Minimum Soil Temperature Research Articles

Variation in microclimate associated with dispersed-retention harvests in coniferous forests of western Washington

Green-tree or structural retention is becoming increasingly common as a method of regeneration harvest in the Pacific Northwest. Amelioration of microclimatic stress is assumed to be one mechanism by which overstory retention enhances the survival of forest organisms and the potential for ecosystem recovery following timber harvest. We examined patterns of transmitted light (photosynthetic photon flux density, PPFD), air and soil temperature, and soil moisture across a broad gradient of dispersed retention in mature, coniferous forests at three locations in western Washington. Treatment means and within-treatment variation (coefficients of variation among sample points within treatments) were compared for warm, sunny days in 6–7-year-old experimental harvest units representing 0, 15, 40, and 100% retention of original basal area. Multiple linear regression was used to explore relationships between microclimate and plot-scale measures of forest structure (including overstory attributes, understory vegetation, and logging slash). PPFD and mean and maximum air and soil temperatures decreased with level of retention. PPFD showed the strongest response, but did not differ between 40 and 100% retention. Mean and maximum air temperatures were significantly greater at 0 and 15% retention than at 100%. Among harvest treatments (0, 15, and 40%), mean air temperature was significantly lower at 40 than at 0%, but maximum air temperature did not differ among treatments. Mean and maximum soil temperatures differed only between 0 and 100% retention. Minimum air and soil temperatures and late-summer soil moisture did not differ among treatments. Within-treatment variability (coefficient of variation, CV) did not differ significantly with level of retention for any of the variables sampled, but CVs for soil temperature showed a consistent increase with decreasing retention. In combination, topography, residual forest structure, and understory variables were good predictors of PPFD and mean and maximum temperatures ( R 2 of 0.55–0.85 in multiple regression models), but were poorer predictors of minimum temperatures and soil moisture ( R 2 of 0.10–0.51). Canopy cover appeared most frequently in the models and cover of understory vegetation was a significant predictor in models of soil temperature. Trends in microclimate among experimental treatments were consistent, in large part, with the early responses of bryophyte, herbaceous, and fungal communities at these sites. Our results suggest that 15% retention, the current minimum standard on federal forests within the range of the northern spotted owl, does little to ameliorate microclimatic conditions relative to traditional clearcut logging.

Effect of tillage and mode of straw mulch application on soil erosion in the submontaneous tract of Punjab, India

The submontaneous tract of Punjab comprising 10% of the state, is prone to soil erosion by water. Soils of the area are coarse in texture, low in organic matter and poor in fertility. High intensity rains during the monsoon season result in fertile topsoil removal. There is an urgent need to control soil erosion in this region so as to improve soil productivity. A field study was conducted to estimate the effect of tillage and different modes of mulch application on soil erosion losses. Treatments comprised two levels of tillage, viz. minimum ( T m) and conventional ( T c) in the main plots and five modes of straw mulch application, viz. mulch spread over whole plot ( M w), mulch spread on lower one-third of plot ( M 1/3), mulch applied in strips ( M s), vertical mulching ( M v) and unmulched control ( M o), in subplots in a replicated split plot design. Rate of mulch application was 6 t ha −1 in all modes. Compared with M o, M w reduced runoff by 33%. Runoff and soil loss were 5 and 40% higher under T c than under T m. Though other modes of straw mulch application ( M 1/3, M s and M v) controlled soil loss better than M o, their effectiveness was less than M w. T m was more effective in conserving soil moisture than T c. Compared with M o, M w had 3–7% higher soil moisture content in the 0–30 cm soil depth under T m. Minimum soil temperature of the surface layer was 1.4–2.4 °C lower under M w than under M o. Straw mulching reduced maximum soil temperature and helped in conserving soil moisture. Minimum tillage coupled with M w was highly effective in reducing soil erosion losses, decreasing soil temperature and increasing moisture content by providing maximum surface cover.

Intra-annual tracheid production in balsam fir stems and the effect of meteorological variables

Tracheid production of balsam fir in the Quebec boreal forest (Canada) was studied by repeated cell analysis to investigate the influence of meteorological variables during the growing seasons 1998 to 2000. Wood micro-cores were extracted on a weekly basis throughout the growing season and sections were prepared in order to count the total number of cells produced. From the weekly cell number obtained, the rate of tracheid production was calculated and correlated with meteorological variables. The average total number of cells produced per year was reasonably uniform, increasing only from 36.6 in 1998, to 41.1 in 2000. However, different cell production rates were noted during the growing season. Regression analysis revealed that the cell production rate was largely dependent on minimum air and soil temperature during most of the cell production period. Mean and maximum temperature had less influence on cell production. Moreover, the influence of temperature was higher during earlywood production mainly from the end of May to mid-July. Lagging the weather data by 1–5 days decreased the relationship between temperature and cell production, showing the high correspondence with the same interval where cell production was measured. These results suggest a fast response of the cambium to temperature variation during tree-ring formation.

Effects of experimentally imposed climate scenarios on flowering phenology and flower production of subarctic bog species

AbstractClimate scenarios for high‐latitude areas predict not only increased summer temperatures, but also larger variation in snowfall and winter temperatures. By using open‐top chambers, we experimentally manipulated both summer temperatures and winter and spring snow accumulations and temperatures independently in a blanket bog in subarctic Sweden, yielding six climate scenarios. We studied the effects of these scenarios on flowering phenology and flower production of Andromeda polifolia (woody evergreen) and Rubus chamaemorus (perennial herb) during 2 years. The second year of our study (2002) was characterized by unusually high spring and early summer temperatures.Our winter manipulations led to consistent increases in winter snow cover. As a result, average and minimum air and soil temperatures in the high snow cover treatments were higher than in the winter ambient treatments, whereas temperature fluctuations were smaller. Spring warming resulted in higher average, minimum, and maximum soil temperatures. Summer warming led to higher air and soil temperatures in mid‐summer (June–July), but not in late summer (August–September).The unusually high temperatures in 2002 advanced the median flowering date by 2 weeks for both species in all treatments. Superimposed on this effect, we found that for both Andromeda and Rubus, all our climate treatments (except summer warming for Rubus) advanced flowering by 1–4 days. The total flower production of both species showed a more or less similar response: flower production in the warm year 2002 exceeded that in 2001 by far. However, in both species flower production was only stimulated by the spring‐warming treatments.Our results show that the reproductive ecology of both species is very responsive to climate change but this response is very dependent on specific climate events, especially those that occur in winter and spring. This suggests that high‐latitude climate change experiments should focus more on winter and spring events than has been the case so far.

Soil water dynamics, physical properties and corn and wheat responses to minimum and no-tillage systems in the southern Pampas of Argentina

No-tillage (NT) has become a popular conservation practice in recent years in Argentina. The introduction of no-tillage practices in productive soils could avoid or reduce soil degradation under intensive agricultural management. The objective of this work was to evaluate the effects of minimum tillage (MT) and no-tillage on soil temperature, compaction, and soil water storage, and its effects on crop yields in a productive soil of southeastern Buenos Aires province (Argentina). The study was conducted on a Typic Argiudoll during 1997 (corn) and 1998 (wheat) in a corn–wheat rotation. The experimental design was a split-plot design with four replications, where main plots were tillage treatments, MT and NT, and subplots were N fertilization 0 (0-N) and 150 kg N ha −1 (150-N). Determinations included soil temperature, bulk density, penetration resistance, soil water storage, and corn and wheat yield. NT showed higher soil water storage during the critical growth stage in corn, and most of the wheat-growing season. Soil water storage at 0–80 cm under both tillage systems was frequently below 50% threshold of available water. Mean soil temperature was lower under NT in corn and wheat in the initial stages adversely affecting the initial corn and wheat growth. Maximum soil temperature under MT was higher than under NT, but minimum soil temperature was similar for both tillage systems. NT presented lower thermal amplitude than MT. Bulk density was higher under NT than under MT at 3–8 cm and 13–18 cm depth. Penetration resistance showed differences between tillage systems, being higher under NT at all sampling depths. Corn grain yields were lower under NT than under MT in the 0-N, but there were no differences in the 150-N treatments. Wheat yields were similar for both tillage systems. The adoption of NT in southeastern Buenos Aires could benefit soil conservation without affecting grain production in soils under initial high fertility conditions.

The impact of forest clear-cutting on soil temperature: a comparison between before and after cutting, and between clear-cut and control sites

Soil temperature is one of the most important factors governing biological activity in the soil. This study was conducted to investigate how forest clear-cutting changes soil temperature. Soil temperatures at 0.5, 1.0, 2.0, and 3.0m depths were measured in two neighboring forest watersheds (35°12′N, 140°06′E) in Chiba Prefecture, Japan, from 1994 to 2000. One watershed was clear-cut 5 years after the observations began. After clear-cutting, the annual mean soil temperature at 0.5, 1.0, 2.0, and 3.0m depths rose by about 2.2, 2.0, 1.7, and 1.4°C, respectively. The maximum respective soil temperatures rose by about 3.2, 3.0, 2.2, and 1.8°C. The minimum soil temperature rose slightly (<1°C). The range of temperatures increased by 3.0, 2.4, 1.6, and 1.4°C, respectively. In our study, forest clear-cutting raised maximum and average soil temperatures but hardly changed minimum soil temperature. This is probably because solar radiation dominated in the summer season and increased soil temperature; on the other hand, net long-wave radiation, and releases of latent and sensible heat from the soil surface, were predominant in the cool season.

BREEDING OF FUSARIUM WILT-RESISTANT STRAWBERRY CULTIVAR SUITABLE FOR FIELD CULTURE IN NORTHERN JAPAN

Fusarium wilt of strawberry, which is caused by Fusarium oxysporum f. sp. fragariae, is a very serious soilborne disease found in cooler regions such as Akita Prefecture in Northern Japan. The initial infestation of the susceptible cultivars Morioka-16 and Pajaro with the disease in Akita Prefecture was noted at minimum air and soil temperatures of ca. 15°C at the end of May. As the months passed and the high temperature season (the beginning to the middle of July) drew near, the numbers of plants that became diseases and died increased rapidly. A way to effectively control this disease has yet to be found. Breeding for new resistance strawberry cultivars suitable for open culture of cooler regions was conducted. A thousand and six F 1 seedlings obtained from the crossing with cv. Pajaro (susceptible resistance) and cv. Belle Rouge (intermediate resistance) were grown until 3-5 leaves had appeared, and were then inoculated with a spore suspension (1 x 10 6 spores/ml) of Fusarium oxysporum f. sp. fragariae (Isolate 91-40). Three resistant lines were then selected. The lines, 'WB-A15', 'WB-B22', and 'WB-B33', were not damaged by the disease when they were cultured in an open field heavily infested with Fusarium oxysporum f. sp. fragariae for three consecutive years (1999 to 2001). These results demonstrate that the lines are resistant enough to Fusarium wilt to be grown under conditions in the regions in question.

Thaumasite in Orange County, Southern California: an inquiry into the effect of low temperature

Thaumasite has been found in ∼10 year old permeable concrete exposed to sulfate-bearing ground waters in Orange County, California, an area generally associated with a warm climate. The occurrences have usually been found in carbonated zones at or near the lower surface of concrete slabs in contact with the ground. Daily records of soil temperature over the 1990–2000 decade indicate that during the early part of this decade (1990–1993) daily minimum soil temperatures dipped below 15 °C for appreciable portions of the winter months. Since 1993 a warming trend has been observed, and daily minimum soil temperatures fell below 15 °C for only a very few days. It is not clear whether the thaumasite deposits observed in the subject concretes were formed entirely during the colder pre-1994 winters, or whether the thaumasite development continued even under the warmer temperatures experienced since then.

Light, temperature, and soil moisture responses to elevation, evergreen understory, and small canopy gaps in the southern Appalachians

Small canopy openings often alter understory microclimate, leading to changes in forest structure and composition. It is generally accepted that physical changes in the understory (i.e., microclimatic) due to canopy removal drive changes in basic forest processes, particularly seedling recruitment which is intrinsically linked to soil moisture availability, light and, to a lesser extent, temperature. We examined the impact of small canopy gaps of the type (snags) and size (∼300 m 2) most frequently observed in the southern Appalachians on the understory microclimate. We created artificial canopy gaps at two elevations (a.m.s.l.) by girdling trees in areas with and without a Rhododendron maximum L. (rosebay rhododendron) understory. Soil and air temperature (°C), photosynthetically active radiation (PAR; μmol m −2 s −1), and volumetric soil water content (%WC) in the upper 15 cm of soil were measured along transects generally running north to south through each gap. Overall, PAR was substantially less in rhododendron gaps than in non-rhododendron gaps. We found a slight increase in PAR in non-rhododendron gaps during spring and summer compared to controls. Very little seasonal variation in PAR was observed in rhododendron gaps compared with non-rhododendron gaps. In general, %WC in rhododendron gaps was lower than in non-rhododendron gaps and less variable. We also found a gap response in incident PAR during the spring and summer seasons. There was no significant effect of gap creation on %WC, nor were there site (elevation) differences or effects due to the presence of rhododendron . Further, there was no significant gap effect on mean, maximum, or minimum soil and air temperature; however, there were significant effects from the presence of rhododendron and between sites for PAR and soil and air temperature during certain seasons of the year. Although there is some certainty about measurable responses in key microclimatic variables in rhododendron and non-rhododendron gaps found in this study, we could not be certain if responses represent a significant enough departure from values in undisturbed conditions to elicit a tree recruitment response. Our results indicate that for openings of the size examined here, topography and evergreen understory are the primary determinants of spatial and temporal heterogeneity in understory microclimate.

A geometric solar radiation model with applications in agriculture and forestry

Incoming solar radiation (insolation) is fundamental to most physical and biophysical processes because of its role in energy and water balance. We calculated insolation maps from digital elevation models, using an insolation model that accounts for atmospheric conditions, elevation, surface orientation, and influences of surrounding topography. Herein, we focus on the application of this insolation model for spatial interpolation of soil temperature measurements over complex topography at landscape scales. Existing interpolation techniques generally apply only at continental or broad regional scales and do not capture the high variation of finer scales. In our field study in the vicinity of the Rocky Mountain Biological Laboratory, average soil temperature was correlated with insolation and elevation. Whereas daily minimum temperature was negatively correlated with elevation ( r=−0.730, P<0.05), daily temperature change (maximum minus minimum) was positively correlated with daily insolation ( r=0.504, P<0.01). We generated daily minimum and maximum soil temperature maps based on regression analyses. Residual variation was explained by factors such as vegetation cover. This application demonstrates the importance of characterizing spatial and temporal variation of insolation for studies of energy and water balance.

The first 20 years (1978-1979 to 1998-1999) of active-layer development, Illisarvik experimental drained lake site, western Arctic coast, Canada1

Active-layer thickness, snow depth, minimum soil temperatures, near-surface ground ice, soil heave, and permafrost temperatures have been measured for over 20 years following the 1978 artificial drainage of Lake Illisarvik. Measurements of active-layer thickness and other variables have been made at 25-m intervals along the major and minor axes of the oval-shaped drained-lake bed. Permafrost aggradation commenced in the lake bottom during the first winter following drainage. Before the establishment of vegetation, there was little snow cover, minimum ground temperatures were low, and the active layer was relatively thin. However, both snow depth and minimum ground temperatures have risen where vegetation has grown, the active layer has thickened, and in response, the temperature in permafrost has gradually increased. In the lake bottom, the change in snow depth associated with vegetation growth has been the dominant control on variation in active-layer thickness and not summer weather conditions, which are well correlated with thaw depths along an active-layer course established in the adjacent tundra. Changes in elevation of the surface of the lake bed have been measured with respect to some 40 bench marks anchored in permafrost, and indicate vertical movements of the surface associated with frost heave, thaw subsidence, and the growth of aggradational ice. The ground ice content of near-surface permafrost determined by drilling is in close agreement with the measured uplift of the lake bed. The rate of growth of aggradational ice has been ~0.5 cm a–1 over 20 years.

Low Winter Soil Temperature Affects Summertime Nutrient Uptake Capacity and Growth Rate of Mountain Birch Seedlings in the Subarctic, Swedisn Lapland

Effects of different winter soil temperature on summertime growth rate of individual seedlings of mountain birch (Betula pubescens ssp. czerepanovii) were evaluated in an outdoor pot experiment in subarctic Sweden. The hypothesis tested was that low winter soil temperature could decrease growing-season nutrient uptake capacity and growth rate by injury of the root system; further, the root damage should stimulate growth of replacement roots, which should be reflected by increased summertime biomass allocation to roots. Mountain birch seedlings were exposed to two soil temperatures during wintertime by manipulation of snow depth that accumulated on top of the pots. Minimum soil temperature (hourly recordings) during winter was –1.7°C in the “protected” treatment (deep snow cover) and – 10.5°C in the “exposed” treatment (thin snow cover). The treatments simulated the soil temperature conditions of a local mountain birch forest and heath site, respectively. During June and July, the relative growth rate (RG) and nitrogen accumulation rate (RN) in the exposed treatment were lower compared to the protected treatment. In addition, the seedlings of the exposed treatment allocated a greater proportion of biomass to roots compared to the protected treatment. Thus, leaf growth was reduced in the exposed compared to the protected treatment. We concluded that lower winter temperature in soils can result in stronger root injury that stimulates the growth of replacement roots and reduces nutrient uptake capacity and growth rate during summer. In concert with other possible factors causing root disruption during winter, e.g., frequent freeze-thaw cycles, the mechanism identified here might be important for survival of tree seedlings in subarctic and alpine areas, especially near treelines. The implications are discussed specifically for mountain birch seedling growth and survival in treeless subarctic heath sites and above treelines in northern Europe.

Low Winter Soil Temperature Affects Summertime Nutrient Uptake Capacity and Growth Rate of Mountain Birch Seedlings in the Subarctic, Swedish Lapland

Effects of different winter soil temperature on summertime growth rate of individual seedlings of mountain birch (Betula pubescens ssp. czerepanovii) were evaluated in an outdoor pot experiment in subarctic Sweden. The hypothesis tested was that low winter soil temperature could decrease growing-season nutrient uptake capacity and growth rate by injury of the root system; further, the root damage should stimulate growth of replacement roots, which should be reflected by increased summertime biomass allocation to roots. Mountain birch seedlings were exposed to two soil temperatures during wintertime by manipulation of snow depth that accumulated on top of the pots. Minimum soil temperature (hourly recordings) during winter was –1.7°C in the “protected” treatment (deep snow cover) and – 10.5°C in the “exposed” treatment (thin snow cover). The treatments simulated the soil temperature conditions of a local mountain birch forest and heath site, respectively. During June and July, the relative growth rate (RG) and nitrogen accumulation rate (RN) in the exposed treatment were lower compared to the protected treatment. In addition, the seedlings of the exposed treatment allocated a greater proportion of biomass to roots compared to the protected treatment. Thus, leaf growth was reduced in the exposed compared to the protected treatment. We concluded that lower winter temperature in soils can result in stronger root injury that stimulates the growth of replacement roots and reduces nutrient uptake capacity and growth rate during summer. In concert with other possible factors causing root disruption during winter, e.g., frequent freeze-thaw cycles, the mechanism identified here might be important for survival of tree seedlings in subarctic and alpine areas, especially near treelines. The implications are discussed specifically for mountain birch seedling growth and survival in treeless subarctic heath sites and above treelines in northern Europe.

Changes in microclimate induced by experimental warming and clipping in tallgrass prairie

AbstractIn order to facilitate interpretation and comparison of warming effects on ecosystems across various habitats, it is imperative to quantify changes in microclimate induced by warming facilities. This paper reports observed changes in air temperature, soil temperature and soil‐moisture content under experimental warming and clipping in a tallgrass prairie in the Great Plains, USA. We used a factorial design with warming as the primary factor nested with clipping as the secondary factor. Infrared heater was used in order to simulate climatic warming and clipping to mimic mowing for hay or grazing. The warming treatment significantly increased daily mean and minimum air temperatures by 1.1 and 2.3 °C, respectively, but had no effect on daily maximum air temperature, resulting in reduced diurnal air‐temperature range. Infrared heaters substantially increased daily maximum (2.5 and 3.5 °C), mean (2.0 and 2.6 °C) and minimum (1.8 and 2.1 °C) soil temperatures in both the unclipped and clipped subplots. Clipping also significantly increased daily maximum (3.4 and 4.3 °C) and mean (0.6 and 1.2 °C) soil temperatures, but decreased daily minimum soil temperature (1.0 and 0.6 °C in the control and warmed plots, respectively). Daily maximum, mean and minimum soil temperatures in the clipped, warmed subplots were 6.8, 3.2 and 1.1 °C higher than those in the unclipped, control subplots. Infrared heaters caused a reduction of 11.0% in soil moisture in the clipped subplots, but not in the unclipped subplots. Clipping reduced soil‐moisture content by 17.7 and 22.7% in the control and warmed plots, respectively. Experimental warming and clipping interacted to exacerbate soil‐moisture loss (26.7%). Overall, infrared heaters simulated climate warming well by enhancing downward infrared radiation and by reducing the diurnal air‐temperature range.

Soil carbon dioxide fluxes in northern semiarid grasslands

The high indigenous soil organic carbon content, root biomass, and microbial populations in prairie soils provide a source of carbon dioxide (CO 2) that is important in the carbon budget of grasslands. Soil chambers were used to measure soil CO 2 flux from a grazed mixed-grass prairie (GP), nongrazed mixed-grass prairie (NGP), and grazed western wheatgrass (WWG) [ Pascopyrum smithii (Rybd) Löve] grasslands in the Northern Great Plains, USA. Objectives were to quantify soil CO 2 fluxes for each site and to determine the contribution of soil temperature, soil water content, and air temperature to soil CO 2 flux. Soil CO 2 fluxes were measured on each site about every 21 d at 13:00 h during the 25 April–27 October growing period from 1996 to 2000 for NGP and GP and from 1996 to 1998 for WWG. Dormant period fluxes were measured on the GP from 28 October to 26 April from 1999 to 2001. In addition, five sequential daytime measurements were made on each site for 3 days each year. Fluxes were low in the spring and autumn and peaked concurrent with biomass in late June to mid-July. Maximum fluxes for these dissimilar managed grasslands averaged 5.8 g CO 2-C m −2 d −1 for NGP, 6.9 g CO 2-C m −2 d −1 for GP, and 6.1 g CO 2-C m −2 d −1 for WWG. Soil fluxes measured during the dormant period decreased to near zero during the months of December, January, and February and then increased rapidly in March as soil temperatures increased. Daily soil flux during the growing period averaged 3.5 g CO 2-C m −2 d −1 for NGP, 4.3 g CO 2-C m −2 d −1 for GP, and 4.0 g CO 2-C m −2 d −1 for WWG. Dormant period fluxes for the GP averaged 0.5 g CO 2-C m −2 d −1. Regression analysis indicated that soil temperature accounted for 65%, soil water content 5%, and air temperature 3% of flux variability. Growing period soil CO 2 flux over years averaged 728 g CO 2-C m −2 and dormant period CO 2 flux averaged 86 g CO 2-C m −2. A predictive relationship describing the response of soil CO 2 flux to changes in soil temperature was developed using the minimum, maximum, and optimum soil temperatures for soil CO 2 flux. The model provides an estimate of the important dormant period soil flux component in annual ecosystem carbon budgets.

Modeling Temperature-Dependent Range Limits for the Fire AntSolenopsis invicta(Hymenoptera: Formicidae) in the United States

Abstract We predict the future range of the fire ant Solenopsis invicta Buren within the United States based on climate and its current extreme distributions. To reach that goal, a dynamic model of colony growth with two time steps per day was formulated that operates by colony area, S, and alate production, a. Colony growth rate depended on daily maximum and minimum soil temperatures. Temperature records at 4,537 meteorological stations within the current (near 1.5 million km2) and potential range of S. invicta were obtained from NOAA’s National Climatic Data Center. At each station, a colony was allowed to grow and lifetime female alate production was calculated. Estimated alate production was then examined at current extremes of the fire ant distribution at selected locations in Arkansas, Tennessee, and Oklahoma. Estimates from these locations were used to define four zones of colony proliferation success: certain, possible, undemonstrated, and improbable. An annual precipitation limit (510 mm) was sel...

The impact of forest structure on near-ground temperatures during two years of contrasting temperature extremes

The thermal environment of clear-cut, partially cut, and uncut forest sites in northern Wisconsin are examined for a warm year and a cool year. Temperatures at 0.5 m above and 0.05 m below ground, as well as base 5°C heat sums are computed for each site between May and September and differences between cut and uncut sites compared for the 2 years. Differences in average and minimum air temperature and soil temperature are less than instrumental error, ε=0.3°C. Maximum air temperature differences between the clear-cut and uncut sites drop from 5.7°C in the cool year to 4.7°C in the warm year, while the difference for the partial cut drops from 3.2 to 2.7°C. The results suggest that studies of tree growth or forest development and climate change should consider the effects of forest structure on changes in daily extreme temperatures.

IMPROVEMENT AND VALIDATION OF A DAILY SOIL TEMPERATURE SUBMODEL FOR FREEZING/THAWING PERIODS

The soil temperature submodel of the daily version of the CENTURY ecosystem model, DAYCENT, has been improved for freezing/thawing conditions in soils. The simulation of the soil heat propagation in the model is based on the Fourier heat flow equation and approximated by use of the explicit finite difference scheme. In our study, we propose a tipping bucket algorithm to incorporate the discontinuous freezing/thawing process in the model by means of a calculated fusion energy pool. Daily average, maximum and minimum soil temperatures for each soil layer are estimated. The soil thermal diffusivity for each soil layer is simulated by the method of De Vries using upper and lower limits as well as a correction factor. A correction factor was optimized for the tipping bucket approximation of the freezing/thawing process. The model was tested and validated at three different sites with different climates and soils and showed good agreement with measured soil temperatures during winter periods. The mean deviation for maximum soil temperatures at 10 cm depth during the winter period was less than 1 °C for all locations; for the minimum temperatures the mean deviation was slightly higher. At a depth of 20 cm, mean deviations were higher but can nevertheless be seen as showing good results for the given approximations.

Geographic Information Systems Show Impact of Field Placement on sh2 Sweet Corn Stand Establishment

The objective of this study was to ascertain if stand establishment of sh2 sweet corn (Zea mays L.) would benefit from variable planting depths determined by the use of geographic information systems (GIS). Spring and fall research plots were established in a field [80 × 20 m (262 × 66 ft)] containing Crosby silt loam and Kokomo silty clay loam soil series in Columbus, Ohio. Three sh2 sweet corn cultivars (Starship, Skyline, and Confection) were planted at three depths on the two soil types in the fall study, with an additional transition soil added in the spring. Emergence counts as well as soil moisture and temperature were monitored. In the spring, sites were also sampled for nutrient levels and soil compaction. Significant variability was found within the field with respect to soil moisture, temperature, nutrient levels, and compaction. Seedling emergence fluctuated with average soil moisture increasing in blocks with up to 24% moisture and then leveling off. Daily minimum soil temperatures impacted stand establishment. Although heat units accumulated faster on the Crosby soil, emergence was slower and less complete on these soil series than on Kokomo soil series. Further investigation determined that although temperatures of the Crosby soil were 3 to 4.5 °C (5.4 to 8.1 °F) warmer during the day than the Kokomo soil, temperatures on the Crosby soil averaged 2 °C (3.6 °F) cooler at night. Analysis of emergence patterns and field variability was performed on ArcView mapping software. Although `Skyline' planted at 2 cm (0.8 inches) had the best emergence overall, final stand would have been increased with `Skyline' planted variably at 2 and 4 cm (1.6 inches). Mapping the field under these different scenarios showed that although area with less than 70% stand would exist with a 2-cm uniform planting depth, the entire field would have a stand of 70% or greater with variable planting depth using a high vigor seedlot.

Temperatures of Hibernacula and Changes in Body Composition of Arctic Ground Squirrels over Winter

Soil temperatures near hibernacula of free-living arctic ground squirrels (Spermophilus parryii) were recorded over 3 winters (October–April 1993–1996) at Toolik Lake, Alaska. Means and minima of soil temperature at 20 burrows averaged −8.9 and −18.8°C, respectively. Soil temperatures were <−3°C for, on average, >5 months, which represented the duration of winter that hibernating arctic ground squirrels were actively thermogenic. Individual burrows did not differ significantly in mean soil temperature over 3 years, but significant differences in mean and minimum soil temperatures were observed among burrows. Sites of burrows with shrubby vegetation accumulated more snow and had significantly higher soil temperatures over winter than windswept sites in non-shrubby vegetation. Female ground squirrels hibernated in burrows that had significantly higher mean and minimum soil temperatures than burrows of males, and adults hibernated in burrows with significantly higher soil temperatures than burrows of juveniles. Although ground squirrels occupying colder burrows were predicted to lose more body mass during hibernation than those in warmer burrows, changes in body, fat, and lean masses over winter were not correlated with soil temperature for any sex or age. Relationships between change in body composition of hibernating arctic ground squirrels and temperatures of their hibernacula may be confounded by use of food caches, differing thermal conductance of nests, or differences in individual's energetics of hibernating not related to the gradient between body and soil temperatures.