Intra-Row Weed Control by use of Band Steaming

Soil disinfection by steam is a well-known technique used within horticulture and market gardening. The most common steam application technique is sheet steaming, where the soil is covered with a thermo resistant sheet, which is sealed at the edges and then blowing steam under the sheet so that the steam penetrates through the soil. The method is effective for control of weed, plant pathogens and nematodes. However, high fuel consumption and low capacity are serious disadvantages. Moreover all living organisms, harmful and useful, in the treated soil are killed, and therefore the method is not in line with the basis ideas of organic farming. A new concept and technique for performing band heating has been developed. By heating only a narrow band of 6–8 cm around the rows to a depth of 5 cm, energy savings of more than 90% can be obtained. In practice, the system may be combined with a computer-controlled sowing machine for the subsequent sowing of plants in the centre of the treated bands. The system will result in the crop growing in rows free of plant competition. It was seen that soil temperatures of 80-90°C, were needed to achieve god effect in the field

Impact of temperature on the pullout of reinforcing geotextiles from unsaturated silt

This study investigates the thermal soil-geosynthetic interaction mechanisms of reinforcing geotextiles confined in compacted silt that may be encountered when using mechanically-stabilized earth (MSE) walls as geothermal heat sinks. A thermo-mechanical geosynthetic pullout device was used that incorporates standard components for geosynthetic pullout or creep testing but also heating elements at the top and bottom of the soil box to apply boundary temperatures and dielectric sensors embedded in the soil layer to monitor distributions in temperature and volumetric water content. Two test series were performed: the first involves monotonic pullout of woven polypropylene geotextiles after reaching steady-state conditions under different boundary temperatures without a seating load, and the second involves monotonic pullout of woven polyethylene-terephthalate geotextiles after reaching steady-state conditions under different boundary temperatures with a seating pullout load. The results indicate that the pullout resistance of both geotextiles decreased with increasing temperature. Although heating led to drying of the unsaturated silt layers as expected, measurements from the second test series indicate accumulation of water at the silt-geotextile interface. An effective stress analysis considering thermal softening of soils indicates that the increase in effective saturation at the silt-geotextile interface was the cause of the decrease in pullout resistance with heating

Soil temperature extrema recovery rates after precipitation cooling

From a one dimensional view of temperature alone variations at the Earth's surface manifest themselves in two cyclic patterns of diurnal and annual periods, due principally to the effects of diurnal and seasonal changes in solar heating as well as gains and losses of available moisture. Beside these two well known cyclic patterns, a third cycle has been identified which occurs in values of diurnal maxima and minima soil temperature extrema at 10 cm depth usually over a mesoscale period of roughly 3 to 14 days. This mesoscale period cycle starts with precipitation cooling of soil and is followed by a power curve temperature recovery. The temperature recovery clearly depends on solar heating of the soil with an increased soil moisture content from precipitation combined with evaporation cooling at soil temperatures lowered by precipitation cooling, but is quite regular and universal for vastly different geographical locations, and soil types and structures. The regularity of the power curve recovery allows a predictive model approach over the recovery period. Multivariable linear regression models alloy predictions of both the power of the temperature recovery curve as well as the total temperature recovery amplitude of the mesoscale temperature recovery, from data available one day after the temperature recovery begins

Intra-Row Weed Control by use of Band Steaming

Disinfection of the soil by means of steaming has been a common method for eliminating weeds and fungal diseases. However, surface steaming of soil is a very energy-intensive process, and consequently, efforts have been made to develop a machine for narrow-band steaming of the soil under and around rows of cultivated plants prior to seeding. The use of this machine may achieve up to 90% energy savings, and will also reduce the amount of damage to the flora and fauna. Tests have shown that soil temperatures exceeding 70C will be needed to protect against germination of weed seeds. For band heating such a treatment in 50 cm rows requires about 5.8 GJ/ha

High-temperature environments of human evolution in East Africa based on bond ordering in paleosol carbonates

Many important hominid-bearing fossil localities in East Africa are in regions that are extremely hot and dry. Although humans are well adapted to such conditions, it has been inferred that East African environments were cooler or more wooded during the Pliocene and Pleistocene when this region was a central stage of human evolution. Here we show that the Turkana Basin, Kenya—today one of the hottest places on Earth—has been continually hot during the past 4 million years. The distribution of ^(13)C-^(18)O bonds in paleosol carbonates indicates that soil temperatures during periods of carbonate formation were typically above 30 °C and often in excess of 35 °C. Similar soil temperatures are observed today in the Turkana Basin and reflect high air temperatures combined with solar heating of the soil surface. These results are specific to periods of soil carbonate formation, and we suggest that such periods composed a large fraction of integrated time in the Turkana Basin. If correct, this interpretation has implications for human thermophysiology and implies a long-standing human association with marginal environments

Heat and Moisture Conduction in Unsaturated Soils

Mathematical models are developed for the prediction of heat transfer from hot water pipes buried in the soil. Heat transfer in the absence of moisture transfer is described as a function of the difference between the temperature of the pipe and the temperature of the soil surface. The energy balance is used to determine the longitudinal temperature distribution of the water. The method is extended to describe a system of equally spaced, parallel buried pipes. Soil temperature profiles around the pipes are presented. The model is used to calculate the land area that can be heated by an underground piping system carrying cooling water from the condensers of a 1000 MW nuclear-electric plant. A new development of the phenomenological equations for coupled heat and moisture flow, based on the theory of Irreversible Thermodynamics, is presented. Solutions of the equations for boundary conditions representative of buried piping systems designed for simultaneous soil heating and irrigation are presented

Biochar as a Soil Amendment: A Review of the Environmental Implications

The term 'biochar' refers to black carbon formed by the pyrolysis of biomass i.e. by heating biomass in an oxygen-free or low oxygen environment such that it does not (or only partially) combusts. Traditional charcoal is one example of biochar produced from wood. The term 'biochar' is much broader than this however, encompassing black carbon produced from any biomass feedstock. The use of biochar as a soil additive has been proposed as a means to simultaneously mitigate anthropogenic climate change whilst improving agricultural soil fertility. This paper provides a review of what is known about both of these claims and also about the wider environmental implications of the adoption of this process. The intention of this review is not just to summarise current knowledge of the subject, but also to identify gaps in knowledge that require further research

Application of large underground seasonal thermal energy storage in district heating system: A model-based energy performance assessment of a pilot system in Chifeng, China

Seasonal thermal energy storage (STES) technology is a proven solution to resolve the seasonal discrepancy between heating energy generation from renewables and building heating demands. This research focuses on the performance assessment of district heating (DH) systems powered by low-grade energy sources with large-scale, high temperature underground STES technology. A pilot DH system, located in Chifeng, China that integrates a 0.5 million m3 borehole thermal energy storage system, an on-site solar thermal plant and excess heat from a copper plant is presented. The research in this paper adopts a model-based approach using Modelica to analyze the energy performance of the STES for two district heating system configurations. Several performance indicators such as the extraction heat, the injection heat and the storage coefficient are selected to assess the STES system performance. Results show that a lower STES discharge temperature leads to a better energy performance. A sensitivity analysis of the site properties illustrates that the thermal conductivity of soil is the most influential parameter on the STES system performance. The long-term performance of the STES is also discussed and a shorter stabilization time between one and two years could be achieved by discharging the STES at a lower temperature.This research is part of the seasonal storage for solar and industrial waste heat utilization for urban district heating project funded by the Joint Scientific Thematic Research Programme (JSTP)–Smart Energy in Smart Cities. We gratefully acknowledge the financial support from the Netherlands Organisation for Scientific Research (NWO). We would also like to thank our research partners from Tsinghua University working on the project of the International S&T Cooperation Programof China (ISTCP) (project No. 2015DFG62410). Without their efforts, we would not have been able to obtain the technical data to conduct the case study

Heated soil-water extract effect on bacterial growth: pH or toxic compounds?

Fire-induced soil changes influence indirectly on soil microbial response, mainly due to pH increases and organic matter alterations. Nevertheless, field studies include overlapped effects and it is difficult distinguish the real origin of microbial response. In this work we have performed a laboratory experiment focus on the study of heated soil-water extract effect on bacterial growth, trying to isolate pH and soluble organic carbon alterations induced by heating soil at different temperatures. Bacterial growth was estimated by 3H-leucine incorporation technique which allows isolate bacterial activity response to an alteration. Different heated treatments were applied to unaltered forest soil samples, to simulate moderate (heating at 300 oC) or high (heating at 500 oC) intensity fire. In order to isolate possible pH changes effect, the experience was repeated adding pH buffers to bring the extract to the unaltered soil pH. Preliminary results show bacterial growth inhibition in both heated treatment compared to bacterial growth of the same bacterial suspension incubated with water. The reestablishment of pH improve the bacterial growth of samples incubated in heated soil-water extract, with a more marked effect on incubation soil-water extract from soil heated at 500 oC. These results evidence the importance of pH changes on low pH adapted bacterial community and the presence of other factors presents in the soluble fraction that are limiting bacterial proliferation

Fire severity is more sensitive to low fuel moisture content on Calluna heathlands than on peat bogs

Moorland habitats dominated by the dwarf shrub Calluna vulgaris provide important ecosystem services. Drought is projected to intensify throughout their range, potentially leading to increased fire severity as moisture is a key control on severity. We studied the effect of low fuel moisture content (FMC) on fire severity by using 2 × 2 m rain-out shelters prior to completing 19 experimental fires in two sites in Scotland (UK): a dry heath with thin organic soils and a raised bog with deep, saturated peat, both dominated by Calluna vulgaris. Reduced FMC of the moss and litter (M/L) layer at both sites, and the soil moisture of the dry heath, increased fire-induced consumption of the M/L layer and soil heating at both sites. Increase in fire severity was greater at the dry heath than at the raised bog, e.g. average maximum temperatures at the soil surface increased from 31 °C to 189 °C at the dry heath, but only from 10 °C to 15 °C at the raised bog. Substantial M/L layer consumption was observed when its FMC was below 150%. This led to larger seasonal and daily soil temperature fluctuation, particularly at the dry heath during warm months. The results suggest that low FMC following predicted changes in climate are likely to increase wildfire severity and that the impact on vegetation composition and carbon stores may be greater at heathlands than at peatlands. Managed burning aiming to minimise fire severity (e.g. ignition of the M/L layer and exposure to lethal temperatures of ericoid seeds) should be carried out when the FMC of the M/L layer is above 150% and the FMC of the soil is above 200–300%