.e., the rate that provides the crop N needs) and fertilizer (ammonium nitrate-triple superphosphate-muriate of potash) was applied according to Virginia Cooperative Extension routine soil test recommendations on June 23, 1997. The incorporated biosolids and fertilizer were disced into the soil within 24 hours after application.

The rainfall simulation was performed by a modified sprinkler irrigation system that applied "rainfall" at approximately 2 inches per hour. Three runs were conducted during a 24 hour period on July 8-9 (15 days after treatment applications). Two inches of rainfall were applied to the plots for 60 minutes on the first test day and one inch each was applied during two ý-hour runs (separated by 30 minutes) on day 2. The 1-hour simulation on the first day approximates a storm event that would be expected to occur in Virginia as frequently as once every two years.

Runoff from the plots was measured with an H-flume and stage recorder located at the outlet of each plot. Water samples were collected manually at 3-15 minute intervals from the flumes during the simulations. The samples were analyzed for sediment (total suspended solids-TSS), nutrients (N, P), heavy metals (Cd, Cu, Pb, and Zn), and E. Coli bacteria. Only a single replication of each treatment was used in this demonstration; thus, statistical analysis could not truly differentiate between treatments, and results are presented to provide a feel for the magnitude of differences.

Results

The analysis of the Chesterfield biosolids employed in the study is presented in Table 1. The agronomic application rate provided an estimated 116 lbs plant available N, 765 lbs P2O5, 24 lbs K2O, 68 lbs S, 285 lbs Ca and 77 lbs Mg per acre. Commercial fertilizer was applied to provide 130 lbs N, 50 lbs P2O5, and 100 lbs K2O per acre according to Virginia Cooperative Extension Service soil test recommendations.

Table 1. Chesterfield biosolids nutrient analysis.

Solids	Ag rate	TKN	NH4	Org N	P	K	S	Ca	Mg
%	dt/acre	---------------------------------------%-------------------------------------
15.79	6.2	3.52	0.75	2.77	2.69	0.16	0.55	2.30	0.62

Biosolids must not exceed ceiling limits of all of the trace elements listed in Table 2 in order to be land applied. Biosolids that have trace element concentrations below the Exceptional Quality (EQ) norms and that meet Class A pathogen standards can be applied to land with no limitations. The Chesterfield biosolids, which is typical of the quality of most biosolids currently produced, is EQ with respect to trace elements.

Table 2. Trace elements in Chesterfield biosolids and USEPA recommended concentrations.

Element:		Cu	Zn	Cd	Ni	Pb	As	Hg	Se	Mo
		---------------------------parts per million---------------------------
Chesterfield		525	1040	2.1	29	58	3.2	1.2	2.8	8
USEPA
	Ceiling limit Exceptional quality	4300 1500	7500 2800	85 39	420 420	840 300	75 41	57 17	100 100	75 41

There were little or no changes in the soil concentrations of copper, zinc, cadmium, lead and nickel 15 days after the agronomic rate of biosolids was applied (Table 3)..

Table 3. Metal concentrations in soil.

Metal:		Cu		Zn		Cd		Pb		Ni
Sampling time:		before:	after:	before:	after:	before:	after:	before:	after:	before:	after
Treatment		-------------------------------------------parts per million------------------------------------------
Pasture
	fertilizer biosolids	11 9	11 11	22 20	20 22	<1 <1	<1 <1	19 17	22 20	7 5	5 6
Plowed
	fertilizer biosolids	13 13	12 14	21 22	18 30	<1 <1	<1 <1	19 18	19 18	5 5	7 6

There was less transport of water, total suspended solids (TSS), total Kjeldahl N, and total P from pasture than plowed and disced land. Less or similar amounts of each parameter was transported from biosolids- than fertilizer-amended land, with the possible exception of total N.

Table 4. Composite simulated rainfall loadings of runoff, total suspended solids, total N, and total P.

Parameter:		Runoff	TSS	Total N	Total P
Treatment		acre-inches	------------------lbs/acre------------------
Pasture
	fertilizer biosolids	0.36 0.16	20.9 4.9	0.58 1.32	0.11 0.11
Plowed
	fertilizer biosolids	0.97 0.49	372 197	4.05 3.54	0.77 0.49

Biosolids application did not increase heavy metal or bacteria transport in runoff water (Table 5). The high amounts of E. Coli transported in the runoff likely emanated from the animal manure on the pasture.

Table 5. Composite simulated rainfall pollutant loadings.

Parameter:		Cd	Cu	Pb	Zn	E. Coli
Treatment		--------------------------lbs/acre--------------------------				1010 CFU/acre
Pasture
	fertilizer biosolids	<0.00077 <0.00035	<0.00056 0.00049	<0.00819 <0.00567	<0.00091 <0.00056	5.07 34.2
Plowed
	fertilizer biosolids	<0.00217 <0.00112	0.00462 0.00889	<0.02198 <0.01113	0.00826 0.00770	31.4 15.2
CFU = Colony forming units.

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