Container temperature and moisture for estimating evapotranspiration of nursery crops

The availability of water for agriculture has become an important issue, especially due to the continuing drought in the southeastern USA and because water is one of the most critical inputs for nursery plants. The goal of this study was to estimate the amount of water required for nursery crops based on the soil temperature and moisture measurements of nursery containers. The experiment was conducted at the Center for Applied Nursery Research (CANR), located in Dearing, McDuffie County, Georgia. Fifteen soil temperature probes and fifteen soil moisture probes were installed in three different sizes of containers, including 11.4-, 19.0- and 26.5-L pots filled with a soil mixture consisting of bark, lime, fertilizer, and sand. The probes were connected to an automated data logger, which recorded the container conditions every 15 minutes. At midnight the data logger also calculated the daily extremes and averages. This information was retrieved hourly via a dedicated telephone line and modem by a computer located at the College of Agricultural and Environmental Science-Griffin Campus. At the same time an automatic weather station recorded several weather variables for the same period The experiment was carried out from November 19th 2002 through May 20th 2003. The 11.4-L containers were planted with Ilex chinensis "Bufordi", Dwarf Burford, the 19.0-L containers were planted with Cuppressocyparis "Leylandi" and the 26.5-L containers were planted with Ilex × Ruby Sceptor". The soil moisture and soil temperature probes homogeneity was evaluated through the analysis of the cumulative distribution functions (CDFs) of the 15 minute observations. The Kolmogorov-Smirnov two-sample, two-side test was used to compare all CDFs combinations by treatment. Kolmogorov-Smirnov's test can detect all type of differences that might exist between two distribution functions and a statistic test (D) is calculated. Thereafter, simple equation regressions of one and two order were fitted. Container moisture was affected by the air temperature seasonal variation. High variability and increase of container soil water content for days without rainfall and irrigation was observed during the winter. This phenomenon was probably due to temperature gradient that could transport water from warm to cool fronts. Meanwhile, the soil moisture probes showed an adequate variation of the soil moisture content during the spring. The experiment received 434mm of water from irrigation and 690mm from rainfall. The irrigation efficiencies were 44, 40, and 53% and the total water consumption was 193, 173, and 230mm in the 11.4, 19.0, and 26.5-L containers, respectively. Functional relationships between container temperature and moisture with air temperature provided satisfactory evidences for estimation of water use by nursery crops and could be used for irrigation scheduling to conserve water use.