The Netherlands
February 11, 2025

Biosolarisation is very effective and fairly easy to implement. Organic vegetable growers in Spain have been using this natural method to suppress soilborne diseases for many years. Four weeks of sunshine and high temperatures are a prerequisite for successful biosolarisation. Therefore, the approach could also be interesting for organic growers in other Mediterranean climates.

Plant residues, fertiliser and sunlight

This chemical-free soil disinfection method is widely used in Spain, according to Aureliano Cerezuela Márquez, Crop Specialist at Rijk Zwaan Spain: “It has been applied for quite some time in the region of Murcia, especially in greenhouses for sweet pepper cultivation. In organic farming, the use of rootstocks in combination with biosolarisation is most effective for the control of soil pathogens.”

He explains that after cultivating crops such as tomatoes, peppers, cucumbers, peppers or melons, the growers first shred the plant residues and work them back into the soil, often mixed with fresh sheep or poultry manure. Then they solarise the soil. This whole process, which is performed prior to planting or sowing the next crop, is called biosolarisation.

Controlling soilborne diseases

Scientific research has shown that biosolarisation can help growers to suppress various soilborne diseases. For example, the approach proved to be the best alternative for controlling Phytophthora capsici, P. parasitica and Meloidogyne incognita in pepper cultivation, and trials in tomato and cucumber greenhouses showed similar results. According to factsheets by Best4Soil, a European ‘community of practice’ network, just some of the issues that growers can control with the method include soil fatigue, root-knot nematodes, Phytophthora parasitica, Fusarium solani f. sp. cucurbitae and Fusarium oxysporum f. sp. radicis-cucumerinum.

Sunlight is a must

Sufficient sunlight is the primary prerequisite for successful biosolarisation. “The method is effective between June and August. At least four weeks of sunshine and high temperatures are needed. At the beginning of the solarisation process, it is especially important that several days of continuous sunshine occur. The temperature in the first soil layer has to be raised as fast as possible to kill weed seeds. Otherwise, weeds will grow and push the plastic film upwards, thereby strongly reducing the warming effect of solar radiation on the soil,” states a Best4Soil factsheet.

Transparent plastic film

Besides a period of sufficient sunlight, growers have to moisten the soil and cover it well with a transparent plastic film. This ensures that the temperature in the top 20cm layer of soil reaches 45°C, which kills soil nematodes and fungi in a process is similar to pasteurisation, according to Best4Soil. Adding fresh organic matter (whether plant-crop residues, green manures or fresh animal manure) enhances the solarisation effect and also improves the fertility of the soil.
 

Tomato field trial during biosolarisation (Source: Best4Soil)
 

Soil disinfection for various climates

Growers in warm regions are increasingly adopting this method thanks to its effectiveness for disease control plus its soil health benefits. But what about growers in temperate climates? Other options are open to them. Both inundation/flooding, and anaerobic soil disinfection (ASD) – green manures or fresh organic matter covered with a suitable film, in combination with flooding – do the same. In cooler regions, these have proved to be effective chemical-free methods to ‘reset’ the soil. Like biosolarisation, both of these methods deoxygenate the soil and kill off certain harmful nematodes.

For more details about biosolarisation, ASD or inundation, see the factsheets and videos (in 20 different languages) on the Best4Soil website: www.best4soil.eu.
 

Tomato field trial, subsequent crop (Source: Best4Soil)

Website: http://www.rijkzwaan.nl

Published: February 11, 2025