Eddie Schrevens

Design and analysis of mixture systems: Applications in hydroponic, plant nutrition research

This study demonstrates that nutrient solutions can be defined as ‘mixture systems’. A general methodology for design and analysis of mixture optimization experiments is developed. The emphasis is centered on multivariate investigation of the zone of optimal solution properties as a function of the ion composition and the total ionic strength of the solution. The study of the effects of ion interaction on well-defined solution properties is also possible by this multivariate approach. This work is a valuable tool in mineral nutritional research, because for the first time the chemical feasibility conditions of such solution, combined with additional chemical, physiological or economical constraints, form the foundation of the statistical experimental design theory, which makes the optimization of complex mixtures of ions in relation to well-defined response variables possible.

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.

Dealing with sources of variability in the data-analysis of phenotyping experiments with transgenic rice

The analysis of phenotyping experiments for transgenics deserves special attention. Experiments set up for the detection of interesting phenotypes among transgenic plants have to screen several primary events obtained by transforming with a particular transgene, since expression levels of the transgene differ considerably. Agronomically most interesting lines might have an intermediate level of transgene expression. Therefore, attention should be paid to all transformants and how their expression levels differ. Experimental design and the analysis of the data have to focus on the variability among lines and have to be able to detect small differences in quantitative traits. The mixed model is the most adequate approach to analyse data of phenotyping experiments because it reflects the structure and provides the researcher with important measures to allow broader inferences. The paper explains the model and illustrates it using a screening experiment carried out by the high-throughput phenotyping method of TraitMillTM. Besides inference for a particular experiment and a particular set of lines, the output allows more general predictions for a wider set of non-tested lines. It quantifies the various sources of variability encountered and helps to understand the underlying process. It also helps to optimise the experimental set-up of future experiments. The model presented here has been implemented in the R-language and SAS. The scripts are attached.

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).

Estimating the parameters of a 3-D root distribution function from root observations with the trench profile method: case study with simulated and field-observed root data

Background and aimsRoot length density (RLD) is a parameter that is difficult to measure, but crucial to estimate water and nutrient uptake by plants. In this study a novel approach is presented to characterize the 3-D root length distribution by supplementing data of the 3-D distribution of root intersections with data of root length density from a limited number of soil cores.MethodsThe method was evaluated in a virtual experiment using the RootTyp model and a field experiment with cauliflower (Brassica oleracea L. botrytis) and leek (Allium porrum, L.).ResultsThe virtual experiment shows that total root length and root length distribution can be accurately estimated using the novel approach. Implementation of the method in a field experiment was successful for characterizing the growth of the root distribution with time both for cauliflower and leek. In contrast with the virtual experiment, total root length could not be estimated based upon root intersection measurements in the field.ConclusionsThe novel method of combining root intersection data with root length density data from core samples is a powerful tool to supply root water uptake models with root system information.

Analysis of Potato Canopy Coverage as Assessed Through Digital Imagery by Nonlinear Mixed Effects Models

The characterization of the dynamics of canopy coverage represents a relevant matter of study in the field of crop physiology. The objective of this work was to calibrate a model able to simulate potato canopy coverage as a function of thermal time, but including the error structure in such model. This was accomplished by using a mixed effects modelling approach where random effects were added to the average response model. By applying this modelling approach, the structure of the data was taken into account. Calibration data for the model were obtained from canopy coverage estimates derived from image processing analysis. Digital images were taken periodically within 11 potato fields located in the Mantaro Valley (Peru) during the 2005–2006 growing season. This model gave a better fit in comparison with the traditional fixed parameters model. An additional uncertainty analysis with the objective of estimating the confidence region for the predictions of the mixed effects model was carried out. By exploring the data structure, a more comprehensive overview of the potato canopy coverage was achieved with the mixed effects model.

Sustainability aspects of vegetable production in the peri-urban environment of Bogotá, Colombia.

Although the peri-urban region around Bogotá, Colombia contains a diversified horticulture sector, local vegetable production suffers from a critical lack of research and availability of un-biased, scientifically validated information on crop management. In this study, we identify current trends and deficiencies in fertilisation and pest management for local vegetable production. We relate pesticide type with target pests, evaluate temporal patterns in pesticide and fertiliser use for a key crop (i.e. spinach) and conduct basic nutrient budget accounting. Personal interviews with vegetable growers were combined with a detailed follow-up of management activities and soil nutrient profiles on pilot farms in two different peri-urban municipalities. Most (84%) vegetable growers relied on personal experience, and indicated a lack of unbiased information on fertiliser effectiveness and pesticide action spectra. The majority of farmers used pesticide mixtures on a calendar basis and commonly applied products below recommended doses. Soil nutrient accounts indicate insufficient fertilisation and a progressive depletion of key nutrients. Extraction rates for the principal vegetable crops exceeded by 33.6%, 20.5% and 93.0% soil nutrient availability of N, P and K, respectively. Organic products are included in local fertilisation schemes, with chicken manure as the principal source, at an average application rate of 6 t ha−1. Our findings could help policymakers and local institutions set a research and extension agenda to promote sustainable peri-urban vegetable production and help secure peri-urban livelihoods while ensuring healthy and safe horticultural production.