MOVEMENT OF NITROGEN IN SOILS1

BERT A. KRANTZ, ALVIN J. OHLROGGE, AND GEORGE D. ScARSETH2

THE problem of supplying nitrogen to nonlegumi-nous plants is of extreme importance and is

complicated by the fact that nitrogen in soils is easilyconverted into forms which may be more or lessmobile or more or less available.

Many investigators have studied or observed therelationship between movement of soil moisture andnitrates as well as other soluble salts. Numerousworkers have established the fact that nitrates can bereadily leached from fallow lysimeters, even whenclay soils are used (7).3 However, in cases wherecrops were grown on the lysimeters the leaching lossesreported have been relatively small. In some pot leach-ing experiments using various forms of nitrogen, Ben-son and Darnette (4) and Conrad (5) found thatpractically all the nitrate ions were lost, while nearlyall the ammonium ions were retained by the soils. Thelatter worker included many other inorganic and or-ganic compounds in his investigation and classifiedthem as to whether the nitrogen was carried inanionic, cationic, or intermediate units.

In 1902, King and Whitson (8,9) carried out someexcellent laboratory studies on the upward movementof nitrates in cylinders of fallow soil. Although theyseemed to be concerened largely with the effect ofvarious depths of dust mulches, they did report sometremendously high accumulations of nitrates in thesurface inch. Miller (12) found that on fallow soils,soluble salts tended to accumulate at the surface,especially during dry periods. During a dry summerMalpeux and Lefort (n) found that nitrates placedat the depth of 10 inches appeared in the surface 3inches within n days and nitrates placed 20 inchesdeep appeared in the surface 3 inches within a month.They concluded that this rapid upward movement ofnitrates was chiefly dependent on capillarity ratherthan diffusion. Likewise, Puchner (-13) in studyingthe relationship between the movement of solublesalts and the capillary rise of water in soils, concludedthat the accumulation at the surface increased with therapidity of evaporation. This does not fully agree withLebedev (10) who stated, "Where film and gravi-tational water exist, salt movement is toward the areaof lower concentration which may correspond to oroppose the direction of movement of the water."While this is true, the net effect will be determinedby the relative rates of ion diffusion and water move-ment.

Since Indiana's climate is characterized by frequentmidsummer droughts, it appeared that a net upward

movement of soil moisture could be expected. There-fore, one had to be concerned not only with the formof nitrogen and its placement, but also with the prob-lem of keeping it where it was placed throughout thecritical part of the growing season. Previous work inIndiana had shown that nitrogen applied to corneither at planting or as a side-dressing gave erraticand inconsistent response. The objective of the pres-ent investigation was to study the movement and be-havior of nitrate and ammonium nitrogen in field soilsin relation to rainfall distribution and soil moisturemovement in an effort to understand some of theunderlying principles involved in the effective ferti-lization of corn. This work was carried out in col-laboration with a study of nitrogen fertilization ofcorn (14).

EXPERIMENTAL PROCEDURETo study the behavior of various forms of nitrogen in the

soil, a series of small fallow plots were laid out in the springof 1940 in which (NH^SOi was placed on the plow sole,with and without straw, and placed on the surface withoutstraw. These plots were laid out on Vigo silt loam, Crosbysilt loam, Miami sandy loam, and Clermont silt loam soils.In 1941, a similar experiment was set up including the follow-ing four additional treatments: NaNOs placed on the plowsole with and without straw and (NH^aSOt plus phosphorus,potash, and straw, with and without lime. The plots weresampled several times during the growing season at the fol-lowing depths: o to J4 inch, J4 to I inch, I to 3 inches,3 to 5 inches, 5 to 7 inches, 7 to 9 inches, 9 to n inches,ii to 13 inches, 15 to 17 inches, and 21 to 23 inches.Ammonium and nitrate nitrogen analyses were made on freshtoulene-treated soil samples by a modification of Olsen'smethod (15) in which continuous extraction units were usedwith a closed system. Total nitrogen was determined by theGunning method, modified to include nitrate (2). The pHdeterminations were made by the glass electrode method usinga soil water ratio of one to five.

RESULTS AND DISCUSSIONNITRATES ACCUMULATE AT SURFACE DURING

PROLONGED DROUGHTS

As shown diagramatically in Fig. I, nitrate anionsare not held by the negatively charged soil colloidsand are free to move with soil moisture. During sea-sons of prolonged drought, the net movement of soilmoisture would be expected to be upward.

It was found that in all cases studied, nitratesaccumulated at the surface after a prolonged dryperiod (Figs. 2 and 3 and Tables i and 2). Althoughthe amount of surface nitrate accumulation was lowerin the no-fertilizer plot than in the treated plots, thetrend was the same.

'Journal Paper No. 129, Purdue University Agricultural Experiment Station, Lafayette, Ind. Contribution from the Depart-ment of Agronomy. Acknowledgment is made to the Educational and Research Bureau for By-Products Ammonia, Columbus,Ohio, for fellowship funds that helped make this study possible.

"Fellows in Agronomy and Chief in Agronomy, respectively. Senior author now Assistant Soil Scientist, Division of Soil andFertilizer Investigations, Bureau of Plant Industry, Soils and Agricultural Engineering, U. S. Dept, of Agriculture, at AgronomyDepartment, North Carolina Agricultural Experiment Station, Raleigh, N. C. Part of a thesis submitted by the senior author inpartial fulfillment of the requirements for the degree of Doctor of Philosophy, Purdue University.

3Figures in parenthesis refer to "Literature Cited", p. 195.

189

igo SOIL SCI-ENCE SOCIETY PROCEEDINGS 1943

fimmmm

Ammonia is teld hj ftp clu| pirt-itlr and Is rot rovfablr

FIG. i.—When nitrogen.is in the ammonium form as in am-monium sulfate, it is in the cationic part of the molecule.The ammonium cations in the soil are adsorbed by thenegatively charged soil colloids in an exchangeable formand are not free to move up and down with the soil mois-ture. Organic matter plowed under with ammonium sulfatehelps to keep the nitrogen in the ammonium form, since itsupplies energy for soil microorganisms which will utilizethe free oxygen in the soil. This increased micro-biological

• activity tends to prevent ammonium nitrogen from beingoxidized to nitrate nitrogen. Under warm, moist conditions,in the presence of plenty of oxygen, ammonium nitrogen is-

.nitrified to nitrates rather rapidly. The nitrate anion is notheld by the negatively charged soil colloids and is left freeto move with soil moisture. Either of these forms can beused directly by most plants. The ammonium forms of nitro-gen are eventually converted to nitrates in arable soils.However, when ammonium sulfate is plowed under withorganic matter in the spring, most of it will remain asammonium nitrogen near the plow sole in the moist rootzone throughout the critical part of the corn-growing sea-son, which is frequently droughty in the Middle West. FromPurdue University Agricultural Experiment Station Bulle-tin 482.

When sodium nitrate was placed on the plow sole,a large part of the nitrates was readily moved to thesurface during droughty periods (Table 2), thus be-coming unavailable to plants. These data agree withthe findings of Malpeaux and Lefort (n) in Francewho as early as 1913 recognized the importance ofdeep placement of nitrogen in regions where milddroughts frequently occur. However, they used onlythe mobile nitrate forms of nitrogen and did not trya less mobile form such as ammonium nitrogen.

In the plot where sodium nitrate was placed on theplow sole with straw, there was a nitrate accumulationat the surface (Table 2). However, a large amountof nitrate still remained just below the plow layer.A possible explanation for this is that the heavy rainsin late June and early July moved some of the nitratesdown below the plow sole, and that the layer of strawcut off capillary movement, thus preventing the riseof the nitrates to the surface. After the straw hadbecome decomposed such movement could again takeplace.

RAIN AFTER A PROLONGED DROUGHT MOVESNITRATE INTO MAIN ROOT ZONE

Fig. 5 shows that the nitrates which accumulate atthe surface during droughts are moved back into the

root zone by a good rain. This helps explain the veryerratic responses which have been obtained fromnitrogen top-dressing of corn in different seasons.Also, it suggests that the luxuriant plant responseto a "good summer shower" after an extended droughtperiod may be accredited to the effect of the nitratemoved down into the root zone as well as the mois-ture. Under these conditions, it has been observed thatcorn plants which show severe nitrogen deficiencysymptoms may still temporarily show a positive testfor unassimilated nitrates.

At North Vernon, Ind., on a Qermont silt loam afour tenths inch rain interrupted the soil sampling.The plots were sampled again immediately after therain, and the data showed that the nitrate content inthe surface % mcn> which was 52 p.p.m. before theshower, dropped to 2 p.p.m. after the shower. How-ever, all of the nitrate loss from the top % inch wasaccounted for as a gain in the I- to 5-inch layers.

PLOWED UNDER ORGANIC MATTER RETARDS NITRATEFORMATION AND HOLDS AMMONIUM NITROGEN

IN ROOT ZONE LONGERAs brought out diagrammatically in Fig., i, ammo-

nium salts or ammonium-forming salts plowed underwith active organic matter, providing energy formicroorganisms to bring about a reducing environ-

1000 lol (HHJ,SO. on Plow Salt

-I- IT. Itraw on Plea7is

.s Iti23

— i*x1 HH'^JIt

wflfav///////////,v////////////////////.

V/////7///,

P

^ ' ' fXIN

o 300 tea too ttoo ISO noP.P.M. of Total NiTngtn P.P.M. of H

jo to *>P.P.M. of N x HO;

FIG. 2.—The distribution of nitrate, ammonium, and organicnitrogen in the soil profile as affected by different place-ments of ammonium sulfate, with and without organicmatter. Vigo silt loam, Qoverdale, July 17, 1940. (60 daysafter treatment).

KRANTZ, ET AL.: MOVEMENT OF NITROGEN IN SOILS

1000 It* WH«Jk JO* Top Drttied 22 Dayt previously

tea

<K» floe ISO 110 W tO JO 0 30

P.P.M. of Total Hitnfn P.P.M. of N « NH^ P.PM. of ft 01 AKf

FIG. 3.—The distribution of nitrate, ammonium, and organicnitrogen in the soil profile as affected by different place-ments of ammonium sulfate, with and without organicmatter. Vigo silt loam, Cloverdale, August 8, 1940. (82 daysafter treatment). From Purdue University AgriculturalExperiment Station Bulletin 482.

merit, tend to remain in the less mobile ammoniumform longer than when the organic matter is omitted.In 12 of the 16, 1940 and 1941 samplings, there wasa larger percentage of the plowed-under ammoniumsulfate retained in the moist root zone when strawwas added than when it was omitted.4 Conversely,in 12 out of 16 samplings, there was a greater amountof nitrate in the "1,000 Ibs. (NH4)2SC>4 on plowsole" plot than in the "1,000 Ibs. (NH^SCU plus3 tons straw on plow sole" plot. Even at the end ofthe growing season, much of the plowed under am-monium sulfate still remained near the zone of place-ment, especially where straw had been added. Thepercentages of plowed under ammonium sulfate whichwere still found in the ammonium form in the plotswith and without straw respectively were:

Miami sandy loam, Aug. 15, 1940 (95 days aftertreatment) 42 and ij%

Crosby silt loam, Aug. 20, 1940 (89 days aftertreatment) 69 and 45%

Vigo silt loam, Aug. 30, 1940 (104 days aftertreatment) 63 and 28%

Clermont silt loam, Oct. 15, 1940 (153 days aftertreatment) 50 and 25%

Crosby silt loam, Nov. 22, 1941 (156 days aftertreatment) 53 and 56%

The 1941 plots were kept fallow and sampled twiceduring 1942. Most of the nitrate and ammoniumnitrogen which was found late in the fall of 1941(November 22) was not found in the spring of 1942(May n) and there was practically none left by thefall of 1942. However, it is significant to note theincrease of organic nitrogen in the surface J inchesof the treated plots over that of the check plots. OnOctober 30, 1942, 17 months after treatment, it wasfound that the increase in organic nitrogen accountedfor approximately 95% of the applied nitrogen in theplot in which ammonium sulfate was plowed under

P.PM. of N us NO;

FIG. 4.—The distribution of nitrate, ammonium, and organicnitrogen in the soil profile as affected by different place-ment of ammonium sulfate, with and without organic mat-ter. Vigo silt loam, Cloverdale, August 30, 1940. (104 daysafter treatment).

"The 1940 and 1941 seasons were of below average spring and summer rainfall. Although the data indicate that the additionsof straw tended to bring about a reducing environment at plow depth, it was not pronounced enough to cause any color change.However, in 1942, when extremely wet spring and early summer seasons occurred at one of the corn experiments located on a flat,poorly drained Soil, plowed under carbonaceous residues provided energy for microorganisms to reduce the surrounding soil area.The reduction was revealed by the blue color of the soil adjacent to the plowed under organic matter and verified by chemicaltests.

192 SOIL SCIENCE SOCIETY PROCEEDINGS 1943

with straw and the one in whichphosphorus, potash and limewere also included. In the otherfive treatments, approximately55% to 75% of the applied nitro-gen was accounted for in in-creased organic nitrogen. At theMay n, 1942, sampling (Tablei) the plots with ammoniumsulfate top-dressed or plowedunder contained considerablymore ammonium nitrogen thanwhere straw had been added.Evidently, after a. year's time theincreased microbiological popu-lation had temporarily tied upthe inorganic nitrogen into or-ganic forms.

EFFECT OF LIME, PHOSPHORUS,AND POTASSIUM .WITH OR-GANIC MATTER ON TRANSFOR-MATION OF AMMONIUM SUL-FATE

When phosphorus and po-tassium were plowed under withammonium sulfate and straw(Table i), less ammonium ni-trogen was found than whenphosphorus and .potassium wereomitted, and when lime was alsoadded there was still less am-monium nitrogen. This suggeststhat the lime, phosphorus, andpotassium increased the biologi-cal activity and that the in-creased microbiological popu-lation tied up more of the ap-plied ammonium sulfate. Thissuggestion is strengthened bythe fact that the organic nitro-gen content was correspondinglyhigher where the minerals andlime were added.

TOP-DRESSED AMMONIUM SUL-FATE U N N I T R I F I E D AFTERTHREE AND ONE-HALF WEEKS

PPM of N qs NOjif ic fo ff to ro to if i<o July 17

I -Per cen

2 » s e 10 n if te /e to 22Average Percent Moisture

PPM.ofN.ctf N0'3wxtosoeowtoniao August 6

RAINFALL DISTRIBUTIONCloverdale, Indiana, 1940

June i-n — 1.4212-18— 1.39iQ-25 —0.5126-30—1.18

•Percent Mo/tfln

July

August

i- 8 — 0.379-16 — 2.03

17 —o.oo18-31 — o.oo

1-9 — o.oo10 —0.3911 —O.OO12-26 — o.oo

z * e 6 10 /z if is IB 20 iZAvtraye Per cenf Moisture

PPM. of H. as NO;to 10 30 40 so to n to to me

2728293031

— 2.05— o.oo— o.oo— o.oc-— O.on

August 30

M. of N. us N0$ -Per eenf MoMm

2 4 « e 10 it it it it to ttAverage Per cent Moisture

In 1940, at North Vernon andCloverdale, and in 1941, at La-fayette, Ind., little or no rain fellbetween the time of the top-dress application and thetime of the next sampling. Consequently, after 25, 22,and 15 days, respectively, there was no increase insurface nitrates and all of the ammonium sulfate wasfound in the ammonium form- in the surface inchwhere it was placed (Fig. 3, Table i). There is littlewonder that nitrogen sidedressing for corn so oftenfails to give response in Indiana. Before the next sam-pling time there had been considerable rainfall, buteven after this and subsequent wet periods, practically

FIG. 5.—The relationship between moisture and nitrate movement as shown by determi-nations made after dry periods (July 17 and Aug. 6) and after a subsequent wetterperiod (Aug. 30). Vigo silt loam, Cloverdale, 1940. From Purdue University Agri-cultural Experiment Station Bulletin 482.

none of the top-dressed ammonium sulfate had moveddown below the 3-inch level in the silt loam soils.This was true even at the 1941 Lafayette plots whichexperienced the second wettest October on record.

It appears that as the ammonium cations weremoved down by soil water movement, they wereabsorbed by the soil colloids up to an "apparentsaturation point". As the colloids of the uppermostsoil layers were "saturated", the ammonium ions ap-parently moved down into the next layers until all the

KRANTZ, ET AL.: MOVEMENT OF NITROGEN IN SOILS 193

ammonium ions were absorbed. The "apparent satu-ration capacities" for these silt loam soils were fromabout 350 to 550 p.p.m. of nitrogen in ammoniumform or about 2.5 to 4.0 M.E. per 100 grams of soil.The exchange capacities5 of the Clermont, Vigo, andCrosby silt loams were 8.4, 8.9, and 10.0 M.E. per100 grams of soil, respectively. If Jenny's (6) sym-metry value for NH4+ releasing Ca++ (which is 28.8)is multiplied by these exchange capacities, the valueof 2.5 to 3.0 M.E. per 100 grams of soil would beobtained. It is interesting to note that this value isquite similar to the "apparent saturation capacity"

TABLE i.—The effect of treatment on the nitrate, ammonium,Crosby silt loam

'which was found under these particular field con-ditions.

These data coincide with the finding of Babcock(3) in some studies on ammonium ion retention insoils. He percolated a dilute solution of ammoniumsulfate through 6-inch columns of soil until 500pounds of nitrogen per acre had been added. Hefound that in the sandy loam soil the percentageretained by each inch layer was about constant at13% for the top 5 inches; in a medium clay loam thepercentage retained was about constant at 20% forthe top 4 inches; while in the clay loam 41% was

and total nitrogen content and the average moisture content of, Lafayette, Ind.

Depth,inches

Mois-ture,%*

Treatment, p.p.m.

No fertilizerplowed under

Total NH4+ NO3-

i ,000 Ibs. (NH4)2SO4 top-dressed 1 5 days previously

Total NH4+ N03~

1,000 Ibs. (NH4)2S04 onplow sole

Total NH4+ NO3-

1,000 Ibs. (NH4)2S04+ 3

tons straw on plow sole

Total NH4+ N03-

Sampled Aug. 9, 1941, 51 Days After Treatmento-XK-I!-33-55-77-99-1 111-13I5-I7

2.92.46.18-313.718.921.724.726.2

I,O2O935915925793630660600550

1045543343

40156544544

2,4751,0209409207235606256005io

1,59560553i2I3

51156454444

I,I2O980950

1,005963610590580535

8347i200252I2

2161013030169978

1,045950920935

1,078740560550530

7355

242H5722

122241219127593

Sampled Aug. 20, 1941, 62 Days After Treatmento-XK-i1-33-55-77-99-1 111-1315-17

7.011.713.8H-716.819-521.724.125-6

950900940920615585565560495

17433iiiii

972225977.66

i,487i,4791,0509457185305605605io

444545105632III

108291785443

965900

1,0001,030985710585570540

19747519343227

1815

1148030nn913

1,015940970960

1,103840740705530

47969

!571841022

17175257262216108

Sampled Nov. 22, 1941, 156 Days After Treatmento-X#-i1-33-55-77-99-1 111-1315-1721-23

30.526.727-526.524424.226.728.128.426.1

93091089387070361063359°490490

32222II2II

23 ,24334343

1,2501,053995980833580550 '565535500

867925942IIII

10302224262119181813

950920930990823700620595535440

4426

no8562II

3659H1934193310

975930963938928698633595490440

4333

44 .I2O252II

46791214162022II

Sampled May n, 1942, 326 Days After Treatmento-XX-ii-33-55-77-99-1 111-1315-1721-23

2I.O22.823-724.922.524.026.427.O27-324-3

1,00587890386059052552352552545°

7445432323

76109544455

i, 0601,050965910603513528558483433

12011839932IIII

2440329754568

9209239J5868770650563493483420

84674054n2II

29292517995

. 8810

890885895878858555540550515420

53225n4iii

812127

ii8666ii

*Moisture percentage given as average of all treatments.

5Analyses were made by H. E. Jones of the Agronomy Department, Purdue University.

IQ4 ' SOIL SCIENCE SOCIETY PROCEEDINGS 1943

TABLE 2.—The effect of treatment on the nitrate, ammonium, and total nitrogen content and the average moisture content ofCrosby silt loam, Lafayette, Ind. .

Depth,inches

Mois-ture,%*

Treatment, p. p.m.

- i,25olbs. NaNO3on plow sole

Total NH4+ NO-3

1,250 Ibs. NaNO.,+3 tonstons straw on plow sole

Total NH4+ NOr

1,000 Ibs. 20-20-20 +3tons straw on plow sole

Total NIV N03-

1,000 Ibs, 20-20-20+3tons straw +4 tons lime on

plow sole

Total NH4+ NO3-

Sampled Aug. 9, 1941, 51 Days After Treatmento-Xtf-I1-33-55-77-99-1 111-1315-17

-2.92.46.18-3

13-718.921.724.726.2

I, IIO1,000960965730640625610535

1255432I2I

192763037595536177

1,020960

• 940948

1,037625630618500

8346144322

863222235910393447

i, 060940

- 920930950650590580545

7834

10376D23

I2O2012II16IO988

1,020945920983

1,15063 soo610

' 630550

ii63.288448325

8423H23399675

1 Sampled Aug. 20, 1941, 62 days After Treatmento-XK-i1-33-55-77-99-1 111-1315-17

7-011.713.814.716.8I9.521.724.125-6

955925995980790625575560520

2593532II2

15168694•675629137

9509159839959506046206005io

2166693322

12134658627977713

925920935950

1,150745623600540

H55538128404i

1 6H40503i2317H10

955940955

1,0151,185670630620535

2375

215336iii

121241786221

. 10IO9

Sampled Nov. 22, 1941, 156 Days After Treatmento-Ktf-ii-33-55-77-99-1 111-1315-1721-23

30.526.727-526.524.424.226.728.128.426.1

940890923945730615610590540

3232 •32I2I

450 1 2

2246n21343842

963 ,9239189108035505255555io

17 448

633353i2

3 II

566667991214

935930915925860615570570545'475

4332174993Ii

34459

ii131616IO

975953935955960585555523480485

453310

. ii3ii3

88789869IOii

Sampled May n, 1942, 362 Days After Treatment°-y*X-i1-33-55-77-99-1 111-1315-1721-23

21.022.823-724.922.524.026.427.027-324-3

915895910995678660603560480440

544434.22r2

.18H1410 •10II1091019

9008958809i5740520533495500455

44353322II

4355767667

910873885870720530575520553545

733347223I

4343754445

915915900910988585555525480400

55\476

' 42II

6976875679

*Moisture percentage given as average of all treatments.

retained in the first inch layer and 34 and 22% in thesecond and third.inch layers, respectively. When thesedata of Babcock are converted into p.p.m. of nitrogenas ammonium, the retention values are as follows:Sandy loam soil, 208 p.p.m.; medium clay loam soil,300 p.p.m.; and clay loam soil, 611 p.p.m.

The data (Fig. 4 and Table i) suggest that theammonium ion adsorption capacity of the three siltloam soils studied is great enough to retain ammoni-um ions from at least 1,000 pounds of ammoniumsulfate per acre in the surface 3 inches. In all casesthe amount of absorbed ammonium nitrogen was di-

minished as the season progressed. However, this wasprobably due to nitrification of the absorbed ammoni-um ions ( i) and utilization by soil microorganisms.

SUMMARY AND CONCLUSIONS

In an effort to study the behavior of various formsof inorganic nitrogen in,soils, a series of small fallowplots was laid out on four common Indiana soils.Sodium nitrate and ammonium sulfate were placedat various depths, with and without straw, and theeffect of phosphorus, potash, and lime placed deeply

KRANTZ, ET AL. I MOVEMENT OF NITROGEN IN SOILS 195

with the latter was also studied. Frequent analysesfor ammonium, nitrate, and total nitrogen, moisture•content, and pH were made on samples taken at vari-ous depths. Some of the most pertinent facts foundmay be summarized as follows:

1. Ammonium cations (the reduced form of nitro-gen) were found to be rather immobile in the soilbecause they are adsorbed by the base exchange com-plex, while the nitrate anions (the oxidized form ofnitrogen) were found to move freely with the soilmoisture.

2. During seasons of prolonged .droughts, nitratesmoved upward in the soil to accumulate at the surface.'This was due to the net upward movement of soilmoisture. However, any moderate rainfall moved thenitrates back into the main root zone and made themavailable again to plants. This helps to explain thevery erratic responses which have been obtained inIndiana from nitrogen side-dressing for corn.

3. When ammonium sulfate was plowed under, alarge portion of the applied nitrogen remained in theammonium form in the moist root zone throughoutthe growing season. When ammonium sulfate wasplowed down with straw, providing energy for bac-teria to bring about a reducing environment, nitrateformation was retarded and even more nitrogen re-mained in the less mobile ammonium form. In the lat-ter case on silt loam soils, 55 to 65% of the appliednitrogen still remained in the ammonium form 100to 150 days after treatment.

4. The addition of lime, phosphorus, and'potassi-um, along with plowed-under carbonaceous organicmatter and ammonium sulfate, increased biologicalactivity and temporarily tied up more of the appliednitrogen in the organic form.

5. Ammonium sulfate applied as a top-dressing re-mained on the surface of the soil and was completelyunnitrified after 23 to 25 dry days. Even after heavy•fall rains practically no ammonium nitrogen moved'.below the 3-inch level in the silt loam soils. The sur-

face layers of soils had an "apparent saturation capaci-ty" of about 350 to 550 p.p.m. for ammonium nitro-gen.