Soil Heat Flow Research Articles

A sigmoidal model for predicting soil thermal conductivity-water content function in room temperature

Apparent thermal conductivity of soil (λ) as a function of soil water content (θ), i.e., λ(θ) is needed to determine the heat flow in soil. The function of λ(θ) can be used in heat and water flow models for simplicity. The objective of this study was to develop a sigmoidal model based on logistic equation for entire range of soil water contents and a wide range of soil textures that can be used in simulation of heat and water flow in respected modes. Further, performance of the developed sigmoidal model along with two other models in literature was evaluated. In the proposed sigmoidal model, the constants of this model are estimated based on empirical multivariate equations by using soil sand content and bulk density. The sigmoidal model was validated with good accuracy for a wide range of soil textures, as the relationship between the measured and predicted λ showed slope and intercept values of nearly 1.0 and 0.0, respectively. Comparison of the results obtained by sigmoidal model with those obtained from Johansen and Lu et al. models indicated that, the sigmoidal model was superior to the other two models in prediction of λ for a wide range of soil textures and soil water contents. Furthermore, comparison with a recently proposed model by Xiong et al. indicated that our sigmoidal model is superior. Therefore, our developed sigmoidal model can be used in heat and water flow models to predict the soil temperature and heat flow.

Analysis and simulation of ecological environment response of ground source heat pump system under thermal equilibrium

This work is designed to study the thermodynamic equations of groundwater source heat pump in hot summer and cold winter, and to determine the optimal operating conditions of groundwater source heat pump by means of the thermodynamic analysis of source heat pump, flow, unit, pump power, evaporation side and condensation side. Practice has proved that the equipment runs stably and with high efficiency. By comparison, the ground source heat exchangers were compared with conventional chillers and boiler. The results showed that the underground heat pump had higher energy consumption, lower primary energy consumption, reduced CO2 emissions, and reduced environmental pollution during operation, proving that the underground heat pump had obvious advantages over the conventional cooling and heating system. Meanwhile, this also shows that the long-term operation of ground heating system has caused the instability of ground heating system, the accumulation of cold and heat in ground-water, and the variation of ground temperature, which not only reduces the system efficiency, but it also affects the physical properties of soil itself and the soil heat flow, and will also cause changes in soil microbial environment and vegetation ecological environment, thus affecting the whole ecological environment.

Aeolian sand cover affects the soil hydrothermal state and permafrost degradation on the Qinghai-Tibet Plateau

Aeolian sand significantly affects permafrost degradation, but the effect of the aeolian sand on the permafrost on the Qinghai-Tibet Plateau remains unknown. The sand layer thickness is critical to its role. However, little quantitative research has been conducted on the effect of the sand layer thickness on its role. In this study, using CoupModel, we investigated the differences in the impact of the aeolian sand cover on the hydrothermal state of permafrost with 20 different sand layer thicknesses (10 ∼ 200 cm, 10 cm increment) and analyzed the mechanisms that explain the different impacts. The results reveal that the active layer is where the aeolian sand has the most impact on the permafrost. The aeolian sand layer accumulates precipitation into the soil below the sand, thereby significantly drying the shallow soil layer of the current stratum. Moreover, the thicker the sand layer, the more water accumulates in the underlying soil layer. In the middle-upper active layer, the initial soil heat storage, soil heat flow interception, and liquid water and ice contents govern the soil temperatures that increase in cold seasons and decrease in warm seasons as the sand layer thickens. Near the bottom of the active layer, the initial soil heat storage and soil heat flow interception control the soil temperatures that increase in cold seasons but fluctuate between sand layer thicknesses of 50 cm, 70 cm, and 120 cm in warm seasons as the sand layer thickens. Permafrost degradation is enhanced by sand layers thinner than 150 cm and retarded by sand layers thicker than 150 cm, respectively. The thermal state, soil properties, and accumulation process of the aeolian sand also contribute to this effect of the aeolian sand on the permafrost. In the plateau aeolian deserts, the sparse vegetation promotes permafrost degradation and the thinner seasonal snow cover protects permafrost. Moreover, under the different climate during the geological history period, the island or discontinuous permafrost might be formed due to the pluvial-radiation talik caused by the thicker sand layer or dunes.

Effect of Long-Term Semiarid Pasture Management on Soil Hydraulic and Thermal Properties

Semiarid pasture management strategies can affect soil hydraulic and thermal properties that determine water fluxes and storage, and heat flow in unsaturated soils. We evaluated long-term (>10 years) perennial and annual semiarid pasture system effects on saturated hydraulic conductivity (ks), soil water retention curves (SWRCs), soil water thresholds (i.e., volumetric water content (θv) at saturation, field capacity (FC), and permanent wilting point (PWP); plant available water (PAW)), thermal conductivity (λ), and diffusivity (Dt) within the 0-20 cm soil depth. Forage systems included: Old World bluestem (Bothriochloa bladhii) + legumes (predominantly alfalfa (Medicago sativa)) (OWB-legume), native grass-mix (native), alfalfa + tall wheatgrass (Thinopyrum ponticum) (alfalfa-TW), and annual grass-mix (annual) pastures on a clay loam soil; and native, teff (Eragrostis tef), OWB-grazed, and OWB-ungrazed pastures on a sandy clay loam soil. The perennial OWB-legume and native pastures had increased soil organic matter (SOM) and reduced bulk density (ρb), improving ks, soil water thresholds, λ, and Dt, compared to annual teff and alfalfa-TW (P < 0.05). Soil λ, but not Dt, increased with increasing θv. Grazed pastures decreased ks and water retention compared to other treatments (P < 0.05), yet did not affect λ and Dt (P > 0.05), likely due to higher ρb and contact between particles. Greater λ and Dt at saturation and PWP in perennial versus annual pastures may be attributed to differing SOM and ρb, and some a priori differences in soil texture. Overall, our results suggest that perennial pasture systems are more beneficial than annual systems for soil water storage and heat movement in semiarid regions.

Heat Capacity of Drained Peat Soils

Soil-specific heat capacity (cp) and volumetric heat capacity (Cv) are recognized as a fundamental soil property essential for the accurate prediction of soil temperature and heat flow. This study presents the analysis of these thermal properties for drained peat soils in Poland. The objectives of this study were to (i) measure and develop a method for determining cp, (ii) analyze the (Cv) data for undisturbed soil samples from surface layers, and (iii) test the applicability of the cp value for calculating Cv of drained peat soils using the mixing model concept. The cp value was measured under laboratory conditions using a modulated differential scanning calorimetry (MDSC) for 18 soil layers sampled in six degraded peat soil profiles. The Cv was estimated for undisturbed triplicate soil samples from the 22 depths (66 samples) by using a dual-needle probe. The cp data for the organic soils were linearly temperature-dependent (MDSC) for the temperature range considered (−20–30 °C). The overall average cp value was equal to 1.202 J g−1 K−1 at a temperature of 0 °C. An increment in temperature of 1 °C corresponded to an increase in cp of 0.0043 J g−1 K−1 on average. Nevertheless, the lowest cp value was obtained for moss samples whereas the highest value represents alder peats. The Cv data measured using the heat thermal probe (HTP) method changed linearly with changes in the soil moisture content (θv) of the moorsh soils. The volumetric heat capacity calculated using the mixing model was comparable to the mean of measured values obtained on the triplicate samples.

Simulation of Soil Water and Heat Flow under Plastic Mulching and Different Ridge Patterns

The ridge–furrow mulching system with plastic film (RFMS) has been widely used in semi-arid areas in order to improve soil water and heat conditions, crop yields and water use efficiency. It is of practical significance to study the effect of mulching and ridge types on soil water and heat in order to optimize mulching measures and improve the effectiveness of the ridge and furrow system. To clarify the combined effect of soil water and heat beneath the system and the influence of ridge morphology on it, field experiments were conducted with three treatments, including conventional planting in bare land (CK), a ridge–furrow (wide ridge with 70 cm width and 10 cm height, narrow ridge with 40 cm width and 15 cm height) mulching system with complete plastic film (RFWN) and a ridge–furrow (equal ridge with 55 cm width and 15 cm height) mulching system with complete plastic film (RFE). An insufficient irrigation system was adopted and the two-dimensional numerical software HYDRUS-2D was used to simulate the soil water and heat flow under the experimental conditions. The model was calibrated and verified according to test data for the period of 2018 to 2019, which showed good agreement between the simulated and measured values. The simulation results revealed that the ground temperatures of RFWN and RFE were much higher than that of CK, and the average value of 0–25 cm during the growth period could increase by 2.29–4.61%. Compared with CK, RFWN and RFE reduced soil evaporation (84.71–93.73%) and field evapotranspiration (12.02–21.75%), while they increased root water uptake (25.87–40.98%) and T/ET (48.85–80.15%). Plastic film mulching and ridge morphologies affected the infiltration range and the direction of soil water movement, increased soil moisture when there was no rainfall or irrigation and reduced soil water and heat fluctuations, which was more conducive to crop growth, especially under the RFWN system. The simulation method proposed in this paper is an effective technique for calculating the soil water and heat dynamics under different ridge and furrow sections under the condition of film mulching, and it can be used for the optimal management of soil water and heat in this area.

Aluviyal Depositler Üzerinde Oluşmuş Genç ve Gelişmekte Olan Toprakların Isı Akışı ve Isı Miktarının İncelenmesi

Toprak horizonlarındaki ısı akışı ve ısı miktarı, çeşitli toprak ordolarının pedogenik süreçlerine, toprakta biriken potansiyel enerji değişimine, enerji bilançosunun oluşumuna, diğer faktörlerle beraber önemli düzeyde etki yapan temel termo-fiziksel parametrelerdendir. Bu araştırmanın amacı, yarı humid ekolojik koşullar altında ve aluviyal depositler üzerinde oluşmuş genç (Entisol) ve gelişmekte olan (Inceptisol) toprakların profillerinde ölçülen sıcaklık değerlerine bağlı olarak, ısı akışının ve ısı miktarının belirlenmesidir. Inceptisol toprakların genetik horizon gelişimine bağlı olarak Entisol topraklarla karşılaştırıldığında, ısı akışı ve ısı miktarının daha yüksek olduğu belirlenmiştir. Inceptisol ordosuna ait Vertic Haplustept ve Typic Haplustept toprak profillerinde ısı akışı ve ısı miktarı sırasıyla 13.221-50.035 watt m-2 ve 2.285∙106-8.646∙106 J m-2; 7.757-29.284 watt m-2 ve 1.340∙106-5.060∙106 J m-2 aralıklarında değişmektedir. Entisol ordusunun ait topraklarda (Typic Ustifluvent, Mollic Ustifluvent-1, Mollic Ustifluvent-2) ise ısı akışının 8.958-34.300 watt m-2, ısı miktarının 1.548∙106-5.927∙106 J m-2 aralığında değiştiği tespit edilmiştir. Ayrıca, her iki ordoya ait topraklarda derinlik artışına bağlı olarak ısı akışı ve ısı miktarı azalmıştır. Meydana gelen bu değişimin, ordolara ait horizonlardaki kil, ve organik madde miktarları ile toprakların hacim ağırlıklarındaki farklılıkların ısı akışı ve ısı miktarı üzerinde önemli düzeyde etkilemesinden ileri geldiği düşünülmektedir. Ayrıca, herhangi zaman aralığında sıcaklık farkının değişimi; hacimsel ısı kapasitesi, ısısal yayınım ve ısı iletkenliği arasındaki karşılıklı etkileşim horizonlardaki ısı akışı ve ısı miktarını önemli düzeyde etkilemektedir.

Two-dimensional numerical simulations of soil-water and heat flow in a rainfed soybean field under plastic mulching

Abstract Numerical simulation can help understanding water- and heat-flow systems through plastic-mulched soils. An effective simulation approach is crucial to know the role of plastic mulch in a soil ecosystem, which can save water in agriculture. A field experiment was conducted at Gifu University in a rainfed soybean cultivation under plastic mulch and bare soil treatments to clarify the soil water and heat flow mechanism. Furthermore, the two-dimensional numerical software HYDRSUS-2D model with different boundaries at the soil surface was used to simulate water and heat flows. Firstly, soil hydraulic parameters were estimated by inverse solution using laboratory-measured data and then coupled soil-water and heat flows were simulated by optimizing soil thermal parameters by inverse solution. The HYDRUS-2D model simulated water and heat flow through the root zone depths satisfactorily. The root-mean square error (RMSE) was 0.015–0.030, and 0.046–0.055 cm3 cm−3 for the plastic mulch, and bare soil, respectively, in estimating soil moisture and 0.66–1.28, and 0.70–1.54 °C, respectively in estimating soil temperature. Water infiltration was 61% lower in the plastic-mulched soil, which reduced soil evaporation as well as soil-moisture storage changes compared to bare soil. This study can be applied to design and manage different plastic mulching patterns in rain-fed crop cultivation.

The challenges of an in situ validation of a nonequilibrium model of soil heat and moisture dynamics during fires

Abstract. With the increasing frequency and severity of fire, there is an increasing desire to better manage fuels and minimize, as much as possible, the impacts of fire on soils and other natural resources. Piling and/or burning slash is one method of managing fuels and reducing the risk and consequences of wildfire, but the repercussions to the soil, although very localized, can be significant and often irreversible. In an effort to provide a tool to better understand the impact of fire on soils, this study outlines the improvements to and the in situ validation of a nonequilibrium model for simulating the coupled interactions and transport of heat, moisture and water vapor during fires. Improvements to the model eliminate the following two important (but heretofore universally overlooked) inconsistencies: one that describes the relationship between evaporation and condensation in the parameterization of the nonequilibrium vapor source term, and the other that is the incorrect use of the apparent thermal conductivity in the soil heat flow equation. The first of these made a small enhancement in the stability and performance of the model. The second is an important improvement in the physics underpinning the model but had less of an impact on the model's performance and stability than the first. This study also (a) develops a general heating function that describes the energy input to the soil surface by the fire and (b) discusses the complexities and difficulties of formulating the upper boundary condition from a surface energy balance approach. The model validation uses (in situ temperature, soil moisture and heat flux) data obtained in a 2004 experimental slash pile burn. Important temperature-dependent corrections to the instruments used for measuring soil heat flux and moisture are also discussed and assessed. Despite any possible ambiguities in the calibration of the sensors or the simplicity of the parameterization of the surface heating function, the difficulties and complexities of formulating the upper boundary condition and the obvious complexities of the dynamic response of the soil's temperature and heat flux, the model produced at least a very credible, if not surprisingly good, simulation of the observed data. This study then continues with a discussion and sensitivity analysis of some important feedbacks (some of which are well known and others that are more hypothetical) that are not included in the present (or any extant) model, but that undoubtedly are dynamically influencing the physical properties of the soil in situ during the fire and, thereby, modulating the behavior of the soil temperature and moisture. This paper concludes with a list of possible future observational and modeling studies and how they would advance the research and findings discussed here.

Yarı Humid Ekolojik Koşullar Altında Oluşmuş Bazı Vertisol Alt Grup Toprakların Profillerinde Isı Akışının Belirlenmesi

The evaluation of heat flow in soil is necessary for the management of soil temperature regime, determining the amount of heat stored in soil, and modeling soil temperature. In this study, the volumetric heat capacity values calculated for horizons of different soil profiles (Typic Calciustert, Chromic Hapluster, Typic Haplustert) belong to Vertisol order varied between 2.173∙106 J m-3 oC-1 and 2.307∙106 J m-3 oC-1, and the thermal conductivity coefficient values varied between 12.412watt m-1 oC-1 and 21.404 watt m-1 oC-1. The volumetric heat capacity changed in a narrow range due to small variation in bulk density and volumetric moisture content values in soil horizons. Heat flow values were determined as 43.892 watt m-2, 26.424 watt m-2, 10.284 watt m-2 in Ap, Bss 2C horizons of Typical Calciustert profile; 43,910 watt m-2, 22,665 watt m-2, 7,629 watt m-2 in A, Bss1, Bss2 horizons of Chromic Hapluster profile and 35.958 watt m-2, 14.770 watt m-2, 7.530 watt m-2 in Ap, Bss1, Bss2 horizons of Typic Haplustert profile, respectively. The positive difference between the average and the maximum temperature values in the horizons causes downward heat flow in the soil profiles. Although the heat diffusivity coefficients increased towards the lower horizons of soils, it was determined that the heat flow values decreased. Increase in the total porosity due to increase in clay accumulation causes to decreases in volumetric heat capacity and heat flow values.

Evapotranspiração de canaviais em diferentes fases fenológicas por sensoriamento remoto no vale do submédio do São Francisco.

The study aimed to estimate the reference evapotranspiration of sugarcane using the Priestley-Taylor method, comparing with the standard Penman-Monteith-FAO 56 method in the region of the São Francisco Submiddle Valley in the period from 2013 to 2016. Images of the Landsat-8 satellite of the OLI and TIRS sensors acquired from the North American space Agency (NASA) and meteorological data from the Instituto Nacional de Pesquisas Espaciais (INPE) were used, along with the Sistema de Organização Nacional de Dados Ambientais (SONDA) and the Instituto Nacional de Pesquisas Espaciais (INMET). The instantaneous radiation balance, soil heat flow, latent heat flow, crop coefficient (Kc) and Priestley-Taylor coefficient were estimated to obtain the reference evapotranspiration, which ranged from 0.00 to 3.65 mm d-1. The validation proceeded through the correlation between method of crop coefficient applied for Priestley-Taylor and Penman-Monteith. The value of R² 0.75, Pearson coefficient (R) 0.88 (strong correlation) and the mean error found in 1.81 mm d-1 were considered satisfactory. The Priestley-Taylor method was able to estimate the reference evapotranspiration in sugarcane production areas in the region of the São Francisco Submiddle Valley in a satisfactory way.

Measuring dynamic changes of soil porosity during compaction

Soil porosity and pore-size distribution changes in response to compaction are important for heat, water, and air flow in soils. In this study, we used the thermo-time domain reflectometry (thermo-TDR) technique to investigate dynamics of in-situ soil porosity and pore-size distribution as affected by number of traffic passes, water content and soil depth. The study was conducted at a field site located near Clayton, NC, USA. A roller was dragged across the length of a 3- by 12-m plot three to five times to repeatedly compact the soil after tillage. Nine thermo-TDR probes, installed at 2.5-, 7.5-, and 12.5-cm depths (representing 0–5, 5–10, and 10–15 cm depth intervals, respectively) at three locations within the plot, were used to determine dynamic changes in soil porosity after each compaction event. Pore-size distribution changes within the top soil layer were determined for a subset of conditions by measuring in-situ infiltration at low tension using a mini disk infiltrometer. Nine core samples were also collected (considered to be a destructive method) near each thermo-TDR probe for measuring total porosity and water content after each compaction. Results showed that the thermo-TDR technique can accurately monitor the change of soil porosity during soil compaction compared to the destructive core method. Variability of replicated soil porosity measurements by the thermo-TDR technique (with a root mean square error (RMSE) of 0.011 m3 m−3 and mean standard error (MSE) of 0.010 m3 m−3) was lower than that of the core method (RMSE = 0.017 m3 m−3, MSE = 0.019 m3 m−3). As expected, total soil porosity decreased with the number of passes; a major portion of compaction (59–89% of the total porosity decrease) occurred during the first pass. The trend of topsoil (0–5 cm) compaction differed from that of subsoil layers (5–10 and 10–15 cm). Changes in porosity were highly sensitive to soil water content. For the sandy-textured soil in this study, soil porosity decreased as water content increased (during compaction period), and the maximum compaction (associated with the lowest porosity) was reached at an initial water content range between 0.08 and 0.10 g g-1. Above this range, the compaction level decreased with increasing water content. In addition, there was a shift in pore-size distribution for the surface layer. More importantly, pore-size distribution continued to change with additional traffic passes even after soil total porosity became stable.

Liquid‐Vapor‐Air Flow in the Frozen Soil

AbstractAccurate representing freeze‐thaw (FT) process is of great importance in cold region hydrology and climate studies. With the STEMMUS‐FT model (Simultaneous Transfer of Energy, Mass and Momentum in Unsaturated Soil), we investigated the coupled water and heat transfer in the variably saturated frozen soil and the mechanisms of water phase change along with both evaporation and FT process, at a typical meadow ecosystem on the Tibetan Plateau. The STEMMUS‐FT showed its capability of depicting the simultaneous movement of soil moisture and heat flow in frozen soil. The comparison of different parameterizations of soil thermal conductivity indicated that the de Vries parameterization performed better than others in reproducing the hydrothermal dynamics of frozen soils. The analysis of water/vapor fluxes indicated that both the liquid water and vapor fluxes move upward to the freezing front and highlighted the crucial role of vapor flow during soil FT cycles as it connects the water/vapor transfer beneath the freezing front and above the evaporation front. The liquid/vapor advective fluxes make a negligible contribution to the total mass transfer. Nevertheless, the interactive effect of soil ice and air can be found on the spatial and temporal variations of advective fluxes in frozen soils.

Simulation of soil water and heat flow in ridge cultivation with plastic film mulching system on the Chinese Loess Plateau

A widespread measure for improvement of soil water use efficiency (WUE) in the semi-arid region of China is ridge cultivation with plastic film mulching system. However, the modification of soil water and heat flow under this management system is not well understood. The objective of this study was to understand soil water and heat coupling processes by monitoring and modeling of soil water and temperature dynamics in this system that is commonly used on the semi-arid Chinese Loess Plateau. Four treatments were investigated: conventional fertilization (CK, control), recommended fertilization (RF), straw mulching based on RF (SM), and straw mulching in furrows plus plastic film mulching on soil ridges based on RF (FM). Based on the field monitoring results, the process-based model HYDRUS-2D was calibrated to simulate the soil hydrothermal processes for the different treatments, each represented by specific boundary conditions at the soil surface. The model simulations have a good agreement with the field observation, showed that there are significant differences in soil water contents (5%) among the four treatments, with the FM treatment having the highest water storage and the highest WUE. While soil daily mean temperature was very similar, the daily temperature fluctuations were significantly higher under the plastic film mulching compared to the other treatments. The FM treatment performed better during the cold year than a warm year, improved crop production and water resource use through reduced evaporation and elevated transpiration. The modeling approach presented here is an efficient way to clarify the mechanisms of root-zone water and temperature dynamics under mulching and/or tillage that could be adopted for optimizing soil hydrothermal management in this region.

Analysis of interaction of the soil temperature field and structures at the level of the basement of the building

The article describes an analysis of the effect of soil type on temperature field distribution at the level of family house basement. Regarding engineering calculations (heat loss calculation, designing and evaluating constructions), a simple and generally accepted method to determine the course of temperature field adjacent to basement walls is missing. The methods specified in European standards are, in terms of calculation of heat flows in soil, problematic. There is currently an insufficient number of measured values, which could be integrated in a simple calculation method. A certain option concerns continual measuring of temperatures in soil for buildings in situ. The article uses the measurements of soil temperatures in winter in pre-determined depths at the building parts in contact with soil. The measured data from a two-year period were integrated in the model on the basis of statistical evaluation. The main aim of the article is to generate an impulse to create unified outcomes of temperatures of certain soils for pre-selected depths, building structures, and parameters of indoor and outdoor environment.

Magnetic Resonance Monitoring and Numerical Modeling of Soil Moisture during Evaporation

Core Ideas Evaporative drying of soil columns was monitored in high resolution using NMR. Soil moisture data were used for validating a water, vapor, and heat flow model. The Richards approach was insufficient under Stage II conditions. NMR is a feasible technique for soil moisture measurements under Stage II conditions. Evaporation from bare soil surfaces can be restrained to a great extent with the development of a dry layer at the soil surface where capillary hydraulic conductance ceases and water flow proceeds only by gas phase transport. Model calculations and preliminary experiments with model porous media have shown that this surface layer can be very thin. An accurate characterization of these processes is required, which is provided by noninvasive magnetic resonance (MR) methods. The evaporative drying of a silt loam and a sandy loam was monitored at high spatial resolution in laboratory experiments. The MR data were used to assess the performance of two numerical models: (i) the Richards equation, which considers isothermal liquid water flow, and (ii) a coupled soil water, heat, and vapor flow numerical model. The experimental results reveal two distinct drying regimes for both soil types where, at the onset of the second evaporation stage, a dry surface zone developed with increasing thickness over time. This layer revealed that water loss inside the soil coincided with a relatively low evaporation rate as the liquid continuity to the soil surface vanished. The modeling results clearly demonstrated the need to consider heat and vapor flow. It was shown, as a proof of principle, that MR relaxation time spectra may serve as a proxy to follow desaturation processes where spatially resolved transverse relaxation can reveal a secondary evaporation front.

Biochar and Soil Heat and Water Flow

Biochar and Soil Heat and Water Flow

Numerical and experimental study of heat and mass transfers in an Almería-type greenhouse

The present work analyses the effect of natural ventilation in the energy balance of an Almeria-type greenhouse by means of both experimental measurements and numerical modelling. We have observed a great influence of the ventilation heat flux is seen to have a great influence on the greenhouse energy balance, accounting for 30-50% of the inside solar radiation. Inside air temperature and humidity measurements were taken at 12 locations, while crop temperature, photosynthesis, evapotranspiration and stomata resistance were recorded with a portable photosynthesis system. Soil temperature was taken at 1, 10 and 20 cm depth, and soil heat flow at 20 cm depth; solar and photosynthetically active radiations were also measured. Ten 2D and two 3D sonic anemometers were used to measure the airflow through the 4 greenhouse openings. The results indicate that cool outside air enters through the two side openings while warmer air exits through the two roof vents. The low ventilation surface area (5%) allows air renewal rates of less than 20 h-1 for winds speed of 4 m s-1. These reduced ventilation rates produce inside-outside temperature gradients of up to 12°C at midday, when solar radiation is high (800 W m-2). On cloudy days, with radiation around 500 W m-2 and strong winds (7 m s-1), the ventilation system allows air exchange rates of up to 35 h-1, reducing the temperature gradient to appropriate values of 5-6°C. Plant temperatures were 2-10°C higher than the air temperature. The dynamic energy balance model predicts accurately the inside temperature using the outside climatic variables (solar radiation, air temperature and humidity, wind speed and direction) and greenhouse cover, ventilation system, crop and soil characteristic parameters as input.

Importance of soil heating, liquid water loss, and vapor flow enhancement for evaporation

Field measurements conducted by Cahill and Parlange [1998] are reanalyzed to verify if their conclusion that daytime peak values of 60–70 W m−2 of latent heat flux divergence occurred in the 7–10 cm soil layer of a drying Yolo silt loam when maximum values of surface latent heat flux are estimated to have been about 100 W m−2. The new analyses, as similar to theirs as possible, are validated using a numerical simulation of coupled soil moisture and heat flow based on Philip and de Vries [1957] as a test bed. The numerical simulation is extended to include the flow of air induced by diurnal soil heating and evaporative water loss to verify the flux divergence calculations reported in Parlange et al. [1998] that explained the findings of Cahill and Parlange [1998]. It is shown that the conclusions of both of these papers are in error, so that the original version of the Philip and de Vries [1957] theory is consistent with their field measurements after all and the effects of air flow associated with soil heating and liquid water loss (and low frequency barometric pressure variations also considered) are negligible in practice. In an additional investigation enhancement of diffusive vapor flow (first postulated by Philip and de Vries [1957]) and discussed extensively in the literature since is shown to have negligible effects on cumulative evaporation under field conditions. This article is protected by copyright. All rights reserved.

Sazonalidade do Balanço de Energia e Evapotranspiração em Área Arbustiva Alagável no Pantanal Mato-Grossense

Resumo O Pantanal apresenta períodos de inundação que modelam a paisagem e atuam como filtro ao estabelecimento e desenvolvimento de plantas. Perturbações antrópicas ou naturais podem alterar a distribuição da energia disponível no ecossistema. Diante da necessidade de compreensão da variabilidade temporal do balanço de energia em paisagens naturais inundáveis, o objetivo deste estudo foi analisar a sazonalidade do balanço de energia em área arbustiva alagável composta por Combretum lanceolatum Pohl no Pantanal Mato-grossense. As estimativas do fluxo de calor latente (LE) e sensível (H), e da evapotranspiração (ET) foram obtidas pelo método da razão de Bowen entre maio de 2012 e abril de 2013. A energia disponível foi destinada prioritariamente ao LE (64,1%), seguido ao H (35,8%) e quase zero ao fluxo de calor no solo (0,1%). Os componentes do balanço de energia apresentaram forte sazonalidade, com maior LE durante a estação chuvosa e maior H durante a estação seca. A evapotranspiração foi menor durante a estação seca devido ao baixo conteúdo de água no solo e transpiração da vegetação dominante na área de estudo. Os resultados obtidos nesse trabalho sugerem que o ambiente estudado é limitado pela disponibilidade de energia e água.