Soil enzymes play a major role in the mineralization processes of organic materials. The soil enzymes originate from animal, plant and microbial sources and the resulting soil biological activity including the metabolic processes of all these organisms. Information on soil enzyme activities used to determine soil microbiological characteristics are very important for soil quality and healthy

Ridvan KIZILKAYA

Tayfun AŞKIN

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ORIGINAL PAPER161Volume 6 (2005) No. 2 (161-166)THE SPATIAL VARIABILITY OF UREASE ACTIVITY OF SURFACE AGRICULTURAL SOILS WITHIN AN URBAN AREATayfun AŞKIN1, Rıdvan KIZILKAYA21Corresponding author: Assistant Professor, Karadeniz Technical University, Faculty of Agriculture, Department of Soil Science, 52200, Ordu/TURKEY phone: +90 452 230 05 56; Fax: +90 452 225 12 61, e-mail: tayfuna@ktu.edu.tr 2Assistant Professor, Ondokuz Mayıs University, Faculty of Agriculture, Department of Soil Science, 55139, Samsun/TURKEYManuscript received: September 14, 2004; Reviewed: April 5, 2005; Accepted for publication: April 27, 2005ABSTRACTSoil enzymes play a major role in the mineralization processes of organic materials. The soil enzymes originate from animal, plant and microbial sources and the resulting soil biological activity including the metabolic processes of all these organisms. Information on soil enzyme activities used to determine soil microbiological characteristics are very important for soil quality and healthy.KEYWORDS: Spatial variability, soil urease activity, site speciﬁ c management162 Journal of Central European Agriculture Vol 6 (2005) No 2Tayfun AŞKIN, Rıdvan KIZILKAYAINTRODUCTIONBiochemical actions are dependent on or related to the presence of enzymes. Many reactions involving soil organic matter transformations may be catalyzed by enzymes existing outside the microorganisms ([9]) and plant root system ([19], [7]). Each soil may have a characteristic pattern of speciﬁ c enzymes as described by Kuprevich and Scherbakova ([10]). The differences in the level of enzymatic activity are caused primarily by the fact that every soil type ([4]), depending on its origin ([11]) and developmental conditions, is distinct from every other in its content of organic matter, in the composition and activity of living organisms inhabiting it, and consequently, in the intensity of biological processes. Obviously, it is probable that each type of soil has its own inherent level of enzymatic activity ([3], [12]).Large proportions of the nitrogen in many soils are organically bound and the mineralization of these portions is of agricultural importance ([16]). Organic nitrogen compounds in soil can constitute huge amount percent of total nitrogen and the assimilation of this nitrogen by plants and microorganisms is preceded by soil enzymes. Several enzymes are involved in the decomposition of organic nitrogen compounds ([1]). Soil scientists studied the variability of soil properties in conventional statistical terms. Classical statistical procedures assume that variation is randomly distributed within sampling units. Actually, soil properties are continuous variables whose values at any location can be expected to vary according to direction and distance of separation from neighboring samples. Recently, emphasis has been placed on the fact that the variations of a soil property are not completely disordered over the ﬁ eld and this spatial structure must be taken into account in the treatment of the data. Investigators have shown increasing interest in analyzing measured soil parameters for their interdependency over space, i.e., to study the dependency of a measured parameter on location in the ﬁ eld. Typically semivariograms and outocorrelogram have been used to study the spatial structure of soil properties. A literature search revealed limited published studies on spatial behavior of enzyme activity in soils. The objective of this study was to assess the spatial variability of soil urease activity; analysis of the spatial structure was based on the semivariogram analysis under an urban area. MATERIAL AND METHODSStudy Site and DesignThe site selected for this study is on the urban area in Gümüşhacıköy, Amasya, in the northwest Turkey (Latitude, 40053’N; longitude, 35013’W). The study area is located in an urban area. The primary grid consisted of 39 points spaced 4500 by 4500 m (Figure 1).The soils surface soils (0-20 cm depth) were sampled in the spring of 2001. Annual mean of precipitation is 400 mm and temperature is range from - 10 0C to 38 0C. Bulk soil samples were air dried and then crushed to pass through a 2 mm sieve.MeasurementsSelected soil physical and chemical properties were determined by means of appropriate methods: soil particle size distribution by the hydrometer method, pH in 1:2.5 (w/v) in soil: water suspension by pH -meter, soil organic matter by modiﬁ ed Walkley-Black method, CaCO3 content by Scheibler calcimeter, cation exchange capacity (CEC) by Bower method and (0.5 M NaHCO3extractable at pH 8.5) by Olsen method ([14]). Urease activity (UAc) was measured by the method Soil Properties Mean Min. Max. SdSeSand (S), % 46.03 29.0 68.6 11.66 1.87Silt (Si), % 24.07 14.6 33.3 4.96 0.79Clay (C), % 29.91 12.8 43.2 8.27 1.32pH (1:2.5 soil: water suspension) 8.06 7.30 8.60 0.34 0.05Electrical conductivity (EC), dS m-1 0.241 0.127 1.745 0.258 0.041Lime content (LC), % 5.38 0.20 15.86 4.40 0.70Organic matter content (OMC), % 2.23 0.38 5.02 1.10 0.18Cation exchange capacity (CEC), 41.98 23.48 60.02 9.49 1.52Available P, mg kg-1 7.07 4.48 15.38 2.12 0.34Urease activity (UAc), µg N g-1 dry soil 82.99 39.36 129.64 22.06 3.53Table 1. Descriptive statistics for selected properties of soils (n=39)Sd; standard deviation, Se; standard errorTHE SPATIAL VARIABILITY OF UREASE ACTIVITY OF SURFACE AGRICULTURAL SOILS WITHIN AN URBAN AREA163J. Cent. Eur. Agric. (2005) 6:2, 161-166Figure 1. Location of the sampling sites in Gümüşhacıköy, AmasyaDistance, m Pairs Semi variance0 - 253.55366 114 394.210329 166 445.414775 152 543.118996 122 587.023602 101 475.228076 43 601.3Table 2. Semi variance values for urease activityof Hoffmann und Teicher ([8]). A 7.5 ml citrate buffer (pH 6.7) and 10 ml of 10% urea substrate solution were added to 10 g soil, and subsequently the samples were incubated for 3 h at 37 °C. The volume was made up to 100 ml with distilled water at 37 °C. Following filtration through Whatman No. 42 ﬁ lter papers, 1 ml of ﬁ ltrate was diluted to 10 ml with distilled water, and 4 ml of sodium phenolate (12.5% (w/v) phenol + 5.4% (w/v) NaOH) and 3 ml of 0.9% sodium hypochloride were added. The released ammonium was determined spectrofotometrically at 578 nm. Three replicates of each sample were tested, and the control sample without urea was prepared. Results were expressed µ N g-1 dry soil.Statistical AnalysisAll geostatistical analyses were performed on a PC using GS+ package program ([6]). Descriptive statistics were determined by SPSS package program ([17]).RESULTS AND DISCUSSIONSoil PropertiesSome descriptive statistical results for selected soil physical and chemical properties are given in Table 1. The results can be summarized as; soil samples have mostly moderate coarse in texture, alkaline in pH, moderate in organic matter (average of 2.23 %), low in lime content (average of 2.35 %), and free alkaline problem (ESP<15 %) ([15]) (Table 1).Spatial Variability of Urease ActivityDistance on urease activity, pairs and semi variance values were presented in Table 2.The spherical isotropic model was selected, had the smallest RSS value and the biggest r2 value (Table 3), for spatial variability of the urease activity in the study area by GS+ package program ([6]).164 Journal of Central European Agriculture Vol 6 (2005) No 2Tayfun AŞKIN, Rıdvan KIZILKAYANuggetCoSillCo+CA0 or 3A0mC/Co+C%Co/ Co+C%r2 ModelUAc 235.5 554.8 19350 68.7 31.3 0.69 SphericalTable 3. Parameters of spherical isotropic model ﬁ tted to semi variance of UAcTable 4. Descriptive statistics on measured and kriged of UAc valuesDescriptive statistics MeasuredPredicted by Kriging Number of samples (n) 39 1008Minimum 39.36 36.59Maximum 129.64 112.18Mean 82.99 84.34Standard deviation 22.06 8.45The spatial distribution and model parameters of soil urease activity in the study area are schematically illustrated in Figure 2.The zone of inﬂ uence for urease activity was approximately 19.3 km (Table 3). The urease activity was point-kriged, based on spherical isotropic model, on a 1x1 km grid (1008 locations) by using the ten nearest neighboring points. Descriptive statistics were presented in Table 4 on observed and point-kriged UAc values.As shown in Table 4, not only the range of point-kriged urease phosphatase activity values was 36.59 to 112.18 µg N g-1 dry soil but also mean values was 84.34 µg N g-1dry soil, somewhat narrower than the range and mean of the measured UAc values (39.36-129.64 µg N g-1 dry soil and 82.99 µg N g-1 dry soil). Also why standard deviation on kriged UAc values was lower than the measured selected model was true ([18], [13]). A point-kriged map of UAc was illustrated using the same 1008 points that was used to krige UAc in Figure 3.CONCLUSIONKnowledge of the spatial variability of soil biological properties is one of the most important keys in further development of precision quality of agricultural areas. Reliable information on the range of spatial relationships enables deﬁ ning the sampling strategy needed to carry out soil biological properties maps accurately. In this study, a spherical isotropic model was the best ﬁ t semi variogram model for urease activity. Also the range of model was 19.3 km. The nugget effect, representing the undetectable experimental error and ﬁ eld variation within the minimum sampling space, was quite large compared to the sill, which represents total spatial variation. The ratio of nugget variance to sill expressed in percentages can be regarded as a criterion to classify the spatial dependence of soil properties. If this ratio is less than 25%, 2003004005006007000 5000 10000 15000 20000 25000 30000Lag, mSemivariance�(h)=554.8� 1.5� 19350h � - 0.5 ( 19350h )3 �     h � 19350 m Figure 2. The estimated semi-variogram values for UAc.THE SPATIAL VARIABILITY OF UREASE ACTIVITY OF SURFACE AGRICULTURAL SOILS WITHIN AN URBAN AREA165J. Cent. Eur. Agric. (2005) 6:2, 161-166Figure 3. Kriged map of UActhe variable has strong spatial dependence; if the ratio is between 25 and 75%, the variable has moderate spatial dependence; otherwise, the variable has weak spatial dependence ([5]). The ratio of nugget to total variation of UAc was 31.3 % indicating that the spatial correlation of UAc at the large scale was moderate dependence. The information of obtained from geostatistical techniques should be used to gain a better knowledge on spatial distribution of soil biological properties in an urban area. Also, this knowledge should be used as a literature for identifying the sampling strategies in large scale.   REFERENCES[1.] Alexander, M., Introduction to soil microbiology. Second ed., John Wiley & Sons. New York, USA. 1977.[2.] Aon, M.A., Colaneri, A.C., Temporal and spatial evolution of enzymatic activities and physico-chemical properties in an agricultural soil, Applied Soil Ecology (2001) 18:255-270. [3.] Burns, R.G., Enzymes in soils: Some theoretical and practical considerations, in: Burns, R.G. (Ed.). Soil enzymes, Academic Press, London, UK. 1978, pp. 295 – 339.[4.] Chhonkar, P.K., Tarafdar, J.C., Accumulation of phosphatase in soils. Journal of the Indian Society of Soil Science (1984), 32: 266 – 272. [5.] Chien, Y.J., Lee, D.Y., Guo, H.Y., Houng, K.H., Geostatistical analysis of soil properties of Mid-west Taiwan soils, Soil Science (1997) 162: 291-298.[6.] GS+, Geostatistics for the environmental sciences, Gamma Design Software, Plainwell, Michigan, USA, 1998.[7.] Haas, H., Redl, B., Friedlin, E., Stöfﬂ er, G., Isolation and analysis of the Penicillium chrysogenum phoA gene encoding a secreted phosphate-repressible acid phosphatase, Gene (1992) 113: 129 – 133. [8.] Hoffmann, G. G., Teicher, K., Ein kolorimetrisches Verfahren zur Bestimmung der Urease Aktivitat in Boden, Z. Pﬂ anzenernahr. Dung. Bodenk., (1961), 91: 55 - 63.[9.] Hofmann, E., The analyses of enzymes in soils, in: Linskens, H.F., Tracey, M.V. (Eds.), Moderne Methoden der Pﬂ anzenanalyse. Vol.VI. Springer Verlag, Berlin 1963, pp. 416 – 423.[10.] Kuprevich, V.F.,Shcherbakova, T.A., Comparative enzymatic activity in diverse types of soil, in: McLaren, A.D., Skujins, J. (Eds.),  Soil Biochemistry, Vol. 2, Marcel Dekker, New York, USA, 1971, pp. 167-201.[11.] Ladd, J.N., Soil enzymes, in: Vaughan, D., Malcom, R.E. (Eds.). Soil organic matter and biological activity, Martinus Nijhoff Dr. W. Junk Publishers, Dordrecht, Netherlands, 1985, pp. 175 – 221.[12.] Marinari, S., Masciandaro, G., Ceccanti, B., Grego, S., Inﬂ uence of organic and mineral fertilizers on soil biological and physical properties, Bioresource Technology (2000) 72: 9-17. [13.] Öztaş, T., 1996. Eğimli bir arazide erozyonla kaybolan toprak derinliğindeki değişimin Kriging analizi ile belirlenmesi. Tarım-Çevre İlişkileri Sempozyumu “Doğal Kaynakların Sürdürülebilir Kullanımı”, s: 327-335, 13-15 Mayıs, Mersin.(in Turkish)[14.] Rowell, D.L., Soil science: Methods and applications. Longman, UK, 1996.[15.] Soil Survey Staff, Soil Survey Manuel, USDA Handbook No:18, Washington, 1993.[16.] Speir, T.W., Ross, D.J., Soil phosphatase and sulphatase, in: Burns, R.G. (Ed.), Soil enzymes, Academic Press, London, UK, 1978, pp. 197-250.[17.] SPSS, SPSS for Windows, Release 10.0.5, SPSS Inc., USA, 1999. [18.] Trangmar, B.B., Yost, R.S. Uehara, G., Application of geostatistics to spatial studies of soil properties, Advances in Agronomy, Vol. 38, 1985, pp. 45-93.[19.] Voets, J.P., Dedeken, M., Observations on the microﬂ ora and enzymes in the rhizosphere,  Annls. lnst. Pasteur, Paris Suppl. (1966), No. 3: 197-207.

THE SPATIAL VARIABILITY OF UREASE ACTIVITY OF SURFACE AGRICULTURAL SOILS WITHIN AN URBAN AREA

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ORIGINAL PAPER161 Volume 6 (2005) No. 2 (161-166)THE SPATIAL VARIABILITY OF UREASE ACTIVITY OF SURFACE AGRICULTURAL SOILS WITHIN AN URBAN AREATayfun AŞKIN1, Rıdvan KIZILKAYA21Corresponding author: Assistant Professor, Karadeniz Technical University, Faculty of Agriculture, Department of Soil Science, 52200, Ordu/TURKEY phone: +90 452 230 05 56; Fax: +90 452 225 12 61, e-mail: tayfuna@ktu.edu.tr 2Assistant Professor, Ondokuz Mayıs University, Faculty of Agriculture, Department of Soil Science, 55139, Samsun/TURKEYManuscript received: September 14, 2004; Reviewed: April 5, 2005; Accepted for publication: April 27, 2005ABSTRACTSoil enzymes play a major role in the mineralization processes of organic materials. The soil enzymes originate from animal, plant and microbial sources and the resulting soil biological activity including the metabolic processes of all these organisms. Information on soil enzyme activities used to determine soil microbiological characteristics are very important for soil quality and healthy.KEYWORDS: Spatial variability, soil urease activity, site speciﬁ  c management162 Journal of Central European Agriculture Vol 6 (2005) No 2Tayfun AŞKIN, Rıdvan KIZILKAYAINTRODUCTIONBiochemical actions are dependent on or related to the presence  of  enzymes.  Many  reactions  involving  soil organic  matter  transformations  may  be  catalyzed  by enzymes  existing  outside  the  microorganisms  ([9]) and plant root system ([19], [7]). Each soil may have a characteristic pattern of speciﬁ  c enzymes as described by Kuprevich and Scherbakova ([10]). The differences in the level of enzymatic activity are caused primarily by the fact that every soil type ([4]), depending on its origin  ([11])  and  developmental  conditions,  is  distinct from every other in its content of organic matter, in the composition and activity of living organisms inhabiting it, and consequently, in the intensity of biological processes. Obviously, it is probable that each type of soil has its own inherent level of enzymatic activity ([3], [12]).Large  proportions  of  the  nitrogen  in  many  soils  are organically bound and the mineralization of these portions is  of  agricultural  importance  ([16]).  Organic  nitrogen compounds in soil can constitute huge amount percent of total nitrogen and the assimilation of this nitrogen by plants and microorganisms is preceded by soil enzymes. Several enzymes are involved in the decomposition of organic nitrogen compounds ([1]). Soil scientists studied the variability of soil properties in  conventional  statistical  terms.  Classical  statistical procedures assume that variation is randomly distributed within  sampling  units.  Actually,  soil  properties  are continuous variables whose values at any location can be expected to vary according to direction and distance of separation from neighboring samples. Recently, emphasis has been placed on the fact that the variations of a soil property are not completely disordered over the ﬁ  eld and this spatial structure must be taken into account in the treatment of the data. Investigators have shown increasing interest in analyzing measured soil parameters for their interdependency over space, i.e., to study the dependency of a measured parameter on location in the ﬁ  eld. Typically semivariograms and outocorrelogram have been used to study the spatial structure of soil properties. A literature search  revealed  limited  published  studies  on  spatial behavior of enzyme activity in soils. The  objective  of  this  study  was  to  assess  the  spatial variability of soil urease activity; analysis of the spatial structure was based on the semivariogram analysis under an urban area. MATERIAL AND METHODSStudy Site and DesignThe site selected for this study is on the urban area in Gümüşhacıköy, Amasya, in the northwest Turkey (Latitude, 40053’N; longitude, 35013’W). The study area is located in an urban area. The primary grid consisted  of  39  points  spaced  4500  by  4500  m (Figure 1).The soils surface soils (0-20 cm depth) were sampled in the spring of 2001. Annual mean of precipitation is 400 mm and temperature is range from - 10 0C to 38 0C. Bulk soil samples were air dried and then crushed to pass through a 2 mm sieve.MeasurementsSelected  soil  physical  and  chemical  properties  were determined  by  means  of  appropriate  methods:  soil particle size distribution by the hydrometer method, pH in 1:2.5 (w/v) in soil: water suspension by pH -meter, soil organic matter by modiﬁ  ed Walkley-Black method, CaCO3 content by Scheibler calcimeter, cation exchange capacity (CEC) by Bower method and (0.5 M NaHCO3extractable at pH 8.5) by Olsen method ([14]). Urease  activity  (UAc)  was  measured  by  the  method Soil Properties Mean Min. Max. Sd SeSand (S), % 46.03 29.0 68.6 11.66 1.87Silt (Si), % 24.07 14.6 33.3 4.96 0.79Clay (C), % 29.91 12.8 43.2 8.27 1.32pH (1:2.5 soil: water suspension) 8.06 7.30 8.60 0.34 0.05Electrical conductivity (EC), dS m-1 0.241 0.127 1.745 0.258 0.041Lime content (LC), % 5.38 0.20 15.86 4.40 0.70Organic matter content (OMC), % 2.23 0.38 5.02 1.10 0.18Cation exchange capacity (CEC),  41.98 23.48 60.02 9.49 1.52Available P, mg kg-1 7.07 4.48 15.38 2.12 0.34Urease activity (UAc), µg N g-1 dry soil 82.99 39.36 129.64 22.06 3.53Table 1. Descriptive statistics for selected properties of soils (n=39)Sd; standard deviation, Se; standard errorTHE SPATIAL VARIABILITY OF UREASE ACTIVITY OF SURFACE AGRICULTURAL SOILS WITHIN AN URBAN AREA163 J. Cent. Eur. Agric. (2005) 6:2, 161-166Figure 1. Location of the sampling sites in Gümüşhacıköy, AmasyaDistance, m Pairs Semi variance0 - 253.55366 114 394.210329 166 445.414775 152 543.118996 122 587.023602 101 475.228076 43 601.3Table 2. Semi variance values for urease activityof Hoffmann und Teicher ([8]). A 7.5 ml citrate buffer (pH 6.7) and 10 ml of 10% urea substrate solution were added to 10 g soil, and subsequently the samples were incubated for 3 h at 37 °C. The volume was made up to 100 ml with distilled water at 37 °C. Following filtration through Whatman No. 42 ﬁ  lter papers, 1 ml of ﬁ  ltrate was diluted to 10 ml with distilled water, and 4 ml of sodium phenolate (12.5% (w/v) phenol + 5.4% (w/v) NaOH) and 3 ml of 0.9% sodium hypochloride were  added.  The  released  ammonium  was  determined spectrofotometrically at 578 nm. Three replicates of each sample were tested, and the control sample without urea was prepared. Results were expressed µ N g-1 dry soil.Statistical AnalysisAll geostatistical analyses were performed on a PC using GS+ package program ([6]). Descriptive statistics were determined by SPSS package program ([17]).RESULTS AND DISCUSSIONSoil PropertiesSome  descriptive  statistical  results  for  selected  soil physical and chemical properties are given in Table 1. The results can be summarized as; soil samples have mostly moderate coarse in texture, alkaline in pH, moderate in organic matter (average of 2.23 %), low in lime content (average of 2.35 %), and free alkaline problem (ESP<15 %) ([15]) (Table 1).Spatial Variability of Urease ActivityDistance  on  urease  activity,  pairs  and  semi  variance values were presented in Table 2.The  spherical  isotropic  model  was  selected,  had  the smallest RSS value and the biggest r2 value (Table 3), for spatial variability of the urease activity in the study area by GS+ package program ([6]).164 Journal of Central European Agriculture Vol 6 (2005) No 2Tayfun AŞKIN, Rıdvan KIZILKAYANuggetCo oSillCo o+CA0 or 3A0mC/Co+C%Co/ Co+C%r2 ModelUAc 235.5 554.8 19350 68.7 31.3 0.69 Spherical SphericalTable 3. Parameters of spherical isotropic model ﬁ  tted to semi variance of UAcTable 4. Descriptive statistics on measured and kriged of UAc valuesDescriptive statistics MeasuredPredicted by Kriging Number of samples (n) 39 1008Minimum 39.36 36.59Maximum 129.64 112.18Mean 82.99 84.34Standard deviation 22.06 8.45The  spatial  distribution  and  model  parameters  of  soil urease  activity  in  the  study  area  are  schematically illustrated in Figure 2.The  zone  of  inﬂ  uence  for  urease  activity  was approximately 19.3 km (Table 3). The urease activity was point-kriged, based on spherical isotropic model, on a 1x1 km grid (1008 locations) by using  the  ten  nearest  neighboring  points.  Descriptive statistics  were  presented  in  Table  4  on  observed  and point-kriged UAc values.As shown in Table 4, not only the range of point-kriged urease phosphatase activity values was 36.59 to 112.18 µg N g-1 dry soil but also mean values was 84.34 µg N g-1dry soil, somewhat narrower than the range and mean of the measured UAc values (39.36-129.64 µg N g-1 dry soil and 82.99 µg N g-1 dry soil). Also why standard deviation on  kriged  UAc  values  was  lower  than  the  measured selected model was true ([18], [13]). A point-kriged map of UAc was illustrated using the same 1008 points that was used to krige UAc in Figure 3.CONCLUSIONKnowledge of the spatial variability of soil biological properties is one of the most important keys in further development of precision quality of agricultural areas. Reliable information on the range of spatial relationships enables deﬁ  ning the sampling strategy needed to carry out  soil  biological  properties  maps  accurately.  In  this study, a spherical isotropic model was the best ﬁ  t semi variogram model for urease activity. Also the range of model was 19.3 km. The nugget effect, representing the undetectable experimental error and ﬁ  eld variation within the minimum sampling space, was quite large compared to the sill, which represents total spatial variation. The ratio of nugget variance to sill expressed in percentages can  be  regarded  as  a  criterion  to  classify  the  spatial dependence of soil properties. If this ratio is less than 25%, 2003004005006007000 5000 10000 15000 20000 25000 30000Lag, mSemivariance�(h)=554.8� 1.5�19350h� - 0.5 (19350h)3 �     h � 19350 m Figure 2. The estimated semi-variogram values for UAc.THE SPATIAL VARIABILITY OF UREASE ACTIVITY OF SURFACE AGRICULTURAL SOILS WITHIN AN URBAN AREA165 J. Cent. Eur. Agric. (2005) 6:2, 161-166Figure 3. Kriged map of UActhe variable has strong spatial dependence; if the ratio is between 25 and 75%, the variable has moderate spatial dependence;  otherwise,  the  variable  has  weak  spatial dependence ([5]). The ratio of nugget to total variation of UAc was 31.3 % indicating that the spatial correlation of UAc at the large scale was moderate dependence. The information of obtained from geostatistical techniques should be used to gain a better knowledge on spatial distribution of soil biological properties in an urban area. Also, this knowledge should be used as a literature for identifying the sampling strategies in large scale.   REFERENCES[1.] Alexander, M., Introduction to soil microbiology. Second ed., John Wiley & Sons. New York, USA. 1977.[2.] Aon, M.A., Colaneri, A.C., Temporal and spatial evolution of enzymatic activities and physico-chemical properties in an agricultural soil, Applied Soil Ecology (2001) 18:255-270. [3.] Burns, R.G., Enzymes in soils: Some theoretical and practical considerations, in: Burns, R.G. (Ed.). Soil enzymes, Academic Press, London, UK. 1978, pp. 295 – 339.[4.] Chhonkar, P.K., Tarafdar, J.C., Accumulation of phosphatase in soils. Journal of the Indian Society of Soil Science (1984), 32: 266 – 272. [5.] Chien, Y.J., Lee, D.Y., Guo, H.Y., Houng, K.H., Geostatistical  analysis  of  soil  properties  of  Mid-west Taiwan soils, Soil Science (1997) 162: 291-298.[6.] GS+, Geostatistics for the environmental sciences, Gamma  Design  Software,  Plainwell,  Michigan,  USA, 1998.[7.]  Haas,  H.,  Redl,  B.,  Friedlin,  E.,  Stöfﬂ  er,  G., Isolation and analysis of the Penicillium chrysogenum phoA  gene  encoding  a  secreted  phosphate-repressible acid phosphatase, Gene (1992) 113: 129 – 133. [8.] Hoffmann, G. G., Teicher, K., Ein kolorimetrisches Verfahren zur Bestimmung der Urease Aktivitat in Boden, Z. Pﬂ  anzenernahr. Dung. Bodenk., (1961), 91: 55 - 63.[9.]  Hofmann,  E.,  The  analyses  of  enzymes  in soils, in: Linskens, H.F., Tracey, M.V. (Eds.), Moderne Methoden der Pﬂ  anzenanalyse. Vol.VI. Springer Verlag, Berlin 1963, pp. 416 – 423.[10.]  Kuprevich,  V.F.,Shcherbakova,  T.A., Comparative enzymatic activity in diverse types of soil, in: McLaren, A.D., Skujins, J. (Eds.),  Soil Biochemistry, Vol. 2, Marcel Dekker, New York, USA, 1971, pp. 167-201.[11.]  Ladd,  J.N.,  Soil  enzymes,  in:  Vaughan,  D., Malcom, R.E. (Eds.). Soil organic matter and biological activity,  Martinus  Nijhoff  Dr.  W.  Junk  Publishers, Dordrecht, Netherlands, 1985, pp. 175 – 221.[12.]  Marinari,  S.,  Masciandaro,  G.,  Ceccanti,  B., Grego, S., Inﬂ  uence of organic and mineral fertilizers on soil biological and physical properties, Bioresource Technology (2000) 72: 9-17. [13.] Öztaş, T., 1996. Eğimli bir arazide erozyonla kaybolan toprak derinliğindeki değişimin Kriging analizi ile  belirlenmesi.  Tarım-Çevre  İlişkileri  Sempozyumu “Doğal Kaynakların Sürdürülebilir Kullanımı”, s: 327-335, 13-15 Mayıs, Mersin.(in Turkish)[14.]  Rowell,  D.L.,  Soil  science:  Methods  and applications. Longman, UK, 1996.[15.] Soil Survey Staff, Soil Survey Manuel, USDA Handbook No:18, Washington, 1993.[16.] Speir, T.W., Ross, D.J., Soil phosphatase and sulphatase, in: Burns, R.G. (Ed.), Soil enzymes, Academic Press, London, UK, 1978, pp. 197-250.[17.] SPSS, SPSS for Windows, Release 10.0.5, SPSS Inc., USA, 1999. [18.]  Trangmar,  B.B.,  Yost,  R.S.  Uehara,  G., Application  of  geostatistics  to  spatial  studies  of  soil properties, Advances in Agronomy, Vol. 38, 1985, pp. 45-93.[19.] Voets, J.P., Dedeken, M., Observations on the microﬂ  ora and enzymes in the rhizosphere,  Annls. lnst. Pasteur, Paris Suppl. (1966), No. 3: 197-207.

THE SPATIAL VARIABILITY OF UREASE ACTIVITY OF SURFACE AGRICULTURAL SOILS WITHIN AN URBAN AREA

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