Night Frosts Research Articles

Influence of Frost Protection Windmachine with Continuous Oscillation on Microclimate in Tea Fields

To verify the influence of frost protection windmachine with continuous oscillation on microclimate, the experimental study was conducted in a tea field in Zhenjiang, China on a typical radiation frost night. Disturbed airflow variation and protection effect were investigated. Airflow velocity of 8 points at different distance from the machine was measured during an oscillation period with an anemometer, and temperature variation of 48 points at different distance from the machine and different height above the ground was measured with temperature recorders. The changes of airflow velocity and temperature were analyzed. Where the velocity was high, the airflow-disturbed duration was as well as large. Airflow velocity at each point presented a trend of rise, fluctuation, and decline under the action of windmachine with continuous oscillation. The temperature rise with the same distance from the machine was close, among which the 10 m and 20 m away from the machine increased greatly. Disturbed airflow enlarged the temperature difference between the top and the bottom of the canopy. The windmachine with continuous oscillation is proved to be effective for tea frost protection and provides more coverage than traditional anti-frost fan with flabellate oscillation.

Inorganic composition and occult deposition of frost collected under severe polluted area in winter in the North China Plain

Frost as a kind of deposition plays an important role in the removal of atmospheric compounds. However, studies concerning frost in the atmospheric environment were rare although chemical composition in frost samples might be affected by the surrounding atmospheric environment. In this study, a total of 35 frost samples were collected by means of a homemade glass-plate frost condenser under severe polluted condition in the North China Plain (NCP) from Dec. 4, 2018 to Mar. 2, 2019. The pH values and water-soluble ions (WSI) were conducted. The extremely high concentrations of WSI were found, which reflected the severe pollution significantly affecting the level of chemical composition in frost. The major ions were Ca2+, SO42− and HCO3− with averaged concentrations of 1242, 1143, 1076 μeq L−1, respectively. These ions were at least one order of magnitude higher than the previous frost studies. HCO3− was one of the most abundant components in frost. Its high proportion contributed to the ionic balance and led to the alkaline characteristic of frost. SO42− had the almost doubled ratio in frost compared with the concurrent PM2.5 samples. Different from the huge diversity of chemical components in PM2.5, the frost had similar ratio of WSI under great variety of PM2.5 concentrations. It proved that PM2.5 had less effect on the ratio of WSI in frost. Nutrient ions of NH4+, NO3− and K+ accounted for 13.9%, 5.4% and 1.6% of the total averaged concentrations, respectively. On average, per square meter soil would receive 563 μg nitrogen and 123 μg potassium nutrient during a frost night. High occult deposition flux of ions indicated the strong scavenging effect from the frost event. In addition, the occult deposition flux of SO42− was comparable to the dry deposition flux, further emphasizing frost process as a non-negligible atmospheric removal pathway of SO42−.

Humidity observations and column simulations for a warm period at the Mars Phoenix lander site: Constraining the adsorptive properties of regolith

Two recalibrated sets of Phoenix (PHX) near-surface TECP air humidity measurements were compared with results from adsorptive single column model simulations during a warm clear-sky polar midsummer period, PHX sols 50–60. The model's 2 m temperatures were close to the observed values. Relative humidity (RH) is very low during the day but at night RH at 2 m reaches nearly 100% by the Zent et al. (2016) recalibration (Z), and 60–70% by the Fischer et al. (2019) recalibration (F). Model values of RH2m are close to Z and F at night and to F during the day. All three imply low water vapor pressures near the surface at night, 0.03–0.05 Pa, with a rapid increase each morning to 0.3–1 Pa and a decrease in the evening by both F and the model simulation. The model's daily adsorbed and desorbed water is in balance for regolith porosity of 16% (instead of 35% for lower latitudes). The depleted layer of nighttime air moisture extends to only about 200 m above the surface; hence the model's precipitable water content stays around the observed ~30 μm throughout the sol. The model's moisture cycle is not sensitive to tortuosity of the regolith but the in-pore molecular diffusivity should be at least 5 cm2/s for fair agreement with the observations. In the adsorption experiments there is no fog and just a hint of ground frost, as observed during this period. Strong night frosts appear if adsorption is made weak or absent in the model.

Towards a physics-based understanding of fruit frost protection using wind machines

Wind machines are used in the agricultural sector to prevent or mitigate the adverse effects of night frost in spring. In this study we aim to quantify the impact of wind machine operation on the local temperature field in an orchard. To this end, a field experiment is conducted and experimental analysis is combined with numerical simulation studies in order to assess the functional relations between wind machine performance and the dominating physical processes occurring during radiative frost events.Experimental observations showed that the temperature response strongly depends on the radial distance to the fan and the height above the surface. In agreement with previous studies, the wind machine was able to achieve rotation-averaged temperature increases of up to 50% of the inversion strength ( ≈ 3 K) in an area of 3–5 ha at 1 m height. Furthermore, it was observed that even weak ambient winds (<1 m/s) already may cause strong upwind-downwind asymmetries in the protected area, the downwind area being larger.The numerical model, inspired by the field experiment, showed similar spatial temperature responses as compared to observations. Interestingly, it was found that slower rotation times of the wind machine (3 to 6 min) lead to a significant increase of affected area, while the temperature enhancement itself stayed relatively constant. Variation of the horizontal tilt angle showed that, in our model, temperature enhancement was maximized between 8∘ and 16∘. This nearly horizontal flow already facilitates efficient vertical mixing of momentum and heat, presumably due to generation of shear instabilities at the lower edge of the jet. Finally, like in the observations also the numerical result showed strong upwind-downwind asymmetry in the affected area due to background wind.

Artificial Radiation Frost Chamber for Frost Formation on Tea

The Yangtze River region is the main production area for famous, high-quality tea in China. Radiation frost frequently occurs in this region, especially in the early spring during calm and clear nights, and it causes substantial damage to crops, which leads to huge economic losses for tea growers. The formation of frost is difficult to experimentally control due to the complexity and variability of the agro-micrometeorological environment. The objective of this study was to evaluate an artificial radiation frost chamber based on the temperature difference between leaf and air dew point, which was designed for advanced frost-related research. Micro-meteorological data and the frost formation process were monitored in an experimental tea field during typical radiation frost nights to mimic declining temperatures that are consistent with nature. The radiation frost chamber model and main parameters were determined by theoretical calculations and computational fluid dynamics (CFD) simulation. A frost-forming experiment was conducted to evaluate the performance of the frost chamber. The observation results showed that the greatest temperature difference between leaf and air dew point (Tdiffer) was −2.3 °C. The simulation results showed that the desublimation cooling rate of the air vapor was greater than sublimation, and the Tdiffer should be greater than −3.2 °C, which could cause frost to easily form on the leaf. The performance testing results showed that leaf temperature slowly declined after a rapid decrease, which is similar to the natural condition, which results in noticeable frost formation on the leaf.

Low temperatures at higher elevations require plants to exhibit increased freezing resistance throughout the summer months

The frequency and severity of night frosts increase during the summer in the alpine environment as elevation increases. Intra-specific, temporal, and elevational variability in the freezing resistance (FR) of alpine plants during the active growing period has not been documented, especially in regards to the intra-specific distribution of plants at their upper elevational limits of growth.The FR of leaves of 13 species was investigated at regular intervals from June through August, 2017 at elevations between 600 and 3200 m. The examined species have different lower and upper elevational range limits, and either grow exclusively in alpine sites or extend into the subalpine life zone. Each species was sampled twice, close to its upper and lower range limit.For most of the species, leaves exhibited a higher FR (−0,17 K/100 m) at the upper elevational range limit. The intra-specific FR was substantial, covering an amplitude of 7–15 K (>15 K in Pinus). Fully-expanded leaves had a lower level of FR in June. Evergreen leaves had a higher FR than deciduous leaves throughout the summer. Frost hardening in evergreen and a decrease in FR in deciduous leaves was observed in August; whereas, deciduous leaves at that time had already begun to senesce.Ecotypes growing at their upper elevation limit were more frost hardy than individuals of the same species growing near the lower level of their elevation range. The most severe summer frosts occurred in June when leaves were fully expanded and their FR was lowest. Thus, the highest risk of frost damage to plants at alpine sites occurs in June, even though the most frost-susceptible phase of leaf expansion may have already passed.

Deep supercooling enabled by surface impregnation with lipophilic substances explains the survival of overwintering buds at extreme freezing.

The frost survival mechanism of vegetative buds of angiosperms was suggested to be extracellular freezing causing dehydration, elevated osmotic potential to prevent freezing. However, extreme dehydration would be needed to avoid freezing at the temperatures down to −45°C encountered by many trees. Buds of Alnus alnobetula, in common with other frost hardy angiosperms, excrete a lipophilic substance, whose functional role remains unclear. Freezing of buds was studied by infrared thermography, psychrometry, and cryomicroscopy. Buds of A. alnobetula did not survive by extracellular ice tolerance but by deep supercooling, down to −45°C. An internal ice barrier prevented ice penetration from the frozen stem into the bud. Cryomicroscopy revealed a new freezing mechanism. Until now, supercooled buds lost water towards ice masses that form in the subtending stem and/or bud scales. In A. alnobetula, ice forms harmlessly inside the bud between the supercooled leaves. This would immediately trigger intracellular freezing and kill the supercooled bud in other species. In A. alnobetula, lipophilic substances (triterpenoids and flavonoid aglycones) impregnate the surface of bud leaves. These prevent extrinsic ice nucleation so allowing supercooling. This suggests a means to protect forestry and agricultural crops from extrinsic ice nucleation allowing transient supercooling during night frosts.

Diferenças de temperatura mínima entre o abrigo meteorológico e a relva em noites com geadas

A phenomenon called thermal inversion, in which there is the accumulation of colder and denser air in the layers closer to the soil, occurs in radiative frost nights, resulting in a temperature gradient with differences between the meteorological screen and grass, which vary depending on cooling conditions. Knowing this temperature difference assists in taking preventive measures against radiative frosts, as well as in estimating the probability of their occurrences. In this context, this study aimed to verify the adjustment of different probability distributions to determine the differences between the minimum temperature measured in the meteorological screen and grass temperature below 0 °C for eight regions of the Paraná State, as well as the probability of occurring these differences and adjust estimation equations of grass temperature from minimum air temperature. Temperature differences between the screen and grass were calculated and probability distributions of their occurrences were adjusted in order to determine risks per intervals of temperature differences. Estimation equations of grass temperature were adjusted from minimum screen temperatures. Average gradients of minimum temperature were observed between the screen and grass ranging from 4.2 to 6.3 °C in the analyzed regions. The average temperature difference measured in the meteorological screen and grass for the Paraná State was 5 °C. The probabilistic model of normal distribution is the most suitable for determining the probability of occurring the differences between the screen and grass temperatures for the Paraná State. Regional relief and climate conditions influence the magnitude of the minimum temperature gradient measured in the meteorological screen and grass. Estimation equations can be useful to determine the grass temperature based on the minimum air temperature for periods in which there is no such data and thus provide a subsidy for studies of risk analysis of frosts. The results of this analysis are empirical and the equations should be used in regions in which they were adjusted aiming at a higher accuracy.

Review of air disturbance technology for plant frost protection

Confronted with severe frost damage to plants, methods, technologies and equipment have been developed and applied during the past century. The paper presents a comprehensive review on the most effective and active technology to protect plants from radiation frost based on air disturbance technology. The working principle of the technology was elaborated with frost protection mechanism, structures and applicability of three types of working patterns: conventional wind machines, selective inverted sink and portable vertical blowing. As an automatic mechanized technology, control strategy, applicable occasion and proper parameters are introduced for each type of working pattern. The operation of the technology and equipment depends on plant critical temperature, prevailing climatic conditions, thermal inversions strength, as well as costs. The frost protection performance and effectiveness of conventional horizontal wind machines, selective inverted sinks and helicopters are discussed and compared from the cost-effectiveness and application aspects, and the feasibility of selective inverted sinks is still controversial. Therefore, conventional wind machines are the best choice for plant frost protection and consequently are widely used in temperate and subtropical areas throughout the world. The frost protection application with helicopters is not easy to use during the frost nights with high cost. The paper also provides researchers with some perspectives on improving air disturbance technology and its equipment, and some practice recommendations for growers. Keywords: thermal inversion, plant frost protection, air disturbance technology, wind machine, cost-effectiveness, control technology DOI: 10.25165/j.ijabe.20181103.3172 Citation: Hu Y G, Asante E A, Lu Y Z, Mahmood A, Buttar A N, Yuan S Q. Review of air disturbance technology for plant frost protection. Int J Agric & Biol Eng, 2018; 11(3): 21–28.

Human noroviruses in the faeces of wild birds and rodents-new potential transmission routes.

Human noroviruses (HuNoVs) are one of the leading global causes of diarrhoeal diseases and are transmitted mainly from person to person but also through contaminated food, water and fomites. The possible zoonotic nature of NoVs has occasionally been discussed, although the viruses are generally considered to be host-species-specific. We investigated whether wild birds and rodents could serve as carriers of HuNoVs, thereby transmitting the virus to humans directly or indirectly by contaminating foods. All samples, 115 avian and 100 rat faeces collected in springs 2009-2013 from dump sites, and 85 faeces from yellow-necked mice trapped in late autumn 2008 and 2009 after the rodents entered human settlements due to the first night frosts, were screened for HuNoV using real-time reverse transcription PCR. HuNoVs were detected in 31 (27%) faecal samples of wild birds, in two (2%) faecal samples of rats and in no samples of mice. Most (25) of the positive bird samples and both rat samples contained genogroup II, and six positive bird samples contained genogroup I HuNoV. The avian species shedding faeces containing HuNoVs were identified as gulls and crows using DNA barcoding. Our results show that wildlife, birds and rats in particular, is capable of spreading HuNoVs in the environment.

Modification of Water Application Rates and Intermittent Control for Sprinkler Frost Protection

Abstract. To validate the feasibility of an automated frost protection sprinkler system, a sprinkler irrigation system with an optimal water application rate was designed, constructed, and tested in a tea field. A modified calculation model of the water application rate was provided by simulation with different values of airflow velocity, air temperature, air humidity, and spray water temperature. An intermittent control strategy was provided using a modified model that included the start and stop time of the system and adjustment of the water application rate. Tea field experiments were conducted to evaluate the effect of frost protection based on this control strategy during frost night events. The results showed that a variable water application rate was better suited for frost protection, and the modified intermittent control automatically regulated the water application rate. In early spring and winter heavy frost nights, the canopy temperature (Tc) of the irrigated area remained above -1.2°C and 0°C, respectively, which is higher than the critical damage temperature for tea plants. The Tc of the irrigated area was approximately 2.8°C higher than that of a non-irrigated area. Moreover, the irrigated area with the modified model had a slower temperature rise after sunrise compared with the non-irrigated area, which was beneficial for frost protection. This sprinkler control strategy is an effective frost protection method that could be applied for in tea fields in the Yangtze River region. The calculation and simulation procedure of the water application rate would be applied for constructing sprinklers for different micrometeorological environments. Keywords: Frost protection, Intermittent control, Spraying water temperature, Sprinkler irrigation system, Tea, Water application rate.

A review of air disturbance technology for plant frost protection

Confronted with severe frost damage to plants, methods, technologies and equipment have been developed and applied during the past century. The paper presents a comprehensive review on the most effective and active technology to protect plants from radiation frost based on air disturbance technology. The working principle of the technology was elaborated with frost protection mechanism, structures and applicability of three types of working patterns: conventional wind machines, selective inverted sink and portable vertical blowing. As an automatic mechanized technology, control strategy, applicable occasion and proper parameters are introduced for each type of working pattern. The operation of the technology and equipment depends on plant critical temperature, prevailing climatic conditions, thermal inversions strength, as well as costs. The frost protection performance and effectiveness of conventional horizontal wind machines, selective inverted sinks and helicopters are discussed and compared from the cost-effectiveness and application aspects, and the feasibility of selective inverted sinks is still controversial. Therefore, conventional wind machines are the best choice for plant frost protection and consequently are widely used in temperate and subtropical areas throughout the world. The frost protection application with helicopters is not easy to use during the frost nights with high cost. The paper also provides researchers with some perspectives on improving air disturbance technology and its equipment, and some practice recommendations for growers. Keywords: thermal inversion, plant frost protection, air disturbance technology, wind machine, cost-effectiveness, control technology DOI: 10.25165/j.ijabe.20181103.3172 Citation: Hu Y G, Asante E A, Lu Y Z, Mahmood A, Buttar A N, Yuan S Q. Review of air disturbance technology for plant frost protection. Int J Agric & Biol Eng, 2018; 11(3): 21–28.

Strawberry leaf surface temperature dynamics measured by thermal camera in night frost conditions

Strawberry leaf surface temperature dynamics measured by thermal camera in night frost conditions

Responses of Tree Seedlings near the Alpine Treeline to Delayed Snowmelt and Reduced Sky Exposure

Earlier snowmelt changes spring stress exposure and growing-season length, possibly causing shifts in plant species dominance. If such shifts involve trees, this may lead to changes in treeline position. We hypothesized that earlier snowmelt would negatively affect the performance of tree seedlings near the treeline due to higher spring stress levels, but less so if seedlings were protected from the main stress factors of night frosts and excess solar radiation. We exposed seedlings of five European treeline tree species: Larix decidua, Picea abies, Pinus cembra, Pinus uncinata, and Sorbus aucuparia to two snow-cover treatments (early and late melting, with about two weeks difference) combined with reduced sky exposure during the day (shading) or night (night warming), repeated in two years, at a site about 200 m below the regional treeline elevation. Physiological stress levels (as indicated by lower Fv/Fm) in the first weeks after emergence from snow were higher in early-emerging seedlings. As expected, shade reduced stress, but contrary to expectation, night warming did not. However, early- and late-emerging seedlings did not differ overall in their growth or survival, and the interaction with shading was inconsistent between years. Overall, shading had the strongest effect, decreasing stress levels and mortality (in the early-emerging seedlings only), but also growth. A two-week difference in snow-cover duration did not strongly affect the seedlings, although even smaller differences have been shown to affect productivity in alpine and arctic tundra vegetation. Still, snowmelt timing cannot be discarded as important for regeneration in subalpine conditions, because (1) it is likely more critical in very snow-rich or snow-poor mountains or landscape positions; and (2) it can change (sub)alpine vegetation phenology and productivity, thereby affecting plant interactions, an aspect that should be considered in future studies.

Metabolite Profiling of adh1 Mutant Response to Cold Stress in Arabidopsis.

As a result of global warming, vegetation suffers from repeated freeze-thaw cycles caused by more frequent short-term low temperatures induced by hail, snow, or night frost. Therefore, short-term freezing stress of plants should be investigated particularly in light of the current climatic conditions. Alcohol dehydrogenase (ADH) plays a central role in the metabolism of alcohols and aldehydes and it is a key enzyme in anaerobic fermentation. ADH1 responds to plant growth and environmental stress; however, the function of ADH1 in the response to short-term freezing stress remains unknown. Using real-time quantitative fluorescence PCR, the expression level of ADH1 was analyzed at low temperature (4°C). The lethal temperature was calculated based on the electrolyte leakage tests for both ADH1 deletion mutants (adh1) and wild type (WT) plants. To further investigate the relationship between ADH1 and cold tolerance in plants, low-Mr polar metabolite analyses of Arabidopsis adh1 and WT were performed at cold temperatures using gas chromatography-mass spectrometry. This investigation focused on freezing treatments (cold acclimation group: −6°C for 2 h with prior 4°C for 7 d, cold shock group: −6°C for 2 h without cold acclimation) and recovery (23°C for 24 h) with respect to seedling growth at optimum temperature. The experimental results revealed a significant increase in ADH1 expression during low temperature treatment (4°C) and at a higher lethal temperature in adh1 compared to that in the WT. Retention time indices and specific mass fragments were used to monitor 263 variables and annotate 78 identified metabolites. From these analyses, differences in the degree of metabolite accumulation between adh1 and WT were detected, including soluble sugars (e.g., sucrose) and amino acids (e.g., asparagine). In addition, the correlation-based network analysis highlighted some metabolites, e.g., melibiose, fumaric acid, succinic acid, glycolic acid, and xylose, which enhanced connectedness in adh1 network under cold chock. When considered collectively, the results showed that adh1 possessed a metabolic response to freezing stress and ADH1 played an important role in the cold stress response of a plant. These results expands our understanding of the short-term freeze response of ADH1 in plants.

Sprinkler irrigation system for tea frost protection and the application effect

Abstract: A sprinkler irrigation system was designed and applied for a tea field to achieve frost protection through latent heat released when water turning into ice. Frost protection effects during night were tested at different irrigation application rates by monitoring air temperature around tea canopy (Tc). Temperature sensors were arranged at different distances from the sprinkler. The preliminary results showed that, when the sprinkler system worked continuously at the application rate of 2-4 mm/h before sunrise, tea canopy was covered with ice and Tc remained around 0°C, preventing tea plants from frost damage. But no more temperature rise was obviously observed at the application rates above 4 mm/h, which means less cost effectiveness. The system was stopped after sunrise when background air temperature rose back to 0°C and Tc increased by 2.2°C in one hour, while Tc of non-irrigated area increased by 4.8°C, which might cause thawing injuries to tea plants. The leaf surface temperature was lower than Tc, and the difference between the leaf surface temperature and Tc decreased with the increase of application rate. Therefore, the sprinkler irrigation system could achieve tea frost protection, and the recommended application rate was 2-4 mm/h for better protection effect. The system should keep running throughout frost night till half an hour after sunrise. The start and stop of the sprinkler irrigation system should be controlled based on Tc. Keywords: sprinkler irrigation, frost protection, Camellia Sinensis L, application rate, temperature rise, frost damage DOI: 10.3965/j.ijabe.20160905.1315 Citation: Hu Y G, Zhao C, Liu P F, Asante E A, Li P P. Sprinkler irrigation system for tea frost protection and the application effect. Int J Agric & Biol Eng, 2016; 9(5): 17－23.

Vegetation dynamics at the upper elevational limit of vascular plants in Himalaya.

A rapid warming in Himalayas is predicted to increase plant upper distributional limits, vegetation cover and abundance of species adapted to warmer climate. We explored these predictions in NW Himalayas, by revisiting uppermost plant populations after ten years (2003–2013), detailed monitoring of vegetation changes in permanent plots (2009–2012), and age analysis of plants growing from 5500 to 6150 m. Plant traits and microclimate variables were recorded to explain observed vegetation changes. The elevation limits of several species shifted up to 6150 m, about 150 vertical meters above the limit of continuous plant distribution. The plant age analysis corroborated the hypothesis of warming-driven uphill migration. However, the impact of warming interacts with increasing precipitation and physical disturbance. The extreme summer snowfall event in 2010 is likely responsible for substantial decrease in plant cover in both alpine and subnival vegetation and compositional shift towards species preferring wetter habitats. Simultaneous increase in summer temperature and precipitation caused rapid snow melt and, coupled with frequent night frosts, generated multiple freeze-thaw cycles detrimental to subnival plants. Our results suggest that plant species responses to ongoing climate change will not be unidirectional upward range shifts but rather multi-dimensional, species-specific and spatially variable.

Spatial and temporal variation in weather events critical for boreal agriculture: III Frost and winter time fluctuation

In the boreal zone of Europe, differences between the four seasons are considerable. Also, the within-season variation in climatic conditions is substantial. This has many impacts on agriculture that are exceptional when compared to any other environmental zone in Europe. All the meteorological data were based on weather observations made by the Finnish Meteorological Institute. Likelihood (%) for soil frost (≤ 0 °C at 20 cm soil depth) at nine weather stations, and late snow cover (&gt; 1 cm) (10 km × 10 km grid) were estimated for late spring. Probabilities (%) of night frost at the ground surface (March-September) were calculated at nine weather stations by frequencies of the lowest observed night-time temperature: a) between –2 and –5 °C (mild), b) ≤ –5 °C (moderate) and c) ≤ –9 °C (severe). Also, the probabilities (%) of night frost in mid-summer were estimated (≤ –1 °C for at least five hours). Furthermore, a significant shift from mild to below-freezing conditions was measured in winter as a period of at least ten days with daily maximum temperatures above 0°C followed by at least a 10-day period with daily mean temperatures below –5°C in order to characterize high fluctuating winter conditions. All these except late snow cover constitute high risks to crop production. Deep soil frost may postpone sowings, while in advanced springs, night frost may cause damage. For winter crops and perennials, shifts from mild to cold spells outside the growing season are particularly detrimental. Again the data may have many other applications beyond the assessments highlighted in this paper.

Raised bed agriculture in northwest Europe triggered by climatic change around 850 BC: a hypothesis

A sudden decline of solar activity around 850 calendar years BC caused a shift to a cool and wet climate in northwest Europe. Food production suddenly became problematic because of shorter, wetter growing seasons and increased night frost. This climate change triggered innovation and the development of a new agricultural system in continental northwestern Europe: arable farming on raised beds (Celtic field banks) laid out in a more or less checked pattern. This kind of agriculture mitigated the effects of the climate shift by providing better drainage and lessening damage by night frost and thus lengthening the growing season. Once the advantages of this kind of cultivation, soil enrichment and optimum root growth besides the hydrological effects, became obvious it will have been practised on a large scale and introduced when people thought it useful, independent of the local hydrological situation.

On the use of encapsulated phase change materials pebbles and pellets as freeze protection method for low-stature plants/crops

The use of phase change materials (PCMs) in encapsulated pebbles or pellets as freeze protection method for low-stature plants/crops is proposed and discussed at the conceptual level. Utilizing a simplified geometrical model, it is shown that, for practical applications, small encapsulated-PCM pebbles/pellets of 1-cm sized could provide the necessary heat to prevent the freezing during typical freezing time. Taking into account the balance between the loss of energy on a typical frost night and the latent energy stored in the encapsulated PCMs-pebbles/pellets, the amount of such pebbles/pellets per unit of soil-area was calculated and resulting in the use of less than 2% of the soil-area. The preliminary results at conceptual level are encouraging, however, additional work and R&D is require before its real practical efficacy can be put to test. The choice of the suitable crops, the specific environmental conditions during the freezing time, the manufacture recyclability and environmental impact of the pcm-pebbles/pellets are some of the aspects which must be carefully addressed.