RE SEARCH Many more questions around biofumigation BIOFUMIGATION IS NOT ORGANIC SOIL DECONTAMINATION (OSD) Some people sometimes confuse the method of biofumigation with the already existing anaerobic Organic Soil Decontamination (OSD). This is a completely different technique, however. In OSD, large amounts of fresh organic material are worked into the soil, grass, for example, which is then closed off tight with plastic sheeting. Some people sometimes confuse the method of biofumigation with the already existing anaerobic Organic Soil Decontamination (OSD). This is a completely different technique, however. In OSD, large amounts of fresh organic material are worked into the soil, grass, for example, which is then closed off tight with plastic sheeting. The decomposition of this large amount of fresh organic material withdraws oxygen from the soil. The lack of oxygen in the soil and the decomposed matter, which is released during the decomposition process, have a killing force on a large number of nematode species, soil-borne fungi and a number of root-spreading weeds. In this method, the nature of the material is therefore less important than in biofumigation. Research has shown that a large number of soil pathogens can be controlled very well with OSD. The effect can be compared to, or is sometimes even better than chemical soil decontamination. to roll the topsoil and, if necessary, irrigate it afterwards in the same way as is done in chemical soil disinfection. Factors such as the soil temperature, soil humidity and soil type also have a great influence on the effects. What appears to be very important is that the soil temperature is sufficiently high as well as the extent of the release of the toxic compounds. This means that the crop must be grown during the summer months so that, at the end of the summer, or at the beginning of the autumn, when the soil temperatures are sufficiently high, the crop can be worked into the soil. Also good for the organic substance content In addition to the possible disinfectant effect on soil pathogens, the cultivation of biofumigation crops also has some of the positive effects of a green manure crop. Examples are the improvement of the organic matter content and the structure of the soil, the prevention of sand blowing up/erosion and the stimulation of healthy soil life. A green manure crop can also act as a trap crop for certain nematode species, for example Chinese radish for beetroot nematodes. However, green manure crops and biofumigation crops can also have an adverse effect on soil life. It is sometimes possible that harmful nematode species and fungi increase instead of the opposite and that an infection spreads up to an unacceptable level. For example, Sudan grass is known to be an excellent host for the root-lesion nematode. There is quite a risk that the biofumigation effect – the production of Prussic acid-like gases after the crop has been worked into the soil – is insufficient to destroy this increase, which takes place during the cultivation of the Sudan grass. It is therefore extremely important to know whether and how well the harmful species can grow on the biofumigation crop. This will prevent the controlling of one problem becoming the start of another. Tagetes is a biological alternative to kill the root-lesion nematode. Many things not yet clear The major part of the research into biofumigation crops has been carried out in laboratories or in greenhouses. The results, which mostly come from abroad, vary a great deal. Experience with trials is still very limited, at least in the Netherlands. Many things are not yet clear and many questions are still unanswered. Which crops are the most effective for use in biofumigation? When and how are they grown? How are they best worked into the soil? What are the effects of the temperature and type of soil and how can a biofumigation crop be incorporated into the cropping plan/crop rotation. And the most important question: how effective is this technique with controlling harmful soil organisms? Potato World 2010 • number 2 37 Pagina 36
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