RE SEARCH Many more questions around biofumigation Biofumigation – a biological technique to control soil diseases – has recently attracted the interest of agricultural Holland. That this is the case came recently to light at the Healthy Soil day, which was held at the Vredepeel Research Institute in the eastern part of the Netherlands. Researchers Johnny Visser and Gerard Korthals of PPO (Practical Plant and Environment Research) in Lelystad have listed all the possibilities in a follow up to the first exploratory research results. them into isothiocyanates. These gaseous substances, which are related to the active substance of the chemical soil disinfectant Monam, are toxic for various insects, soil fungi and nematodes. In addition to cabbage-type crops, there are other plant species that can also be used as a biofumigation crop. One of them is Sudan grass, a crop that is used in arboriculture as a soil disinfectant. When this crop is worked into the ridge, it starts to decompose, whereby toxic Prussic acid-type compounds are released. Soil-based diseases such as fungi and nematodes can cause considerable damage in a crop such as the potato. oil-based diseases such as fungi and nematodes can cause considerable damage in a crop such as the potato. A wellplanned crop rotation system is the basis for controlling this type of soil-based disease. In addition, supplementary measures are sometimes needed such as the application of chemical agents or alternative organic control measures. The Tagetes plant, the African marigold, is the organic alternative to control the meadow nematode, and the leaves of the Chinese radish or yellow mustard can be used as a trap crop for the beet eelworm. A possible future alternative is the biofumigation crop. S Toxic gases comparable to Monam Biofumigation means that crops or crop debris are worked into the ground resulting in mainly gaseous substances which have a toxic reaction on the pests and diseases in the soil. It was the cruciferous plants, in particular, which include cabbage-type crops, that can be used for biofumigation. Many cruciferous varieties contain a rather high glucosinolate content, for example. These sulphurous compounds, which these plants usually contain, probably play a role in the defence of the plant against insects, for example. Glucosinolates are stored in the plant cells and in that form, they are not toxic. When the crops are cut and the plant cells are consequently destroyed, the glucosinolates are released. The myrosinase enzyme then converts Highest concentration during bloom The effects of a biofumigation crop partly depends on the toxic substance content that develops after it has been worked into the soil and the period of time that these gaseous compounds remain in the soil. The toxic action increases as the concentration builds up and the period is longer. In most cruciferous plants, the glucosinolate content in the crop is at its highest during the bloom stage. This is approximately six to eight weeks after sowing. It is of the utmost importance that the biofumigation crop is properly chopped up at that moment and can start its action. If the crop is chopped very finely, the conversion can take place quickly, as a result of which the concentration of toxic fumes can be very high within a short period of time. To stop any gases escaping from the soil, it is advisable In most cruciferous plants, the glucosinolate content in the crop is at its highest during the bloom stage. Potato World 2010 • number 2 35 Pagina 34
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