Influence of cropping systems on soil biochemicalproperties in an arid rain-fed environment

A. V. Rao, J. C. Tarafdar, S. K. Sharma, Praveen-Kumar &R. K. Aggarwal

Central Arid Zone Research Institute, Jodhpur-342003, Rajasthan, India

(Received 24 January 1994, accepted 6 June 1994)

The effect of eight crop rotations was studied for 3 years (1990–92) onenzyme activities, nitrifying bacteria, VAM spores, organic matter, NO3–Nand available-P, on loamy-sand soil under desert conditions. Inclusion of thelegume crops, clusterbean or mung bean in the rotation had a beneficial effecton these parameters over fallow–pearl millet, resulting in a significant increasein pearl millet production. Continuous clusterbean for 3 years in rotationgave the maximum increase in soil organic matter, NO3-N, available P andenzyme activities (dehydrogenase, acid and alkaline phosphatases, nitroge-nase) over continuous pearl millet while the trend was reversed for thenitrifying bacteria and VAM spores population. In general, the effect on soilbiochemical properties was greater in surface soil (0–15 cm) than subsoil.However, the build up of VAM spores was greater in subsoil.

The results demonstrate that in arid sandy soils, in order to improve soilquality, legumes, particularly clusterbean, should appear for more than 1 yearsuccessively in legume–cereal rotations.

©1995 Academic Press Limited

Keywords: arid zone; biological fertility; crop rotation; clusterbean; mungbean; pearl millet

Introduction

In arid regions, the low production levels could be ascribed to two important factors,i.e. moisture stress and lack of nutrients. The enhancement of soil fertility thusassumes importance for sustained agricultural productivity in the drought-proneregions. Given the socio-economic conditions of farmers and the low and erraticrainfall, the extensive use of chemical fertilizers to augment crop production is a riskyproposition, so the yearly monoculture of cereals, as practised in this region, generallyresults in decreased soil productivity over the years.

Alternative agricultural cropping systems are being sought to maintain soil qualityand productivity levels at low input costs. Management systems using animal-cropresidues, legumes and green manure crops in the rotations regulate soil microbiologicalactivity, organic matter decomposition and thus nutrient recycling and organic matterturnover (Biederbeck et al., 1984; McGill et al., 1986; Doran & Smith, 1987).Through better conservation of C and N, organic farming practices also regulatenitrogen supply during plant growth periods (Power & Doran, 1984). The recycling ofnutrients, particularly nitrogen, and the proper balance between organic matter and

Journal of Arid Environments (1995) 31: 237–244

0140–1963/95/020237 + 08 $12.00/0 © 1995 Academic Press Limited

Table 1. Some characteristics of the soil used in the study

Parameters Quantity

Soil classification CamborthidSand (%) 87·1Silt (%) 5·5Clay (%) 6·9pH (soil:water, 1:2·5) 8·1Electrical conductivity (dSm–1) 0·2Organic matter (%) 0·34Total N (mg kg–1) 310NO3–N (mg kg) 1·87Total P (mg k–1) 270Olsen-P (mg kg–1) 7·0Organic-P (mg kg–1) 50·0Field capacity (10% WHC) 150 mm m–1profileNitrifying bacteria (x104 g–1) 0·4Nitrogenase activity (n moles C2H4h–1) 52·0Acid Phosphatase activity (n Kat 100 g–1dry soil) 2·4Alkaline Phosphatase (n Kat 100 g–1 dry soil) 4·2Dehydrogenase activity (n Kat g–1 dry soil) 2·0VAM propagules (100 g–1 dry soil) 70

soil biological activities have been shown to be necessary components of productivesoil in alternative cropping systems (Molope, 1987; Doran et al., 1990).

Thus, cropping systems which promote efficient and sustainable agriculturalproductivity should be evaluated in different agro-climatic conditions for their effecton soil biochemical properties (Visser & Parkinson, 1992). The present investigationis an attempt to study the effect of different rain-fed cropping systems in a loamy-sandsoil in an arid climate, on soil biological diversities and status of organic matter andnitrogen as indicators for soil productivity.

Materials and methods

The plots established in 1990 were located in an arid climate typified by cool wintersand hot dry summers with drought spells at different stages of crop growth. Annualprecipitations for 3 years 1990–92 (crop growth period) were 770·2, 182·1 and 383·4mm, respectively, with 91% occurring from July to September. Treatments includerotation of both fallow and annual legume and cereal crops (normally grown in thisarid region) on a loamy sand (Table 1). The treatments were 3-year cycles: Fallow (F)– PM (Pearl millet — Pennisetum americanum (L.) Leeke) – F; PM–PM–PM; MB(Mung bean — Vigna radiata (L.) R. Wilczek) – PM–MB; CB (Clusterbean —Cyamopsis tetragonoloba (L.) Taubert.) – PM–CB; F–MB–MB; F–CB–CB, MB–MB–MB; and CB–CB–CB. The cropping system preceding the experiment was pearlmillet. The plots were 2·5 m 3 5 m and replicated three times in a randomized blockdesign. The crops were sown in July with the onset of the monsoon and harvested inOctober on maturity. Soil samples were collected at 0–15 cm and 15–30 cm depthswith a soil auger after 3 years of rotation. Within each of three replicates, three soilcores from each depth were combined to make a representative sample. All sampleswere sieved (2 mm) and stored for 7 days at 4°C before biological analyses wereconducted.

A. V. RAO ET AL.238

During the 1993 kharif season (June to September), i.e. after completion of thecropping system, pearl millet CV MH-179 was grown uniformly in all the treatmentsin rows of 50 cm apart with 10 cm distance in between plants without any fertilizers.The precipitation over the period from June to September was 220 mm. At maturitythe crop was harvested and grain and straw yields were recorded.

For the assay of acid and alkaline phosphatases, the procedure of Tabatabai &Bremner (1969) was followed, using acetate buffer (pH 5·4) and borax-NaOH buffer(pH 9·4), respectively, with p-nitrophenol phosphate as the substrate, after reaction for1 h at 35°C. Dehydrogenase activity (DHA), a measure of microbial activity wasassayed by the method of Tabatabai (1982). The soil sample was incubated with2,3,5-tri-phenyltetrazolium chloride, and the production of triphenyl formazon wasdetermined by measuring absorbance at 485 nm. Nitrogen fixing ability (N2-aseactivity) of the soils was determined by incubating 50 mg of soil in 3 ml of N-free semi-solid malate medium at 30 ± 1°C for 2 days. The tubes were then incubated with 10%C2H2 for 24 h and the gas mixture was analysed for the production of C2H4 in anAIMIL-NUCON gas chromatograph employing a poropak-T column. The popula-tions of nitrifying bacteria were estimated by MPN method (Alexander & Clark,1965). Viable VAM spores were isolated and counted following the wet sievingmethod, as described by Furlan & Fortin (1975). Available P, NO3-N and organicmatter were analysed by adopting standard methods (Jackson, 1967). Data wereexpressed on an oven-dry basis.

Standard errors of means were calculated and least significant difference testsconducted (Sokal & Rohlf, 1981).

Results and discussion

The activities of dehydrogenase, nitrogenase and both acid and alkaline phosphataseswere significantly different between the crop rotations used with the highest following3 years continuous legume cropping (Table 2). However, between the two legumes,i.e. clusterbean and mung bean in rotation, activities did not differ significantly at15–30 cm depth. No specific trend in enzyme activities in the surface soil wasobserved. Activities of phosphatases were significantly higher under clusterbean; whilemung bean significantly stimulated dehydrogenase and nitrogenase activities com-pared to those of clusterbean. The activities of enzymes varied with the depth. Ingeneral, the enzymatic activities were higher in the surface soil than in the subsoil(15–30 cm). The activities of acid and alkaline phosphatases increased by 44 and 92%in surface soil (0–15 cm) compared with in the subsoil. Further, there was a reductionin dehydrogenase activity of 46% and an absence of nitrogenase activity in the subsoil.Among the soil enzymes, nitrogenase was most affected by crop rotations and incontinuous legume rotation its activity increased three-fold over cereal rotation.

The results clearly demonstrate that the presence of legumes in the rotationpromoted a strong rhizosphere effect. As soil enzymes are mainly microbial in origin,the differences between rotations may be due to the pattern of root exudation whichinfluences the different groups of micro-organisms and causes temporal diversity(Altiere, 1987). Higher enzyme activity in the legume than in the cereal sequence maybe due to increase in below-ground inputs of C and N under legumes which oftenincrease microbial populations, their activity and subsequent enzyme synthesis beyondthat observed for conventional systems using commercial fertilizers (Doran et al.,1987; Fraser et al., 1988).

An increase in soil organic matter content over initial level due to crop rotation wasobserved. The degree of increase, however, varied with the cropping systems. Themaximum increase was observed in the legume sequence, particularly with clus-terbean, and the minimum was observed under the fallow-pearl millet rotation (Table3). In general, the increase was higher in the surface layer than in the subsoil. The

CROPPING SYSTEMS ON SOIL FERTILITY 239

Tab

le 2

.C

hang

es in

enz

yme

stat

us a

t tw

o di

ffere

nt s

oil d

epth

s af

ter

3 ye

ars

of c

rop

rota

tion

in a

n ar

id s

oil

Aci

d p

hosp

hata

se a

ctiv

ity

Alk

alin

e ph

osph

atas

e ac

tivi

tyD

ehyd

roge

nas

e ac

tivi

tyN

itro

gen

ase

acti

vity

*(n

Kat

100

g–1

dry

soi

l)(n

Kat

100

g–1

dry

soi

l)(p

Kat

g–1

dry

soi

l)(n

mol

es C

2H4h

–1)

Rot

atio

n0–

15 c

m15

–30

cm0–

15 c

m15

–30

cm0–

15 c

m15

–30

cm0–

15 c

m

F-P

M-F

2·42

1·71

6·75

4·18

9·31

6·49

52·8

3P

M-P

M-P

M3·

202·

088·

994·

8110

·16

8·09

62·8

7M

B-P

M-M

B3·

182·

259·

024·

9610

·63

7·96

73·0

0C

B-P

M-C

B3·

632·

239·

714·

7810

·26

7·47

76·6

7F

-MB

-MB

3·80

2·36

9·41

4·96

11·7

28·

1912

7·10

F-C

B-C

B3·

972·

499·

545·

2111

·10

8·22

115·

47M

B-M

B-M

B3·

852·

749·

635·

4913

·17

8·52

180·

67C

B-C

B-C

B4·

253·

0011

·64

5·57

12·6

08·

3118

1·57

LS

D (

p=0·

05)

0·16

0·20

0·36

0·43

0·45

0·16

5·87

* N

ot d

etec

tabl

e at

15–

30 c

m.

A. V. RAO ET AL.240

Tab

le 3

.C

hang

es in

nitr

ifyin

g ba

cter

ial p

opul

atio

n, V

AM

spo

res,

Olse

n-P,

org

anic

mat

ter

and

NO

3-N

con

tent

afte

r 3

year

s of

cro

p ro

tatio

n at

two

diffe

rent

dep

ths

Nit

rify

ing

bact

eria

No.

of

VA

Msp

ores

Ols

en-P

(p.

p.m

.)O

rgan

ic m

atte

r (%

)N

O3-

N (

p.p.

m.)

(104

g–1

dry

soi

l)(1

00 g

–1ai

r-d

ry s

oil)

Rot

atio

n0–

15 c

m15

–30

cm0–

15 c

m15

–30

cm0–

15 c

m15

–30

cm0–

15 c

m15

–30

cm0–

15 c

m15

–30

cm

F-P

M-F

0·44

0·17

100

170

5·56

3·76

0·35

0·25

2·32

2·00

PM

-PM

-PM

1·65

0·50

310

390

6·20

5·57

0·38

0·24

2·26

1·32

MB

-PM

-MB

0·93

0·34

130

150

7·75

5·39

0·39

0·26

2·46

1·55

CB

-PM

-CB

0·77

0·41

160

360

7·29

4·80

0·38

0·25

2·39

1·44

F-M

B-M

B0·

980·

3160

180

7·98

4·58

0·45

0·26

2·85

1·62

F-C

B-C

B0·

710·

3117

020

07·

864·

530·

410·

273·

771·

63M

B-M

B-M

B1·

170·

3880

180

8·28

4·34

0·50

0·33

3·43

2·04

CB

-CB

-CB

0·87

0·43

150

210

9·22

4·37

0·59

0·46

4·27

3·36

LS

D (

p=0·

05)

0·18

0·11

17·5

38·2

0·57

0·59

0·01

0·01

0·07

0·06

CROPPING SYSTEMS ON SOIL FERTILITY 241

Table 4. Grain and straw yields of pearl millet after3 years of crop rotation in an arid soil

Yield (t. ha–1)

Rotation Grain Straw

F-PM-F 3·4 16·8PM-PM-PM 3·8 17·6MB-PM-MB 4·4 19·0CB-PM-CB 5·3 19·8F-MB-MB 5·6 19·4F-CB-CB 5·3 19·4MB-MB-MB 6·3 22·0CB-CB-CB 6·8 23·2LSD (p=0·05) 0·8 3·1

variations in organic matter could be due to the type of residues left by crops inrotation. Similar observations were reported by Odell et al. (1982). The maximumorganic matter accumulation under clusterbean may be due to more leaf fall and lowerC:N ratio of residues compared to other crops, consequently, microbial activityincreased leading to higher decomposition. Further, the greater availability of carbonand nitrogen resulted in more microbial biomass and thus a higher build-up of soilorganic matter (Doran & Smith, 1987). Higher levels of NO3-N and Olsen-P in thesurface soil in the continuous clusterbean rotation also support this observation. Thisleads to higher N-supplying capacities in legume-grown soils for succeeding cerealcrops (Kathju et al., 1987).

Crop rotation significantly affected the VAM spore number in the soil. It varied from80–490 kg–1 soil depending on the crop in rotation (Table 3). Maximum VAM sporenumbers were observed in the continuous pearl millet rotation. In general, more sporeswere observed in 15–30 cm depth than in surface soil. These results support ourprevious findings that among the crops, pearl millet is the best VAM host under aridclimates (unpublished data). The population of nitrifying bacteria was also affected bycrop rotation with the greatest population noted in the continuous pearl milletrotation. However, the number of nitrifying bacteria does not seem to be directlycorrelated with observed NO3-N level which indicates that the pattern depends on thelevel of decomposition of the crop residues.

The improvement in soil productivity/soil quality, as reflected by the enhancementin the activities of various enzymes, levels of beneficial micro-organisms and organicmatter following certain crop rotations, is further substantiated by the data on grainand straw yields of pearl millet (Table 4). Grain and straw yields of pearl millet afterlegumes were significantly improved compared to the yields after a fallow orcontinuous pearl millet. Maximum enhancement of production of pearl millet wasobserved after 3 years of continuous legumes followed by 2 years and 1 year oflegumes.

Conclusions

Plant roots exert an influence on the soil environment biologically. They are a majorsource of organic carbon needed for many microbial processes. Roots are particularlyeffective in this role because of their intimate contact with soil pores (Campbell, 1978).Plant roots also release CO2 and other organic compounds that may have various

A. V. RAO ET AL.242

effects on microbial activity. The significant effect of crop rotations with legumes isdue to the lower C/N ratios in their crop residues. Fallowing in crop rotationaccelerates the loss of soil organic C (Biederbeck et al., 1984). In general, soilbiological properties were significantly altered by 3 years of continuous rotation of bothclusterbean and mung bean, indicating a strong rhizosphere effect promoted by thepresence of clusterbean and mung bean roots. This study also emphasizes theimportance of selective crop rotation on biological improvement of soil, particularly indesert sandy soils whose inherent fertility status is quite low.

On the basis of the results described herein, it can be concluded that crop rotationinvolving legumes for more than 1 year successively, is an effective managementpractice with respect to increasing the content of organic matter, NO3-N, available P,as well as improving the level of biological and enzymatic activities in the deserticsandy soils, leading to the higher production of pearl millet as the immediatelyfollowing crop.

This work has been financially supported under an USDA funded Project No. IN-ARS-676(FG-IN-716).

References

Alexander, M. & Clark, F.E. (1965). Nitrifying bacteria. In: Black, C.A., Evans, D.O., White,J.L., Ensminger, L.E. & Clark, F.E. (Eds), Methods of Soil Analysis Chemical andMicrobiological Properties, pp. 1477–1483. Madison, WI: American Society of Agronomy.1572 pp.

Altiere, M.A. (1987). Agroecology, the Scientific Basis of Alternative Agriculture. Boulder, CO:Westview Press. 374 pp.

Biederbeck, V.O., Campbell, C.A. & Zentner, R.P. (1984). Effect of crop rotation andfertilization on some biological properties of a loam in southeastern Saskatchewan. CanadianJournal of Soil Science, 64: 355–367.

Campbell, C.A. (1978). Soil organic carbon, nitrogen, and fertility. Dev. Soil Science, 8:173–271.

Doran, J.W. & Smith, M.S. (1987). Organic matter management and utilization of soil andfertilizer nutrients. In: Mortvedt, J.J. et al. (Eds), Soil Fertility and Organic Matter as CriticalComponents of Production System. SSSA Special Publication 19, pp. 53–72. Madison, WI: SSSA.235 pp.

Doran, J.W., Fraser, D.G., Culik, M.N. & Liebhardt, W.C. (1987). Influence of alternative andconventional agricultural management on soil microbial processes and nitrogen availability.American Journal of Alternative Agriculture, 2: 99–106.

Doran, J.W., Mielke, L.N. & Power, J.F. (1990). Microbial activity as regulated by soil waterfilled pore space. Symposium on ecology of soil microorganism in the micro-habitatenvironment. In: Transactions of the 14th International Conference of Soil Science, Vol.III, pp.94–99. International Society of Soil Science, Kyoto, Japan.

Fraser, D.G., Doran, J.W., Sahs, W.W. & Lesoing, G.W. (1988). Soil microbial populationsand activities under conventional and organic management. Journal of Environmental Quality,17: 585–590.

Furlan, V. & Fortin, J.A. (1975). Formation of endo-mycorrhizae by Endogone calospora onAllium cepa under three temperature regimes. Naturaliste Canadien, 100: 467–478.

Jackson, M.L. (1967). Soil Chemical Analysis. New Delhi: Prentice Hall of India Private Limited.498 pp.

Kathju, S., Aggarwal, R.K. & Lahiri, A.N. (1987). Evaluation of diverse effects of phosphateapplication on legume of arid areas. Tropical Agriculture, 64: 91–96.

McGill, W.B., Cannon, K.R., Robertson, J.A. & Cook, F.D. (1986). Dynamics of microbialbiomass and water soluble organic C in Breton after 50 years of cropping to two rotations.Canadian Journal of Soil Science, 66: 1–19.

Molope, M.B. (1987). Soil aggregate stability: the contribution of biological and physicalprocesses. South African Journal of Plant Soil, 4: 121–126.

CROPPING SYSTEMS ON SOIL FERTILITY 243

Odell, R.T., Walker, W.M., Boone, L.V. & Oldham, M.G. (1982). The marrow plots: a centuryof learning University of Illinois Agricultural Experimental Station Bulletin 775, Urbana, IL.

Power, J.F. & Doran, J.W. (1984). Nitrogen use in organic farming. In: Hauck, R.D. (Ed.),Nitrogen in Crop Production, pp. 585–598. Madison, WI: American Society of Agronomy.793 pp.

Sokal, R.R. & Rohlf, F.J. (1981). Biometry — The Principles and Practice of Statistics in BiologicalResearch. (2nd Edn). New York: W.H. Freeman & Co. 859 pp.

Tabatabai, M.A. (1982). Soil enzymes. In: Page, A.L. (Ed.), Methods of Soil Analysis. Part 2.Chemical and Microbiological Properties, (2nd Edn.), pp. 903–947. Madison WI: AmericanSociety of Agronomy. 1572 pp.

Tabatabai, M.A. & Bremner, J.M. (1969). Use of p-nitrophenyl phosphate for assay of soilphosphatase activity. Soil Biology and Biochemistry, 1: 301–307.

Visser, S. & Parkinson, D. (1992). Soil biological criteria as indicators of soil quality: soilmicroorganisms. American Journal of Alternative Agriculture, 7: 33–37.

A. V. RAO ET AL.244