G De Rijck

pH Influenced by the elemental composition of nutrient solutions

Abstract Nutrient solutions can be considered as aqueous solutions of inorganic ions. The pH of a nutrient solution is a property that is inherent to its composition. If another pH is aimed at, this can only be reached by changing the elemental composition. The pH of an aqueous solution is determined by the initial concentration of acids and bases. In the case of nutrient solutions, this is dihydrogen phosphate (H2PO4 ‐), bicarbonate (HCO3 ‐) and/or ammonium (NH4 +). In this study, formulas are derived to calculate the pH of a nutrient solution as a function of the concentration of H2PO4 ‐, NH4 +, and/or HCO3 ‐. The pH of a nutrient solution affects the dissociation, complexation, and precipitation reactions occurring in nutrient solutions. These chemical reactions significantly impact elemental speciation and bioavailability, and therefore, have to be taken into account in hydroponic plant nutritional research. The term “speciation”; indicates the distribution of elements among their various chemical and...

Elemental bioavailability in nutrient solutions in relation to precipitation reactions

Abstract In general in hydroponic plant nutritional research as well as in commercial hydroponic plant cropping, the actual nutritional composition is supposed to be exactly the same as the desired one. Furthermore, it is supposed that the nutrients are present in the nutrient solution as free ions. This way of thinking does not take into account the dissociation, complexation, and precipitation reactions occurring in nutrient solutions. These chemical reactions seriously impact elemental speciation and bioavailability. As a result, plants will experience a completely different nutritional composition. An accurate description of the chemical reactions occurring in nutrient solutions gives an accurate insight into mineral composition offered to the plants. This additional information is a valuable tool in interpreting specific effects of the mineral composition of the nutrient solution on dependent variables. A good knowledge of the chemical reactions occurring in nutrient solutions is the first prerequisi...

Cationic speciation in nutrient solutions as a function of pH

In hydroponic plant nutritional research, nutrient solutions are aqueous solutions containing all the essential macro- and micronutrients. In general, nutrient solutions are looked at as static aqueous solutions of inorganic ions. The ions are supposed to be present as free ions. This assumption does not take into account the dissociation, complexation, and precipitation reactions occurring in nutrient solutions and their dynamic equilibrium. All these reactions take place at the same time and interact with each other, affecting elemental speciation and bioavailability. In this research, only speciation calculations are carried out. For a standard nutrient solution, containing Fe(HEDTA) as iron chelate, elemental speciation is calculated for a pH range from 2.0 to 9.0. For all anions present in the nutrient solutions, the formation of precipitates, ion pairs, and soluble complexes as a function of pH are graphically represented.

Comparison of the mineral composition of twelve standard nutrient solutions

Abstract In the past, a large number of standard nutrient solutions has been devised. To investigate if there is an essential difference between these standard solutions, the mineral composition of 12 standard nutrient solutions formulated between 1865 and 1994 are compared with each other. Half of these standard solutions contain ammonium (NH4 +) in a millimolar range. The effect of elemental speciation of the micronutrients in the 12 standard solutions on bioavailability is compared. The macronutrient composition is represented in trilinear coordinates, making a clear comparison of the proportions of both the cations and the anions possible. Also the pH and the total amount of ions present are compared.

Multifactorial optimisation of the nutrient solution for hydroponically grown chicory plants

Abstract This research elaborates a methodology for experimenting with the mineral composition of nutrient solution in a multifactorial way using mixture theory. Under an open plastic greenhouse chicory plants were cultivated in hydroponics. To investigate, in a multifactorial way, the influence of the anion composition of the nutrient solution, an experimental design was setup with the independent variables NO − 3 , H 2 PO − 4 , SO 2− 4 and Cl − , using a mixture approach. A specific mixture model was fitted to the macromorphological measurements of both the vegetative and the reproductive growth phase. For two response variables (number of leaves and forcing efficiency), the models were used to represent the response surface over the experimental region. The nitrate concentration of the nutrient solution applied during the vegetative growth of the chicory plants was the most important factor in influencing both vegetative and reproductive growth of the chicory plants. A high nitrate concentration in the nutrient solution during the vegetative growth phase resulted in luxuriant vegetative growth, while the reproductive growth was poor (low production of chicory heads of inferior quality).

Chemical feasibility region for nutrient solutions in hydroponic plant nutrition

Abstract In experimenting with nutrient solutions in hydroponic plant nutritional research, the chemical feasibility region of the nutrient solution is a conditio sine qua non. If in preparing a nutrient solution some ions precipitate, the desired concentration of the dissolved ions can not be reached. This means that the desired nutritional composition is chemically not feasible. For the six essential macronutrients: potassium (K+), calcium (Ca2+), magnesium (Mg2+), nitrate (NO3 ‐), dihydrogen phosphate (H2PO4 ‐), and sulphate (SO4 2‐), the chemical feasibility region is investigated using the computer speciation program Geochem PC version 2.0. In this way the impact of pH, dissociation reactions, and complexation reactions on precipitation reactions is taken into account. As the total milliequivalent concentration of the nutrient solution increases, the chemical feasibility region reduces.

Thermal conductivity sensing for on-line monitoring and control of the moisture content in rockwool slabs

On-line measuring and controlling the climate in a greenhouse is daily practice and can easily be done with climate computers. An automatic on-line and direct measurement of the moisture content of a substrate with growing plants is a major lack in the general automation of horticulture on substrates. The use of thermal conductivity sensing, makes it possible to measure and control the moisture content on-line in inert substrates like rockwool. In this way it is possible to supply nutrient solution to plants according to their demands. The thermal conductivity of a homogeneous substrate increases if its moisture content increases. Thermal conductivity measurements are fully controlled by a computer, connected with the irrigation system of the greenhouse. Examples of automatic irrigation in a tomato crop on rockwool slabs, where the computer decides if it is necessary to irrigate or not are elaborated.

Comparison of Unifactorial and Mixture Approaches for Optimization of Mixing Time and Flour and Water Contents in Breadmaking Formulas

ABSTRACT A unifactorial approach was compared with a multifactorial approach, based on mixture theory, using bread optimization. The effects of dough weight and formula, as well as mixing time, on bread properties were investigated. The unifactorial approach indicated that increasing the weight of water added to flour increased bread weight. Changing the weight of water in dough also changed the proportion of all the ingredients and total dough weight. The unifactorial approach could not unequivocally indicate the variable responsible for increases in bread weight. Conversely, the multifactorial approach clearly indicated that increased dough weight increased bread weight.