Articles
BEHAVIOUR OF OXAMYL AND PROPAMOCARB IN TWO ROCKWOOL CULTIVATION SYSTEMS: OPEN DRAINAGE AND RECIRCULATION OF NUTRIENT SOLUTION EXCESS
Nutrient solution was applied at a normal rate (2.8 l d-1), a half-normal rate and a double rate to two types of production systems: an open drainage system and a closed cultivation system.
The rockwool substrate was poorly moistened at the lowest rate of nutrient solution supply.
In the other systems the water-saturation of the rockwool in the rhizosphere differed at various places.
Hardly any transformation of oxamyl occurred in the nutrient solution in the supply tank (to which 2200 mg oxamyl was added) in a period of 18 days.
In periods of intense radiation, and thus of high transpiration by the plants, the oxamyl concentration in the solution in the rhizosphere increased above its concentration in the nutrient solution supplied.
At the lowest rate of the nutrient solution supply to the open drainage system the total mass of oxamyl in the rockwool substrate and plants was estimated to be 1900 mg at the end of the experiments.
In systems with the normal rate of supply it was about 1000 mg oxamyl and in the closed cultivating systems it was 2000 mg oxamyl.
The loss to the soil from the open drainage systems was 12 % of the mass of oxamyl applied with the low irrigation rate and 51 % and 65 % with the normal and double rates of supply.
This loss can result in a substantial emission to ground water or surface water in the Dutch glasshouse areas.
Large masses of oxamyl (up to 122 mg per rockwool slab) were measured in the water retained in the rockwool at the end of the experiments.
Residues on polyethene foil and dripper were negligible compared to the residues in the rockwool slab.
A limited number of measurements for propamocarb showed its behaviour to be analogous to that of oxamyl.