Soil-Steaming and Steam-Boiler Blog – for healthy soil and plants

The decontamination of large areas from Japanese knotweed by steaming is further advancing. After the association for sewage treatment Offenburg and the regional board Freiburg have successfully used hot steam to control knotweed in 2009, the regional board Karlsruhe follows their example.

At the beginning of November three large areas close to the city of Sinzheim were steamed by the steaming specialists MSD GmbH, Durbach and Mobildampf, Waiblingen.

Although the regional board Freiburg had had the contaminated areas excavated down to 20 cm depth and the material steamed in specially prepared tipping trailers, the regional board Karlsruhe decided to treat 2 of the 3 areas with the classic method of sheet steaming.

Sheet steaming against Japanese knotweed at Sinzheim

For this purpose the soil was loosened down to 30 cm depth before steaming. After that the area was covered with heat resistant sheets, weighted at the edges and steamed for three to four hours. The soil of the third area was excavated down to 20 cm depth, steamed and put back to its original location.

Container-steaming with tipping trailer

In case that the positive results in 2009 can be achieved as well, more areas will be treated in the same way.

Japanese knotweed (Fallopia Japonica) belongs to the problematic non-native plants (neophytes). The plant originates from the far east and has spread rapidly through Central Europe, the British Isles as well as the United States, causing major damage to dams, walls and streets due to its powerful growth. Furthermore it destroys native plants and endangers biodiversity.

In the West of the German federal state Baden-Württemberg, public offices have been dealing with this issue for more than thirty years. In the Ortenau region, dams have been damaged since Japanese knotweeds destroyed sod causing high water to penetrate into building structures, resulting in fatal problems with their stability.

The regional board of Freiburg reports on studies to control Japanese knotweed with hot steam.

Conventional mechanical methods such as mowing and mulching are not able to diminish the population, they only hinder spread. At present the only remedy available are broad band herbicides such as Round-Up, which are not completely safe. Hence they cannot be used in close proximity to water due to their water damaging effects. Furthermore, they have to be applied over several years in order to significantly decrease the population.

For these reasons, the regional board of Freiburg decided to study the effect of hot steam on larger contaminated areas. In September 2009 about 500 square meters of afflicted soil was excavated down to 30 cm depth to fully remove the soil layers mainly infested by the plant rootstock. The contaminated excavation was steamed in a specially prepared trailer. The steamed ground was put back and the area re-natured.

The lowland adjacent to the river is paved with stones and was specially treated. Since excavation of infested soil was impossible due to the pavement, areas were gradually covered with special steaming hoods and treated. Since then the steamed areas are supervised by staff of the regional board (Mr. Keller, Mr. Martin) and by staff of MSD GmbH (Moeschle-Seifert-Daempftechnik), which has supported the study with technical equipment and expertise.

In a second step, sprouting plant parts in deeper not treated soil layers will be partially steamed with steaming lances reaching up to 1 m into the soil.

Prior to the study MSD GMBH and the association for sewage treatment Offenburg (Mr. Mohn) has already made an initial study in the beginning of 2009. Due to the highly positive results yielded in this first trial, in which no shoots occurred more than half a year after steaming, positive results are expected for the next study as well.

For more information on Japanese knotweed, please check on Wikipedia Wikipedia.

The public sector, such as communities, must also deal with solutions to control wild herbs and weeds.

On squares, streets and sidewalks, weeds amass in gaps and free areas and have to be eliminated. Furthermore, challenges arise due to the steady spread of problematic plants such as the invasion of neophytes.

Invasive Neophytes and other problematic plants

In recent decades many non native plants have been introduced to Central Europe.

Many of these plants cause growing problems due to their rapid growth. Some are harmful to health such as Ambrosia, while others endanger biodiversity since they supplant native plant varieties and detriment the natural habitat. Among these is Japanese knotweed (Fallopia Japonica /Reynoutria Japonica) whose powerful growth suppresses other plants and depending on its location may damage agricultural land or building structures such as dams, streets and walls.

Furthermore, native problematic plants are further advancing such as ragwort which is toxic and can lead to liver damage and even fatal poisoning depending on the ingested dosage. The accelerated spread of ragwort can be traced back to growing area of fallow land and climate change.

In particular the public sector is faced with the challenges to address this issue.

Today two methods are applied for weed control: 1. Mechanical means such as brushing, mulching, bunking and mowing 2. Application of herbicides. In particular the usage of chemical means is limited due to its harmful impact on nature and humans.

Hot steam is an adequate alternative.

Steaming systems for weed control in public spaces are available and can universally be applied. In contrast to mechanical methods, which are quick and simple, steaming provides the advantage that not only superficial plant parts are removed. Hot steam penetrates into all gaps and fights the complete plant. It kills all sprouted plant parts and weed seeds making it really worth the effort. The results are completely weed-free areas which only require to be retreated once or twice a year. No chemicals are needed and the treatment is residue-free.

Steaming and other thermal methods.

Besides hot steam there are other thermal methods used for weed control available on the market such as infrared rays, scarfing and hotwater systems. The efficacy of these methods is often insufficient despite their relatively high energy usage. Radiant heaters preserve surfaces but require long residence times until heat has sufficiently damaged the plant in particular reaching parts underground. Scarfing devices have the same problem, since they show little depth effect.

Hotwater systems may overcome these issues. When applied properly, these systems can kill deeper sprouted plant parts at temperatures higher than 65°C for a positive long term effect. However hotwater systems show high energy losses and massive water consumption. Hot steam does not have these disadvantages.

More than „Hot air“

In contrast to hot water at 100°C, hot steam at 100°C contains about 5 times more energy. Furthermore its density is 1000 times lower. Hence when using hot steam, users need less water and can apply more heat to fight weeds: The result are weed-free areas at relatively low energy and labor cost. Furthermore, low pressure steam generators are very easy to handle.

In contrast to methods using extreme heat and high pressure the application of steam has more positive effects: Soil surface is preserved and freed from weeds, moss and linchen. Steaming even cleans deeper soil layers. Persistent dirt such as gum, etc. is loosened and can be removed easily after steaming.

Steaming systems are suitable for small as well as large areas with different surfaces such as sports and playgrounds, sidewalks, parking lots and cemeteries.

Steam can be applied anywhere.

Steam can be applied in many different areas. Communities can use steam generators not only for effective weed control and cleaning of squares and streets. Steaming systems can also be used to treat municipal green areas, beets and compost or zoological gardens. If coordinated and applied properly a steam generator never stands still.

On the 19.09.2009 (32nd horticulture day) Hohenheim University located close to Stuttgart presented the results of open field tests for weed control.

From June to September 2009 three methods of weed control were tested 4 times repeatedly on parcels of 16m x 1.2 m. On the parcels two Baby-Leaf salads “Batavia red” and “Batavia green” were planted.

The total testing area was divided into 18 plots, on which the three methods were compared with each other: weed control with pick, with herbicide and with soil steaming.

Steaming took place once before seeding after sufficient soil loosening, while herbicides were applied after seeding. Manual seed control with pick took place when weeds started to occur. Control plots were not subject to any weed control means.

Baby-Leaf cultures were harvested after 4 weeks. Then freshmass and drymass of salad and weed of all three test variations were measured and compared (steaming, herbicide, pick).

University Hohenheim yielded the result that after the application of 90°C hot steam, no weeds grew in the cultivation period. On sufficiently steamed areas weed control of Baby-Leaf-Cultures is not necessary.

Nitrate and Ammonium

As expected when examining the steamed soil, a relatively high but harmless concentration of ammonium and after harvest a high concentration of nitrate was measured due to the blocking of nitrifying bacteria through steaming. Ammonifying bacteria however were less affected through hot steam. Hence ammonia accumulates in steamed soil. More detailed results were yielded by S.N. Malowany and I.D. Newston in the middle of the last century already. Normally the ammonia / nitrate ratio normalizes within 6-8 weeks after steaming. This period can be significantly shortened if nitrifying and ammonifying bacteria are injected into the soil right after steaming(Integrated Steaming).

Since the middle of the last century, the effectiveness of humid heat to fight weeds, in particular their seeds, has been researched thoroughly. Within just 5 minutes all seeds can be rendered ungerminable as long as hot steam of 95°C is used steadily.

In practice today there is a trend of shorter treatments with hot steam in particular when fighting weed seeds on open fields. In particular in France, the Netherlands and in Denmark big areas of beet cultures are superficially sterilized to up to 5-10 cm depth using steaming automats. Special hoods with a total area of up to 20 square meters are moved step by step after just 5 minutes of steam injection.

The goal of using short steaming periods however is not the total abolition of resistant pathogens. Here longer steaming times and larger steaming depths are necessary. Instead the focus is the killing of weed seeds on the surface in order to give beet cultures a headstart so they can prevail against other growing weeds.

The results show success. Despite short steaming periods, hot steam can sufficiently harm seeds sufficiently to avoid the penetration of weeds.

This steaming method for superficial seed control is further propagated in Germany as well. This development can be traced back to the lack of available alternatives. In earlier times chemical means were used which are meanwhile prohibited or considered risky.

Furthermore the present discussion about the spread of ragwort and similar plant types drives the promotion of steaming. The market demands even more weed=free products, but due to the market price situation there is no alternative for automatic harvest methods. Hence, beets need to be free of weeds when harvesting.

Steaming as ecological method for seed control gains importance nationally as well as internationally.