Electronic Journal of Polish Agricultural Universities (EJPAU) founded by all Polish Agriculture Universities presents original papers and review articles relevant to all aspects of agricultural sciences. It is target for persons working both in science and industry,regulatory agencies or teaching in agricultural sector. Covered by IFIS Publishing (Food Science and Technology Abstracts), ELSEVIER Science - Food Science and Technology Program, CAS USA (Chemical Abstracts), CABI Publishing UK and ALPSP (Association of Learned and Professional Society Publisher - full membership). Presented in the Master List of Thomson ISI.
2008
Volume 11
Issue 4
Topic:
Agronomy
ELECTRONIC
JOURNAL OF
POLISH
AGRICULTURAL
UNIVERSITIES
Michalska B. , Nidzgorska-Lencewicz J. 2008. VARIABILITY OF DAILY TEMPERATURE CONDITIONS IN BARE SOIL PROFILE, EJPAU 11(4), #02.
Available Online: http://www.ejpau.media.pl/volume11/issue4/art-02.html

VARIABILITY OF DAILY TEMPERATURE CONDITIONS IN BARE SOIL PROFILE

Bożena Michalska, Jadwiga Nidzgorska-Lencewicz
Department of Meteorology and Climatology, West Pomeranian University of Technology in Szczecin, Poland

 

ABSTRACT

The research covered the results of automatic measurements of bare soil temperature at four standard depths: 5, 10, 20 and 50 cm, recorded every hour (UTC). The data were reported by the weather station located at Lipki in the vicinity of Stargard Szczeciński over 2001–2005. Soil temperature at four depths was described by mean monthly, seasonal and yearly values in the hourly pattern over twenty-four hours. It was found that the highest mean monthly temperature in the bare soil layer up to 10 cm is reached in July, while at the greater depths it is reached in August. The entire bare soil profile down to 50 cm depth reached its lowest temperature in January. A spring change in the thermal stream direction took place in the last decade of March, while the autumn change was observed in the middle of September. The greatest temperature variability was recorded in the soil horizon up to 5 cm from 4:00 to 6:00 p.m. (UTC), particularly in March, while the lowest temperature variability occurred at the depth of 50 cm in August. The greatest bare soil temperature variability was observed in the afternoon in the horizon up to 20 cm, particularly in June and July.

Key words: bare soil, temperature, hourly time pattern.

INTRODUCTION

Soil temperature depends on many factors such as: thermal conduction, moisture, soil porosity, the environment and radiation balance [5,7]. In case of bare soil, the temperature is modified by plant stand and depends on the genus and development stage of the plant, particularly in time of the greatest demand for water and over intensive transpiration [1,2,10]. Many researches undertaken by climatologists and agrometeorologists concerned time pattern of soil temperature in particular months, seasons or years. However, there are few studies into the hourly pattern in soil over twenty-four hours due to the lack of such measurements at meteorological stations. So far, the attempts of evaluation of changes in soil thermal conditions in twenty-four hours are usually partial and concern short periods [3,6,10]. In Poland soil temperature measurements are carried out at Institute of Meteorology and Water Management (IMGW) stations at four depths of 5, 10, 20 and 50 cm with soil thermometer and at 100 cm depth with soil depth thermometer. The temperature reading down to 0.5 m depth is carried out at 6.00 a.m., 12.00 and 6.00 p.m. UTC. Hence, the majority of research into daily temperature variability in the soil concerned changes taking place during the day. Introduction of automatic measurements at Lipki in the vicinity of Stargard Szczeciński, facilitated temperature monitoring at the four depths at hourly intervals, which allowed for defining the monthly, seasonal and yearly soil temperature.

The aim of this research was defining in detail the daily bare soil temperature variability and its extent for the profile down to 50 cm. The results of the present research should fill in the gap in this type of soil climate studies and can be used for planning agronomic and plant protection practices.

MATERIAL AND METHODS

The present study was based on hourly (according to UTC) results of automatic measurements of bare soil temperature over 2001-2005. Thermistor sensors of ST1 type manufactured by DELTA-T, 125 x 4.8 mm in size, with the accuracy of ± 0.2°C in the temperature range from -20 to +80°C, were placed in a horizontal position in the soil at four standard depths of 5, 10, 20 and 50 cm, at the agrometeorological station located at Lipki in the vicinity of Stargard Szczeciński. The station is situated in the central part of Szczecińska Lowland (φ53°21, λ 14°58, Hs 30 m AMSL) on light, acid brown soil made of boulder sand with clay insertions at the depth of 70 cm, with no ground water ascension. Soil temperature at the four depths was described by monthly and seasonal mean values: spring (March – May), summer (June – August), autumn (September – November), winter (December – February) and yearly values in hourly daily pattern. Temperature in the soil profile down to 50 cm was plotted using mean monthly values. The variability of soil temperature at different depths was estimated by showing the standard deviation from hourly values in the successive months, seasons and throughout the year.

RESULTS AND DISCUSSION

Monthly mean values of bare soil temperature at the four depths show that over 2001-2005 in Szczecińska Lowland, the coldest month was January, with the temperature ranging from 0.7°C in the surface layer to 2.4°C in the deepest layer. The warmest month, as for the soil temperature at the depths of 5 and 10 cm, was June (20.2°C and 19.4°C, respectively), while at greater depths (20 and 50 cm), the highest temperature was observed in August – 18.5°C and 17.6°C (Table 1 and Fig. 1). Temperature at the depth of 50 cm was almost constant in the last decade of March and in mid-September. Isotherms in the soil profile observed at the end of March and in September are connected with a change in thermal stream direction, which coincides with the research in different soils and different regions of Poland, e.g. in Vistula Marshland [4], Szczecińska Lowland [9], and in Puławy [11]. Tautochrones of mean monthly soil temperature over 1961-1980, developed by Koźmiński and Michalska [8], show that at the majority of Polish stations, the temperature in March  in the soil profile down to the depth of 50 cm was the same. Similar results were reported also by Jakusik at al. [4] at Radostowo Station. At the stations in the south-west of Poland, particularly on sandy soils, the March tautochrone clearly deviated to the right, indicating higher temperature in shallower soil layers. In the north-east of Poland, at Biebrza Valley station, located on peat soil, the tautochrone deviated to the left, indicating a thermal stream direction from deeper soil layers to the surface.

Table 1. Mean (a), maximum (b), minimum (c) and standard deviation (d) of bare soil temperature (°C) at the depths of 5, 10, 20 and 50 cm for respective months (2001-2005)
 

I

II

III

IV

V

VI

VII

VIII

IX

X

XI

XII

5 cm

a

0.7

1.2

3.1

8.4

14.8

17.7

20.2

19.7

15.0

9.8

5.0

1.9

b

6.7

7.7

11.2

16.6

23.2

27.4

28.0

28.3

23.2

15.9

10.6

6.0

c

-1.8

-1.5

-1.6

1.5

8.0

9.9

13.1

13.2

6.9

2.0

1.3

-2.9

d

2.1

1.9

2.8

2.7

2.4

2.6

2.3

2.2

2.4

2.8

2.3

1.8

10 cm

a

1.0

1.7

3.2

8.1

14.2

17.0

19.4

19.3

15.1

10.2

5.6

2.5

b

6.1

7.3

9.0

13.9

21.1

22.9

24.7

24.7

21.3

14.8

10.6

6.0

c

-0.5

0.0

-0.1

2.5

8.7

11.0

14.3

14.5

8.6

3.4

2.6

-0.8

d

1.9

1.7

2.4

2.3

2.0

2.1

1.9

1.8

2.1

2.4

2.1

1.6

20 cm

a

1.3

1.8

3.2

7.8

13.3

16.0

18.3

18.5

15.0

10.4

6.0

2.8

b

5.8

6.9

7.8

12.3

18.8

21.1

22.5

22.5

20.4

13.9

10.6

5.8

c

-0.1

0.0

0.0

2.6

8.5

11.3

14.1

14.8

9.9

4.3

3.0

0.1

d

1.8

1.6

2.1

2.1

1.9

1.8

1.7

1.5

1.9

2.2

2.0

1.5

50 cm

a

2.4

2.8

3.5

7.3

11.9

14.6

16.8

17.6

15.2

11.5

7.5

4.4

b

6.0

6.3

6.5

9.9

15.5

17.5

18.8

19.4

18.6

13.9

11.4

7.0

c

1.4

1.3

1.2

3.8

8.7

12.1

13.9

15.2

12.5

7.0

5.2

1.9

d

1.3

1.3

1.5

1.5

1.4

1.3

1.2

0.9

1.4

1.7

1.6

1.2

* mean monthly soil temperature calculated from hourly values

 

March
– May

June
– August

September
– November

December
– February

January
– December

5 cm

a

8.7

19.2

9.9

1.3

9.8

b

23.2

28.3

23.2

7.7

28.3

c

-1.6

9.9

1.3

-2.9

-2.9

d

5.6

3.1

4.7

1.9

7.4

10 cm

a

8.5

18.6

10.3

1.7

9.8

b

21.1

24.7

21.3

7.3

24.7

c

-0.1

11.0

2.6

-0.8

-0.8

d

5.0

2.4

4.4

1.7

6.8

20 cm

a

8.1

17.6

10.5

2.0

9.5

b

18.8

22.5

20.4

6.9

22.5

c

0.0

11.3

3.0

-0.1

-0.1

d

4.6

2.1

4.1

1.6

6.3

50 cm

a

7.6

16.3

11.4

3.2

9.6

b

15.5

19.4

18.6

7.0

19.4

c

1.2

12.1

5.2

1.2

1.2

d

3.7

1.6

3.4

1.4

5.4

Fig. 1. Mean monthly temperature of bare soil at the depths of 5, 10, 20 and 50 cm (2001-2005)

In the warm half of the year (April – September), the smallest soil temperature fluctuations at the Lipki station occurred at the depths of 5 to 10 cm and reached on average 0.5°C, while in the cold half of the year (October – March) – at the depths of 10 to 20 cm where the mean temperature fluctuation was only 0.2°C. Thermal stratification of the soil in this season indicates loss of heat in shallower layers for the benefit of the air and heat supply from deeper layers. The mean fluctuation between the outermost soil layers (5-50 cm) in the cold season was 1.7°C, while in the warm one – 2.1°C. The annual bare soil mean temperature at the depth of 5 and 10 cm was the same (9.8°C) and at the depths of 20 and 50 cm it was smaller, 9.5°C and 9.6°C, respectively. Annual amplitude of soil temperature decreased with depth from 19.5°C at 5 cm to 15.1°C at 50 cm. The absolute highest temperature in the whole profile, fluctuating between 28.3°C at 5 cm to 19.4°C at 50 cm, was recorded on August 1 2002. In case of the absolute lowest soil temperature  there were recorded different dates of its occurrence in the upper and lower layers of the profile. In the subsurface layer, the lowest recorded soil temperature was on 13th December 2002 with the value -2.9°C at the depth of 5 cm and -0.8°C at 10 cm. At greater depths absolute daily minimum temperature was recorded several times, at 20 cm in January, at 50 cm in March with the respective values of -0.1°C and 1.2°C. Over the five years of research, the deepest soil layer was not frozen at all but according to the study of Koźmiński and Michalska [9] there were also years, for example 1963, when the daily absolute minimum soil temperature at the Lipki station at 50 cm was -5.0°C on January 11, and minus temperature at this depth was recorded also in March and in April. The results obtained from twenty-four hour measurements at the automatic station are comparable to standard measurements (three times a day) because the fluctuations (mean values  over 2001–2005) at 10 and 20 cm did not exceed  0.2°C from April to September, and at 5 cm depth – 0.1°C. At the deepest level of 50 cm the fluctuations in measurement results were 0°C in all the months of the year the same fluctuation was observed at all remaining depths in cold season of the year.

The analysis of the standard deviation shows that soil temperature variability decreased with depth. The greatest standard deviation over the year, monthly mean deviation calculated from hourly values, occurred in October and March and it ranged from 2.8 at the depth of 5 cm to 1.7 at 50 cm. The lowest temperature variability in topsoil was observed in December and 50 cm deep in August (Table 1).

In the annual mean temperature of bare soil, the highest values (11.3°C) were recorded at the depth of 5 cm at 5.00 p.m. (UTC) and the lowest between 7.00 and 8.00 a.m. (Fig. 2). The greater the depth the lower the differences between extreme temperature values and simultaneously there was a  time shift of temperature extremes. At the depth of 50 cm, the daily changes of the mean annual temperature were inconsiderable; the amplitude was only 0.2°C. The highest temperature (9.8°C) was noted from 1.00 to 9.00 a.m., while the lowest (9.6°C) from 2.00 to 8.00 p.m. The standard deviation of temperature throughout the 24 hours at this depth was 1.3, while its greatest value was noted in the subsurface layer (5 cm) – ranging from 2.1 between 5.00 and 10.00 a.m. to 2.6 between 3.00 and 7.00 p.m. (Fig. 3).

Fig. 2. Mean annual temperature of bare soil at the depths of 5, 10, 20 and 50 cm according to hours (2001-2005)

Fig. 3. Standard deviation of mean hourly temperature of bare soil at the depths of 5, 10, 20 and 50 cm (2001-2005)

Thermal isopleths of the daily soil temperature distribution in particular months show a gradual increase in temperature variability from January to July, and then its decrease from August to December (Fig. 4). Absolutely no daily temperature variability was recorded at the depth of 50 cm in January. In the soil layer of lower depth (10 and 20 cm), the differences in this month reached 0.1°C while at 5 cm – 0.3°C. The lowest (0.5°C) temperature at these depths was recorded between 9.00 and 11.00 a.m. and the highest (0.8°C) between 4.00 and 6.00 p.m., which taking into account difference between UT and CET, extreme temperatures in January and in the remaining months of the cold season occur an hour earlier. The greatest daily temperature fluctuations took place at the depth of 5 cm in June and July. Mean amplitude in the two month was 5.1°C but in June the temperature was on the average 2°C lower than in July. In the twenty-four hour temperature variability in bare soil profile down to the 50 cm deep, the greatest fluctuations were noted between 4.00 and 7.00 p.m. and concerned summer months. The smallest variability, indicating almost complete isothermy, occurred in March between 8.00 and 10.00 p.m. and in April between 9.00 and 10.00 a.m. Thermal isopleths of monthly mean soil temperature depict a thermal stream direction at different times throughout 24 hours (Fig.4). In March the change of thermal stream direction can be observed during twenty-four hours from the winter direction, from deeper layers to the surface of the soil, into summer direction, from the surface deep into soil. Whereas from October to February mean monthly soil temperature values indicate that throughout 24 hours the thermal stream is directed from deeper layers towards the surface of the soil.

Fig. 4. Mean monthly temperature of bare soil at the depths of 5, 10, 20 and 50 cm according to hours (2001-2005)

Temperature variability expressed by the standard deviation demonstrates different daily patterns; it is the greatest at the depth of 5 cm and regardless of the month, the highest deviation values were noted between 4.00 and 6.00 p.m., and the lowest ones between 9.00 and 10.00 a.m. (Fig. 5). At the depth of 10 cm, two-hour shift was observed in the highest and the lowest deviation values, accompanied by a simultaneous decrease in their amplitude, and at 20 cm there was noted a six-hour shift as compared with the topsoil. At the depth of 50 cm the lines depicting daily standard deviation values for all the months are parallel to one another, which indicates that there is no temperature variability at this depth.

Fig. 5. Standard deviation of mean hourly temperature of bare soil at the depths of 5, 10, 20 and 50 cm (2001-2005)

Fig. 6. Mean seasonal temperature of bare soil at the depths of 5, 10, 20 and 50 cm according to hours (2001-2005)

The bare soil mean daily temperature pattern in the four seasons shows that at the depth of 5 and 10 cm the most similar temperature values were recorded in spring and autumn, particularly in the afternoon and early evening, while the greatest differences were observed in the morning (Fig. 6). Throughout the 24 hours soil in autumn was warmer than in spring; the greater the depth the greater the differences (1.2°C at the depth of 5 cm to 2.5°C at the depth of 20 cm). At the depth of 50 cm temperature in autumn was higher than in spring by 4.0°C. The daily mean seasonal temperature pattern for the soil at this depth does not show any significant differences. The lines demonstrating the daily soil temperature pattern at the depth of 50 cm in four seasons were parallel.

CONCLUSIONS

  1. Over 2001-2005, in climatic conditions of agrometeorological station at Lipki, located on light, acid brown soil, the change in the thermal stream direction in bare soil, from the winter to the summer direction was observed in the last decade of March, while the change from the summer direction to the winter one – in mid-September.

  2. The annual daily mean temperature of bare soil showed the highest values at the depth of 5 cm at 5.00 p.m. UTC, and the lowest at 7.00 to 8.00 a.m. at the same depth. The greater the depth, the lower daily amplitude; reaching the value of almost 0 at the depth of 50 cm.

  3. The greatest soil temperature variability was recorded at the depth of 5 cm between 4.00 and 6.00 p.m., particularly in March and October, while the lowest variability – 50 cm deep in August.

  4. The greatest temperature variability in the layer of the depth up to 20 cm was noted in June and July in the afternoon and the lowest, indicating entire isothermy, in the evening in March, and in the morning in April.

  5. The most similar daily soil temperature values were observed in spring and autumn at the depth of 5 and 10 cm, particularly in the afternoon and early evening. In autumn soil was warmer than in spring at any time of day and night and the differences increased with depth.


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Accepted for print: 29.09.2008


Bożena Michalska
Department of Meteorology and Climatology,
West Pomeranian University of Technology in Szczecin, Poland
Kazimierza Królewicza 4, 71-550 Szczecin, Poland
email: bozena.michalska@zut.edu.pl

Jadwiga Nidzgorska-Lencewicz
Department of Meteorology and Climatology,
West Pomeranian University of Technology in Szczecin, Poland
Kazimierza Królewicza 4, 71-550 Szczecin
email: jlencewicz@agro.ar.szczecin.pl

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