GEM model for soilless cultures: review of process descriptions and suggestions for improvement

Abstract

UK The GEM model developed for soilless cultures consists of different submodels (A) for applications to crops grown on mats by drip irrigation, (B) for spray applications to crops grown on such mats, and (C) is for spray applications to crops grown in pots in an ebb/flood system (GEM-A, GEM-B, and GEM-C). The descriptions of the processes for pesticide behaviour in these submodels were reviewed, considering also their consistency with measurements available in the literature. For GEM-A it is recommended to include sorption to the mats, the foil surrounding the mats and the irrigation pipes and to include partitioning between the water in the mats and the plant roots. For GEM-B it is recommended to include direct contamination of the substrate mats and the troughs resulting from spray and Low Volume Mister (LVM) applications. For GEM-B and GEM-C it is recommended (i) to revise the procedures for calculating the initial concentrations in the air and the condensation water, (ii) to include deposition onto the roof by spray and LVM applications, (iii) to revise the procedure for calculating the volatilisation rates from the plant surfaces. For GEM-C it is recommended (i) to omit the sorption equilibration between the bottom 10 cm of the soil in the pots and the water on the ebb/flood tables, (ii) to revise the procedure for the flux in the gas phase between the greenhouse air and the top layer of the soil in the pots, and (iii) to use a crop-specific value for the fraction of the surface area covered by the pots.

Testing of the Greenhouse Emission Model for application of plant protection products via drip irrigation in soilless cultivation

“…They showed a positive correlation between the octanol water coefficient (Kow) and sorption to stonewool. Boesten et al (2019) analysed the effect of this sorption on the water concentration in the slabs. An increase of 1% was expected for dimethomorph, a substance with a Kow of 479, hence for pymetrozine and imidacloprid with a Kow of 0.646 and 3.17, respectively, the effect of sorption to stonewool on the concentration will be almost negligible.…”

“…The effect of the plastic pipes on the concentration of pymetrozine and imidacloprid is expected to be also very low (Boesten et al, 2019). Boesten and Matser (2017) found by doing exploratory calculations that partitioning to the roots of isomers of dimethomorph may lead to 30% decrease in concentration for a fully grown cucumber cropping system.…”

GEM 4 model for soilless cultures: model description and parameterisation

“…plus the deposition percentages of the last three items as proposed by Boesten et al (2019). As indicated, the dose is applied over 2 hrs.…”

“…where g is a proportionality factor (-) to account for the fact that probably only a very small fraction of the roof is covered by this deposit, A r,i is the initial value of A r immediately after application 7 and r a,r is the laminar boundary layer resistance (d m -1 ) at the roof surface. The factor g is set at 0.01 (Boesten et al, 2019).…”

“…for application of pesticides to stonewool via the irrigation water (Van der Linden et al, 2017;Wipfler et al, 2020). Also, the process descriptions for soilless cultivation were reviewed (Boesten et al, 2019). All of these activities generated a number of proposals to improve model concepts.…”