Articles
DISTRIBUTION AND EMISSION OF OXAMYL IN A ROCKWOOL CULTIVATION SYSTEM WITH OPEN DRAINAGE OF THE NUTRIENT SOLUTION
In these cultivation systems some pesticides are applied to the plants via the nutrient solution.
This application raised questions concerning the distribution of the compound over the individual plants and the emission to soil and surface water.
Research has been carried out on a nursery of 1.8 ha with eggplants, grown in an open drainage system.
Plants were grown in rockwool slabs, which were enveloped in a polyethene film.
Excess nutrient solution drained from slits in the envelope directly to the soil and then to ground water and surface water.
The distribution and emission of oxamyl applied via the central tank was compared with the application via injection at a tap of a section of the glasshouse.
The distribution of the compound was more uniform when applied per section than when applied via the central mixing tank to all sections.
Due to the low rate of water supply in January, it took eight days to distribute oxamyl from the section tap to all plants in the section.
At a much larger water supply to the full-grown crop in June one day was adequate to supply all plants with oxamyl.
In January the amount of oxamyl in excess nutrient solution from the rockwool slabs was 2.2 % of the dose applied and in June 44.2 %. This excess nutrient solution flows via the soil into the soil drainage system and then via the drainage pit to the surface water.
In June the emission of oxamyl via the central drainage pit was estimated to be 8.6 % of the dose applied.
After application of an average of 31.3 mg oxamyl per plant the content in the eggplant fruits remained under the maximum residue level of 1 mg per kg.
At the end of the harvest season, three months after the final application of oxamyl no residues were found in the rockwool, on the polyethene foil or in the leaves of the eggplants which were to be composted.