Relationship between air and media temperature in frequently irrigated containerized nursery plants

The media temperature of containerized plants has a distinct impact on crop growth and development, water and nutrient uptake. Ultimately, it influences the marketable quality of the plant. Containerized plants suffer due to a low root zone temperature during the winter and a high root zone temperature during the summer months. Understanding the relationship between media temperature and weather conditions is the first step towards the development of strategies that could reduce crop risks associated with extreme temperatures in the root zone. The objective of this study was to determine the relationship between the media temperature (MT) and the air temperature (AT) of containerized nursery crops subjected to short irrigation intervals. The study was conducted at Monrovia Growers, located in Cairo, Georgia, USA, during the summer of 2005 and the spring and summer of 2006. Data from 2006 were used to develop various models and the data from 2005 were used for model evaluation. The experiment consisted of a 14.7-Lplastic container with five replicates. Media temperature, air temperature and solar radiation were recorded at 15-min intervals. Weather data were obtained from an automated weather station located 20 m from the experimental site. Irrigation was applied six times daily using a micro-irrigation system consisting of microsprayers (spitters). The MT gradient (ΔMT) and AT gradient (ΔAT) were determined every 2 h, from 0600 h to 2000 h, in May, June, July, and August. The investigation lasted for 10 d each month. For all 10-d periods, a significant (P <0.05) correlation between ΔAT and ΔMT was found during the day. The correlation between ΔAT and ΔMT was affected by the time lag between AT and MT. The relationship between ΔAT and ΔMT varied for different time periods during the day and for all 10-d periods that were analyzed. Our results demonstrated that media temperature and air temperature have a significant correlation. However, this correlation seems to be a function of the time of day. Specific equations were, therefore, developed for estimating ΔMT as a function of ΔAT for different time periods of the day and for different months. These equations could successfully predict media temperature as a function of air temperature for time periods of less than an hour. Further work will consider other variables, such as solar radiation, media moisture and the temperature of the irrigation water.