LEACHING OF NUTRIENTS AND PESTICIDES FROM THE SOIL PROFILE

D. V. Calvert 1

Great concern has been expressed in recent yearson the possible contamination of our waterways withfertilizers and pesticides originally applied in agriculturalendeavours. Ecologists have charged that fertilizers areserious polluters of the environment (8). Considerableanguish was brought to the agricultural community by aproposal made by the Illinois Control Board (22) to limitthe amount of nitrogen that can be applied to Illinoiscornfields. Data to substantiate these charges and proposalsof legislation were not available in many cases. Manyimmediate investigations of our land management practiceswill be necessary to find what production practices haveto be modified in order to assure that pollution fromagricultural sources is kept at a minimum if the nationis to meet the 1985 goal of "the concept of zero -discharge" as conceived by the Environmental ProtectionAgency (9).

It appears that fertilization practices have affectedthe nutrient content of some waterways, based on anumber of recent research reports. For example, Binghamet al. (2) found that both drainage water and nitrate-nitrogen (NO3-N) losses from a 389 hectare (960 acre)citrus watershed near Riverside, California were substantial,representing 40 to 50% of the water entering the watershedand about 45% of the nitrogen applied each year as ferti-lizer. Harmeson and larson (14) and Harmeson et al. (15)reported that the nitrate content of surface waters inIllinois sampled prior to 1956 did not exceed the USPSStandard of 45 rng per liter. This standard has since beenequalled or exceeded in at least 9 major streams. Highnitrate concentrations were associated with areas ofintensive agricultural production where soils werewell-drained, fertile, rich in organic nitrogen and wherehigh levels of fertilizer nitrogen were applied. Increasednitrate concentrations were correlated with increasedstream flow, both reaching maximums during late winterand early spring with minimums attained in late summerand early fall. This pattern would suggest an agricultural

1 Associate Professor of Soil Chemistry, AgricultUral Research

Center, IFAS, University of Florida, Fort Pierce.

source of nitrate as the principal contributor in view ofthe constancy of seasonal nitrogen outputs from sewagetreatment plants.

It has been speculated that nutrient enrichment ofwaterways would be greatest in areas composed mainlyof sandy soils and intensively sprayed and fertilized cashcrops such as exist in Florida (19). This speculation appearsto be at least partly right when we turn our attention to theresults of research studies conducted in Florida. Forexample, Calvert and Phung (4) reported losses of nitrogenfrom a newly developed grove near Fort Pierce, Florida ofapproximately 35% of the applied nitrogen. Forbes et a/.(12) reported NO3-N concentration in soil water fromboth cultivated and uncultivated deep sandy soils of Floridato range from 1 to 17 ppm at the 12O-cm depth. Theconcentrations are similar to the 0.3 to 8 ppm NO3-Nrange previously reported (4). Graetz et a/. (13) in Floridafound that approximately 45% of the nitrogen applied tomillet planted on Eustis fine sand leached below the rootzone. This soil is well-drained and has little biodegradablecarbon in the lower horizons, hence it was speculated thatmicrobial denitrification did not occur. Studies conductedby the Central and Southern Florida Flood Control District(7) have shown that average phosphorus concentrationstend to increase with increasing "drainage density". This"drainage density" index is simply the total length ofdefined waterways (both natural and manmade) withinthe watershed divided by the watershed area. Drainagedensity consequently provides a valid general indicatorof phosphorus concentrations since the type of agriculturalland used is basically the same.

Soil herbicide residue studies conducted by Tuckerand Phillips (24) indicate that herbicides used in groveson Florida's deep sands at recommended rates aredissipated to a large extent before reaching ground waterlevels. Similar studies are in progress on bedded groves inFlorida's flatwoods. Wheeler et aI. (26) found that neitheracarol nor chlorobenzilate miticides had significant long-lasting effects on soil microbiological populations and thatboth chemicals had rapid rates of disappearance from the2 flatwood soils studied.

The main purpose of my talk today is to review

78

the nutrient and pesticide movement studies conductedin conjunction with the SWAP drainage investigation nearFort Pierce, Florida. It will be my pleasure to personallyshow you our facilities for conducting the SWAP relatedresearch for those accompanying us on the Short CourseTour. I would like to briefly explain the SWAP drainageresearch study in relation to the pesticide and nutrientmovement studies for those not remaining for the tour.

The SWAP project is,a cooperative research effortof the Agricultural Research'Service of the United StatesDepartment of Agriculture and the University of FloridaInstitute of Food and Agricultural Sciences. Its primaryobjectives were to evaluate systems of water managementand tile drain sludge control on Florida flatwood soils(spodosols). The research project is entitled Soil-Water-Atmosphere-Plant relationships (SWAP) and was establishedby the U. S. Congress in January, 1968. The SWAP drainagestudy at the ARC Fort Pierce basically is a 25-acreIysimeter study on production and management of citrusgroves on tile-drained flatwoods soils.

We took advantage of the highly organized anddeveloped cooperative drainage study to intensify ourefforts to investigate the possible losses of pesticides andfertilizer from citrus groves on these types of soils, aidedby a research grant sponsored by the EnvironmentalProtection Agency. The SWAP field study was designed toinvestigate the effect of 3 types of land preparation and 2drain line designs on the growth of 12 different citrus scion-rootstock combinations. We have a total of 9 plots made upof 3 replications of each of 3 tillage or land preparationtreatments. Tillage treatments are DT (deep tillage), DTL(deep tillage plus lime) and ST (surface tillage). Deep tillagewas accomplished with a tile trencher to a depth of 106 cm(42 inches) continuously across the landscape for eachhectare plot (2.5 acres). Deep-limed plots received 55 tonsper ha (25 tons per acre) of dolomitic agricultural limestonebefore deep mixing.

The objectives of this study are multiple and I willdeal today with only those allied to nutrient and pesticidemonitoring. Three research objectives along these lines wereto 1) monitor the loss of surface-applied fertilizers andpesticides through surface runoff and drainage from a citrusgrove located on Florida flatwood soils, 2) establishbase-line (background) data for concentration levels ofagricultural chemicals for the area under investigationand 3) evaluate the effect of selected carefully defined

agricultural management systems upon pollution of soilwater.

Now I would like to briefly review with you some ofthe results we have obtained toward meeting these

objectives.

designs, open and submerged drains, had little, if any, effecton nutrient and pesticide movements (4, 25). Nitrate-Nconcen~rations were only slightly lower in submerged linesthan in the open drains. Phosphate concentrations andorthophosphate-phosphorus (PO4-P) discharge wereessentially the same from both types of drains.

Our greatest differences and probably mostmeaningful results from the study have come as a result ofthe tillage treatments imposed in the SWAP drainage area.Briefly, we have found the nutrient movement resultingfrom the 3 tillage treatments to be as follows: Greatestleaching losses through the soil profile for both PO4-P andNO3-N have occurred from the ST plots. Concentrationsof PO4-P appearing in the drainage water from ST plotswere higher than expected and may indicate fixationmechanisms occur to a lesser degree in the A horizons ofOldsmar fine sand than other associated soils (3). Both DTand DTL plots leached very little PO4-P into drains,apparently due to the greater surface and chemical naturefor retention of PO4-P provided by the deep tillage. TheDTL treatment did give significantly more NO3-Nmovement into the drains than the DT treatments whichwa~ probably due to the higher nitrification rate found forthe DTL soil (20).

Not only have concentrations of nutrients in the tileout-flow water varied considerably with tillage treatments,but they have also varied with amount of discharge water,rate and time of fertilization (3) (Table 1) and season(Tables 2 and 3). Monthly NO3-N concentrations in thedrainage water from the SWAP tillage treatments did notexceed 8 ppm in the period May, 1971 through April,1972. The United States Public Health Service has selected10 ppm NO3-N as the critical limit above which water isconsidered unsafe for drinking purposes (6). Concentrationsof PO4-P in the waters from DT and DTL were very low(0.4 ppm) while concentrations ranged from 0.2 to 0.9 ppmin ST water (3). There was a trend for both NO3-N andPO4-P to increase in concentration with increase inrainfall, particularly in the summer months. Nutrientconcentrations in drainage water sampled from thesurrounding perimeter ditch system and from the drains ofa non-tilled non-agricultural (check treatment) area nearbyand in the water at the discharge outfall for the overallproject generally were much lower than that found in thedrainage water from the tilled and cropped areas. Theoutfall sump water did not exceed 2.5 ppm NO3-N in thepeak period of August, 1971 (unpublished data, FloridaAgricultural Experiment Station).

The lower concentration of phosphates in the ditchand outfall can probably be explained by phosphorusfixation with clay materials in the ditch banks and by itsabsorption by plants in and near the water. There is also adilution effect caused by water coming from unfertilizedareas. Nitrates are probably assimilated by absorption byplants and by denitrification in the near-anaerobic con-

NUTRIENT MONITORING (LONG TERM STUDY)

First, we found that our 2 different types of drain

79

TIbI. 2. Me.n concentretlon and drain dilCh.~ per month of N.P end K under 3 ~ of soil m8\8g8ment during Mev thr~Octob.- 1971.XV

Meendildta9/monthz

Soiltr881ment

ConcentrationMeenz R8IgBEI8Inent

qn..4.84 .1.19 b2.28 b

me/llter5.02 . 0.68-7-2.04 b 0.32-3.154.07 . 0.75-7.34

N~-N STDTDTL

ditions of the ditd1 bottom. The. results are similar tothose obtained in e cooperative study between the u. S.Geological Survey end the Centrel end Southern FlorideFlood Control District of the Chandler Slough (7, 17)whid1 indicated thet a segment of undistu~ mersh8t the lower end of the wetershed is effective in reducingthe phosphorus conc»ntretions. Phosphorus concentrationswere reduced 25% to 55% in the water after flowingthrough the marsh aree.

Totel disd1..ge of nutrients is a function of bothnutrient concentration and volume of water flow in a givenperiod. I am indebted to E. H. Stewart, USDA-ARSHydrologist at the SWAP drain. site, for supplying uswith a continuous record of weter flow from e8d\ drainline and for surface runoff values for each tillage plot,as well as a reco'rd of the total flow from the overall SWAParea during the periods when the nutrients and pesticideswere monitored. Results of the hydrologic studi"conducted et the SWAP site have been Sl.Hnmarized el.-where (1, 23). Mean monthly disd1arges of NO3-N andPO4-P in the drainage water ~re generally greater fromthe ST treatment than either DT or DTL treetrnents (3)

(Table 1), Peak disd1arges of both nutrients were obtain.tduring August, 1971, es shown in Figs. 1 and 2; this coin-cided with a large epplication of fertilizer prior toest~lishing a cover crop for erosion control. Meen monthly

0.68 .0.16 b0.10 b

PO4-P ITDTDTL

0.83 a0.27 b0.17 c

OA7-{}.900.10-0.38o.OO-4-~

7:'- .3.17 b2.»b

STDTDTL

7.66 a8.15 .4.46 .

K

XRep"oduced from the Journal of Envlronment8i Ouellty, 412):186, 1976, by penn_Ion of the Amerlc8n SocIetY of AeronCMnY13).

YHigh reinfe" period.

ZMeen, follo~ by dlff8r8ftt 1ett8n are ,i~lflcently different(P-o.06), . Irldic818d bv Duncen', multipte ~ test.

T~e ,. Fertilizer N. Pend K eppliedlhe end -ter dilctlarvedfrom 3 till. tr881menu.K

T.~. 3. Me.n concentr8tion and dr8/n discharge per month of N.P and K under 3 ~ of soil management during Novemt»r1971 thr~ ApiJ 1972.xy-w;u~~~ -

ST DT DTLF8ftiIiZ8r -'P'ied

N P KDet8 MeandilCh~lmondtz

Concentmion

Meetlz R8ng8Soil

u.tment

--m3Jhakg/ha Elen.nt

1971M8YJuneJulyAuptSept8mberOctober

M.n

3.877.907.90

41.6010.3210.32

1.~3.453.45

18.111.131.13

222

1,398768

1,385804883876

247790~818431572677

12687951370S339541484

malll-1.51 a 0.40-2.810.72 b 0.43-1.001.20 a 0.8-2.00

kglha0.62 a0.23 b0.29 b

N~-N ITOTOTL

PO4-P ITDTDTL

0.4280.07 bO.OO7c

0.19-0.700.02-0.300.00-0.01

0.18 .0.02 b0.01 b

1972F8bru8YAprilMevJun.July

~

10.3210.3210.3216.6815.68

1.131.131.131.731.73

8.578.578.57

13.0313.03

787886836

3.325677

1,278

432391468

1,369388em

K ITDTDTL

2.76.3.73 .3.12 .

1.01-4.102.0 -5.201.6 -5.20

1.48 81.38 .0.92 b

XReproduced from the Journal of Environmental Quality, 4(2):185, 1975, by permiliion of the AmericM SocIety of Aeronomy(3).

XReproduced from the Joumel of Envlronment8 Quel/ty.4(2):184.1975. by perm_Ion of the ~rlcan SocIety of A,onomy (3) y Low r8inf81 period.

ZFr~ ~ supplied by E. H. S~rt. USDA-ARS. Aer. R8.c-n." Fort PIerce, Fl.

ZM... fotlo_d by different Ien.n are li~iflC81tly different(P-o.05), . Indic8t8d by Duncan', multiple range teat.

4.0-12.44.5- 8.802.2- 6.Y

3.218.668.66

34.458.678.57

628523672

1.889486769

80

NO3-N discharges for May through October, 1971 (wetperiod) amounted to 4.8 kg/ha for ST, 1.2 kg/ha for DTand 2.3 kg/ha for DTL treatments (Table 2); while meanmonthly discharges for the low rainfall period of Nov-ember, 1971 through April, 1972 amounted to 0.6 kg/hafor ST, 0.2 kg/ha for DT and 0.3 kg/ha for DTL (Table 3).Mean monthly PO4-P discharges were in the order of0.6 kg/ha for ST, 0.2 kg/ha for DT and 0.1 kg/ha for DTLin the high rainfall period and 0.2 kg/ha for ST, and 0.02kg/ha for DT and 0.01 kg/ha for DTL in the low rainfallperiod.

Nitrate-nitrogen losses in the subsurface drainagewater from the ST, DT, and DTL plots were equivalentto 31.9, 8.3 and 15% respectively, of the nitrogen appliedin the fertilizer (3) (Table 4). Orthophosphate-P lossesfrom the DT and DTL plots were considerably less thanfrom the ST plots. Those losses were equivalent to 14.2.3.4 and 2.0% of the phosphorus applied to the ST, DT.

DTLpiots, respectively.

MONTHS

Fig. 1. The effect of 3 soil preparation treatments on N~-Ndischarged in drainage water during May, 1971 through July,1972. [Reproduced from the Journal of Environmental Quality,4(2):184, 1975, by permission of the American Society ofAgronomy (3)].INTENSIVE STUDIES OF NUTRIENT LEACHING

MONTHS

Fig. 2. The effect of 3 soil prep.-.ion treatments on PO4-P (ortho-phosphates) discharged in dr.~ ~er during May, 1.971through July, 1972. [Reproduced from the Journef ofEnvironmental Quality, 4(2):184, 1975, by permitS ion of theAmerican Society of Agronomy (3)].

Table 4. Estimated loa of nutrienU In drainage ~er from ploUunder 3 systems of soil management expreaed as % of totalnutrientS applied.z

Soiltreatment NO3-N PO4.p K

STDTDTL

31.98.3

15.0

'..23.42.0

62.335.523.2

Several short-term intensive studies on NO3-N,PO4-P and pesticide losses in both surface and subsurfacedrainage water from the 3 SWAP tillage systems have beenconducted in the past 2 years (5). The pesticide portionof these studies will be summarized separately. Thesestudies were conducted during the drier portions of theyears so that we cou1d control the water (irrigation)variable more preciselY - Losses were examined afterapplying irrigat.ions amounting to 12.9,7.6,5.6 and 3.&cmof water and fertilizations amounting to 530 kg per ha ofan 8-2-8 (42 kg/ha nitrogen as amR1onium nitrate and50 kg/ha PO4-P as superphosphate) fe~tilizer and nominalapplications of 2,4-D, chlorobenzilate and terbacil. Anex~ption was the 5.6-cm irrigation period when plotswere not treated with fertilizer and pesticides prior toirrigation. The preceding fertilization had been made 2months prior to the 5.6-cm irrigation. Each intensivestudy period lasted 14 days, commencing with fertilizationand immediately followed by irrigation.

A series of smooth nutrient concentration anddischarge curves with well-defined peaks were obtainedfrom these studies (5). Examples of the type of curveobtained by intensive sampling are presented in Figs. 3and 4 for NO3-N and PO4-P discharges in the subsurfacedrainage water during parts of May and June, 1974 (12.9cm of irrigation was applied on May 21). We are hopefulthat these curves will be useful in the formulation ofmathematical models having predictive value for futureleaching events.

Surface-tilled plots .gave greater NO3-N dis~ari8s(Table 5), 14.4 kg/ha NO3-N, in the 14-day period afterthe 12.9-cm irrigation than either DT or DTL, which were0.6 and 4.8 kg/he NO3-N, respectively. Discharges from

ZReproduced from the Journel of Environmental auelity, 4(21:185,1976, by permillion of the American-Society of Agronomy (31.

81

_I...~.....~E~

z."

0Z

~

...\r D~~&~

00

80

60

40

20IT

30 31

DTL were higher, however, than from DT, probablybecause this mixed and limed soiJ has a higher nitrificationrate, as Phung showed (20). ST plots discharged up to0.38 kg/ha PO4-P in the 14-day period following the12.9-cm irrigation, but phosphate discharges from DT andDTL were only 0.07 and up to 0.11 kg/ha PO4-P in the14-day period, respectively (5).

The contribution of surface runoff water to theoverall nutrient enrichment of the ditch water was low forthe DT plots, less than 0.65 kg/ha NO3-N for DTL andless than 0.44 kg/ha for DT after the 12.9-cm irrigation,and was zero for ST since there was no runoff from theST area during any of the irrigation studies (5).

It was especially interesting to find that drainagefrom the 5.6-cm irrigation without fertilization did notinitiate significant discharge of nutrients from the profiles.This tends to indicate that time of fertilization definitely isone of the factors causing enrichment of the tire outflow.

Estimated percentage losses of NO3-N were sizablefrom the 12.9- and 7.6-cm irrigations for both ST and DTLtreatments (5). ST lost nitrogen equivalent to 34.0% and12.6%, respectively, of the nitrogen appJied in fertilizerWhile DTL losses were equivalent to 12.9 and 8.3%,respectively, of the applied nitrogen after the 12.9- and 7.6-cm irrigations. Loss of PO4-P from ST was 3.7 and 1.3%of applied phosphorous and 1.3 and 0.1% from DTL afterthe 2 irrigations, respectively. Losses of NO3-N andPO4-P generally were insignificant for the 5.6- and 3.8.cmirrigations (5).

21 -22-~ .." i6 21 L"MAY JUNE

1974

Fig. 3. leaching r8P0nte of NO3-N to r.lar grCNe fertili~8tion~d 12.9 cm of irrigation. [Reproduced from the Journal ofEnvironmental Quality, 512):lln press), 1976, by permission ofthe American Society of Agronomy 15)).

PESTICIDE MOVEMENT

Water samptes collected during each of the intensivestudy periods were divided into 2 parts, one for nutrientanalysis and the other frozen and delivered to WillisWheeler. Associate Professor in the Food ScienceDepartment in Gainesville. Dr. Wheeler was responsiblefor the determination of pesticide content of the water

through gas-liquid chromatography. Pesticides used forthis study were chlorobenzilate, a miticide applied to citrustrees and used at a rate of 1.4 kg/ha; 2,4-0 applied at a rateof 3.7 kg/ha in a 1-m swath over the "pop up" sprinklerirrigation system at the SWAP site; and terbaciJ applied at4.5 kg/ha applied as a 3-m band around the base of thetrees. The pesticide-movement results selected fordiscussion today were collected during and after the 12.9cm irrigation previously discussed in the nutrient studies.The chemicals listed above were applied on March 5, 1974and irrigation of the plots started several hours thereafter.Irrigation continued for 39 hours until a total of 12.9 cmof water was applied to the plots. Water samples were takenwhen flow started in the drains and every 2 hours thereafterfor a period of 60 hours; then one sample per day for 7more days and then 2 samples were collected per weekthereafter.

Table 5. To~ dischwge of NO3-N and PO4-P in subsurl-drainage ~er in respon. to 4 irrigation arnounts.z

-

Amount of i~on""e"'"'Soil - .,.,Ji8d (cm.""~~: '

treatment 12.9 7.6 5.6 -ka/haN93.-N

".4 5.3 2.2 0.9O;8;c 0.4 0.001 0.014.8 3.2 0.1 0.01

g/ha PO4-P388 136 -64.0 4272 5 0.4 T~

107 4 3.0 T~

ITOTDTL

STDTDTl

ZReproduced from the Journal of Environmental Quality, 5(2):(In p~), 1976, by permission of the Amef'ican Society of Agro-nomy (5).

82

Data obtained during the first 26 hours of samplecollection illustrate some trends of how pesticides canmigrate downward through soil when applied to the surfaceof a sandy soil. Terbacil was found in highest concentrationin the DTl water initially, and it remained highestthroughout the initial 26-hour period (25). ST was initiallyquite low in terbacil followed by rapid increase over thesampling period, with a peak at 20 hours. The DTtreatment remained low and fairly constant in terbacilthrou~out the the 26-hour period studied. Maximumterbacil found in the drainage water in this study were124, 110 and 60 parts per billion for the ST. DTl andDTl treatments, respectively.

The DT soil treatment drainage water exhibited ahigher 2,4-0 concentration than did the other 2 treat-ments (25). The DTl treatment drainage water showedthe lowest concentration; this being sharply divergentfrom the terbacil situation. Maximum 2,4-D concentrationsin the drain. water during the 26-hour period wereapproximately 110, 48 and 35 parts per billion for DT,DTL and ST. respectively.

Chlorobenzilate has not been detected so far in anyof the water samples analyzed (25). Sampling and analysishave been continuous for the last 2 years and this materialhas been applied several times during this period.

Pesticide concentration data for the open drainsexhibited differences in some cases and similarities inothers. The DTL treatment showed the lowest levels ofterbacil while the DT and ST treatments had comparablelevels. DTl was the highest, however, for submergeddrains. The open-drain data for 2,4.D was similar to thatpresented earlier for the submerged drains (25).

RELATED STUDIES CONDUCTED IN THE FIELD,GREENHOUSE, AND LABORATORY

Other studies, both on and off the drainage site butsupporting the pesticide and nutrient move~ent researchat the site, have been conducted in several departmentson the main campus in Gainesville. These studies aredesigned to supply information to help explain thedifferences among treatments obtained at the field site.I would now like to point out a few of the supportingstudies that have been carried out.

Phung and Fiskell (21) found that oxygen depletionin poorly-drained soil profiles is followed by denitrificationand ferrous iron and manganous-manganese productionprior to sulfide production.

Phung (20) found that factors involved in oxidation-reduction changes in the 3 soil modifications were 1) sourceof organic matter as energy, 2) a rapid loss of nitrate in thetop 6 inches of soil compared to a slow loss in the blackspodic horizon when the soil is flooded and 3) ferrous ironand hydrogen sulfide dev,lopment was found to be more

rapid in DTL and DT than in undisturbed surface soil andundisturbed spodic (organic hardpan layer) horizon. Phung(20) also found that the oxygen content of the drainoutflow water was considerably hi~er in ST than in DT orDTL and that submerged vs open drain outflows were onlyoccasionally different.

Fiskell and Calvert (10) made a comprehensive studyof the chemical properties of ST. DT and DTL profiles with~ple cores to 10 depths per treatment. Soil cores were15 cm long and were taken to a depth of 150 cm. Theynoted that depth of dolomitic lime incorporationdrastically affected nitrification and they attributed tonitrate formation the pH changes found after ammoniumsulfate incubation. Only 14 tons/he of free dolomiteremained after 2 years from the original 55 tons/ha appliedhence they attributed this loss to denitrification and soilreaction which would explain the rather high calcium levelsfound in the drainage water over this period.

Fiskell and Calvert (10) further showed thatredistribution of organic matter from the A (surface) andBh (organic hard pan) horizons by deep tillage hid 25%v..iability to the 105-cm depth end that the sum ofexchangeable cations (field CEC) to the 75-cm depth wasin the order DTL > DT> ST.

Studies conducted by Fiskell and Mansell (11) onphosphorous retention showed that deep tillage of thespodosol increased Langmuir maximum sorption from 6to 96 ppm with a further increase of about 20 ppm forDTL soil. They also noted that phosphorous sorptionincreased with contact time for the unmixed organic pan.DT and DTL ~ples. bu~as most rapid for the unmixedsurface horizon and the top of the organic pan horizon.They did not show that incorporation of limestone used inDTL influenced the quality of phosphorous leached fromthe soil over the DT treatment (without deeply placedlimestone).

Kanchenasut (16) in her laboratory investigations ofthe ST profile showed thet sorption of phosphorous by thesoil did limit the movement of phosphorous as the soilsolution moves through weter-saturated cores from thesurface (A1) end spodic (B2h) horizons. Water desaturetiontended to decreese the mobility of phosphorous in these 2horizons even further. Mobilities for phosphorous endchlorine were similar and rapid during water flow throughcores from the subsurface (A2) horizon.

Mansell et 8/- (18) observed in enother study usingsoil from the SWAP site that water-soluble herbicides suchas terbacil were very mobile in the A2 horizon (white sendylayer directly under the surface layer). even for the lowconcentrations of herbicides applied to the soil.

These are only a few of the studies conducted inconjunction with the SWAP drainage site. There were manyother studies conducted in the past few years that are notreported here, especially in relation to the study of water

83

flow through the 3 soil management systems (hydrology),

SUMMARY

low concentrations, nearly zero, observed in water fromthe check area during identical time periods. The higheroverall nutrient content from the grove area would confirmthat the agricultural practice of fertilization does increasenitrogen and phosphorous nutrient concentrations in thewater. However, the lower concentrations in the perimeterditch and at the outfall shpws that these nutrientconcentrations are reduced significantly before beingdischarged into the drainage canals administered by theCentral and Southern Florida Flood Control District.

Rate of water discharge through the drains had aconsiderable influence upon the discharge of flux for both2,4-0 and terbacil. Scatter in the data is significant, but theflux of either herbicide appeared to increase from zero upto a maximum or peak zone and decrease down to aninsignificant value. The discharge of pesticide was almostcomplete within approximately 2 days after irrigationand closely follo~d the disd\arge of drainage water. Themagnitude of peak disd\arge flux for 2,4-0 was less thanfor terbacil. Chlorobenzilate molecules were not detectedin the drain water.

Thus, a combination of subsurface drainage and deeptillage appeared to offer the advantages of 1) greatercapacity to retain infiltrated water against drainage loss,2) providing a "buffering capacity" against very fast ratesof water table rise during rainy periods, but increasingsurface runoff over surface tilled and 3) permitting themaintenance of an aerobic, unsaturated root zone whichhas a large capacity to attenuate leaching losses of nitrogenand phosphorous, and thus minimize pollution of nearbydrainage canals.

LITERATURE CITED

1

2.

3.

4.

5.

Alberts, R. R., E. H. Stewart and J. S. Rogers. 1971.Ground water recession in modified profiles ofFlorida flatwood soils. Soil Crop Sci. Soc. Fla. Proc.31:216-217.Bingham, F. T., S. Davis and E. Shade. 1971. Waterrelations, salt balance and nitrate leaching lo.s of a960-acre citrus watershed. Soil Sci. 112:410-418.Calvert, D. V. 1975. Nitrate, phosphate and potas"sium movement into drainage lines under three soilmanagement systems. J. Environ. Qual. 4: 183-186.

and H. T. Phung. 1971. Nitrate-nitrogen movement into ;:.rainage lines under differ-ent soil management systems. Soil Crop Sci. Soc.FI.. Pro. 31 :229-232.

, E. H. Stewart, R. S. Mansell andJ. G. A. Fiskell. 1976. Movement of nitrate and phos-phate throultt soil and drain tile outlets. J. Environ.Qual. (In press).Case, A. A., A. Gelperin, P. C. Ward and E. F. Win-ton. 1970. The health effects of nitrates in w8ter"In: Nitrate and water supply: Source and control,

6.

Our results from the leaching studies show thatdrainage of the 3 soil management systems are greatlydifferent. Drainage rates for tile in the ST plots are muchhigher than for DT and DTL plots. Deep tillage on thesesoils tends to incorporate clay and organic materials fromthe subsoil layers into the sandy surface soil, therebydecreasing the hydraulic conductivity of the soil in theroot zone. Poorer drainage characteristics of DT and DTLplots provided improved soil-water storage capacities.however. There were also increased cation exchangecapacities which in turn resulted in larger growth rates foryoung citrus trees than those planted in ST plots.

Hydraulic response of the ST soil was particularlyrapid and of greater magnitude than for DT and DTL soils.Not only were peak flow rates approximately 2 to 3 timesgreater for ST drains than for the other drains, butaccumulative drainage of water from ST drains was alsomore than twice that for DT and DTL. Deep tillage of thetile-drained soil appeared to decrease the magnitude ofmaximum drainage rates and prolong "temporary" soil-water storage over very long periods of time.

Deep tillage of the tile-drained soil appeared todecrease the quantity of NO3-N leached, and this decreasemay be partially due to the net influence of denitrificationduring transport of NO3-N throu~ the DT and DTL mils.

Peak loss rates of phosphorous from drain linescoincided with those for nitrogen. As expected, deep tillagedrastically decreased leaching losses of phosphorousfertilizer. Unexpectedly however, deep liming of deep-tilled soil did not appear to influence leaching of

phosphorous.These and other data suggest that the tile drainage

of this spodosol provides rapid lateral water flow and tendsto circumvent flow vertically through the chemicallyreactive but slowly permeable spodic horizon. Thesubsurface drainage of this layered spodosol tends toincrease leaching losses of fertilizer nutrients.

Deep tillage of the tile-drained soil tended, however,to decrease drainage, increase cation exchange capacity ofthe A2 layer and decrease nutrient leaching rates.

Our data show that higher concentrations of nutrientsin the drainage water usually followed fertilizations,especially those followed by heavy rainfall. Irrigations of2 to 3 cm, except where applied excessively forexperimental purpose, and low rainfall apparently hadlittle, if any, effect on nutrient concentrations in the df'ainwater. Evidently, a quantity of water above the waterholding capacity of the soil is needed, either from rainfallor irrigation to initiate significant nutrient movement.

The higher concentrations of nutrients observed inthe drainage water after fertilization contrasts with the

84

responses. Ph.D. Dissertation. University of Florida,Gainesville, 209 p.

7. 21,

8. 22.

23.9.

10.

Proc. 12th Sanitary Eng. ConI. Univ. of Illinois,Urbana p. 40-65.Central and Southern Florida Flood Control District.1975. lake Okeechobee-Kissimmee basin waterquality summary information. March 20, 1975.Commoner, Barry. 1968. Threats to the integrity ofthe nitrogen cycle: Nitrogen compounds in soil,water, atmosphere and precipitation. Annual meeting,A mer. Assoc. Adv. Sci. Dallas, TX.Environmental Protection Agency. 1974. Proposedcriteria for water quality. EPA Office of WaterPlanning and Standards, Vol. 1.Fiskell, J. G. A. and D. V. Calvert. 1975. Effect ofdeep tillage, lime incorporation and drainage onchemical properties of spodosol profiles. Soil Sci.120: 132-139.

24.

25.11

26.

and J. G. A. Fiskell. 1972. A reviewof redox reactions in soils. Soil Crop Sci. Soc. Fla.Proc.32:141-145.Stanford, George. 1973. Rationale for optimumnitrogen fertilization in corn production. J. Environ.Qual. 2: 159-165.Stewart, E. H. and R. R. Alberts. 1971. Rate ofsubsurface drainage as influenced by groundwaterlevel in modified profiles of Florida flatwood soils.Soil Crop Sci. Soc. Fla. Proc. 31 :214-215.Tucker, O. P. H. and W. F. Wardowski. 1973. TheFlorida citrus industry's commitment to a betterenvironment. J. Environ. Qual. 2:70-74.Wheeler, W. B. and R. W. Mansell. 1974. Movementof chlorobenzilate. terbacil and 2,4-0 through soilinto subsurface- drain line outflow water. J. Agr.Food Chern. 23: (In Press).

, O. F. Rothwell and O. H. Hubbell.1973. Persistence and microbiological effects ofacarol and chlorobenzilate in two Florida soils.J. Environ. Qual. 2:115-117.

12.

13.

and R. S. Mansell. 1975. Effect ofP rate, time and profile modifications on P equili.bria in a spodosol. Soil Crop Sci. Soc. Fla. Proc.34:(ln Press).Forbes, R. B., C. C. Hortenstine and E. W. Bistline.1974. Nitrogen, phosphorus, potassium and solublesalts in solution in a Blanton fine sand. Soil CropSci. Soc. FIB. Proc. 33: 202-205.Graetz, D. A., l. C. Hammon and J. M. Davidson.1974. Nitrate movement in a Eustis fine sand planted.to millet. Soil Crop Sci. Soc. Fla. Proc. 33:157-160.Harmeson, R. H. and T. E. larson. 1970. Existing1eve1s of nitrates in water-the Illinois situation.In: Nitrate and water supply: Source and control.Proc. 12th Sanitary Eng. Con'., Univ. of Illinois,Urbana. p. 27.39.

QUESTIONS

14.

15.

16.

17.

18.

19.

0: When you were talking about 2.5 times theamount of nitrogen needed, you were referring to mature,bearing trees, weren't you?

Caillert: Yes, because I was speaking of treesproducing 500 boxes per acre (50 tons per ha).

0: What are the standards for nutrient content inwater going into drainage ditches and away from the fieldwhere it was applied? Aren't some nutrients necessary inthe various bodies of water?

Calvert: I'm curious about that myself. The onlystandards I've seen are those by the U. S. Public HealthService, in which 10 ppm is too high in water to be used fordrinking. Beyond that there doesn't appear to be anystandard.

Regarding nutrients in the water, we actually fertilizefish ponds to increase fish size and numbers. The shellfishindustry depends on nutrient-rich water. and the reasonit isn't so good around Ft. Pierce is because the drainagewater is flushed out of the area by the inlet. So we may betrying to prevent something that may prove detrimentalin the long run. We do need to know what levels aresatisfactory or even necessary.

Ecologists are concerned about nitrates andphosphates in runoff water because of eutrophicationor dying of lakes, due to sedimentation of algae and otherorganic matter which grows profusely under conditions ofhigh nutrient levels in the water. Whether man is doing

20.

, F. W. Sollo and T. E. Larson. 1971.The nitrate situation in Illinois. J. Amer. WaterWorks Assoc. 63:303-310.Kanchanasut. 1974. Influence of soil, water contentand flow velocity upon miscible displacement ofphosphate and chloride in undisturbed cores of aspodosol. M. S. Thesis. Soil Sci. Dept. Univ. of Fla.Lamonds, A. G. 1974. Chemical characteristicsof the lower Kissimmee River, Florida. UnitedStates Department of the Interior, Geological Survey,(USGS). (In Press).Mansell, R. W., W. B. Wheeler, Uta Elliott and MarkShaurette. 1971. Movement of acarol and terbacilpesticides during displacement through columns ofWabasso fine sand. Soil Crop Sci. Soc. Fla. Proc.31:239-243.Nelson, L. B. 1972. Agricultural chemicals in relationto environmental quality: Chemical fertilizers, pres-ent and future. J. Environ. Qual. 1: 1-6.Phung, H. T. 1972. Reduction processes in modifiedspodosol systems and their effect on some plant

86

or so before it dried, while the dry fertilizer would stillbe sitting in granular form on the soil surf~. Too,subsequent rain or irrigation would have to dissotve thenutrients in granular form before soil infiltration. Thus,the liquid fertilizer would appear to be- better distributedand thus better utilized by the plant..

very much to accelerate this process remains to be seen.Certainly, man appears to have some influence on' it.

Q: In the application of fertilizer,. wou.ld there be agreater loss of nutrients from liquid or dry formulatioos?

Calvert: This is purely a guess, but I would thinkthere would be less loss from liquid fertilizer. The re~nis that the liquid fertilizer could penetrate the soil 1 cm