Giulia Carmassi

Modeling Salinity Build-Up in Recirculating Nutrient Solution Culture

Abstract This paper presents a simple model for the changes in ion concentration and electrical conductivity (EC) of the recirculating nutrient solution in a closed-loop soilless culture of tomato (Lycopersicon esculentum Mill.). The model was designed on the basis of a balanced equation for plant nutrient uptake: for macrocations (K+, Mg2+ and Ca2+), a linear dependence of concentration on crop water uptake was assumed, while for non-essential ions, such as sodium (Na+), a non-linear function was used. The model was developed for closed-loop hydroponic systems in which crop water uptake (namely, transpiration) is compensated by refilling the mixing tank with complete nutrient solution. In these systems, EC gradually increases as a result of the accumulation of macro-elements and, principally, of non-essential ions, like Na+, for which the apparent uptake concentration (i.e., the ratio between nutrient and water uptake) is lower than their concentration in the irrigation water. For model calibration, data from both the literature and a previous work were used, while validation was performed with data from original experiments conducted with tomato plants in different seasons and using water with different sodium chloride (NaCl) concentrations (10 and 20 meq/L). The results of validation indicate that the model may be a useful tool for the management of closed-loop hydroponics, because it simulates rather well the salt accumulation that occurs in the recirculating nutrient solution when it is prepared with irrigation water of poor quality. Furthermore, the model is able to estimate the amount of crop evapotranspiration that leads to a value of EC at which flushing is necessary, thus enabling one to predict the water and nitrogen runoff of the semi-closed soilless culture.

Spatial and temporal distribution of mineral nutrients and sugars throughout the lifespan of Hibiscus rosa-sinensis L. flower

Although the physiological and molecular mechanisms of flower development and senescence have been extensively investigated, a whole-flower partitioning study of mineral concentrations has not been carried out. In this work, the distribution of sucrose, total reducing sugars, dry and fresh weight and macro and micronutrients were analysed in Hibiscus rosa-sinensis L. petals, stylestigma including stamens and ovary at different developmental stages (bud, open and senescent flowers). Total reducing sugars showed the highest value in petals of bud flowers, then fell during the later stages of flower development whereas sucrose showed the highest value in petals of senescent flowers. In petals, nitrogen and phosphorus content increased during flower opening, then nitrogen level decreased in senescent flowers. The calcium, phosphorus and boron concentrations were highest in ovary tissues whatever the developmental stage. Overall, the data presented suggests that the high level of total reducing sugars prior the onset of flower opening contributes to support petal cells expansion, while the high amount of sucrose at the time of petal wilting may be viewed as a result of senescence. Furthermore, this study discusses how the accumulation of particular mineral nutrients can be considered in a tissue specific manner for the activation of processes directly connected with reproduction.

EFFECTS OF CALCIUM AND SALINITY STRESS ON QUALITY OF LETTUCE IN SOILLESS CULTURE

Lettuce (Lactuca sativa L.) var. ‘Lollo rossa’ was grown in a floating hydroponic system. Six saline treatments were used, adding different concentrations of calcium chloride (CaCl2) to the nutrient solution (mol m−3): 0, 2.5, 5, 10, 15, 20, which, respectively, corresponds to an electrical conductivity of 2.5, 3, 3.5, 4.4, 5.4, 6.3 dS m−1. In plants subjected to moderate salinity stress the growth was not affected and yields were not statistically significant; however, the data shows a slight decline in 20 mol m−3 CaCl2 treatments. Nitrate contents in the leaf decreased when the concentration of CaCl2 in nutrient solutions increased. Other quality parameters were positively affected by treatment with CaCl2, especially at moderate concentrations such as 5 and 10 mol m−3. In fact, both the content of phenols and antioxidant power increased at moderate salt concentrations and reduced in the treatment with 20 mol m−3 CaCl2. The content of chlorophyll and carotenoids were not affected by treatment even at high salt concentrations. The use of CaCl2 did not result in nutrition imbalances in plants either. In fact, the ratio K/Na remained unchanged in the various treatments, as well as the contents of microelements.

RESPONSE TO SODIUM CHLORIDE SALINITY AND EXCESS BORON IN GREENHOUSE TOMATO GROWN IN SEMI-CLOSED SUBSTRATE CULTURE IN A MEDITERRANEAN CLIMATE

The effects of sodium chloride (NaCl) salinity and boron (B) toxicity were investigated in greenhouse tomato (Solanum lycopersicum L.) plants grown in closed soilless culture under the typical climatic conditions occurring in the Mediterranean regions. The experiment was conducted under semi-commercial conditions. Two NaCl (2.0 and 10.0 mol m−3) and B (27.8 and 185.0 mmol m−3) concentrations were combined to produce four different types of raw water used to prepare the nutrient solutions. The fertigation treatment did not affect significantly the uptake of water and mineral elements apart from that of sodium (Na), chloride (Cl), and B. The use of B-enriched water increased the accumulation of this element in the leaves, which showed marginal chlorosis and necrosis within 35–40 days from planting. No or minor effects of NaCl and B concentrations in the irrigation water were found on leaf area development, biomass accumulation, crop yield and fruit quality.

Effects of Treated and Untreated Wastewater from Municipal Solid Waste (MSW) Leachates on the Nutritional State of Viola spp.: Sodium, Potassium, Calcium, and Magnesium

The scarcity of water for different uses has created a need for using nonconventional water resources, such as wastewater and saline water. Their use could contribute to reduced water resource consumption in arid areas and biosphere contamination. Wastewaters are normally unbalanced solutions rich in sodium (Na+), calcium (Ca2+), magnesium (Mg2+), sulfate (SO4 2−), and chloride (Cl−), which can cause damages to crops, but if they are treated, their quality can increase. The aim of this trial was to study the effects of pure, diluted, sand-filter depurated, and phytodepurated wastewater from municipal solid waste (MSW) leachates, compared with groundwater on the nutritional state of the ornamental plant Viola spp. The experimental design was unifactorial (type of irrigation water). Five treatments were tested: R9.0 [wastewater, electrical conductivity (EC) 9.0 dS m−1], R4.5 (wastewater, EC 4.5 dS m−1), D4.5 (depurated water, EC 4.5 dS m−1), FD4.5 (phytodepurated water, EC 4.5 dS m−1), and P (groundwater, EC 1.5 dS m−1). Nutrient (Na+, K+, Ca2+, and Mg2+) concentrations and partitioning per fraction (flowers, aerial vegetative fraction, including stems and leaves [called AVF], and roots) were studied. Similar total Na+ extractions were found in the 4.5 dS m−1 treatments, being greater than in the 9.0 dS m−1 treatment, all of the surpassing the control. Nevertheless, there were Na+ partitioning per fraction differences depending on Na+ concentration. Total K+ extraction was the greatest in FD4.5, related with its greater root concentration. Potassium was mainly located in AVF, followed by flowers. Calcium and Mg2+ extractions showed a similar behavior. The greatest Ca2+ extraction was noticed in control plants, which is related with Ca2+ accumulation in roots.

Modelling Evapotranspiration of Container Crops for Irrigation Scheduling

Irrigation is now recognized as an important component in the agriculture economy of Mediterranean regions. As practiced by many growers, it is often based on traditional application methods that fail to measure the supply of water needed to satisfy the variable requirements of different crops. In order to achieve more profitable and sustainable cropping systems, it is essential to modernize existing irrigation systems and improve irrigation water use efficiency (WUE). Up-to-date methods of irrigation should likewise be based on sound principles and techniques for attaining greater control over the soil-cropwater regime and for optimizing irrigation in relation to all other essential agricultural inputs and operations. Accurate predictions of crop water requirements are necessary for an efficient use of irrigation water in container crops cultivated both outdoors and in greenhouse. Irrigation scheduling (IS) has conventionally aimed to achieve an optimum water supply for productivity, with soil or container water content being maintained close to field capacity. Different approaches to IS have been developed, each having both advantages and disadvantages but despite the number of available systems and apparatus, not entirely satisfactory solutions have been found to rationalize IS, assuring optimal plant growth with minimal water use (Jones, 2004). Many growers, especially in the Mediterranean regions, use simple timers for automated irrigation control of containerized crops and scheduling is based on their own experience. Evapotranspiration (ET) is the primary process affecting crop water requirements and, therefore, its knowledge is essential for efficient irrigation management. ET is the combined process of evaporation from soil or substrate and leaf transpiration. Evapotranspiration requires two essential components: a source of energy and a vapour transport mechanism. Energy is needed for phase change from liquid to vapour in sub-stomatal cavities whereas the leaf-to-air vapour pressure gradient ensures that water vapour crosses leaf stomata. In container-grown plants, ET is affected by many factors, both environmental (e.g. air temperature, radiation, humidity, wind speed) and plant related characteristics (e.g. growth