PHOSPHATASE AND UREASE ACTIVITIES IN A TROPICAL SANDY SOIL AS AFFECTED BY SOIL WATER-HOLDING CAPACITY AND ASSAY CONDITIONS

This article was downloaded by: [University of Auckland Library]On: 06 November 2014, At: 17:10Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Communications in Soil Science and Plant AnalysisPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/lcss20

PHOSPHATASE AND UREASE ACTIVITIES IN A TROPICALSANDY SOIL AS AFFECTED BY SOIL WATER-HOLDINGCAPACITY AND ASSAY CONDITIONSS. N. Sall a & J. -L. Chotte aa Laboratoire de Bio-pédologie , Centre IRD-ISRA , B.P. 1386, Dakar, SénégalPublished online: 19 Aug 2006.

To cite this article: S. N. Sall & J. -L. Chotte (2002) PHOSPHATASE AND UREASE ACTIVITIES IN A TROPICAL SANDY SOIL ASAFFECTED BY SOIL WATER-HOLDING CAPACITY AND ASSAY CONDITIONS, Communications in Soil Science and Plant Analysis,33:19-20, 3745-3755, DOI: 10.1081/CSS-120015919

To link to this article: http://dx.doi.org/10.1081/CSS-120015919

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

http://www.tandfonline.com/loi/lcss20

http://www.tandfonline.com/action/showCitFormats?doi=10.1081/CSS-120015919

http://dx.doi.org/10.1081/CSS-120015919

http://www.tandfonline.com/page/terms-and-conditions

http://www.tandfonline.com/page/terms-and-conditions

PHOSPHATASE AND UREASE ACTIVITIESIN A TROPICAL SANDY SOIL AS

AFFECTED BY SOIL WATER-HOLDINGCAPACITY AND ASSAY CONDITIONS

S. N. Sall* and J.-L. Chotte

Laboratoire de Bio-pedologie, Centre IRD-ISRA,

B.P. 1386, Dakar, Senegal

ABSTRACT

A set of tests was performed to adapt enzyme assays (phosphatase,

urease) to conditions of poor sandy soils of West African semi-

arid zone. The pH buffer, substrate concentration, incubation time

were studied. Moreover, effects of soil water content (5% WHC,

100% WHC, 200% WHC) and drying–rewetting cycles were

considered. Phosphatase activity peaked at pH close to soil pH.[6]

By contrast, urease was the highest for pH buffer of 10. Optimal

substrate concentrations were 5 mM and 720 mM for phosphatase

and urease, respectively. The tested incubation time (30 min,

60 min, 90 min, 120 min) had no impact on enzyme assays. Urease

activity was not modified either by soil water content or by

drying–rewetting cycles. For the phosphatase, the highest activity

was recorded for soil incubated at 100% WHC. Air-drying

3745

DOI: 10.1081/CSS-120015919 0010-3624 (Print); 1532-2416 (Online)

Copyright q 2002 by Marcel Dekker, Inc. www.dekker.com

*Corresponding author. E-mail: [email protected]

COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS

Vol. 33, Nos. 19 & 20, pp. 3745–3755, 2002

©2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016

Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

17:

10 0

6 N

ovem

ber

2014

depleted this activity. Soils incubated at 5% and 200% WHC were

not sensitive to drying–rewetting cycles.

INTRODUCTION

Soil enzymes play an essential role in organic matter decomposition and

nutrient cycling. They are thought to be accurate indicators of soil functioning,

being sensitive to ecological stress and land management.[1 – 3] They are greatly

affected by soil organic matter content[4 – 7] and often are used as indices of

microbial activity.[1,8,9] Invertase, protease are assumed to be an accurate

“fertility index.”[10] Other enzymes (e.g., Catalase) are reported to be very

sensitive to biotic factors.[11] Soil phosphatase activity encompasses the activity

of enzymes bound to soil colloids and humic substances, free phosphatases in the

soil solution, and phosphatases associated with living and dead plant or microbial

cells.[12,13] Soil phosphatase activity has often been proposed as an index of the

soil potential for organic phosphorus mineralization and biological activity.[9,14]

Similarly, urease could be used as an indicator of the potential rate of degradation

of nitrogen compounds, such as proteins.[2,12]

Enzyme assays are performed under controlled conditions of temperature,

buffer pH and incubation time. As one reviews the literature, considerable

variations exist among assay procedures. Though these procedures are well

documented, there is a need for further verifications in order to adapt the method

to soils and environments not explored so far.

This present study is part of a research program dealing with the role played

by soil biota in the functioning of tropical sandy soils and nutrient cycling in low

input West African farming systems. Objectives of this study were to (1) adapt

enzyme assays to conditions of the poor soils with weak biological activities

encountered in Senegal and (2) determine the effect of soil water content and

drying–rewetting cycles on enzyme activities as a model to simulate the impact

of conservation[5,15 – 17] of soils sampled at different period of the rainy season.

MATERIALS AND METHODS

Soil

The soil was sampled to 0–10 cm depth from a typical Oxisol (Thysse

Kaymor, 13.450N, 15.40 0W) in June before the clearance of a 20 year-old fallow.

Six replicates were pooled, air-dried, sieved to ,2 mm and stored at room

temperature pending processing. Contents of organic carbon, and nitrogen,

SALL AND CHOTTE3746



Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

17:

10 0

6 N

ovem

ber

2014

assimilable phosphorus,[18] clay (dia. ,2mm), and sand (dia. .50mm) were

11.3%, 0.81%, 11.2 ppm, 10.4%, and 55.3%, respectively.

Enzyme Assays

Phosphatase Activity

Air-dried soils (100 mg) were incubated with 400mL of citrate–phosphate

buffer and 100mL of a 5 mM disodium paranitrophenyl phosphate solution

(SIGMA) at 378C according to the procedure of Tabatabai and Bremner.[19] The

reaction was stopped by the addition of 100mL of CaCl2 (0.5 M) and 400mL of

NaOH (0.5 M). It was necessary to add calcium chloride (CaCl2) first to prevent

any dissolution of humic substances and dispersion of clay minerals.[15] Released

phenols were estimated colorimetrically at 400 nm with a spectrophotometer

(Ultrospec 3000, Pharmacia-Biotech). Two controls, i.e., soil without substrate,

substrate without soil, were assayed under the same conditions as those for soil

samples in order to check the absence of colored components extracted by the

buffer or CaCl2–NaOH treatment, and of trace amounts of p-nitrophenol in p-

nitrophenyl phosphate reagent, respectively.

Urease Activity

For the determination of urease activity, 100 mg of the soil were incubated

at 378C with 50mL of 720 mM urea solution (SIGMA) and 400mL of borate

buffer (0.1 M). Released ammonium was extracted with 3 mL of KCl (2M)

solution, and determined colorimetrically by a modified Berthelot reaction.[20]

Tested Parameters

For both enzyme activities the tested parameters were:

. Buffer pH ranged from 4 to 11 and from 6 to 12 for the phosphatase and

urease activity, respectively,

. Substrate concentration were 2.5 mM, 5 mM, 10 mM, 15 mM, and

20 mM, and 90 mM, 180 mM, 360 mM, 720 mM, 1.4 M, and 2.8 M for

the phosphatase and urease activity, respectively,

. Incubation times were 30 min, 60 min, 90 min and 120 min for both

activities.

Analyses were performed on 5 replicates.

PHOSPHATASE AND UREASE ACTIVITIES 3747



Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

17:

10 0

6 N

ovem

ber

2014

Water-Holding Capacity

Soil water content was adjusted to contrasted water potential humidity

equivalent to 5%, 100%, and 200% of the soil water-holding capacity that is

respectively to 0.45 g 100 g21 soil, 9.00 g 100 g21 soil, and 18.00 g 100 g21 soil.

Soil samples (5 replicates) were processed as follow:

. Incubated for a week at 378C,

. Then air-dried for a week at room temperature,

. Moistened at the initial water content and incubated for a week at 378C.

Enzyme activities were performed at each step of this process in order to

determine (i) the impact of water content on the initial enzyme activities and (ii)

any change on enzyme activities as a result of drying–rewetting cycle.

For both activities, the incubation time was fixed to 1 hour.

Statistics

Data were subjected to analysis of variance using the Super Anova

Computer program and means were compared with the PLSD Fisher’s test

ðp # 0:05Þ:

RESULTS AND DISCUSSION

Effect of Buffer pH

Phosphatase activity peaked at pH 6, and to a lesser extent at pH 9 (Fig. 1),

indicative of the predominance of acid phosphatase in the soil, this activity

(2.11mg p-NP released/g/h) being 4 times higher than alkaline phosphatase

(0.51mg p-NP released/g/h). Margesin and Schinner[21] observed also the

relationship between soil pH and optimum pH for soil phosphatase activity, this

activity being thought to be soil-specific. Alkaline phosphatase in soil is thought

to arise entirely from microorganisms, while acid phosphatase is largely

produced by plant roots.[22,23]

By contrast, the maximum activity of urease was recorded at pH 10 (Fig. 2).

Our optimal pH for urease activity is close to that already reported by other

investigators,[24,25] despite the use of a different buffer. The pH optimum of soil

urease varied with the diversity of vegetation, micro-organisms, and soil fauna as

sources contributing to the enzyme activity and sites that allowed entrapment of

the enzyme within colloidal humus and organic-mineral complexes.

SALL AND CHOTTE3748



Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

17:

10 0

6 N

ovem

ber

2014

Figure 1. Effect of pH buffer on phosphatase activity. Data are given as a means of five

replicate samples, bars indicate standard deviation.

Figure 2. Effect of pH buffer on urease activity. Data are given as means of five replicate

samples, bars indicate standard deviation.




Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

17:

10 0

6 N

ovem

ber

2014

Effect of Substrate Concentration

Variation in substrate concentration (S) allowed the calculation of the

Michaelis constant (Km) and the maximum enzyme reaction velocity (Vm) for

both enzyme activities (Table 1). These calculations were performed by plotting

S/V against S to determine the intercept and the slope of the linear transformation

of the Michaelis–Menten equation ½S=V ¼ ðKm=VmÞ þ ð1=VmÞðSÞ�: When this

graphical method of calculation is used, the intercept is Km/Vm and the slope is

1/Vm.[26] Our results indicated that the substrate concentrations used for

phosphatase (5 mM) and for urease (720 mM) were not limiting factors.

Though our Km values for phosphatase and urease were consistent with

those of the literature,[17,27] strict comparison are not justified as different buffers,

pH optimum, and soils have been used.

Effect of Incubation Time

No significant impact of the duration of the incubation was recorded on the

phosphatase and urease activities (data not shown). The substrates were

hydrolyzed to the same extent, even for the shortest incubation time.

Effect of Water Content

Accordingly to above results, for the water content effects, we measured

activities with a buffered 5mM substrate solution at pH equaled to 6 for acid

phosphatase and a buffered 750 mM substrate solution at pH equaled to 10 for

urease.

Initial Water Content

The highest phosphatase activity was recorded for the soil incubated at

100% WHC (Table 2). Significant correlation between phosphatase activity and

Table 1. Km and Vm Values for Phosphatase and Urease by

Methods Described

Activity Km (mM) Vm (mg p-NP or N/g/min)

Phosphatase 1.36 2.55

Urease 55.9 0.74

SALL AND CHOTTE3750



Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

17:

10 0

6 N

ovem

ber

2014

Table 2. Effects of Wetting, Drying, and Rewetting in Phosphatase and Urease Activities (Mean of 5 Replicates ^ Standard Error); For

Each Enzyme Activity, Means with the Same Letter in the Same Line Are Not Significantly Different (P , 0:05)

Phosphatase (mg p-NP Released/g Dry Soil/min) Urease (mg N.NH4/g Dry Soil/min)

Wetting Drying Rewetting Wetting Drying Rewetting

5%WHC 1.972 ^ 0.100a 2.005 ^ 0.121a 1.964 ^ 0.074a 0.543 ^ 0.092a 0.611 ^ 0.024a 0.629 ^ 0.047a

100%WHC 2.967 ^ 0.085b 2.022 ^ 0.092a 3.427 ^ 0.116c 0.648 ^ 0.065a 0.678 ^ 0.050a 0.594 ^ 0.054a

200%WHC 0.731 ^ 0.097a 0.771 ^ 0.090a 1.120 ^ 0.117c 0.668 ^ 0.117a 0.653 ^ 0.044a 0.660 ^ 0.071a

PH

OS

PH

AT

AS

EA

ND

UR

EA

SE

AC

TIV

ITIE

S3

75

1



Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

17:

10 0

6 N

ovem

ber

2014

soil water content have been reported.[22,28] Above 100% WHC, water impedes

the development of soil microorganisms responsible for this activity.

By contrast, urease activity was not modified by the initial moisture

content, being of the same magnitude whatever the soil moisture content

(Table 2). The urease activity increased from 5% WHC to 200% WHC, but the

differences were not significant.

Drying–Rewetting Cycle

The drying–rewetting cycle did not significantly modify the urease

activity, whatever the initial soil moisture content (Table 2). Similar results were

recorded by Gould et al.[29] and Dalal[5] who detected a non-significant effect of

soil moisture content on urease activity. However, opposite conclusions were

drawn by others. For instance, early work conducted by Skujins and McLaren[30]

concluded on a negative impact of drying of a field moist soil, while an increase

of urease activity was observed by Palma and Conti[31] and Bandick and Dick[32]

in a soil recently amended with manure. Urease activity in soils has been found to

be persistent for long periods due to some form of enzyme protective mechanism

existing in soils. This mechanism of protection could prevent the enzyme from

alteration due to external factors such as desiccation.

It is difficult to account for this divergence between our results and those

obtained in the literature. However differences in the assay procedure (buffered

versus un-buffered incubation) might be advocated to explain this discrepancy.

Moreover, the soil characteristics (i.e., soil organic and clay content) and their

sensitivity to drying according to their properties may be responsible for these

differences.

For the soil incubated at 5% WHC and at 200% WHC, any significant

effect of the soil drying and rewetting procedure was observed on phosphatase.

By contrast this procedure had a significant impact of phosphatase assayed on

soils incubated at 100% WHC. The air-drying procedure depleted significantly

the enzyme activity. This observation is inconsistent with that of Eivazi and

Tabatabai[17] who noted that air-drying increased the activity of acid

phosphatase. The following rewetting stage allowed the initial phosphatase

activity to be recovered. Phosphatase measured in soil reflects the activity of

enzymes bound to soil colloids, and to humic substances, free phosphatases in

soil solution, and phosphatases associated with living and dead plant or microbial

cells.[12,13] Alike for the urease activity the discrepancy between our result and

that of the literature may arise from differences in soil properties. As a matter of

fact, the soil used by Eivazi and Tabatabai[17] has twice clay content that the soil

used in this study. Enzymes associated to micro-aggregates are likely to be less

sensible to drying in this clay soil than those in our sandy soil. The decrease of

SALL AND CHOTTE3752



Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

17:

10 0

6 N

ovem

ber

2014

phosphatase activity after air-drying could be attributed to the disappearance of

soil bacteria, remaining activity originating from surviving fungi and plant

debris.

CONCLUSIONS

Air-dried soils have been used extensively for studies of soil enzyme

activities. This procedure greatly facilitates the transfer of soil samples from field

experimentation to laboratory facilities. However, there is evidence that air-

drying of soils can significantly affect the activities of soil enzymes. The extent to

which enzymes are affected depend largely on the type of enzyme.[33 – 36] In this

study on a sandy soil, phosphatase was clearly affected by air-drying, while no

effect was measured for urease. Therefore, any treatment resulting in a

modification of soil moisture content would alter enzyme activity. Consequently,

this constraint should be taken into consideration before adopting any decision

concerning the accuracy of enzyme assays performed on soil samples from field

experimentation. The storage of soils in plastic bag at 48C pending analyses

seems to be adequate to avoid change in enzyme activity.[37]

REFERENCES

1. Dick, R.P. Soil Enzyme Activities as an Indicators of Soil Quality. In

Defining Soil Quality for a Sustainable Environment; Doran, J.W.,

Coleman, D.C., Bezdicek, D.F., Stewart, B.A., Eds.; American Society of

Agronomy: Madison, WI, 1994; 107–124.

2. Tabatabai, M.A. Soil Enzymes. In Methods in Soil Analysis; Page, A.L.,

Miller, R.H., Keeney, D.R., Eds.; American Soil of Agronomy: Madison,

WI, 1994; 775–783.

3. Kramer, S.; Green, D.M. Acid and Alkaline Phosphatase Dynamics and

Their Relationship to Soil Microclimate in Semiarid Woodland. Soil Biol.

Biochem. 2000, 32, 179–188.

4. Ladd, J.N.; Butler, J.H.A. Short-Term Assay of Soil Proteolytic Enzymes

Using Proteins and Dipeptide Derivatives as Substrate. Soil Biol. Biochem.

1972, 4, 19–30.

5. Dalal, R.C. Urease Activity in Some Trinidad Soils. Soil Biol. Biochem.

1975, 7, 5–8.

6. Tabatabai, M.A. Effect of Trace Elements on Urease Activity in Soils. Soil

Biol. Biochem. 1977, 9, 9–13.

7. Speir, T.W. Studies on Climosequence of Soil in Tussock Grassland. XI.

Urease, Phosphatase and Sulfatase Activities of Top Soils and Their




Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

17:

10 0

6 N

ovem

ber

2014

Relationships with Other Properties Including Plant Available Sulfur. N.Z.

J. Sci. 1977, 20, 159–166.

8. Kumar Jha, D.; Sharma, G.D.; Mishra, R.R. Soil Microbial Population

Numbers and Enzyme Activities in Relation to Altitude Profiles. Soil and

Forest Degradation. Soil Biol. Biochem. 1992, 24, 761–767.

9. Dick, W.A.; Tabatabai, M.A. Potential Uses of Soil Enzymes. Meeting of

Soil Microbial Ecology: Application in Agricultural and Environmental

Management; Marcel Dekker, Inc.: New York, 1993; 95–127.

10. Skujins, J. History of Abiotic Soil Enzymes Research. In Soil Enzymes;

Burns, R.G., Ed.; Academic Press: New York, 1978; 1–49.

11. Asmar, F.; Eiland, F.; Nielson, N.E. Interrelationship Between Extracellu-

lar Enzyme Activity, ATP Content, Total Counts of Bacteria and CO2

Evolution. Soil Biol. Fertil. 1992, 14, 288–292.

12. Skujins, J. Extracellular Enzymes in Soil. CRC Crit. Rev. Microbiol. 1976,

4, 383–421.

13. Nannipieri, P.; Grego, S.; Ceccanti, B. Ecological Significance of the

Biological Activity in Soil. In Soil Biochemistry; Bollag, J.M., Stotzky, G.,

Eds.; Marcel Dekker, Inc.: New York, 1990; Vol. 6, 293–355.

14. Speir, T.W.; Ross, D.J. Soil Phosphatase and Sulphatase. In Soil Enzymes;

Burns, R.G., Ed.; Academic Press: London, 1978; 197–215.

15. Tabatabai, M.A. Soil Enzymes. In Method of Soil Analysis, Part 2, 2nd Ed.;

Page, A.L., Miller, R.H., Keeney, D.R., Eds.; Agron. Monogr.; ASA and

SSSA: Madison, WI, 1982; 9, 903–945.

16. Ciardi, C. Soil Heating to Distinguish the Contribution of Abiotic and

Extracellular Activities to the Overall Enzyme Activity in Soil.

Agrochimica 1998, 22, 3–4.

17. Eivazi, F.; Tabatabai, M.A. Phosphatases in Soils. Soil Biol. Biochem.

1977, 9, 167–172.

18. Dabin, B. Application Des Dosages Automatiques a L’analyse Des Sols.

3eme Partie. Cah. ORSTOM, Ser. Pedol. 1967, 5, 257–286.

19. Tabatabai, M.A.; Bremner, J.M. Use of p-Nitrophenyl Phosphate for Assay

of Soil Phosphatase Activity. Soil Biol. Biochem. 1969, 1, 301–307.

20. Kandeler, E.; Gerber, H. Short-Term Assay of Soil Urease Activity Using

Colorimetric Determination of Ammonium. Biol. Fertil. Soils 1988, 6,

68–72.

21. Margesin, R.; Schinner, F. Phosphomonoesterase, Phosphodiesterase,

Phosphotriesterase and Inorganic Pyrophosphatase Activities of Forest

Soils of the Alpine Area-Effect of pH on Enzyme Activity and Extractibily.

Biol Fertil. Soils 1994, 18, 320–326.

22. Speir, T.W.; Cowling, J.C. Phosphatases Activities of Pasture Plants and

Soils: Relationship with Plant Productivity and Soil P Fertility Indices.

Biol. Fertil. Soils 1991, 12, 189–194.

SALL AND CHOTTE3754



Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

17:

10 0

6 N

ovem

ber

2014

23. Dinkelaker, B.; Marschner, H. In Vivo Demonstration of Acid Phosphatase

Activity in Rhizosphere of Soil-Grown Plants. Plant Soil 1992, 144,

199–205.

24. Tabatabai, M.A.; Bremner, J.M. Assay of Urease Activity in Soil. Soil Biol.

Biochem. 1972, 4, 479–487.

25. Frankenberger, W.T., Jr.; Johanson, J.B. Effect of pH on Enzyme Stability

in Soils. Soil Biol. Biochem. 1982, 14, 433–437.

26. White, A.; Handler, P.; Smith, E.L. Principles of Biochemistry, 4th Ed.;

McGraw-Hill Publ.: New York, 1968; 223–246.

27. Pettit, N.M.; Smith, A.R.J.; Freeman, R.B.; Burns, R.G. Soil Urease

Activity, Stability and Kinetic Properties. Soil Biol. Biochem. 1976, 8,

479–484.

28. Harrison, A.F. Relationship Between Intensity of Phosphatase Activity and

Physico-chemical Properties in Woodland Soil. Soil Biol. Biochem. 1983,

15, 93–99.

29. Gould, W.D.; Cook, F.D.; Webster, G.R. Factors Affecting Urea Hydrolysis

in Several Alberta Soils. Plant Soil 1973, 38, 393–401.

30. Skujins, J.; McLaren, A.D. Persistence of Enzymatic Activities in Stored

and Geologically Preserved Soils. Enzymologia 1968, 34, 213–225.

31. Palma, R.M.; Conti, M.E. Urease Activity in Argentine Soils: Field Studies

and Influence of Sample Treatment. Soil Biol. Biochem. 1990, 22,

105–108.

32. Bandick, A.K.; Dick, R.P. Field Management Effects on Soil Enzyme

Activities. Soil Biol. Biochem. 1999, 31, 1471–1479.

33. Zantua, M.I.; Bremner, J.M. Comparison of Methods of Assaying Urease

Activity in Soils. Soil Biol. Biochem. 1974, 7, 291–295.

34. Zantua, M.I.; Bremner, J.M. Preservation of Soil Samples for Assay of

Urease Activity. Soil Biol. Biochem. 1975, 7, 297–299.

35. Burns, R.G. Enzyme Activity in Soil: Some Theoretical and Practical

Consideration. In Soil Enzymes; Burns, R.G., Ed.; Academic Press: New

York, 1978; 295–340.

36. Burns, R.G. Enzyme Activity in Soil: Location and a Possible Role in

Microbial Activity. Soil Biol. Biochem. 1982, 14, 423–427.

37. Pettit, N.M.; Gregory, L.J.; Freeman, R.B.; Burns, R.G. Differential

Stability of Soil Enzymes Assays and Properties of Phosphatase and

Arylsulphatase. Biochim. Biophys. Acta 1977, 485, 357–366.




Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

17:

10 0

6 N

ovem

ber

2014

Documents

PHOSPHATASE AND UREASE ACTIVITIES IN A TROPICAL SANDY SOIL AS AFFECTED BY SOIL WATER-HOLDING CAPACITY AND ASSAY CONDITIONS