Tomato Crop Performances under Chemical Nutrients Monitored by Electric Signal

Abstract

Fertigation is considered an efficient alternative to the enhanced use of chemical fertilizers. Since most of the fertigation systems rely on a theoretical electrical conductivity value of the nutrient solution, we tried to evaluate if this is the real need of the plants as well as if all the nutrients are needed at once. Therefore, we analyzed the electrical signals of the nutrients applied individually or in different mixes, correlating the electrical signals with the leaf gas exchange processes, studying the relation between the electrical signals and different plant phenological stages and the influence of the treatments on the lycopene content, nutritional composition, and antinutritional factors as well as the mineral bioavailability of tomato fruits cv. Brillante F1. The study was carried out in a greenhouse under controlled conditions. Ten different treatments consisting of MaEs (major elements) (V1—MgSO4, V2—KNO3, V3—K2SO4, V4—Ca(NO3)2, V5—KH2PO4, V6—KCl, V7—MgSO4 + KNO3 + KH2PO4, V8—K2SO4 + Ca(NO3)2 + KCl, V9—the mix of V1 to V6, commonly used in agricultural practices, V10—one nutrient each day) were applied daily when plants were 42 days old. The results showed that the values of the electrical signals varied depending on the treatment and the plant phenological stage. Five different trends of the electrical signals were identified. In addition, the shape of the signals varied during the day in accordance with the photosynthesis and the amount of CO2 registered. The results of the treatments’ influence on the nutritional composition and lycopene content of tomato fruits suggested that plants do not need all the nutrients at once; the highest values are registered for K2SO4 fertilization. However, this fertilizer also had the highest registered tannin, saponin, and trypsin inhibitors content, constituting a disadvantage considering the high nutritional values and lycopene content. Regarding the bioavailability of zinc, calcium, and iron for the human diet, regardless of the treatment applied, phytic acid did not affect the availability of zinc and calcium, but it had a negative impact on iron availability; also, the amount of oxalate could impair the bioavailability of calcium. The study suggests that tomato plants do not need all nutrients at once for quality fruits. However, further studies are needed in order to develop a fertigation scheme based on a smart nutrient use that provides an improved nutritional composition and mineral bioavailability. In addition, it is necessary to evaluate the influence of treatments on yield.