James Milford

Measurement and Simulation of the Ventilation Rates in a Naturally Ventilated Azrom-Type Greenhouse in Zimbabwe

A simple greenhouse ventilation model, based on the stack and wind effects (the main driving forces for natural ventilation) was adapted, calibrated, and validated using measured air renewal rates in a three-span naturally ventilated Azrom-type greenhouse in Zimbabwe. Crop transpiration rates were monitored using stem heat balance sap flow gauges installed on the main stems of rose plants to continuously monitor whole-plant transpiration (WPT). This allowed continuous and automatic determination of full scale air renewal and leakage rates using the water vapor balance method. The model was fitted to experimental data of ventilation rates, and discharge and wind effect coefficients were determined. The results show a good fit between measured and predicted values (R2 = 0.80 and 0.82 for winter and summer, respectively), although there is a general over-estimation of the greenhouse air renewal rates, particularly during the night. The model, nevertheless, adequately describes the natural ventilation process in the greenhouse all year round. The model can be used as a design tool to evaluate and optimize the effects of different ventilation configurations and strategies on greenhouse air renewal rates, and as a component in a greenhouse climate model in order to further evaluate the effects of ventilation strategies on the inside greenhouse and crop microclimate, and thus lead to better greenhouse climate control.

Education and training in agricultural meteorology: current status and future needs

Abstract The present status of education and training in agricultural meteorology is reviewed in relation to the agreed objectives of this interdisciplinary science. The major educational contribution of the agronomy faculties to the educational and research effort is acknowledged. The significant part played by the World Meteorological Organization Regional Meteorological Training Centres in the training of technical and scientific personnel is reviewed. The heterogeneous training facilities and programmes of the Regional Meteorological Training Centres are described. The absence of a scientifically based evaluation system of the training effort in agricultural meteorology is noted. In the 21st century the socio-economic gap between the richest developing and the poorest developed countries is likely to widen. Thus, the requirements for education, research and services in agricultural meteorology are likely to diverge especially in the field of applications. The major aim of the developing countries remains the increase in quantity and nutritional quality of food and fibre production. The aim of the developed countries will most likely centre on sustainable agricultural systems environmentally compatible with the requirements of an urban society. Educational facilities in agricultural meteorology will have to adapt to such a gradually changing situation nationally, regionally and internationally. Advantages from remote learning techniques and commercial systems are also likely to follow. Research priorities will be reviewed in view of changing national objectives. Agricultural meteorology will have to be integrated into the major research efforts of national priority. Growing competition in the field of meteorological services will also affect agricultural meteorology. The services of proven use to the agricultural community are likely to succeed in the 21st century as the free market economy gains ground.