Thermal characterization of a tropical rice soil in relation to puddling, flood-water depth and percolation rate

SOIL T E C H N O L O G Y

vol. 4, p. 167-175

Cremlingen 1991 I

THERMAL CHARACTERIZATION O F A T R O P I C A L RICE SOIL IN R E L A T I O N TO PUDDLING, FLOOD-WATER DEPTH AND P E R C O L A T I O N RATE RK. Sharma, Palampur S.K. De Datta, Los Bafios Summary Effects of puddling, flood-water depth and percolation rate on the thermal properties of a tropical rice soil were studied under field and glass-house conditions. Puddling increased volumetric heat capacity (Cv), but decreased thermal conductivity (Kt), thermal diffusivity (Dt) and damping depth (D) compared to a nonpuddled soil. A percolation rate of 40 m m d -1 showed higher Kt, Dt and D than zero percolation. The values of Kt, Dt and D were highest with 50 mm and lowest with 10 mm floodwater depth. The Cv did not change with different flood-water depths or percolation rates. Consequently, puddling, 40 m m d -1 percolation and 50-100 mm submergence kept the maximum temperature of surface 100-150 mm soil at relatively low level under tropical conditions. These treatments also buffered soil against extreme diurnal temperature fluctuations. The time lag between maximum solar radiation and maximum temperature of submerged soil varied, on an average, between 1.2 hours at soil surface ISSN 0933-3630 (~)1991 by CATENA VERLAG, W-3302 Cremlingen-Destedt,Germany 0933-3630/91/5011851/US$ 2.00 + 0.25 SOIL T E C H N O L O G Y ~ cooperating Journal of C A T E N A

and 11.6 hours at 300 mm soil depth; which is more than that in an upland soil.

1

Introduction

Soil thermal regime is determined by the thermal properties of soil, which in turn affect the magnitude of heat flux into the soil profile. Thermal properties of soil, such as volumetric heat capacity, thermal conductivity, thermal diffusivity and damping depth, are greatly influenced by the porosity and moisture content of soil ( G H I L D Y A L & T R I P A T H I 1971, YADAV & SAXENA 1973, ACHARYA & G U P T A 1975). While such studies have been conducted in detail in upland soils ( C H A U D H A R Y & S A N D H U 1982), information with respect to submerged rice soils are negligible ( S H A R M A & DE DATTA 1985, S H A R M A et al. 1988). Because of completely different hydro-physical conditions, rice soils must have thermal properties different from upland soils. Rice is an important crop of tropical areas where soil temperature may exceed the critical limits for rice. According to YOSHIDA (1981), optimum temperature range for the emergence, tillering,

168

Sharma de De Datta

anthesis and ripening of rice is 25--30~'C, 25 31°C, 30 33°C and 2('~25°C, respectively. Even a small variation in soil temperature can cause a significant effect on rice growth and yield (VAMADEVAN 1971). A knowledge of the effects of the various cultural practices and soil factors on thermal properties of rice soil will be helpful in alleviating the ill effects of supra-optimal soil temperatures on rice, if any. With this objective a study was conducted to investigate the effects of puddling, flood-water depth and percolation rate on diurnal temperature fluctuations and associated thermal properties in a tropical rice soil.

2

Materials and methods

The study was conducted during the 1984 dry season at the International Rice Research Institute, Manila, Philippines. Diurnal temperature fluctuations in flood-water (water impounded in the rice field), and soil upto 300 m m in depth at 50 m m depth-intervals were monitored in three trials, in relation to puddling, flood-water depth and percolation rate. The temperature was recorded at hourly interval for 24 hours, starting at 0600 hours, using copper (+) and constantan (-) thermocouples and an Omega digital thermometer (Model 2175 A). Such observations were made on three different dates. The trend in temperature data being the same for three dates, data for one of the dates were used in this paper. Puddling of soil (clay loam) was done with an animal-drawn mouldboard plough followed by repeated harrowings. In nonpuddled plots, soil was submerged with water, and rice seedlings were transplanted using wooden pegs. The temperature measurements were made at the flowering stage of rice.

Three flood-water depths (10, 50, 100 mm) were maintained in the rice plot (clay loam) by using 2 rex2 m metal sheets, placed 100 mm deep in soil and protruding 10, 50 and 100 mm above the ground surface. Flood-water temperature was recorded at 5, 25 and 50 mm below the water surface for 10, 50 and 100 mm deep flood-water, respectively. The temperature measurements were made at the active tillering stage. The effect of percolation rates (0 and 40 mm d 1) on soil temperature of a silty clay soil was studied in a glass-house experiment. Rice was grown in 570 mm diameter and 420 m deep metal drums, under 30 m m constant water head, maintained by using a Mariotte siphon system. Different percolation rates were regulated by means of hypodermic needles (26 gauge) fixed in the drainage tubes provided at the bottom of each drum. The experimental details are given elsewhere ( S H A R M A et al. 1989). The temperature measurements were made in the centre of the drum at the active tillering stage of crop. The temperature data so collected were fitted to the following equation ( H I L L E L 1980): T ( Z , t ) = T + A z s i n { w t + W(z) + W0}(1)

where T ( Z , t ) is the temperature (°C) at depth Z (cm) and time t (hours), w the radial frequency (2 rr/24), t the absolute unit of time (hours), 7" the average soil temperature (°C), Az the temperature amplitude at depth Z (°C), W(z) the phase lag (radians). W0 is an arbitrary chosen phase constant such that the phase lag W(z) at the soil surface is equal to zero when the time is 6 AM. Hence, t = 6 hours at 6 AM, 13 hours at 1 PM, 23 hours at 11 PM, and so on. The temperature data computed from eq (1) were SOl[. I E{'HNOLO(}Y

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169

Thermal Properties o f a Rice Soil

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Time (hr) Fig. 1 : Effect o f flood-water depth on the diurnal temperature fluctuations in a wetland rice soil. used to determine the time at which the maximum temperature peak occurred at a given depth, damping depth, volumetric heat capacity, thermal conductivity and thermal diffusivity. Damping depth (D) is a characteristic soil depth at which the temperature amplitude decreases to a fraction 1/e of the amplitude at soil surface (Ao). A power regression equation was developed between soil depth (Z) and temperature amplitude (Az) to determine the damping depth (Ao/e i.e. Ao/2.718). SOIL TECHNOLOGY

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Volumetric heat capacity (Cv, j m - 3 K -1) was determined from eq (3) which is a simplified version of DE VRIES (1975) quoted by H I L L E L (1980): Cv = fsCs + fwCw + faC,~

(2)

where f and C denote the volume fraction and heat capacities of solid (s), water (w) and air (a) phase of soil, respectively. In a puddled and submerged soil, air phase is absent and the volume of water phase is practically equal to the total porosity of soil. Considering specific heat

170

Sharma & D e Datta

capacities of soil solids and water equal to 0.2 and 1.0 Cal g-i °C, the equation (2) may be simplified as: Cv = (0.2Db + O) x 4.19

x 10 6

(3)

where Db is the bulk density of soil (g cm -3) and ® the volumetric moisture content at saturation (cm3cm-3). The factor 4.19x106 is used to convert Cal cm -3 into J m 3. For computing thermal conductivity (Kt, J m -~ sec 1 K - l ) the following relationship was used ( H I L L E L 1980):

D

=

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-

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(2Kt/Cvw)l/2or D2Cvw 2

(4)

where D is the damping depth, Cv the volumetric heat capacity of soil and w the radial frequency per second (2 ~/86400). Thermal diffusivity (Dt, m 2 sec -1) was calculated as the ratio of thermal conductivity (Kt) and volumetric heat capacity (Cv). The computations of these thermal properties were made for the top 100 m m soil.

3 3.1 3.1.1

temperature variation than deep water, as was also reported by V A M A D E V A N (1971). The situation, however, was reversed within the soil profile. Higher maximum temperature peaks were maintained under deep submergence, and the peak-temperature differences increased progressively with soil depth. The 10 and 50 mm flood-water depths yielded the same temperature profiles, especially between 200 and 300 mm soil depth. Average soil temperatures at all depths were higher under deeper flood-water by 1.0 1.4°C.

Results and discussion Diurnal temperature fluctuations Flood-water depth:

Maximum temperature of flood-water was relatively higher with 10 mm submergence, and decreased with increasing flood-water depth (fig. 1). Diurnal temperature amplitudes in the top 50 m m soil were also higher under shallower submergence (tab. 1). It revealed that shallow water was more susceptible to

Percolation rate:

A percolation rate of 40 mm d I kept the maximum temperature of the top 50 m m soil lower than zero percolation (fig. 2). Below 50 mm, however, maximum temperatures were either the same (between 100 and 150 m m depth) or higher in percolated soil; the reason being the different modes of heat transport in the two cases. In nonpercolated soil heat was transported to deeper layers only through conduction, whereas in percolated soil, in addition to conduction, percolation water also transported some heat to lower soil layers. Like maximum temperature, average temperature and diurnal temperature amplitudes also were lower in percolated soil within 0~ 50 mm depth (tab. 1). The trend was reversed below this soil depth.

3.1.3

Effect of puddling:

Puddled soil had a maximum temperature of flood-water and of soil upto 150 m m depth that was lower than nonpuddled soil by 0.6 to 1.0°C (fig. 3). On the basis of average temperature, the top 150 m m of puddled soil was SOIL IECHNOLOGY

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Thermal Properties o f a Rice Soil

Treatment Tillage: Puddling

171

Parameter

Soil depth (mm) 0

50

100

150

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Y (oc) Az (°C) h (hrs)

29.5 3.87 14.9

29.7 1.57 18.8

29.8 1.24 20.4

29.9 0.81 22.0

30.1 0.65 23.8

30.1 0.48 24.2

30.2 0.35 24.6

Az h

30.0 4.37 14.3

30.1 2.20 18.0

30.0 1.57 19.2

30.1 1.16 22.1

30.0 0.78 00.2

30.2 0.48 00.6

30.2 0.40 01.7

30.1 6.37 13.6

29.9 2.98 16.6

29.8 1.63 18.8

29.6 1.25 21.2

29.5 0.93 23.1

29.4 0.68 00.2

29.4 0.65 00.9

30.4 5.94 14.4

30.6 2.97 18.1

30.2 2.00 19.6

29.9 1.38 21.5

29.7 1.00 23.8

29.6 0.66 00.9

29.6 0.44 00.9

31.2 5.10 15.0

31.0 2.25 18.5

30.9 1.82 20.0

30.7 1.31 22.7

30.8 0.96 23.5

30.8 0.71 00.9

30.8 0.48 01.7

Az h

28.8 3.72 13.4

29.4 1.85 15.9

29.5 0.94 18.2

29.5 0.61 20.5

29.4 0.62 22.8

29.3 0.65 23.2

28.8 0.58 22.9

T Az h

28.4 3.32 ,13.6

29.0 1.64 17.2

29.3 1.07 19.7

29.5 0.89 21.8

29.7 0.79 23.6

29.7 0.68 23.8

29.7 0.70 23.4

Non-puddling

Flood-water depth (mm):

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T Az h

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Tab. 1" Effect o f tillage, floodwater depth and percolation rate on average soil temperature T, diurnal temperature amplitude (Az) and time of occurrence of maximum temperature peak (h). cooler by 0.2q3.5°C than nonpuddled soil; the differences decreased with depth (tab. 1). Similarly temperature amplitudes were also lower in this zone of puddled soil. Thermal regimes between 200 and 300 mm depth were the same in puddled and nonpuddled soil. Puddling affects soil temperature by lowering the bulk density and percolation rates of soil. Low bulk density causes lower thermal conductivity and higher volumetric heat capacity due to reason discussed in the next section. A decrease in the thermal conductivity reduces net heat flux into

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the soil, but increases the temperature amplitudes at the soil surface. A reduction in percolation rate should also increase the temperature of the surface soil layer, as discussed above (fig. 2). But contrary to this, fig. 3 showed a relatively low maximum temperature and temperature amplitude in the surface layer of puddled soil. This variation was attributed to the better canopy cover in puddled plots. The temperature of the irrigation water was about 34°C. Longer stagnation under relatively thick foliage in puddled plots lowered the maximum tem-

Sharma & De Datta

172

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Effect of percolation on the diurnal temperature fluctuations in a wetland rice

soil.

Treatment

Volumetric heat capacity ( × 1 0 6 J m 3 k l)

Thermal conductivity (J m 1 s e c t K 1)

Thermal diffusivity (× 10 -6 m 2 sec I)

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0.17 0.25

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Effect of tillage, flood-water depth and percolation rate on thermal properties of soil (0-100 mm depth). Tab. 2:

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A co.peratmg hmrnal ol ('A'IPNA

173

Thermal Properties o f a Rice Soil

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Fig. 3: Effect o f puddling on the diurnal temperature fluctuations in a wetland rice soil. perature of irrigation water, thereby narrowing the temperature amplitude. These data indicate that, depending on the crop growth stage, canopy cover is as important a factor as soil physical properties in affecting soil thermal regimes. The time of occurrence of temperature peaks varied substantially with different treatments (tab. 2). The time was delayed by puddling, increasing percolation rate, and flood-water depth. On average, maximum temperature peaks at 0, 50, 100, 150, 200, 250 and 300 mm depths occurred at 14.2, 17.6, 19.4, 21.7, 23.5, 00.2 and 00.6 hours, respectively. The maximum solar radiation was received at 13.00 hours. Thus, the time lag between

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maximum solar radiation and maximum soil temperature at 0, 50, 100, 150, 200, 250 and 300 mm depth was 1.2, 4.6, 6.4, 8.7, 10.5, 11.2 and 11.6 hours, respectively. Time lag in a bare upland sandy loam soil has been reported to be 2.0, 2.5, 3.0 and 6.0 hours at 50, 100, 150 and 300 mm depth, respectively (CHAUDH A R Y & S A N D H U 1982). Thus, irrespective of soil depth, the time lag is greater in a submerged than in an upland soil. This is attributed to the higher volumetric heat capacity of a submerged than of an upland soil.

174

3.2

Sharma & De Datta

Thermal properties

Important thermal properties of soil as affected by different treatments are shown in tab. 2. Volumetric heat capacity (Cv) of an upland soil increases with bulk density because the specific heat of the soil remains the same, Cv becomes a function of bulk density. At the same bulk density, Cv increases with moisture content because the specific heat of water is about 5 times higher than soil solids. Under submerged conditions, on the other hand, a decrease in bulk density would increase the volumetric moisture content of soil by increasing its total porosity. This would increase Cv of soil. That is why Cv of the puddled soil layer, having 0.90 Mg m 3 bulk density, was higher than that of nonpuddled soil having 1.17 Mg m 3 bulk density. Thermal conductivity (Kt) of puddled soil was also relatively low. This was attributed to the higher moisture content of the puddled layer, because Kt of water is about one fifth that of soil solids. Higher bulk density (and thus lower saturation water content) of nonpuddled soil provided better thermal contact between soil particles to increase Kt. Thermal diffusivity (Dt), which is a ratio of Kt to Cv, was low in puddled soil. Low Dt would cause intensive warming up of surface layer of puddled soil. A C H A R Y A & G U P T A (1975) showed that the coefficient of thermal diffusivity is highest at around 0.2 0.3 bar suction. Damping depth (D) is related to Kt and Dt. D increases with an increase in these parameters. Hence, puddled soil showed lower D than nonpuddled soil, because of its relatively low Kt and Dt values. A percolation rate of 40 mm d i did not affect Cv but increased Kt. The Cv remained unaffected because percolation

does not change soil porosity. Because of an increase in Kt, Cv remaining the same, Dt also increased with percolation. Increase in Dt was attributed to the additional downward heat flux along with percolation water. In nonpercolated soil heat was transported only through conduction. Increase in Dt resulted in higher D. Like percolation, flood-water depth did no affect Cv. The Kt, and, thus, Dt and D were highest under 50 mm and lowest under l0 mm flood-water depth. This may possibly be attributed to the better insulation provided by the deeper flood-water which may decrease loss of heat from the soil profile.

4

Conclusions

Soil thermal properties were markedly affected by puddling, flood-water depth and percolation rates. Volumetric heat capacity of soil increased with puddling. Thermal conductivity, thermal diffusivity and damping depth were high in nonpuddled soil, with 40 mm d i percolation and 50 m m flood-water depth. Puddling, deeper submergence (50100 ram) and 40 mm d -1 percolation lowered the maximum temperature of the top 5(~150 mm soil layer and buffered the soil against extreme temperature fluctuations. Moderation of thermal regime even in the top few millimeters of soil affects the rice yield significantly (VAMADEVAN 1971) because about 75% of rice roots are concentrated in the top 100 m m soil ( S H A R M A et al. 1987). Thus, proper tillage and water management in rice fields are crucial for regulating proper soil thermal regimes and improving rice production. SOIL FE(HNOIOGY

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Thermal Properties o f a Rice Soil

References ACHARYA, C.L. & GUPTA, R.P. (1975): Thermal diffusivity values based upon time dependent soil temperature distribution. J. Indian Soc. Soil Sci. 23, 1 7. CHAUDHARY, T.N. & SANDHU, B.S. (1972): Soil temperature and plant growth. In: Review of soil research in India, Part I. 12th Intern. Congr. Soil Sci., New Delhi, India, 48-59. GHILDYAL, B.P. & TRIPATHI, R.P. (1971): Effect of varying bulk densities on the thermal characteristics of lateritic sandy clay loam soil. J. Indian Soc. Soil Sci. 19, 5-10. HILLEL, D. (1980): Fundamentals of Soil Physics. Academic Press, New York. SHARMA, P.K. & DE DATTA, S.K. (1985): Puddling influence on soil, rice development and yield. Soil Sci. Soc. Am. J. 49, 1451-1457. SHARMA, P.K., DE DATTA, S.K. & REDULLA, C.A. (1987): Root growth and yield response of rainfed lowland rice to planting method. Expl. Agri. 23, 305-313. SHARMA, P.K., DE DATTA, S.K. & REDULLA, C.A. (1988): Tillage effects on soil physical properties and wetland rice yield. Agron. J. 80, 34-39. SHARMA, P.K., DE DATTA, S.K. & REDULLA, C.A. (1989): Effect of percolation rate on nutrient kinetics and rice yield in tropical rice soils: I. Role of soil organic matter. Plant and Soil 119, 111-119. VAMADEVAN, V.K. (1971): Temperature regimes under different water depths and their effects on the growth and yield of rice. I1 Riso 20, 21-29. YADAV, M.R. & SAXENA, G.S. (1973): Effect of compaction and moisture content on specific heat and thermal capacity of soils. J. Indian Soc. Soil Sci. 21, 129-132. YOSHIDA, S. (1981): Fundamentals of Rice Crop Science. Intern. Rice Res. Inst., Los Bafios, Laguna, Philippines. p. 269. Addresses of authors: Pradeep K. Sharma Associate Professor (Soils) Department of Soil Science H.P.K.V., Palampur - - 176 062 (H.P.) India S.K. De Datta Principal Scientist & Program Leader Rainfed Lowland Rice Ecosystem IRRI, P.O. Box 933 Manila, Philippines

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