The microclimates of two contrasting propagation systems, a polyethylene-covered mist unit and a low-technology, non-mist polyethylene propagator, were examined in detail over a two year period. Both systems were able to maintain relative humidities (r.h.) of over 90% for much of the time; r.h. below 60% was associated with peaks in irradiance of over 1000 µmol m<sup>-2</sup>s<sup>-1</sup>. Leaf-to-air vapour pressure difference (VPD) tended to vary in a manner similar to irradiance, remaining close to zero during night, and often reaching values over 3.0 kPa during early afternoon. Maximum VPD in the non-mist system was associated with opening of the propagator lid, which caused an immediate decline in r.h. When the propagator lid was kept closed, VPD under mist was consistently 2–3 times higher than under non-mist. The relationship between VPD and irradiance was found to vary both diurnally and from week to week. In general, a large part of the variation in VPD was unaccounted for by irradiance, as air temperature in both systems increased during the day, producing a higher VPD for a given irradiance later in the day. In addition, the influence of irradiance on the different components of VPD differed between the two systems. Spatial variation in microclimate was of a similar magnitude in both systems. These results highlight the suitability of the non-mist propagation system for use in rural tropical areas. The implications of the results for development of operational guidelines are discussed.
Newton, A.C.; Jones, A.C. Characterisation of microclimate in mist and non-mist propagation systems. The Journal of Horticultural Science (1993) 68 (3) 421-430.