An integrated method for irrigation scheduling of potted plants

Hourly meteorological and soil water potential data collected during the summer season on a container crop of 2-year-old plants of Hypericum hidcote were used to develop a methodology that integrates climate-based (AET = ETo x K-c) and soil-based methods (soil water potential measurements by tensiometers) for the automatic control of the irrigation of plants growing in pots. Hourly ETo values were calculated by the CIMIS equation, derived from the Penman formula. Tensiometric data, by a soil-specific tensiometric curve, were transformed into pot water weight and used to estimate actual hourly evapotranspiration (AETt). AETt values were compared with AET data provided by precision balances (AETb). A good relationship was found between AETt and AETb (R-2 = 0.7***), so AETt values were used to calculate hourly crop coefficient (K-c) by the AETt/ETo ratio. As the crop coefficients obtained by using AETb (K-cb = AETh/ETo) and by AETt (K-ct = AETt/ETo) shows no significant statistical differences, hourly AET values were calculated as ETo x (K-ch) over bar, where (K-ch) over bar is a 7-day average. The relationships between AET, calculated by the integrated system (ETo x (K-ch) over bar), and AETb shows an R-2 = 0.685*** and slope = 0.77. The introduction of the actual K-c (AETt/ETo) in (K-ch) over bar calculation determined an increase in the accuracy of AET estimation, with R-2 and slope increasing to 0.896*** and 0.907, respectively. According to the above results, the integrated system allows the calculation of an operational K-c for ornamental crops that can be used to correctly manage the irrigation of plants growing in containers, also if tensiometer malfunctioning or lack of representativity occur.