DIVISION S-4-SOIL FERTILITYAND PLANT NUTRITION

Organic Carbon and Nitrogen Changes in Soil Under Selected Cropping Systems1

R. C. ZlELKE AND D. R. CHRISTENSON2

ABSTRACTThe use of different cropping systems is one means of conserving

soil organic matter. This study was conducted to evaluate the effectof 9 yr of selected cropping systems on organic C (WBC), N levels(TKN), and N mineralization characteristics (BMN) of a Charityclay (Aerie Haplaquepts). The six cropping systems consisted ofcombinations of corn (Zea mays L.), oats (Arena sativa L.), alfalfa(Medicago sativa L.), sugarbeets (Beta vulgaris L.), and navy beans(Phaseolus vulgaris L.). Each crop in each system was fertilized atrecommended rates. Cropping systems that contained corn had upto 10% more WBC and 7% more TKN at the time of sampling thansystems that did not contain corn. Nitrogen mineralization charac-teristics correlated linearly with WBC and TKN using S81 soil sam-ples but not with WBC, TKN, or N uptake in a greenhouse studyusing F81 soil samples. The uptake and response to applied N inthe greenhouse indicated that 9 yr of cropping with a particularsystem had an effect on the N supplying capacity of the soil. Reduceduptake and larger responses to applied N were observed for systemsthat did not contain corn and that lost larger amounts of C and Nover the 9-yr cropping period.

1 Journal Article no. 11570, Michigan Agric. Exp. Stn., East Lan-sing, MI 48824. Received 16 Apr. 1985.2 Graduate Research Assistant and Professor, Dep. of Crop andSoil Sciences, Michigan State Univ., respectively.

Additional Index Words: crop residue, crop rotation, mineraliza-ble N, soil N, soil organic matter.

Zielke, R.C., and D.R. Christenson. 1986. Organic carbon and ni-trogen changes under selected cropping systems. Soil Sci. Soc. Am.J. 50:363-367.

ORGANIC MATTER conservation has long been apriority of soil scientists. Salter and Green (1933)

demonstrated that soil organic matter transformationscould be described by first-order kinetics, and moreimportantly, that organic matter losses could be min-imized under different cropping systems. Althoughthese transformations are relatively slow, it is well es-tablished that the equilibrium concentration will pri-marily be a function of the amount of residue returnedto the soil (Haas et al., 1957; Larson et al., 1972).Barber (1979) observed increased organic C and Nlevels in response to increased fertilizer N as well. Morerecently Rasmussen et al. (1980) reported that tillagepractices (cropped vs. fallowed) and quantity of resi-due added were more influential than residue type andquality [animal manure vs. wheat (Triticum aestivum

364 SOIL SCI. SOC. AM. J., VOL. 50, 1986

Table 1. Crop system, annual N applied, total N applied, and estimated residue returned for six cropping systems studied, 1972 to 1981.

Systemno.

123456

Yearl

CroptO

OO

OtB

O•*

•*

Ntkgha-

20728

1641745656

Year 2

Crop

SB*SB*CCB1A

Nkgha-

5684

164174280

Year3

Crop

C1B1

SB#B1

N

kgha-

164285628

Year 4

Crop

SB*SB*

SB*

N

5656

56

Total Napplied

- kgha- ————1314562

1314948474364

Residuereturned^

Mgha-743982614448

T C = corn (Zea mays L.), SB = sugar beet (Beta vulgaris L.), B = navy beans (Phaseolus vulgaris L.), O = oat (Avena sativa L.), and A = alfalfa (MedicagosativaL.).

J Annual application.§ Total returned, 1972 to 1980. Estimated from data presented by Lucas et al., 1977.1 Experimental units sampled fall 1981, corn or navy beans grown in 1981; sugar beets grown in 1982.* Experimental units sampled spring 1981; sugar beets grown in 1981.

L.) straw]. They also observed that the changes oc-curred mainly in the top 0.20 m of the soil.

Since N mineralization and organic matter trans-formations are assumed to follow first-order kinetics(Stanford and Smith, 1972; Hsieh et al., 1981), it isreasonable to expect that soils under cropping systemsthat return a larger amount of residue and/or receivedifferent amounts of fertilizer N for long periods oftime will have variable potentials to mineralize N.The objectives of this research were (i) to determinethe magnitude and direction of change of organic Cand total N levels of a Charity clay (Aerie Hapla-quepts) after 9 yr of cropping under systems that re-ceived different amounts of fertilizer N and returneddifferent quantities of crop residue, and (ii) to measurethe relative effect of cropping system on N availabil-ity, as measured in the laboratory and the greenhouse.

MATERIALS AND METHODSField Experiment

A field study was initiated in 1972 from which six crop-ping systems were selected for this study (Table 1). The sys-tems were selected on the basis of the amount of crop res-idue returned to the soil. The estimates of residue returnedreported in Table 1 were based on data presented by Lucaset al. (1977). The amount of residue was calculated usingannual residue return rates of 10, 6.0, 3.0, 5.5, and 8.0 Mgha~' for corn (Zea mays L.), sugarbeets (Beta vulgaris L.),navy beans (Phaseolus vulgaris L), oats (Avena sativa L.),and alfalfa (Medicago sativa L.), respectively; representingaverage yields of 7.5, 4.5, 1.8, 2.9, and 4.9 Mg ha-', respec-tively, for the listed crops. Each crop was grown each yearand the experimental design was a randomized completeblock with four replications, giving a total of 76 experimen-tal units.

Since the experimental area was large, one set of experi-mental units to be planted to sugarbeets in 1981 was sam-pled in the spring (S81) and a separate set of units to beplanted to sugarbeets in 1982 was sampled in the fall (F81).Both sets had been sampled at the initiation of the experi-ment in 1972.

Soil samples for laboratory and greenhouse studies weretaken from the surface 0.20 m using a 2.54-cm diam probe.Samples for S81 and F81 consisted of 20 and 80 cores perexperimental unit, respectively. The larger number of coresfor F81 was taken to obtain a sufficient volume of soil fora greenhouse study. All soil samples were air dried, passedthrough a 1-mm sieve, and mixed thoroughly prior to sub-sampling.

The soil is classified as a Charity clay (Aerie Haplaquepts).

The particle size distribution of the surface soil was 15.0%sand, 39.3% silt, and 45.7% clay. The cation exchange ca-pacity was 290 mmol (+) kg~l (neutral ammonium acetate),and the soil pH was 7.9 (1:1 soil/water suspension).

Greenhouse ExperimentA greenhouse experiment was conducted on the F81 sam-

ples as a vegetative test for N availability. The experimentaldesign consisted of a 3 by 6 factorial arranged as a random-ized complete block with three levels of N fertility (0, 37.5,and 75.0 mg N kg"1 soil), six cropping systems (Table 1),and four replications. Three consecutive crops were grown:oats, corn, and oats.

Initially each culture (1-25 kg air-dry soil) received 63 and50 mg P and K kg"1 soil, respectively, to ensure that N wasthe only nutrient limiting growth. Each culture was thinnedto three corn plants and 20 oat seedlings. Calcium nitratewas added to give the N rate desired after thinning the firstcrop. No additional N was added. During the experiment,daytime temperatures ranged from 20 to 28 °C and the nighttemperature was 20°C. The photoperiod was 16 h d"1 andthe moisture content was periodically adjusted to 200 g kg"1.At the end of each 35-d growth period the plants were clippedat the soil surface, dried at 60°C and ground to pass a 0.5-mm sieve. The soil was then passed through a 8-mm sieveand replanted with the next crop.

Laboratory AnalysesSoil organic C (WBC) was determined by the method of

Walkley-Black (Jackson, 1958). Total Kjeldahl N (TKN) wasdetermined on a subsample ground to pass a 0.16-mm sieveusing the micro-Kjeldahl/steam distillation method de-scribed by Bremner (1965b). Mineralizable N (BMN) in thesoil was measured by the aerobic incubation method de-scribed by Bremner (1965a). Ammonium and NOf-N (in-cluding NOf-N) released upon aerobic incubation were de-termined by the alkaline phenate and Cd reduction methods(Technicon Industrial Methods 1973a, b, respectively).

Total N in the plant tissue was determined using the mi-cro-Kjeldahl/steam distillation method. Cumulative uptakeof N was calculated from the oven-dry weight and N con-centration in the tops. All chemical analyses of both plantand soil materials reported were a mean of duplicate deter-minations except for BMN, which was the mean of triplicatedeterminations. Analysis of variance was determined on theaverage values utilizing the field design of six treatments andfour replications.

RESULTS AND DISCUSSIONIn this study, the N fertilizer requirement and res-

idue return rate of each crop were considered to be an

ZIELKE & CHRISTENSON: ORGANIC CARBON AND NITROGEN CHANGES IN SOIL 365

Table 2. The effect of cropping system on selected properties ofsoils sampled in the spring (S81) after 9 yr of cropping, f

Croppingsystem}

Walkley-Black C (WBC)

72 S81 AC

Total-KjeldahlNITKN)

72 S81 AN

6 *&

C-SBB-SBC-C-C-SBC-C-B-SBO-B-SB0-A-B-SBCV(%)

I6.7a116.5a16.8a16.6a16.3a16.6a5.0

15.5b14.7a16.3c15.8bc14.6a14.8a2.8

1.2ab1.8b0.5a0.8ab1.7b1.8b-

1.97a1.96a1.96a1.94a1.92a1.97a4.3

1.87bc1.77a1.90c1.86bc1.76a1.79ab2.8

BNM§

S81

mgkg-O.lOabc 30.5ab0.19c0.06aO.OSab0.16bc0.18bc

-

29.0a33.4bc35.3c30.2ab31.6ab6.9

T Means of four replications, duplicate determinations,t C = corn, B = navy bean, SB = sugar beet, O = oat, A = alfalfa.§ Bremner mineralizable N, 14-d aerobic incubation.1 Means followed by the same letter within a column are not significantly

different, a = 0.05 (Duncan's new multiple range test).

inherent difference between the systems selected. Itwas not feasible to apply a constant amount of fertil-izer N to each of the systems studied (Table 1). Assuch, fertilizer and crop residue effects are inseparable.Since the C/N ratios and mineral N remaining in thesoil were not significantly different among croppingsystems (data not shown), it was assumed that thequantity of residue returned was the major factor af-fecting WBC and TKN. The estimated quantity of res-idue returned (Table 1) clearly shows that inclusionof corn in a system increased the amount of residuereturned. The water and wind erosion potentials (Uni-versal Soil Loss equation k value = 0.28 and WindErodibility Group = 7) of this soil were low; conse-quently, it was assumed that erosion would not be afactor contributing to WBC and TKN differences be-tween systems. Since mineral N at both sampling datesaccounted for <10 mg kg"1 of soil (or 0.56% of theavg TKN), all of the N was attributed to organic N.

The WBC and TKN results for S81 and F81 werenot pooled because the variances were not homoge-neous as determined by Bartlett's test (Steel and Tor-rie, 1980). The results from the two sampling dateswill therefore be interpreted separately.

Spring 1981 SamplingIn 1972 WBC and TKN were not significantly dif-

ferent among cropping systems (Table 2). After 9 yrof cropping, significant differences in WBC, TKN, andthe amount of C and N lost (AC and AN) existed. TheO-A-B-SB, B-SB, and O-B-SB systems lost a signifi-cantly larger amount of C and N than the C-C-C-SBsystem (Table 2). None of the systems studied, sig-nificantly increased WBC or TKN, but cropping sys-tems containing corn resulted in up to 10% more WBCand 7% more TKN due to the larger amount of residuereturned (Table 1). The smallest average rate of C losswas measured for the C-C-C-SB system (k = 0.33%yr-1, where k = 100(WBC0-WBCt)/9WBC0). The larg-est average rate of C loss was measured for the O-A-B-SB, B-SB, and O-B-SB systems (k = 1.20% yr-1).Similar trends were observed for changes in TKN.These results are in contrast to results obtained byLarson et al. (1972), who observed a greater tendencyfor accumulation of N from alfalfa than from cornresidues. Our results can be attributed to the fact thatalfalfa was grown only two times between 1972 and

Table 3. Simple correlation (r) matrix of selected soil propertieof the spring (S81) soil samples.

Parameter WBC TKN BMN AC AN

WBCTKNBMNACAN

1.000.96*»0.79**

-0.60**-0.54**

1.000.80**

-0.50*-0.51*

1.00-0.58**-0.57**

1.000.84** 1.00

*,** Significantly correlated at a = 0.05 and 0.01 levels, respectively.

Table 4. The effect of cropping system on selected propertiesof soils sampled in the fall (F81) after 9 yr of cropping, t

Croppingsystem}

Walkley-Black C (WBC) Total-Kjeldahl N (TKN) BMN§

72 F81 AC 72 F81 AN F81

gkg" mgkg-1

C-SB 15.2a 0.9a 1.75a 1.78a -O.OSa 27.1abcB-SBC-C-C-SBC-C-B-SBO-B-SBO-A-B-SBCV (%)

17.6a16.6a17.4a16.8a16.4a5.0

15.6a16.0a16.4a15.2a15.8a4.5

2.0b0.6al.Oa1.6b0.6a-

1.88a1.82a1.92a1.83a1.79a5.0

1.68a1.75a1.78a1.67a1.75a5.3

0.20c0.07ab0.14bc0.16bc0.04ab-

26.4ab30.6c29.9bc25.9a28.8abc6.9

t Means of four replications, duplicate determinations.} C = corn, B = navy bean, SB = sugar beet, O = oat, A = alfalfa.§ Bremner mineralizable N, 14-d aerobic incubation.II Means followed by the same letter within a column are not significantly

different, a = 0.05 (Duncan's new multiple range test).

1981 (Table 1). Apparently the beneficial effects of al-falfa on WBC and TKN were not observable underthese management practices in the time interval in-vestigated.

In general, AC was well correlated with AN (r =0.84, Table 3) Nitrogen mineralized in a 14-d incu-bation (BMN) was shown to be significantly differentamong systems (Table 2). The C-C-B-SB and C-C-C-SB systems produced the highest BMN estimates andalso received the largest amount of crop residue. Fur-thermore, BMN was linearly related to WBC and TKN(r = 0.79 and r = 0.80, respectively, Table 3) and toAC and AN (r = -0.58 and r = -0.57, respectively).These correlations are in line with results obtained byFerguson (1967), who observed increased C and Nlevels and increased NO^~-N production in responseto repeated application of straw residue. In the presentstudy no NH^-N or NOj-N was detected at the endof the incubation period.

There was no significant linear relationship betweensugarbeet yield parameters and WBC, TKN, or BMN.In fact, no significant differences in sugarbeet yield orquality among cropping systems occurred in the fieldstudy (data not shown). The lack of significant cor-relation or yield difference was most likely due to ad-equate fertilization with commercial N sources.

Fall 1981 samplingThe F81 results are reported in Tables 4 and 5. Again

WBC and TKN were not significantly different amongsystems in 1972. After 9 yr, WBC and TKN were notsignificantly different, although AC and AN were sig-nificantly different for some systems (Table 4). The B-SB and O-B-SB systems lost more C than the othersystems. Nitrogen loss from the B-SB system was sig-nificantly greater than AN for the C-SB, C-C-C-SB,and O-A-B-SB systems, but was not significantly dif-

366 SOIL SCI. SOC. AM. J., VOL. 50, 1986

Table 5. Simple correlation (r) matrix of selected soil properties___________of the fall (F81) soil samples.___________

Parameter WBC TKN BMN AC AN UNCl CUUPON

WBC 1.00TKN 0.95** 1.00BMN 0.23 0.26AC -0.34 -0.35AN 0.01 -0.03UNCl 0.47* 0.47*CUUPON 0.48* 0.48*

Table 6. The effect of cropping system on the cumulative uptakeand cumulative response to N applied in the greenhouse, t

1.00-0.42 1.00-0.10 0.68** 1.00

0.27 -0.38 -0.36 1.000.25 -0.38 -0.41 0.94** 1.00

*,** Significantly correlated at a = 0.05 and 0.01 levels, respectively.

ferent than AN for the C-C-B-SB or O-B-SB systems.Changes in the C/N ratio were not significantly dif-ferent (data not shown). As expected, AC was linearlyrelated to AN (r = 0.68, Table 5).

Mineralizable N was significantly different for somesystems (Table 4) and, in general, paralleled trendsobserved in S81 (i.e., where AC and AN were high,WBC, TKN, and BMN were low). Again the C-C-C-SB and C-C-B-SB systems produced the largest amountof BMN. However, there was no significant linear re-lationship of BMN to WBC, TKN, AC, AN, or cu-mulative uptake of N by the zero N treatments (CU-UPON) in the greenhouse (Table 5) as has beenreported in similar greenhouse/incubation studies(Ryan et al., 1971; Gasser and Kalembasa, 1976). Ap-parently the use of aerobic incubation methods as ameans of assessing soil N availability for fall acquiredsoil samples is of little use. Vegetative tests (CU-UPON) are more laborious and in the present caseresulted in only slightly better correlations with WBCand TKN (r = 0.48, r = 0.48, respectively, Table 5).Qualitatively, BMN estimates for the F81 samples were,smaller than S81 BMN estimates. A similar trend wasobserved for the C/N ratios. This may be related tothe mineralization/immobilization status of residuereturned to S81 soils the previous fall.

Greenhouse StudySignificant differences in cumulative uptake of N

(cumulative uptake = sum of N uptake for each crop-ping period) in the greenhouse at the various N ratesoccurred between some systems (Table 6). At the zeroN rate the O-B-SB system resulted in significantly loweruptake than the C-SB and C-C-C-SB systems. At theintermediate N rate the C-C-C-SB and C-C-B-SB sys-tems again resulted in a significantly larger uptake thanthe O-B-SB system. Uptake by the C-SB system at thehigh N rate was less than the other cropping systems.This result is unexplained considering AN for this sys-tem was —0.03, and the BMN value was not signifi-cantly different from other systems. There is no evi-dence or justification to attribute this result to Nimmobilization.

The O-B-SB and B-SB systems had the highest re-sponse (uptake at 75 mg N kg"1 divided by uptake at0 mg N kg"1) to fertilizer N applied in the greenhouse,suggesting that these systems have reduced capacityto supply N to a growing crop. This reduced capacitywas masked at the high N rate as indicated by a lackof significance between uptake by systems that hadhigher BMN values (Table 6). The O-B-SB and B-SBsystems returned the least amount of residue and alsoreceived smaller amounts of fertilizer N over the 9-yr

Croppingsystem}

C-SBB-SBC-C-C-SBC-C-B-SBO-B-SBO-A-B-SB

Nitrogen applied (mg kg'1)

0

43.2b138.5ab43.2b41.8ab37.3a41.4ab

37.5

92.5a93.8ab99.7c98.3bc90.6a95.6abc

75

128a137b137b138b134b138b

Response§

2.98a3.61bc3.18ab3.32abc3.64c3.34abc

t Means of four replications, duplicate determinations.j C = corn, B = navy bean, SB = sugar beet, O = oats, A = alfalfa.§ Response = uptake at 75 mg kg"' divided by uptake at 0 mg kg'1.1 Means followed by the same letter within a column are not significantly

different, a = 0.05 (Duncan's new multiple range test).

cropping period (Table 1). Consequently, N fertilizerrecommendations for these systems may need to beincreased if optimal crop production is desired.

The hypothesis that crop yield parameters in thefield may be affected by fluctuating C and N levelsand associated N mineralization characteristics has notbeen verified despite the fact that these soil propertieswere significantly affected by cropping system. How-ever, the greenhouse results do indicate that the N-supplying characteristics of some systems have beenaltered in a short period of time. The greenhouse re-sults also illustrate that CUUPON was very closelyrelated to uptake by crop 1 (UNCl), indicating thatshort term vegetative tests may be adequate for theassessment of response to applied N (r = 0.94, Table5)-

In conclusion, results of the present study indicatethat different cropping systems had an effect upon theC and N status of a soil even over a relatively shorttime period. In general, systems returning smallamounts of residue resulted in significantly larger lossesof C and N. Since BMN was linearly related to WBCand TKN in the S81 study, and CUUPON was lin-early related to WBC and TKN in the F81 greenhousestudy, it is reasonable to expect continued changes inthe N-supplying capacity of the soil. For systems con-taining corn there is evidence that the capacity to mi-neralize soil N has increased relative to the other crop-ping systems.

These results suggest the following ranking of thesystems studied for C and N conservation and pos-sibly long-term soil productivity:

C-C-C-SB = C-C-B-SB > O-A-B-SB- C-SB > O-B-SB = B-SB .

This order may be subject to change over time, and,hence, these types of studies will need to be repeatedperiodically.

SIMS: SOIL pH ON DISTRIBUTION AND PLANT AVAILABILITY OF MN, CU, AND ZN 367

121.Gasser, J.K.R., and S.J. Kalembasa. 1976. Soil nitrogen: IX. The

effects of leys and organic manures on the available-N in clay andsandy soils. J. Soil Sci. 27:237-249.

Haas, H.J., C.E. Evans, and E.F. Miles. 1957. Nitrogen and carbonchanges in Great Plains soils as influenced by cropping and soiltreatments. USDA Tech. Bull. 1164. U.S. Government PrintingOffice, Washington, DC.

Hsieh, Y.P., L.A. Douglas, and H.L. Motto. 1981. Modeling sewagesludge decomposition in soil: II. Nitrogen transformations. J. En-viron. Qual. 10:59-64.

Jackson, M.L. 1958. Soil chemical analysis. Prentice-Hall, Inc., En-glewood Cliffs, NJ.

Larson, W.E., C.E. Clapp, W.H. Pierre, and Y.B. Morachan. 1972.Effect of increasing amounts of organic residues on continuouscorn. II. Organic carbon, nitrogen, phosphorus and sulfur. Agron.J. 64:204-208.

Lucas, R.E., J.B. Holtman, and L.J. Connor. 1977. Soil carbon andcropping practices, p. 333-351. In W. Lockeretz (ed.) Agricultureand energy. Academic Press, New York.

Rasmussen, P.E., R.R. Allmaras, R.C. Rhode, and N.C. Roager, Jr.1980. Crop residue influences on soil carbon and nitrogen in awheat-fallow system. Soil Sci. Soc. Am. J. 44:596-600.

Ryan, J.E., J.L. Sims, and D.E. Peaslee. 1971. Laboratory methodsfor estimating plant available nitrogen in soil. Agron. J. 63:48-

Salter, R.M., and T.C. Green. 1933. Factors affecting the accumu-lation and loss of nitrogen and organic carbon in cropped soil. J.Am. Soc. Agron. 25:622-630.

Stanford, G., and S.J. Smith. 1972. Nitrogen mineralization poten-tials of soils. Soil Sci. Soc. Am. Proc. 36:465-472.

Steel, R.G.D., and J.H. Torrie. 1980. Principles and procedures ofstatistics: A biometrical approach. 2nd ed. McGraw-Hill BookCo., New York.

Technicon Industrial Systems. 1973a. Ammonia in water and wastewater. Industrial method no. 98-70w. Technicon Industrial Sys-tems, Tarrytown, New York.

Technicon Industrial Systems. 1973b. Nitrate and nitrite in waterand waste water. Industrial method no. 100-70w. Technicon In-dustrial Systems, Tarrytown, New York.