Use of CropSyst as a tool to predict water use and crop coefficient in Japanese plum trees

The development of a method to estimate the seasonal crop coefficient (Kc) would be of great benefit to irrigated agriculture. We examined the simulation capacities of CropSyst for determining crop water use of Japanese plum under varying growing conditions. These conditions involved weather changes occurring during a period of three years (2010-2012), different pruning intensities, and the use of two cultivars having different vigor and maturity time (Prunus salicina Lindl. 'Angeleno' and 'Red Beaut'). Crop evapotranspiration (ETc) was determined using the soil water balance method. Midday stem water potential (Ψstem) was determined using a pressure chamber. Two parameters of the CropSyst crop model: crop coefficient at full canopy (Kc,fc) and maximum plant hydraulic conductance (Cmax) were parameterized in 2010 season to predict Kc, while 2011 and 2012 were used for validation. In 2011 and 2012, 'Angeleno' trees were subjected to severe summer pruning so that tree size would be smaller than in 2010. The influence of the high vigor and early harvest of 'Red Beaut' was tested in 2011. The results of 2010 parameterization revealed that Kc,fc and Cmax had a distinctive seasonal pattern. This parameterization was adequate to simulate Kc and Ψstem for 'Angeleno' in other seasons and smaller trees than in 2010. The parameters adjusted in 2010 were not adequate to simulate the behavior of the more vigorous cultivar of 'Red Beaut'. In 'Red Beaut', the factor that best explained the need to adapt CropSyst parameters was the difference in vigor but not the time of the removal of fruit sinks. To accurately simulate Kc and Ψstem in 'Red Beaut' it was required to use slightly higher values of Kc,fc and Cmax during a specific midsummer period.