Tillage Effects on Soil Thermal Properties in a Semiarid Cold RegionM. A. Arshad* and R. H. Azooz

ABSTRACTTillage and residue management may sufficiently alter soil thermal

properties in cold, semiarid regions, causing significant changes incrop growth. Soil thermal diffusivity (Dh) and heat flux density C/s) weremeasured in conventional tillage (CT), no-tillage (NT), and modifiedno-tillage where surface residue was pushed away from a 7.5-cmzone above the planting row (MNT) on a Donnelly silt loam (TypicCryoboralf) in northern British Columbia during barley (Hordeumvulgare L.) growing seasons of 1992 and 1993. The Dh for 0- to 30-cmdepth ranged from 0.00126 to 0.00194 m2 h'1 in NT, 0.00129 to0.00196 m2 h"1 in MNT, and 0.00133 to 0.00199 m2 h'1 in CT duringthe two growing seasons. Differences in Dh were highly related to soilwater content, where soil water in NT a MNT > CT during most ofthe growing season. Mean diurnal temperature at 5-cm depth duringthe first 3 wk after planting in 1992 was 12.4°C in MNT, 11.2°C inNT, and 13.3 °C in CT. Mean of maximum soil heat flux at 5-cmdepth was lower by 10.0 W m-2 in MNT and by 20.7 W m"2 in NTthan in CT in 1992 and it was lower by 23.7 W m~2 in MNT and by34.7 W m-2 in NT than in CT in 1993. Seed-row residue removal inMNT increased soil temperature, maintained soil water similar to NT,and led to increased seed-zone heat flux density.

RESIDUE-COVERED SURFACE, coupled with other mi-croclimate factors, affects heat exchange at the soil

surface (Azooz, 1991; Payne and Gregory, 1988; Wier-enga et al., 1982). Crop residue, among other factors(soil type, water, and crop canopy), has a major impacton soil thermal conductivity and heat capacity (Steiner,1994), solar reflectivity (Von Hoyningen-Huene, 1971;Brutsaert, 1982), and net heat exchange (Hanks et al.,1961). The quantity and orientation of the crop residue

Northern Agriculture Research Centre, Agriculture and Agri-Food Can-ada, Box 29, Beaverlodge, AB, Canada TOH OCO. Received 28 July 1994."Corresponding author (arshadc@em.agr.ca).

Published in Soil Sci. Soc. Am. J. 60:561-567 (1996).

has also been reported to have a significant effect onpartitioning of net radiation (i.e., soil heat flux, sensibleheat flux, and latent heat flux) at the soil-atmosphereinterface (Bristow, 1988). These effects can be observedin the different rates of drying between bare and mulchedsoil surfaces and the resultant differences in soil tempera-ture (Horton et al., 1994). Thus, no-tillage practicesaffect crop growth and yield through reciprocal effectson soil temperature and water (Kaspar et al., 1990).

Numerous studies have shown that surface residuecover affects soil thermal properties by reflecting soilradiation and reducing evaporation (van Wijk et al.,1959; Van Doren and Allmaras, 1978) and by affectingthe temperature gradient and total heat transfer coefficientof the canopy-soil system (Azooz, 1991). In addition,tillage-induced changes in soil moisture and porosity caninfluence soil thermal conductivity and volumetric heatcapacity (Allmaras et al., 1977; Wierenga et al., 1982).Loosening of soil by tillage alters the heat flux throughchanged surface roughness, which in turn changes thearea of the soil surface in contact with the atmosphere(Jalota and Prihar, 1990). Thermal conductivity in anundisturbed soil was greater than in a disturbed soil,apparently due to the different distribution and geometryof water menisci (Azooz and Arshad, 1995; Kaune etal., 1993).

Long-term reduced soil disturbance under NT resultsin changes in organic matter, aggregate-size distribution,bulk density, and water retention compared with CT(Arshad et al., 1990; Arshad and Dobb, 1991; Carter,1992). These tillage-induced physical changes contributeto changes in soil temperature, heat flux, and thermaldiffusivity (Hay etal., 1978; Johnson and Lowery, 1985).

Abbreviations: CT, conventional tillage; NT, no-tillage; MNT, modifiedno-tillage.

562 SOIL SCI. SOC. AM. J., VOL. 60, MARCH-APRIL 1996

In the agricultural area of northern British Columbia,a data base for the effect of long-term continuous CTand NT systems and residue management on soil heatflux density and thermal diffusivity is lacking. Suchdata are needed because the rate of heat movement andresultant soil temperature can significantly affect cropgrowth during the short growing season in this coldregion. Therefore, the objectives of this study were to(i) evaluate the effects of long-term continuous NT andCT on soil thermal diffusivity and heat flux density and(ii) investigate whether residue removed from a stripcentered over the planting rows in NT results in a warmertopsoil layer and alters the soil thermal diffusivity in thiscold region.

MATERIALS AND METHODSThe studies were conducted at Dawson Creek (55°46'N,

120°21'W), British Columbia, Canada on a Donnelly siltyloam (a fine-loamy, mixed, frigid Typic Cryoboralf). The0- to 15-cm soil depth had 28% sand, 49% silt, and 23% clay.The site was in its 14th (1992) and 15th year (1993) undercontinuous CT and NT. Mean (15-yr) annual and growingseason (May-September) air temperatures at the study site are1.4 and 12.2°C, respectively. Mean annual and growing seasonprecipitation are 470 and 290 mm, respectively. The 1992 and1993 growing seasons were characterized by a dry periodwithout rain throughout the first 3 wk after planting. Severalstorms occurred during July to August 1993 and were largeenough to create near-saturated soil conditions continuouslyduring July in MNT and NT treatments, but not in the CTtreatment. Annual precipitation was 303 mm in 1992 and 439mm in 1993. The growing season precipitation was 178 mmin 1992 and 322 mm in 1993.

Tillage treatments were: CT (one fall tillage with a deeptillage cultivator equipped with chisels and a working depthof 12 to 15 cm, two operations with a heavy-duty cultivatorto a depth of 8 to 10 cm in spring, and seeding with a double-diskpress drill), NT (direct seeding with a zero-till press drill withresidue left on the soil surface), and MNT (same as NT exceptsurface residue pushed away from a 7.5-cm-wide zone centeredover the crop rows at planting). Treatments were replicatedfour times in a randomized block design. Blocks were 30 mlong by 20 m wide and individual plots were 30 m long and5 m wide. Barley (Hordeum vulgare L.) was grown in bothseasons, planted on 15 May 1992 and on 31 May 1993 withseeding depths of 38 mm and row spacings of 19 cm.

In the field, hourly soil heat flux (Js) was measured usinga heat flow transducer (Model HFTO-3, Radiation and EnergyBalance Systems, Seattle, WA)'. The transducer consisted ofa thermopile encapsulated in high thermal conductivity epoxyto prevent ground potential pickup. The manufacturer's speci-fications of the transducer are: thermal conductivity = 1.22 Wm~' K~', nominal resistance = 2Q, nominal size = 3.856-cmdiam. by 0.393 cm thick, and the nominal calibration factor= 40 W rrT2 mV~'. The manufacturer provides a calibrationfactor (Cf) for each transducer that is different from the nominalcalibration factor. Transducers were installed horizontallythrough 7.5-cm-diam. by 7.7-cm-deep pits. Transducers wereinserted into the soil at 5-cm depth from the side of the pitsclosest to the row. After installing transducers, these pits werepacked carefully using the same original layers of the soil.

Heat flux was computed from the thermopile voltage (K,) by7S = V,d. Hourly soil heat flux was recorded from 5 to 94d after planting (19 May-16 August) in 1992 and from 3 to70 d after planting (2 June-8 August) in 1993 using a CR7datalogger (Campbell Scientific Inc., Logan, UT).

Soil thermal conductivity was measured using the transient-state cylindrical probe method (Model TC2, Soiltronics, Burl-ington, WA) to a depth of 67.5 cm in 7.5-cm increments. Theprobe consisted of a 70Q heating element and a copper-constantan thermocouple embedded in a 6-cm-long and 0.09-cm-diam. stainless steel tube. A heating cycle of 100 s using2.5 V was applied. Temperature rise during the first 6 s ofheating was not used in the calculations, as it is influenced bythe probe and does not represent the soil characteristics (asindicated by the manufacturer). Moreover, the theoretical equa-tion, which uses the linear relation between the temperaturerise and logarithm of time, does not apply in the initial stage(Marquardt, 1963). Probes were installed vertically into undis-turbed soil on each measurement date. To create a good thermalcontact at the thermal conductivity probe-soil interface, adummy probe 5 cm long by 0.06-cm diam. was pushed verti-cally into the soil to a given depth. Following insertion of thedummy probe, measurements were made at 0 to 6 cm (lengthof the thermal conductivity probe); thereafter successive 7.5-cm-diam. by 7.5-cm-deep pits were made with thermal conduc-tivity measured at 7.5-to 13.5-, 15.0- to 21.0-, 22.5- to 28.5-,30.0- to 36.0-, 37.5- to 43.5-, 45.0- to 51.0-, 52.5- to 58.5-,and 60.0- to 66.0-cm depths. A 125-cm-long by 125-cm-widesheet of plywood was used to obstruct the incoming radiationonto the measurement area. Measurements were obtained dur-ing the morning hours (07:00 to 11:00 h) on 1, 12, 25, 33,45, 56, 67, 77, 102, and 117 d after planting (15 May-9 Sept.)in 1992, and on 7, 18, 33, 47, 64, and 78 d after planting(7 June-16 Aug.) in 1993.

Soil volumetric heat capacity was calculated from the sumof the volumetric heat capacities of different components ofthe soil (de Vries 1963):

Cv = l.92Xm + 2.51X0 + 4.18XW [1]where Cv is the volumetric heat capacity of the soil (MJ m~3

K~'); and Xm, X0, and Xw are the volume fraction of soilmineral, organic matter, and water components, respectively.Organic C was determined by the H2SO4-permanganate method(Nelson and Sommers, 1982).

Soil thermal diffusivity was determined from the measuredthermal conductivity (K) and calculated volumetric heat capac-ity (Cv) of the soil (Nakshabandi and Kohnke, 1965):

A"c, [2]

1 Use of trade names of equipments are given for convenience of thereader and do not imply endorsement of these brands.

where A is the thermal diffusivity of the soil (m2 s '), andK is the soil thermal conductivity (W m"1 K~').

Soil water content at the time of measuring soil thermalconductivity was also determined at 0- to 15-, 15- to 30-, 30-to 45-, and 52.5 to 67.5-cm depths by inserting a waveguidevertically 15 cm (length of waveguide) into the soil on eachmeasurement date and using time domain reflectometry (Model6050X1 Trase System, Soil Moisture Equipment, Santa Bar-bara, CA).

The percentage of residue cover was determined 1 wk afterplanting using the line-transect method of Laflen et al. (1981).Residue was collected from four areas per plot (1m2) randomlyselected and air dried; subsamples were oven dried at 60°Cfor 3 d to determine the oven-dry weight of each sample.

Hourly soil temperature was recorded with 32-gauge copper-constantan thermocouples in planted rows at 0-, 5-, 10-, 20-

ARSHAD & AZOOZ: TILLAGE EFFECTS ON SOIL THERMAL PROPERTIES 563

and 50-cm depths at 5 to 91 d after planting (19 May-16August) in 1992 and at 3 to 70 d after planting (2 June-8August) in 1993 using a CR7 datalogger. These depths wereselected to evaluate the effects of tillage and residue manage-ment on soil thermal properties in and below the tilled zone.Thermocouples were installed horizontally through 7.5-cm-wide by 20-cm-long by 50-cm-deep pits. Thermocouples wereinserted 10 cm into the soil from the side of pits closest tothe row. After installing thermocouples, these pits were packedcarefully using the same layers of the soil and to the samebulk density.

Soil thermal conductivity, water content, temperature, andheat flux were measured in triplicate in each of the fourreplications, at randomly selected points. Data were evaluatedwith the analysis of variance technique. Data were analyzedseparately for each measurement date and soil depth (SASInstitute, 1990). When the F test indicated significant differ-ences at the 0.05 probability level (P < 0.05), means wereseparated by the protected least significant difference method(Steel and Torrie, 1980).

RESULTS AND DISCUSSIONSoil Thermal Diffusivity

At most sampling periods and soil depths, thermaldiffusivity in CT was greater than in NT and MNT in1992, but not in 1993 (Fig. 1). Most of the time, thermal

2.1 -

1.5 -

1.2-

0-15 cm 1992 '

15-30 cm 1992

30-45 cm 1992

45-67.5 cm 1992

0-15 cm 1993

15-30 cm 1993

30-45 cm 1993

45-67.5 cm 1993

0 20 40 60 80 100 120 0 20 40 60 80 100 120DAYS AFTER PLANTING

Fig. 1. Mean soil thermal diffusivity (n = 12) of various soil layersdetermined from measured thermal conductivity and volumetricheat capacity under no-tillage (NT), modified no-tillage (MNT),and conventional tillage (CT) treatments as a function of days afterplanting during 15 May to 9 Sept. 1992 and 7 June to 16 Aug.1993. The vertical bars represent LSD(O.OS).

Table 1. Mean soil water contents (0,) averaged across all thesampling data collected during 15 May to 9 Sept. 1992 andduring 7 June to 16 Aug. 1993.

Depth

15 May-9 Sept. 1992

NTt MNT CT

7 June-16 Aug. 1993NT MNT CT

0-1515-3030-4552.5-67.5

0.223$0.23a0.27a0.28a

0.21a0.22a0.24a0.27a

O.lSbO.lSb0.19b0.21b

3 — 3

0.38a0.39a0.43a0.40a

0.36a0.37a0.39a0.36a

0.22b0.32b0.30b0.32b

t NT = no-tillage, MNT = modified no-tillage, and CT = conventionaltillage.

t Means for a given year followed by the same letter in the same row donot differ significantly at P < 0.05.

diffusivity in MNT was not different from NT. Meansoil water contents for the 0- to 45-cm depth in 1992and 1993 were 0.17 and 0.28 m3 irT3 in CT, 0.22 and0.37 m3 nr3 in MNT, and 0.24 and 0.40 m3 irT3 inNT, respectively (CT < MNT < NT). Soil water contentin the CT soil exceeded that in NT soil for all depthsand years (Table 1). During the study period, watercontent at 0- to 30-cm depths ranged from 0.17 to 0.63m3 rrr3 in no-tillage treatments (NT and MNT) and 0.12to 0.44 m3 m~3 in CT treatment (Fig. 2). Differencesin soil water content between the no-tillage treatmentsand CT may be related to loosening of soil in CT bytillage, which increases surface roughness and potentialevaporation (Allmaras et al., 1972). According to All-maras et al. (1977), soil water content can be amendedby tillage, which in turn can influence soil thermal con-ductivity and volumetric heat capacity and therefore soilthermal diffusivity. In this study, the long-term no-tillagesystems increased aggregate stability, organic matter,and water storage capacity (Arshad and Dobb, 1991)and consequently resulted in higher soil thermal conduc-tivity and volumetric heat capacity under NT and MNTrelative to CT in most cases (Table 2). For example,soil thermal conductivity for the 0- to 15-cm depth in

2.0--

1.8 -

1.6-

1.4-

1.2-2.2 -

2.0 -

1.8 -

1.6 -

1.4 -

1.2-

A

£%£. 0-15 cm 1992 -A An

^^#+ NTD MNT ~

15-30 cm 1992 JA.

&

%$-

4t 0-15 cm 1993QtfjS^ffh

^*^^fiPt +&&

15-30 cm 1993

0.20 0.30 0.40 0.50 0.60 0.20 0.30 0.40 0.50 0.60WATER CONTENT (m3m~3)

Fig. 2. Mean soil thermal diffusivity (n = 3) as a function of watercontent under no-tillage (NT), modified no-tillage (MNT), and con-ventional tillage (CT) treatments.

564 SOIL SCI. SOC. AM. J. , VOL. 60, MARCH-APRIL 1996

Table 2. Mean soil volumetric heat capacity (C») and thermalconductivity (K) averaged across all the sampling data collectedduring 15 May to 9 Sept. 1992 and during 7 June to 16 Aug.1993 for different tillage management treatments, t

Table 3. Mean diurnal soil temperature at various depths aver-aged across different time periods for different tillage manage-ment treatments.

Depth

cm

0-1515-3030-4552.5-67.5

0-1515-3030-4552.5-67.5

Cv

NT

1.98aJ1.90a2.04a2.04a

2.66a2.58a2.70a2.56a

MJ m-3 K-

MNT

15 May-91.95a1.84ab1.89a1.98a

7 June-162.56a2.46ab2.61a2.45a

i

CT

Sept. 19921.71b1.70b1.68b1.78b

Aug. 19932.05b2.27b2.15b2.21b

K

NT

0.89a0.90a0.94a0.95a

1.22a0.97a0.99a1.07a

W m - ' I

MNT

0.88a0.89a0.91a0.94a

1.19a0.94a0.93aI.Ola

c-'CT

0.83b0.85b0.86a0.88b

0.97b0.88a0.74b0.79b

t NT = no-tillage, MNT = modified no-tillage and CT = conventionaltillage.

$ Means for C, or K followed by the same letter in the same row do notdiffer significantly at P < 0.05.

1992 was 0.83 W ar1 K~' in CT, 0.88 W m~l K~' inMNT, and 0.89 W m~l K"1 in NT. The correspondingvalues for volumetric heat capacity were 1.71 MJ m~3

K-' in CT, 1.95 MJ nT3 K~' in MNT, and 1.98 MJm~3 K~' in NT. Both the thermal conductivity and volu-metric heat capacity in 1993 were higher than in 1992.This is attributed to significantly greater soil water in1993 when soil remained wet for most of the growingseason because of frequent heavy rainstorms. Thermaldiffusivity under the no-tillage treatments was generallylower than under CT in 1992 but no differences werefound in 1993 except lower values for the CT than NTand MNT at the45-to 67.5-cm depth (Fig. 1). In contrast,Hay et al. (1978) reported larger thermal diffusivityin a direct-drilled barley field than in a plowed fieldthroughout the growing season. They attributed theseresults to higher bulk density and stone contents in thedirect-drilled plots and to moisture content differencesbetween the two treatments. In our study, the lowerthermal difFusivity in NT and MNT than CT was probablycaused mainly by proportionately greater volumetric heatcapacity, relative to thermal conductivity, of the wetterno-tillage treatments. For example, compared with CT,thermal conductivity in NT increased to only 7.2% in1992 while the corresponding increase in volumetric heatcapacity was 15.8% at 0- to 15-cm depth. However,increase in both the thermal conductivity and volumetricheat capacity in NT relative to CT was about 25 %. Ourresults for thermal diffusivity (Fig. 2) are similar to thetrend observed for a silt loam soil by Potter et al. (1985),who reported that the thermal diffusivity reached a maxi-mum at volumetric water contents near 0.20 m3 m~3

then decreased linearly for all tillage treatments withfurther increases in water content. According to Sellers(1965), soil thermal diffusivity, which determines theheating or cooling rate accompanying a given tempera-ture profile, is greatest at volumetric water contentsbetween 8 and 20%. Within this range the thermal con-ductivity is near its maximum values and volumetric heatcapacity is relatively small. As a result, the heating orcooling rate is impeded at very low water content by

Timeperiod

199219-31 May

1-30 June

1-31 July

1-25 Aug.

19933-30 June

1-31 July

1-10 Aug.

Tillaget

CTMNTNTCTMNTNTCTMNTNTCTMNTNT

CTMNTNTCTMNTNTCTMNTNT

Soilsurface

13.5ai12.6a11.3b17.8a17.2a15-lb20.4a18. 6b17.7b17.9a16.2b15.9b

16.5a16.4a15.2b16.4a15.9a15. la16.2a15.7a14. 5b

5 cm

13.3a12.4a11. 2b17.3a16.2abIS.lb19.3a18.3ab17.0b17.2aIS.Sa15.7a

16.2a16.1a15.2b16.5a15.9abIS.lb16. laIS.Sa14.3b

10 cm

°C12.9a12.2a11. Ib16.6a15.3ab14.6b18.6a17.6ab16.5b16.7a15.6ab14.5b

15.7a15.7a14.6b15.9a15.6ab14.5b16.0a15.3ab14.3b

20 cm

12.2a11.3ab10.9bIS.ga15.2ab14.0b18.2a16.7a16.3a16.4a15.4a13. 8b

15.3a15. Oa14.1b15.3a14.6a14.2a15.8a14.9a14.2a

50cm

11.3a11.2a9.9b

15.3a13. 8b13.2b16.6a16.4a16.3a16. la14.7a13. 3a

13. 6a13.5a13.1a14.6a13.7a13.2a15.6a14.7a14.2a

t NT = no-tillage, MNT = modified no-tillage and CT = conventionaltillage.

t Means for a given time period and year followed by the same letter inthe same column do not differ significantly at P < 0.05.

poor conductivity of the soil, and at very high watercontent by the large heat capacity of the soil.

Soil TemperatureMean diurnal soil temperature for different periods

under CT, MNT, and NT treatments are shown in Table3. Mean diurnal soil temperature within the upper 10-cmdepth under CT and MNT systems was generally greaterthan under NT early in the growing seasons. The differ-ences in mean diurnal temperatures between MNT andCT soils were not significant. Removal of residue abovethe seed row in MNT resulted in an increased soil temper-ature relative to NT, while preserving soil moisturesimilar to that in NT.

Averaged across the period from 19 to 31 May 1992,the MNT treatment lowered the mean diurnal temperaturein the dry period by 0.9°C at the soil surface, 0.9°Cat the 5-cm depth, and 0.7°C at the 10-cm depth belowthe mean diurnal temperature of CT soil (Table 3). Forthe same period, the NT treatment lowered the meandiurnal soil temperature by 2.2°C at the soil surface,2.1°C at the 5-cm depth, and 1.8°C at the 10-cm depthbelow the mean diurnal temperature of CT soil. Thus,residue removal in the MNT treatment offset, to a consid-erable degree, the depressed root zone temperatures ob-served for NT. Surface residue cover in CT was lowerby 69% in 1992 and 71% in 1993 than in NT, whileresidue areal density was lower by 0.53 kg m~2 in 1992and 0.49 kg m~2 in 1993 than in NT (Table 4). Residuecover and areal density in MNT were close to that inNT. Surface residue limits soil warming by reflectingsolar radiation (Horton et al., 1994; van Wijk et al.,1959). The effect of residue removal in MNT on thediurnal fluctuation and on the time during a day that

ARSHAD & AZOOZ: TILLAGE EFFECTS ON SOIL THERMAL PROPERTIES 565

Table 4. Residue cover and areal density of no-tillage (NT), modi-fied no-tillage (MNT) and conventional tillage (CT) at the studysite during 1992 and 1993 growing season.

Tillage

CTMNTNT

Residue

1992a

4.7btS9.8a73.8a

cover

1993

3.9b60.2a75.2a

Residue areal density

1992. 2

0.14bO.S9a0.67a

1993

0.12b0.60a0.61a

t Means followed by the same letter in the same column do not differsignificantly at P < 0.05.

temperature exceeded a certain critical value are shownin Fig. 3. Seed zone (5-cm depth) soil temperature wasabove 14°C for at least 54 h in NT, 99 h in MNT, and114 h in CT during 20 to 26 d after planting in 1992,and 92 h in NT, 109 h in MNT, and 107 h in CT during3 to 9 d after planting in 1993. This implies that whendealing with suboptimal temperatures, a common occur-rence in the study area, the more time spent above somecritical temperature, the more positive the effect is likelyto be. The reverse is true for supraoptimal temperature(Horton et al., 1994; Bristow and Abrecht, 1991).

Seed Zone Soil Heat Flux DensityMean daily soil heat flux at the 5-cm depth of MNT

was similar to that of CT during the first 40 d after

24 -

U 16 -

3

IWa.aH

12 -

8-

24 -

20 -

12 -

8-

3 to 9 June 1992(20 to 26 days after planting5-cm depth

3 to 9 June 1993(3-9 days after planting)5-cm depth

50 100TIME (h)

150

Fig. 3. Mean hourly soil temperature (n = 12) of 5-cm depth underno-tillage (NT), modified no-tillage (MNT), and conventional tillage(CT) systems during the early growing seasons in 1992 and 1993.

planting (Fig, 4). Except for cloudy days, heat fluxdensity was drastically reduced under NT in comparisonto MNT and CT. Considerable differences in mean dailysoil heat flux density were observed among treatments.Mean daily heat flux ranged from —0.01 to 1.73 MJm-2 A-\d~' in NT, from -0.16 to 2.11 MJ irT2 d-2 A-\ inMNT, and from -0.31 to 2.44 MJ m-2 d~' in CT in1992. They ranged from -0.56 to 0.49 MJ irT2 d~' inNT, from -0.63 to 1.09 MJ nr2 d~' in MNT and from-0.67 to 1.46 MJ m~2 d~' in CT in 1993. Mean dailyheat flux throughout the first 10 wk after planting underNT was always less than under MNT and CT (whichwere generally similar) during 1992 and during the first6 wk in 1993 (Table 5). The changes in soil thermaldiffusivity may affect the penetration of heat into thesoil. The mean daily heat flux values averaged acrossthe first 10 wk after planting were 0.77 MJ m~2 d~' in1992 and 0.25 MJ m~2 d'1 in 1993 in NT, 1.06 MJm-2 d~' in 1992 and 0.45 MJ m'2 d'1 in 1993 in MNT,and 1.15 MJ nr2 d~' in 1992 and 0.57 MJ nr2 d'1 in1993 in CT (Table 5). The higher heat flux density underthe CT than under NT and MNT may have been causedby the increased volumetric heat capacity under the NTsystem, which agrees with the results for silt loam soilreported by Johnson and Lowery (1985). They concludedthat the tillage treatment causing the least amount of soildisturbance and highest percentage of crop residue coverhas the highest volumetric heat capacity and lowest heatflux density. The residue-free strip centered over theseed rows in MNT led to increased soil warming at the

-oN

S

1aQX

IH

H

2.5 -

2.0-

1.5

1.0

0.5

0.0-

-0.5 -

2.5 -

2.0 -

1.5 -

1.0 -

0.5 -

0.0 -

-0.5 -

S cm depth 1992

5 cm depth1993

0 5 10 15 20 25 30 35DAYS AFTER PLANTING

40 45

Fig. 4. Mean daily soil heat flux density (n = 12) of 5-cm depth underno-tillage (NT), modified no-tillage (MNT), and conventional tillage(CT) treatments during the first 40 d after planting. The verticalbars represent LSD(O.OS).

566 SOIL SCI. SOC. AM. J., VOL. 60, MARCH-APRIL 1996

Table S. Mean daily heat flux density (/,) averaged across theweekly data at 5-cm depth for different tillage managementtreatments during 1992 and 1993 growing seasons.

Weekafter ————planting NTf

1992 1993

MNT CT NT MNT CT

12345678910mean

0.44bt0.38b0.72b0.64b1.24bl.lSbO.SOc1.12b0.68b0.69b0.77b

0.63aO.SSal.lla0.78a1.60a1.32bl.lOb1.46a0.92al.OSal.Ooa

0.68a0.66a1.12a0.83a1.72a1.63a1.23a1.59a0.99a1.06al.lSa

IJ 111 U

O.SSb0.33a0.30a0.22b

-0.20aO.OOb0.90c0.32bO.SOc

-O.lOa0.25b

0.54a0.45aO.SOa0.36aO.lla0.12a1.30b0.54aO.SSb

- 0.30a0.45a

0.69aO.Sla0.62a0.45a0.16a0.25a1.60a0.66a1.20a

- 0.40a0.57a

t NT = no-tillage, MNT = modified no-tillage, and CT = conventionaltillage.| Means for a given year followed by the same letter in the same row do

not differ significantly at P < 0.05.

surface similar to that in CT, thereby increasing the rateof heat exchange between the soil surface and the top5-cm layer. Chung and Horton (1987) also found thatsoil temperature and heat flux density increased mostrapidly in partial mulch cover soil compared with mulchcover soil, and that partial mulch cover did not have alarge effect on the water content at the 5-cm depth, whereplant seeds are located. Diurnal fluctuation of heat fluxat 5-cm depth was more dynamic in CT than in NT,with MNT intermediate (Fig. 5). Figure 5 shows the

cP

's£

§waxff<

Ii_i

100 -

80-

60-

40 -j

20 -

o:-20 -

-40 -

100 -

80 -;

60 -

40 -

20 -

-40-

3 to 9 June 1992 (20 to 26 days after planting)5 cm depth

• NTa MNTA CT

3 to 9 June 1993 (3-9 days after planting)5-cm depth

0 20 40 60 80 100TIME (h)

120 140 160

Fig. 5. Mean hourly soil heat flux density (n = 12) of 5-cm depthunder no-tillage (NT), modified no-tillage (MNT), and conventionaltillage (CT) systems during the early growing seasons in 1992 and1993.

effect of residue removal in MNT on diurnal fluctuationof heat flux and on the time during a day that heat fluxexceeded a critical value. Heat flux was above 25 Wirr2 for 15 h in NT, 45 h in MNT, and 79 h in CTduring 20 to 26 d after planting in 1992, and above25 W m~2 for 0 h in NT, 13 h in MNT, and 31 h inCT during 3 to 9 d after planting in 1993. The 1992soil heat flux values were substantially higher than thoseof 1993 (Table 5). This was probably due to the differ-ences in soil moisture conditions and thermal diffusivitybetween the two years.

These results demonstrate the role of residue manage-ment in increasing the soil heat flux density indicatinggreater ability of MNT soils to conduct more heat, havesignificantly increased root zone soil temperature in no-tillage and consequently to increase the heat transfer intothe seed zone compared with NT.

CONCLUSIONSThe soil under long-term continuous no-tillage prac-

tices (NT and MNT) had higher heat storage capacitythan under CT, resulting from higher soil water content.Thermal diffusivity of MNT and NT soil during thegrowing season was impeded by increased heat capacity.Presence of crop residue and the lack of soil disturbancein MNT and NT reduced the rate of soil drying andincreased water storage compared with CT. The MNTdid not alter soil thermal diffusivity in comparison toNT, but it was still lower than CT, suggesting thatsoil water content was the dominant factor controllingdiffusivity. Soil temperature and heat flux density inMNT were more similar to those in CT than in NT.This study indicated that residue rearrangement ratherthan soil disturbance with CT is more important in provid-ing optimum soil water content, temperature, and heatflux in cold regions. This is especially important insemiarid, cold regions where soil water can also limitplant growth. A modified no-tillage residue managementsystem that pushes residue away from the seed rowappears to be an important strategy to improve growingconditions in semiarid, cold regions as well as increasesoil quality for the future.

ACKNOWLEDGMENTSThis study was funded under the Canada-British Columbia

Soil Conservation Agreement. We would like to thank Dr. C.Chang and Dr. A.J. Franzluebbers for their critical reviews.Field assistance provided by J.L. Dobb, F. Breault, and W.Henderson is gratefully acknowledged.

ARSHAD & AZOOZ: TILLAGE EFFECTS ON SOIL THERMAL PROPERTIES 567

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