sludge application effects on runoff, infiltration, and water quality

WATER RESOURCES BULLETINVOL. 29, NO. 1 AMERICANWATER RESOURCES ASSOCIATION FEBRUARY 1993

SLUDGE APPLICATION EFFECTS ON RUNOFF,INFILTRATION, AND WATER QUALITY'

A. C. Bruggeman and S. Mostaghimi2

ABSTRACT: Land application of sewage sludge requires carefulmonitoring because of its potential for contamination of surfacewater and ground water. A rainfall simulator was used th investi-gate the effects of freshly applied sludge on infiltration, and onrunoff of sediment and nutrients from agricultural crop lands. Rainwas applied to 16 experimental field plots. A three-run sequencewas used to simulate different initial moisture conditions. Runoff,sediment, and nutrient losses were monitored at the base of eachplot during the simulated rainfall events. Sludge was surfaceapplied and incorporated at conventionally-tilled plots and surfaceapplied at no-till plots, at rates of 0, 75, 150 kg-N/ha. Steady-stateinfiltrability increased as a result of sludge application, althoughthe no-till practice was more effective in increasing the infiltrabilitythan the sludge application. No-till practices greatly reducedrunoff, sediment, and nutrient losses from the sludge treated plots,relative to the conventional tillage practices. Incorporation ofthe sludge was effective in reducing nutrient yields at theconventionally-tilled plots. This effect was more pronounced duringthe third rainstorm, with wet initial conditions. Peak loadings ofnutrients appeared during the rainstorm with wet initial condi-tions.(KEY TERMS: sludge; land application; infiltration; runoff; nutri-ents; water quality.)

INTRODUCTION

Application to agricultural lands is a cost-effectivealternative for disposal of sewage sludge. Secondarybenefits of application of sludge to agricultural landsinclude nutrient supply to crops, increase of soilorganic matter content, and improvement of soil prop-erties. However, the potential hazards of surfacewater and groundwater contamination from land dis-posal of sewage sludge is a major environmental con-cern. Potential problems of land application of sewage

sludge have been reviewed by Kelley et al. (1984).These problems include accelerated eutrophication ofsurface waters by phosphorus, ground water contami-nation by leaching of nitrate, and health risks fromtransfer of pathogenic organisms to humans or ani-mals and from the uptake of trace elements (heavymetals) by plants.

Several authors have studied the effect of sludgeapplication on the quality of runoff water from agri-cultural lands. Kelling et al. (1977) found significantlylower runoff and sediment losses from sludge treatedareas, relative to untreated areas. However,orthophosphorus (P04-P), total phosphorus (Pt), andnitrite plus nitrate (N02+N03) loads in runoff waterfrom the sludge treated plots increased, compared tothe control plots. Dunnigan and Dick (1980) foundthat surface application of sewage sludge resulted inhigher loadings of nitrogen (N) and phosphorus (P) inrunoff water, as compared to loadings from plots inwhich sludge was incorporated into the soil.

The beneficial impacts of sludge applications toreduce surface runoff and soil erosion can be relatedto reduction of raindrop impact by the surface protec-tive sludge layer and increased infiltration as a resultof the improvement of the physical condition of thesoil (Mostaghimi et al., 1988). Significant increases inaggregation and large pore space as a result of sludgeapplication were observed during a one-year fieldstudy by Kladivko and Nelson (1979). Otis (1985),however, reported that application of waste watereffluent significantly reduced the hydraulic conductiv-ity and infiltration rate of soils due to pore clogging.He attributed pore clogging to the suspended solids in

'Paper No. 92037 of the Water Resources Bulletin. Discussions areopen until October 1, 1993.2Respectively, Graduate Research Assistant, 200 Seitz Hall, Agricultural Engineering Department, VirginiaPolytechnic Institute and

State University, Blacksburg, Virginia 24061; and Associate Professor, 308 Seitz Hall, Agricultural Engineering Department, VirginiaPolytechnic Institute and State University, Blacksburg, Virginia 24061.

15 WATER RESOURCES BULLETIN

Bruggeman and Mostaghinii

the waste water effluent, which mechanically sealedthe entrances to the larger pores. In addition, thenutrients in the waste water, which stimulated thebiological activity in the soil, causing breakdown ofthe structural units of the soil and, in turn, increasedpore clogging. Chang et al. (1983) indicated that theamount of sludge required to cause significantchanges in soil properties was much greater than theamount normally used to satisfy crop nutrientsrequirement.

The objective of this study was to investigate theshort-term impacts of sludge application method,application rate, and tillage practice on infiltration,runoff, and sediment and nutrient losses from agricul-tural lands.

MATERIALS AND METHODS

Sixteen experimental field plots, located at VirginiaTech's Price's Fork Agricultural Research Farm, 10km west of Blacksburg, were used for this study(Mostaghimi et al., 1988). Plots are located on aGroseclose silt loam soil (clayey, mixed mesic TypicHapludult). The soil is deep and well drained with aslowly permeable subsoil. The plowed surface (Ap)horizon is typically 25 cm thick, with a loam textureand moderately fine granular structure. Soil charac-teristics are presented in Table 1.

Each plot had a surface area of 0.01 ha (18.3m x5.5m). Metal borders were installed around each plotto prevent surface and subsurface runoff from flowingacross the plot boundaries. The 30 cm high borderswere inserted to a depth of about 15 cm. A concretegutter with a pipe outlet at the base of each plot col-lected and transported the runoff to an H-flume. Allplots were planted in winter rye in the fall andsprayed with paraquat, a week before the simulationruns, in early spring of the following year. No-tilltreatments were established on the killed rye stand.Crop residue was measured by randomly locating a0.6 x 0.6 m square in each plot and removing allresidue in the square for laboratory analysis.Conventional tillage was represented by removingcrop residue from the plots, tilling to a depth of 15-20cm with a power-take-off (PTO) driven rototiller, anddisking.

Anaerobically digested, polymer conditionedsewage sludge was obtained from the James Riverplant in Hampton Roads, Virginia. General character-istics of the sludge are given in Table 1. Sludge wasdistributed over the plots by subdividing each plotinto four equal-sized subareas. The sludge was

WATER RESOURCES BULLETIN 16

spread, as uniformly as possible within the subareas,using rakes. Within each tillage treatment two sludgeapplication rates, representing 150 kg-N/ha and 75kg-N/ha, and an untreated control plot, were estab-lished. Loading rates were determined using themethodology suggested by Simpson et al. (1985). Thesludge was black in color and fairly crumbly whenapplied. The high and low application rates providedan average sludge layer of approximately 1.0 and 0.5cm, respectively, although no uniform cover wasobtained. Sludge was surface applied to all no-tillplots. For the conventional tillage plots, sludge wasboth incorporate and surface-applied. The plots withthe incorporated treatments were retilled to incorpo-rate the sludge into the upper 15-20 cm of the soilprofile. Two replications of each treatment required atotal of 16 plots. Plot treatments are listed in Table 1.All treatments were randomly assigned to the experi-mental plots.

TABLE 1. Soil and Sludge Characteristics and Plot Treatments.

Soil Characteristics

Type: Groseclose Silt LoamPercent* Sand 17.9Percent Silt 58.9Percent Clay 23.2Percent Organic Matter 3.7Bulk Density 1.39 g/cmInitial Moisture Content 19.2%

Sludge Characteristics

Type: Anaerobically Digested Sewage SludgePercent Solids 16.0Percent NH4-N 0.96Percent TKN 3.02Percent Phosphorus 2.0pH 7.3

Plot Treatments

Sludge SludgeTillage Application ApplicationMethod Method Rate

No-Till N/A 0No-Till Surface 75No-Till Surface 150Conventional N/A 0Conventional Surface 75Conventional Incorporated 75Conventional Surface 150Conventional Incorporated 150

*All percentages are on a dry weight basis.NOTE: N/A = NotApplicable.

Sludge Application Effects on Runoff, Infiltration, and Water Quality

A rainfall simulator (Dillaha et al., 1987) was usedto apply approximately 90 mm of rainfall to the plotsover a two-day period. A 60-minute initial dry run(Ri) was followed 24 hours later by a 30-minute wetrun CR2), followed 30 minutes later by another 30-minute very wet run (R3). The three-run sequence isa common artificial rainfall sequence used for erosionresearch in the U.S. to represent different initialmoisture conditions (Dillaha et al., 1987). A 40-45mm/hr rainfall rate was used for all simulations. Aone-hour storm with a 40-45 mm/hr intensity has a2-5 year return period in Southwest Virginia(Hershfield, 1961). The sludge was applied 24 hoursbefore the first simulated rainstorm. Rainfall withinthe 24 to 48 hours after the application of sludge isexpected to result in extremely high loadings of nutri-ents to surface runoff, since sludge had been appliedwithin the previous 24 to 48 hours. The plots werecovered with plastic sheets between the runs whennatural rainfall appeared imminent. At all othertimes the plots were uncovered to dry naturally.Rainfall simulator rates and uniformity were mea-sured for each event, using 12 volumetric raingageswithin each plot.

Runoff rates were recorded at the base of each plotusing a 15-cm H-flume equipped with an FW-1 stagerecorder. Runoff water samples were collected manu-ally from the plots discharges at the flumes, at three-minute intervals throughout the runoff process. Thesamples were frozen immediately after collection andstored for subsequent analysis. Laboratory analyseswere conducted to determine total suspended solids(TSS), ammonium (NH4-N), nitrate (N03-N), totaland total filtered kjeldahl nitrogen (TKN and TKN),orthophosphorus (P04-P), and total and total filteredphosphorus (Pt and Ptf). All nutrient analyses wereconducted according to the EPA Standard Methods(U.S. EPA, 1979). No bacteriological analysis wasdone. Detailed information on sampling methods andsample analysis are presented by Mostaghimi et al.(1988). Sediment-bound nitrogen (N5b) was computedby subtracting total filtered nitrogen from totalKjeldahl nitrogen. Sediment-bound phosphorus (b)was obtained by subtracting tf from P. Nutrient andsediment losses were calculated from the concentra-tions of each sample by assuming that the averageflow rate was equal to the average of flow rates atbeginning and end of the three-minute samplinginterval. Variations in runoff, sediment, and nutrientyields between the different treatments were ana-lyzed using Tukey's studentized range test at the 5percent and 10 percent significance level.

RESULTS AND DISCUSSION

Infiltration and Peak Runoff

Infiltration and runoff rate data collected duringthe first (dry) run (Run 1) and the third (very wet) run(Run3) are presented in Table 2. Runoff rates record-ed during the second (wet) run (Run2) were generallyhigher than those from Runl, but always lower thanRun3. The effect of the initial soil moisture condi-tions, as represented by the sequence of runs, is mostobvious when comparing Runi and Run3 data. Thus,data on Run2 are not presented here. For most treat-ments, steady-state conditions were approached atthe end of the third (30 minute) run, as can be seen inFigures 1-3, except for the sludge treated no-till plotsand the conventionally-tilled plots, without sludgetreatment and with sludge incorporated at a rate of75 kg-N/ha, for which runoff rates were still increas-ing. The near-steady-state infiltration rate was com-puted as the difference between rainfall applicationand runoff rate at the end of the third run, andreferred to as final infiltration rate for the purpose ofdiscussing infiltrability in this paper. Infiltrability ofsilt loam soils, measured under ponded conditionswhen the infiltration rate decreases to its final value,has been found to vary between 5-10 mm/hr (Hillel,1971). These values compare relatively well with thevalues of 2.4 mm/hr and 17.7 mm/br, for the nontreat-ed no-till and conventionally-tilled plots, respectively,measured during the experiment.

Application of sludge generally increased infiltra-tion rates and reduced peak runoff rates. The surfaceapplication of sludge formed a protective layer on thesoil surface, which reduced surface sealing caused byraindrop impact. The sludge cover also increased thehydraulic resistance of the surface, thus reducingpeak runoff rates. Final infiltration rates at the no-tillplots increased by 78 percent and 20 percent for the75 kg-N/ha and 150 kg-N/ha treatments, respectively,when compared to the treatments with no sludgeapplication. Application of 150 kg-N/ha was found tobe the most effective in increasing infiltration at theconventionally-tilled sites, resulting in an averageincrease of 394 percent in steady state infiltrability,compared to the control plots, whereas an increase of10 percent was found for application rates of 75 kg-N/ha. However, infiltration rates, cumulative infiltra-tion, and peak runoff rates within a tillage systemwere not statistically different with regard to sludgeapplication rate and application method.

Infiltration and peak runoff rates were more affect-ed by the different tillage practices than by the differ-ent sludge application rates. This effect is evident

17 WATER RESOURCES BULLETIN

Bruggeman and Mostaghimi

TABLE 2. Infiltration and Runoff During Dry Run (Runi) and Wet Run (Run3).

Treatment Infiltration as Percentof Rainfall Peak Runoff

FinalInfiltration

RateApplicationSludge

Application Runi Run3 Runi Run3Method (kg-N/ha) (percent) (percent) (mm/br) (mm/hr) (nun/br)

NO-TILL

N/A 0 85edt 48abc** 12.5bc 27.9ab 17.7abcSurface 75 97d 78a 2.6c 14.2b 31.5aSurface 150 96d 61a 7.5bc 24.8ab 21.3ab

CONVENTIONAL TILLAGE

N/A 0 8led 15c 22.8ab 44.5a 2.4cSurface 75 88ed 17c 17.7abc 45.la 1.OcIncorporated 75 68e 15c 34.4a 40.la 4.3bcSurface 150 9Oed 43abc 15.6abc 31.5ab 14.8abcIncorporated 150 9Oed 33bc 19.9abc 33.8ab 8.9bc

sMeans within the same colunm with different letters (e,d) are significantly different at the 0.10 probability level according to Tukey's stu-dentized range test.

**Mes within the same column with different letters (a,b,c) are significantly different at the 0.05 probability level according to Thkey's stu-dentized range test.

NOTE: N/A = Not Applicable.

from the data presented in Table 2, since the finalinfiltration rate for the no-till control treatment (0 kg-N/ha) is much higher than those reported for anyother treatment under conventional tillage. Theimpact of no-till treatments on increasing infiltrationrates is most pronounced under the very wet condi-tions (Run3) when, at the no-till plots, on the average,62 percent of the rain infiltrated, compared to 25percent on the conventionally-tilled plots. Under thedry conditions (Runi), 93 percent of the rain infiltrat-ed onto the no-till plots and 83 percent for the conven-tionally-tilled plots. The surface residue left at theno-till plots was found to offer a higher hydraulicresistance and a better protection against surfacesealing than the surface cover provided by the sludgelayer. Erosion of the sludge layer as well as cloggingof the soil pores by the infiltrating sludge particlesduring the first run may have reduced the beneficialeffects of the sludge application during the later runs.The effect of pore clogging is more prominent than theeffect of erosion at the no-till sites, where less erosionof the sludge layer and higher infiltration ratesenhanced infiltration of sludge particles into the larg-er pores. This resulted in higher infiltration rates forthe lower sludge application rates. At the convention-ally-tilled plots, more sludge eroded from the surface,relative to the no-till sites. The high sludge applica-tion rates at these plots proved more beneficial inmaintaining high infiltration rates because a suffi-cient amount of sludge was left at the surface to pro-tect the soil against raindrop impact and preventexcessive pore clogging.

WATER RESOURCES BULLETIN 18

The infiltration data of the incorporated treat-ments compared to the data of the surface treatmentsdo not indicate enhancement of soil physical proper-ties by sludge incorporation. These results wereexpected because of the short period of time betweensludge application and rainfall events. Incorporationof sludge at high sludge application rates, was moreeffective in reducing surface runoff than incorporationof sludge at low application rates. This is most likelycaused by the higher amount of sludge whichremained at the surface and provided protectionagainst raindrop impact.

The presented results show potential benefits ofsludge application on no-till agricultural land inreducing surface runoff water quality problems.However, increased infiltration rates under no-till(particularly when sludge is also applied) indicate apotential for ground water pollution under such prac-tices.

Runoff, Sediment, and Nutrient Yields

Runoff, sediment, and nutrient yields from the no-till plots were lower, compared to the conventionally-tilled plots (Table 3). At the 0.10 probability level nosignificant differences were detected between the loss-es from any of the controls or surface treatments mea-sured during Run 1. While during Run3 at the 0.10probability level significant differences in runoffamount, NH4-N, and sb losses were detected

Sludge Application Effects on Runoff, Infiltration, and Water Quality

between the two tillage systems. For the no-till treat-ments, yields of runoff, sediment, and nutrients wereleast for sludge application rates of 75 kg-N/ha.Exceptions were observed for the NH4-N and N5byields during Run3, which were lowest for the controlplots (0 kg-N/ha) and increased with increasing appli-cation rates. For the conventional tillage treatments,greatest runoff, sediment, and sediment-bound nutri-ent yields were associated with the plots with nosludge application. Although during the third run(Run3) sediment-bound nutrient yields were greaterat the plots where sludge was applied. Apparently,the significant reduction in sediment yield associatedwith sludge application reduced sediment-boundnutrient losses. Losses of NH4-N from the convention-ally-tilled plots with surface applications of 75 kg-N/ha and 150 kg-N/ha were, respectively, 4 and 10times greater than those from the control treatmentson which no sludge was applied. Loss of nitrates, con-sidered a serious problem with sludge applicationbecause of potential water contamination, was not

affected by sludge application rates (data not shown).The original N composition of the sludge may partial-ly account for this result because a significant propor-tion of the total N in anaerobically digested sludge ispresent as NH4-N, and very little is present as N03-N(Mostaghimi et al., 1988). This study was not conduct-ed long enough for nitrification to play a significantrole. Losses of P04-N from the conventionally-tilled,sludge treated plots, were approximately two to threetimes as high as the amounts lost from the controlplots.

Surface application of sludge resulted in greaterlosses of nutrients during the final run (Run3) thanduring the initial run. This effect is evident fromTable 3, where runoff, sediment, and nutrient yieldsfrom the initial run and final run, as well as the totallosses from all three runs, are presented. The effectwas most pronounced for the no-till treatments,where 21 percent of the total nutrient yields from thecontrol plots (0 kg-N/ha) appeared during the initialrun, whereas 9 percent and 14 percent of the total

TABLE 3. Runoff, Sediment, and Nutrient Losses for Dry and Wet Runs, and Totals for all Three Runs,from No-Till and Conventionally-Tilled Plots with Sludge Applied to Surface.'

TreatmentRunoff

(mm)TSS

(kg/ha)NH4

(kg/ha)P04

(kg/ha)N8b

(kg/ha)'sb

(kg/ha)TillageSystem

ApplicationRate

RUN1

No-TillNo-TillNo-TillConventionalConventionalConventional

075

1500

75150

6.81.21.88.95.24.3

5011328

1279223105

0.060.080.440.161.051.50

0.010.000.020.010.040.07

0.130.040.153.010.322.09

0.040.000.040.510.150.23

RUN3

No-TillNo-TillNo-TillConventionalConventionalConventional

075

1500

75150

11.7abc24.9a8.8ab

19.5c18.5bc12.5abc

5784347

2460656341

0.06d30.55de0.7Ode0.27de2.64de2.93e

0.030.030.090.030.100.07

0.390.481.250.861.261.34

O.22de0.03dO.29de0.37de0.87e0.43de

TOTAL

No-TillNo-TillNo-TillConventionalConventionalConventional

075

1500

75150

24.lab7.3a

14.2a40.3b33.3b22.5ab

141463

10249161129555

0.16a0.69ab1.53ab0.6Oab5.52ab6.79b

0.050.030.150.070.180.21

0.780.561.746.712.165.84

0.420.040.421.371.180.81

'Data are averages of two plots.2Means within the same column and run with different letters (a,b,c) are significantly different at the 0.05 probability level according toTukey's studentized range test.

3Means within the same column and run with different letters (d,e) are significantly different at the 0.10 probability level according toThkey's studentized range test.

19 WATER RESOURCES BULLETIN

Bruggeman and Mostaghimi

nutrient losses from the plots with sludge applica-tions of 75 kg-N/ha and 150 kg-N/ha, respectively,were lost during the first run. For the conventionally-tilled plots, where no sludge was applied, 31 percentof the total nutrient losses occurred during the firstrun, compared to 23 percent and 25 percent for sludgeapplications of 75 and 150 kg-N/ha, respectively. Highrunoff rates appeared immediately after the start ofRun3, whereas, during the initial run (Run 1), signifi-cant runoff appeared only 40 minutes after the startof the rainfall. This resulted in high sediment andnutrient yields from the third run (Run3) compared toRuni. Similar results were found by Nelson andRomkens (1970) and many others during rainfall sim-ulator studies. Sediment losses were generally leastduring Run2, while runoff and nutrient lossesincreased throughout the sequence of rainfall events.The lower application rates did not reduce nutrientavailability sufliciently enough to reduce losses fromthe conventionally-tilled plots during the more vul-nerable conditions of the third rainstorm (Run3).

The total runoff, sediment, and nutrient yields,reported in Table 4, indicate that, among the treat-ments investigated, surface application of sludge tono-till plots is the most preferable treatment forsurface water quality protection. Runoff and sedimentlosses from the sludge treated plots were greatest

when sludge was incorporated into the conventional-ly-tilled plots. Nutrient yields increased in the orderof no-till (surface application) < conventional tillage(incorporated) < conventional tillage (surface applica-tion). Losses of both sediment-bound and solublenutrients from conventionally-tilled plots were great-ly reduced when sludge was incorporated. The effectof the tillage system on nutrient losses is most pro-nounced under dry conditions, as can be seen from thefact that only 13 percent of the total nutrient yieldsfrom the no-till plots is lost during Run 1, compared to66 percent during Run3. The losses for the initial andfinal runs at the conventionally-tilled plots were 24percent and 47 percent of the total losses of all threeruns, respectively.

Runoff, sediment, NH4-N and P04-P loadings foreach five-minute interval during the dry and wet runsare presented in Figures 1-3. These figures illustratethe impacts of tillage practices and application meth-ods on sediment and nutrient loadings to surfacewater. Application of sludge to no-till plots significant-ly reduced runoff and sediment losses during the first45 minutes of rainfall (Figure 1). Consequently, nutri-ent loadings from all no-till plots were low during theinitial part of the run. As the rainstorm progressed,NH4-N loadings increased. Maximum loadings at theend of the run were 0.01, 0.02, and 0.11 kg/ha for the0, 75, and 150 kg-N/ha application rates, respectively.

TABLE 4. Runoff, Sediment, and Nutrient Losses for Dry and Wet Runs, and Totals for all Three Runs,from No-Till and Conventionally-Tilled Plots with Surface Application and Incorporation of Sludge.1

TreatmentRunoff(mm)

TSS(kg/ha)

NH4(kg/ha)

P04(kg/ha)

Ngb(kg/ha)

sb(kg/ha)

TillageSystem

ApplicationRate

RUN1

No-TillConventionalConventional

SurfaceSurfaceIncorporated

1.5b24.8a8.9a

20b164ab544a

o.26d31.4ledO.85e

0.010.050.02

0.090.210.53

0.02dO.19eO.15e

RUN3

No-TillConventionalConventional

SurfaceSurfaceIncorporated

6.9b15.6a16.3a

45b498a756a

o.62b2.79aO.65b

0.060.080.04

0.871.301.51

O.16dO.66eO.44de

TOTAL

No-TillConventionalConventional

SurfaceSurfaceIncorporated

10.8b27.9ab34.8a

82b841ab

1750a

1.11b6.16a2.03b

0.090.190.08

1.154.002.58

O.23bO.99a0.77ab

1Data are averages of four plots: two replicates of two application rates (75 kg-N/ha, 150 kg-N/ha).2Means within the same column and run with different letters (a,b,c) are significantly different at the 0.05 probability level according toTukey's studentized range test.

3Means within the same column and run with different letters (d,e) are significantly different at the 0.10 probability level according toTukey's studentized range test.

WATER RESOURCES BULLETIN 20

Sludge Application Effects on Runoff, Infiltration, and Water Quality

21 WATER RESOURCES BULLETIN

Run 1 Run3300

200 'o(I)

100

0 10 20 30 40Time (mm)

Run3

60 70

o kg—N/ho

-300 0.6-

• 200 0.4

100 0.2

0.0

75 kg—N/ho

300

200

100

300

0£

0 Runoffa- TSS

NH4=0.4 ________z -APO4

££ 0.2

A AA A A A LA' 0 10 20 30 40 50Time (mm)

0Runi06

0a-

=0.4z

Eo.2E00I—

0.0 A-'---" " 0' 0 70CD

150 kg—N/ha

0.60a-

=0.4z

-C

E 0.2E00I-

0.0• 0C

200 0-C

U,100 g

10 20 30 40 50 60Time (mm) Time (mm)

Run3300

Run 1

300

200

100

010 20 30 40 50 60 70Time (mm) Time (mm)

Figure 1. Runoff, Total Solids (TSS), NH4-Nand P04-P Loadings Per Five-Minute Interval During the First (dry)and Third (wet) Run from No-Till Plots for Application Rates of 0, 75, and 150 kg-N/ha.

200 0-C

U,100

Bruggeman and Mostaghimi

During the third run, runoff, sediment, and nutrientloadings increased rapidly and then stabilizedhalfway through the run.

Similar patterns were found for the conventionally-tilled plots, although runoff, sediment, and nutrientloadings were generally higher than those from the

no-till treatments (Figures 2 and 3). Runoff, sediment,and nutrient losses from the 75 kg-N/ha treated plotsstarted before those from the 150 kg-N/ha treatedplots, and stabilized towards the end of the first rainstorm, whereas losses from the 150 kg-N/ha treat-ment did not seem to reach steady state levels before

IncorporatedRun3

Time (mm)

LLJJ 0

Cr)(I)IUtI —

400

Figure 2. Runoff, Total Solids (TSS), NH4-N andP04-P Loadings Per Five-Minute Interval During the First (dry)and Third (wet) Run from Conventionally-Tilled Plots for Application Rates of 75 kg-N/ha.

WATER RESOURCES BULLETIN 22

Run 1Surface applied

Run30£0.6

0,4z

0.2

C

300

,,nn —'LIJU-c

U,C/)

IVU I—

40 50 60Time (mm)

010 20 30 40Time (mm)

300

Sludge Application Effects on Runofl Infiltration, and Water Quality

the end of the storm. Peak loadings for both applica-tion rates reached values of 0.55 kg/ha for NH4-N and0.02 kg/ha for P04-P when sludge was surfaceapplied, whereas the peak loadings from the plotswhere sludge was incorporated averaged 0.12 kg/hafor NH4-N and 0.01 kg/ha for P04-P. Nutrient peak

loadings from the no-till sites were similar to thosefrom the conventionally-tilled, incorporated plots.Sediment loadings, however, reached values of 175kg/ha in the runoff from the conventionally tilledplots, whereas, for the no-till plots, the sediment load-ings did not exceed 13 kg/ha.

Run 1Surface applied

Run3300

.—'LJV Q

(I)(I)IJu I-.

40 50Time (mm)

010 20 30 40Time (mm)

Run 1

a

p0.6

Iz

£E00I-'-S'I-0C

0::

0

0.6000.4z

E 0.2

00I.-

c 00::

Figure 3. Runoff, Total Solids (TSS), NH4-N andP04-P Loadings Per Five-Minute Interval During the First (dry)and Third (wet) Run from Conventionally-Tilled Plots for Application Rates of 150 kg-N/ha.

23 WATER RESOURCES BULLETIN

IncorporatedRun3

300

.,nr '—SLJV

U')U,IJu I—

Time (mm) Time (mm)

Bruggeman and Mostaghimi

Nutrient Concentrations

Peak concentrations of 35 mg/L NH4-N and 1.35mg/L P04-P were measured in the runoff from theconventionally-tilled plots, surface application,towards the end of the first run (Figure 4). Nutrient

30E

-J0'E

concentrations were found to be fairly stable through-out the runs when sludge was incorporated.Concentrations of NH4-N decreased to an averagelevel of 4 mg/L for conventional tillage (incorporated);10 mg/L for no-till (surface treatments); and 15 mg/Lfor conventional tillage (surface treatments) duringR3. Levels of NH4-N in the range of 0.2-2.0 mg/L have

1.5-J

0a-

0.5

0.0

Figure 4. Concentrations of NH4-N and P04-P in Runoff During the First (dry) and Third (wet) Run fromNo-Till and Conventionally-Tilled Plots with Surface Applied and Incorporated Sludge Treatments.

WATER RESOURCES BULLETIN 24

Run 1

50

400 No—T., Surf.. Conv.T. Surf

Conv.T., Inc.

Run3

20

10

50

40

'230E

20z10

0

xz

2.0

70 10 20 .30 40Time (mm)

10 20 30 40 50 60Time (mm)

Run 1 Run32.0

1.5

1.0

0.5

0.Oo- 10 20 30 40 50 60Time (mm)

70 0 10 20 30Time (mm)

40

Sludge Application Effects on Runoff, Infiltration, and Water Quality

been shown to be toxic to some species of freshwateraquatic life (U.S. EPA, 1976). These concentrationswere exceeded for all treatments in this study.Concentrations of P04-P averaged 0.2 mg/L, through-out the runs for the conventional plots, when sludgewas incorporated. Phosphorus concentrations in therunoff water from the conventional and no-till plotswhere sludge was surface applied were three to fourtimes greater than those from the plots where thesludge was incorporated, because of the erosion ofsludge with high amounts of available phosphorusfrom the surface. High phosphorus concentrations areassociated with accelerated eutrophication of waterbodies. The concentration level of 0.01 mg/L P04-P,necessary to support algae growth in surface waters(U.S. EPA, 1976), was exceeded in the runoff from alltreatments.

CONCLUSIONS

This study analyzes the effects of freshly-appliedsewage sludge on infiltration, runoff, and water quali-ty from agricultural land. Runoff, sediment, andnutrient losses from 16 field plots were monitoredduring a three-run sequence of simulated rainfall.Rainfall was applied at a rate of 45 mm/hr over a two-day period beginning 24 hours after the sludge appli-cation. Application of sludge reduced runoff andsediment losses from no-till and conventionally-tilledplots during the first 40 minutes of the storm (45mm/hr), without significantly increasing nutrientlosses. Peak nutrient losses appeared during the verywet conditions of the third rainstorm. Incorporation ofsludge was found to be most effective in reducingnutrient losses from the conventionally-tilled plotsduring the final run. Surface application of sludgereduced the amount of runoff and sediment comparedto incorporation, although the effect was less pro-nounced under the very wet conditions of the finalrain storm.

No-till practices were found to be more effectivethan conventional tillage in reducing runoff andnutrient losses from sludge-applied plots than conven-tional tillage practices. Application of sludge at a rateof 75 kg-N/ha to no-till plots reduced runoff, sediment,and sediment-bound nutrient losses, compared toplots on which no sludge was applied, but sludgeapplication increased losses of NH4. Concentrations ofP04-P in runoff water were lowest when sludge wasincorporated.

A sludge application of 75 kg-N/ha on no-till plotsappears to be the best alternative for sludge utiliza-tion from surface water quality standpoint, although

this study did not take losses of coliform and heavymetals into consideration. The observed higher infil-tration rates for the no-till plots, relative to those forthe conventionally-tilled plots, increase the potentialfor leaching of nutrient to ground water. The long-term effect of sludge application on steady state infil-trability and its effect on runoff and losses ofnutrients, coliforms, and trace elements to surfacewater and ground water should be investigated.

ACKNOWLEDGMENTS

The work upon which this paper is based was supported by theVirginia Agricultural Experiment Station through funds providedby the Virginia Water Resources Research Center.

LITERATURE CITED

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Nelson, D. W. and M. J. M. Romkens, 1970. Transport ofPhosphorus in Surface Runoff. In: Relationship of Agriculture toSoil and Water Pollution. Cornell University Conference onAgricultural Waste Management, Rochester, New York, January19-21, 1970, Cornell University, Ithaca, New York.

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