Effect of Organic Fertilization and Deficit Irrigation Management on Processing Tomato

An experiment was carried out to determine if organic fertilizer and deficit irrigation combination could replace the traditional management of processing tomato crop (mineral fertilizer and irrigation of 100% crop evapotranspiration, ETc), without affecting yield and quality of production. The study was conducted from June 2022 to September 2022 at the experimental farm of the University of Padova, adopting a split-plot experimental design. The experiment was conducted under a plastic tunnel greenhouse where only the roof was covered to avoid the rainfall influence and at the same time to permit air circulation. Four fertilizer treatments, control (no fertilization), mineral fertilizer, unseived compost, and sieved compost (< 2mm) were applied in factorial combination with two irrigation treatments, 100% ETc and 75% ETc. Data on the vegetative, physiological, yield, and quality parameters were collected. The maximum plant height (75.3 cm) and stem diameter (17.0 mm) were recorded on plants fertilized with unseived compost; both of these parameters did not show significant differences in response to the irrigation level. For physiological parameters, significant differences were found among irrigation treatments. During the daytime, the 25% reduction of optimal irrigation water volume determined a reduction of 4.6% for stomal conductance (0.372 mol m^-2 s^-1 at 100% ETc) and of 14.2% for transpiration (4.56 mmol m^-2 s^-1 at 100% ETc). Regarding fluorescence, the highest value (0.769) was recorded for 75% ETc and mineral fertilization, while the lowest (0.733) was for 100% ETc and mineral fertilization. The number of ripe fruits per plant was significantly higher in the treatments with compost (60 fruits plant^-1) than in the unfertilized control (39 fruits plant^-1). The yield was neither influenced by fertilization nor by irrigation level showing an average value of 2 kg plant^-1. Similarly, the qualitative analysis of the tomato fruits showed significantly higher soluble solid content (+5.8%) and pH (+1.4%) at 100% ETc than 75% ETc which showed an average value of 4.11 ˚Brix and 4.20, respectively. The fruits' dry matter content was not significantly influenced by the studied treatments. The results were derived from one year experiment, and they have to be confirmed in future experiments. However, they indicate that compost, whether sieved or not can be a valuable solution for the processing tomato fertilization and that deficit irrigation can be a valuable solution to reduce agricultural water use with only a few effects on plant production and quality parameters.