A research project on soil sterilisation in greenhouses using two environmentally friendly techniques – soil solarisation and biofumigation – has shown that the former is a very effective alternative to using chemicals to sterilise soil and can be used successfully in Malta due to the favourable climatic conditions. Biofumigation was also found to be efficient but not as much as soil solarisation. Both techniques reduce the use of pesticides, improve yields and hence increase farmers’ profits.

Soil solarisation is one of the most effective non-chemical techniques to manage several soil-borne pests, diseases and weeds. It utilises solar energy to heat the soil to a temperature high enough to reduce the number of soil-borne pests and pathogens.

Soil solarisation and biofumigation in the greenhouse.

Biofumigation makes use of natural compounds found in certain plant species, such as examples from the brassica family. This family includes the mustards that contain compounds called isothiocyanates, which are released when these plant tissues are damaged. When present in the soil, these chemicals suppress soil-borne pests and diseases. Mustard plants are cultivated, and when a certain growth stage is reached, they are chopped and incorporated in the soil to control pests and disease.

The efficiency of these two methods was tested on the cultivation of four crops – tomatoes, cucumbers, aubergines and peppers.

The research was carried out by the author at the Government Experimental Farm with the collaboration of the University of Malta Institute of Earth Systems and supervised by Dr Anthony Sacco.

Both techniques reduce the use of pesticides, improve yields and hence increase farmers’ profits

In the research, the efficacy of soil solarisation and biofumigation were compared using local soil in a greenhouse. The effectiveness of the treatments was assessed through their ability in reducing the nematode population in the soil, together with the crop yield, plant length, plant death, root structure, and also weed control. Compared to a non-treatment control each treatment had a significant effect on the nematode population; however, soil solarisation was the most effective.

Crops cultivated in solarised soil produced a significantly higher yield than crops cultivated in the biofumigated soil. They also reached maturity earlier, had a better rooting system and suffered less from diseases.

Soil nematodes cause a lot of damage to plant roots.

Both treatments produced a significantly higher crop yield than the control untreated soil. From a weed control aspect soil solarisation proved to be the best choice under local conditions.

Soil-borne pests, diseases and weeds cause serious problems to agricultural crops, mainly in intensive farming systems. Pests and disease affect root systems, severely diminishing plant vigour, reducing yields significantly and in severe cases also causing plant deaths.

Weeds compete with plants for light, space, water and nutrients. It is difficult to eradicate them, so one of the best ways to control them is to sterilise the soil prior to planting.

In the past, soil sterilisation was mainly carried out by fumigants such as methyl bromide. This gas was very effective; however, it was banned due to its effect on the ozone layer.

Steam sterilisation was also used for this purpose; however it is quite costly and thus it is hardly used any more. Nowadays, there are very few options for soil sterilisation as many soil fumigants have been banned. In the Maltese islands, very few soil fumigants are being used for soil fumigation.

Laurence Attard is a principal agricultural officer at the Government Experimental Farm in Xewkija, which is part of the Gozo Ministry’s Projects and Development Directorate. Mr Attard recently graduated with a M.Sc. in Rural Sciences from the University of Malta following a Steps scholarship award co-financed by the EU Social Fund under Operational Programme II Cohesion Policy 2007-2013. Part of Mr Attard’s studies involved researching environmentally friendly techniques that can be utilised in the Maltese islands to control soil-borne diseases.