C. Blok - Academia.edu (original) (raw)

Papers by C. Blok

Soil properties of importance are dry bulk density, organic matter content, nutrient content and ... more Soil properties of importance are dry bulk density, organic matter content, nutrient content and water holding capacity. Rooting media properties of importance are pH, EC, water retention, water uptake rate, porosity, stability, shrinkage and nitrogen fixation. Miscommunication between producers and user groups can be avoided by measuring the relevant properties using methods users are familiar with. Special attention is needed to interpret total nutrients, extracted nutrients and organic matter content.

In the Netherlands most crops grown in greenhouses reuse drain water. However, in the cultivation... more In the Netherlands most crops grown in greenhouses reuse drain water. However, in the cultivation of amaryllis cut flowers (Hippeastrum) little drainage water is being reused so far because of strong suspicions of inhibitory substances in the drainage water. To reduce the emission of nutrients to the environment an experiment was started on request of the amaryllis growers. In a greenhouse experiment drainage water of amaryllis was treated with advanced oxidation and reused. This was compared with the reuse of drainage water treated with an UV disinfector and a control treatment without the reuse of drainage water. In three years of cultivation, there was no difference in production and no adverse effects were seen in crop growth. This research was funded by the Dutch amaryllis growers, the ‘Topsector Tuinbouw en Uitgangsmaterialen’, the Product Board for Horticulture, the project ‘Samenwerken aan Vaardigheden’ and Koppert.In the Netherlands most crops grown in greenhouses reuse dra...

De doelstelling van het CocoMix project is het ontwikkelen van een substraat waarin geen veen mee... more De doelstelling van het CocoMix project is het ontwikkelen van een substraat waarin geen veen meer is verwerkt. Positief is dat de markt al behoorlijk in beweging is om veen te vervangen. De markt heeft tot op heden een aantal positieve resultaten behaald met verschillende ‘veenvervangers’ (Blok & Verhagen, 2009). Toch blijkt dat altijd nog een percentage veen nodig is om problemen met wortelgroei in de propagationfase te voorkomen. IntroVation is door de SBIR van het ministerie van LNV in staat gesteld een substraat te ontwikkelen dat voor 100% veenvrij is. Kokos is een substraat met een aantal gunstige eigenschappen. Doordat kokos weinig nutrienten bevat (lage EC-waarde) kan de teler de voedingstoffen goed controleren. Daarnaast heeft kokos een gunstig water en luchthuishoudingen kan het na indroging weer makkelijk vocht opnemen. Kokos mist echter een hechtende eigenschap, dit maakt het moeilijk om zwartveen te vervangen. Bovendien is de pH van kokos te hoog en te instabiel. In de...

Hydroponic production systems are challenged by root diseases, but can be made less susceptible t... more Hydroponic production systems are challenged by root diseases, but can be made less susceptible to infection. While the systems are mostly unchallenged by nematodes, pathogens that can live and spread though water still cause loss of yield. Common diseases would be Phytophthora, Pythium, Fusarium and bacteria such as Erwinias and Pseudomonads. Since horticulture cannot be performed in a sterile environment on a commercial scale, insight in population dynamics of pathogens in aquatic systems as well as plants' resilience need to be understood to lower the risk of infection. This paper addresses a number of biological principles in aquatic ecology that could be used in improving system design processes as well as providing the first data on the population dynamics in chrysanthemum production on deep flow systems in The Netherlands using next generation sequencing (NGS). It was observed that free colonisation of the water leads to highly diverse bacterial populations, while inocula...

Acta Horticulturae, 2019

Phalaenopsis is the top-selling ornamental pot plant in the Netherlands, and the area under its p... more Phalaenopsis is the top-selling ornamental pot plant in the Netherlands, and the area under its production was 242 ha in 2014. Previously, production systems of Phalaenopsis (open or free to drain systems) resulted in high emission of nutrients to the ground and surface water, approximately 1500 kg N ha-1 year-1 , in the Netherlands. Little is known of the response of Phalaenopsis to water reuse systems, as orchids have been exempt from recirculation obligations owing to their salt sensitivity. Regulations aimed to reduce nitrogen (N) emissions to a maximum of 150 kg ha-1 year-1 in 2018, with the ultimate goal being 0 kg ha-1 year-1 , in 2027. Wageningen University and the Research Business Unit Greenhouse Horticulture were commissioned by the government as well as the Phalaenopsis grower association of the Netherlands to develop a system that could achieve the current goal of a maximum of 150 kg N ha-1 year-1. A recirculation system with UV disinfection and the reuse of drain water was utilized at the experimental site in Bleiswijk. Two recirculation treatments were tested with the aim to maintain the current production and quality levels while also lowering the emissions to the standard of 2018, with the possibility of further improvements to achieve the desired standards for 2027. The aim of the first reuse treatment was to discard small amounts of drain water to keep sodium at a maximum of 1.2 mmol L-1. In the second treatment, as much drain water was reused as possible. Emissions of N were reduced to 182 and 60 kg ha-1 year-1 , respectively. Plant growth parameters including leaf number, total leaf area, and number of spikes and flowers, showed no significant differences. In this experiment reuse of drain water reduced emissions considerably without any adverse effects on plant growth or disease incidence.

Acta Horticulturae, 2019

Competition for freshwater resources, and legal restrictions on discharge of agrochemicals (plant... more Competition for freshwater resources, and legal restrictions on discharge of agrochemicals (plant protection products and fertilisers) increase pressure on agricultural practice to improve water-use-efficiency of crop production globally. Zero-discharge greenhouse crop production can be an effective solution to both problems. Preliminary results of experiments with cucumber and sweet pepper on stone wool substrate in two greenhouse compartments showed that productivity did not significantly differ in zero-discharge growing compared to standard growing strategies. In this paper we present the final evaluation of the sweet pepper trial (December 2014-November 2015). In the reference compartment a total amount of 465 m 3 ha-1 y-1 (169.3kg N) was discharged. In the zero-discharge compartment there was no discharge during cropping. The nutrient composition of irrigation and drain water was analysed weekly (compared to two-weekly in reference) and nutrient stock composition was changed accordingly. Drain water was filtered with a flatbed filter (no rinsing water) and upon changes in fertigation, the new fertigation solution was first distributed throughout the entire irrigation system by a circulation pump, before application. An irrigation strategy was developed for the end of the cropping season, aiming to drain substrate slabs and to empty drain tanks as much as possible and reduce the amount of remaining nutrients in the slabs, without compromising productivity. Water-use-efficiency of the zero-liquid discharge strategy was lower than in de reference strategy, due to a more vegetative crop growth.

IV International Symposium on Irrigation of Horticultural Crops, 2004

Measurements of crop transpiration have been carried out by the Applied Plant Research station in... more Measurements of crop transpiration have been carried out by the Applied Plant Research station in Naaldwijk for many years with increasingly better weighing equipment. Ultimately a weighing gutter system has been developed that operates well under practical conditions and is a useful tool in crop management. The APR-Naaldwijk weighable gutter system monitors the water management of greenhouse crops and offers information for checking and automatically regulating the water supply. The collected data offer additional information on climate control and fresh weight growth of the crop. The system and results from testing are presented in this paper.

International Symposium on Growing Media 2007, 2009

The aim of the study was to get accurate data on the effects of mixing container media components... more The aim of the study was to get accurate data on the effects of mixing container media components and to match these data against models for mixing container media. It was accepted that the mixing of two container media components was related linearly to the amounts of material mixed, for parameters such as degradability. For other parameters the extra material necessary to compensate for the effect of interstitial filling had to be taken into account. Four different two component mixes were measured for 36 different ratios in all. Moisture content, air content, shrinkage, density and EC and pH were measured for each mixture. A formula based on measured densities of the components and the mix was used to predict moisture/air content in the mixes. It is concluded that the formula and the underlying method underestimate the water content in relatively wet materials such as peat-coir products and overrate the moisture content for relatively dry materials such as peat and flax straw mixes. The increase in density of the mix may be calculated either by measuring the volume loss or the density increase of one or more test mixes, from modelling a simplified particle size distribution, or from an empirically calculated relationship with particle size distribution parameters.

International Symposium on Growing Media and Soilless Cultivation, 2014

Recycling of the nutrient solution during cultivation of greenhouse crops reduces the total input... more Recycling of the nutrient solution during cultivation of greenhouse crops reduces the total input of water and fertilizers and decreases emission of nutrients to the environment. However growers fear accumulation of harmful substances in the drain water. For this reason drain water in practice is regularly discharged into the environment. In this study drain water from a commercial rose grower in The Netherlands was tested with a phytotoxicity test (Phytotoxkit) during a period of one year. The Phytotoxkit was used to assess growth response of drain water without disinfection; drain water disinfected with UV; drain water disinfected with UV and peroxide. In this phytotoxicity test, garden cress (Lepidium sativum) and mustard (Sinapis alba) are grown in a Phytotoxkit container on a filter paper moistened with the drain water under analysis. After incubation for three days in a climate-controlled cabinet, root length is measured. The Phytotoxkit showed growth decrease caused by untreated drain water disappeared when using a UV disinfection of 100 MJ.cm-2 or UV disinfection of 100 MJ.cm-2 combined with 10-25 ppm peroxide. Untreated drain water caused growth responses of-20% root length in only 3 out of 10 sample moments. Control of drain water with the Phytotoxkit provides the grower information about the presence of phytotoxic substances in the drain water and the effectiveness of treatments. The Phytotoxkit thus can prevent unnecessary discharge of drain water to the environment.

Dit onderzoek had als doel om de werking van electrolysewater te verbinden met de chemische eigen... more Dit onderzoek had als doel om de werking van electrolysewater te verbinden met de chemische eigenschappen en op zoek te gaan naar veilige toepassingen als gewasbehandeling voor de glastuinbouwsector. Vijf producenten hebben voor dit onderzoek de gewenste samenstelling van electrolysewater aangeleverd. Alle producten met daarin 36-65 ppm vrij chloor waren binnen vijf minuten 100% effectief tegen de bacterie, Erwinia chrysanthemi en de schimmel, Botrytis cinerea. De grenzen van gewasschade in de kiemplantentest werden sterker bepaald door de hoeveelheid natriumzout en EC gehalte van de electrolysevloeistof dan de hoeveelheid vrij chloor. In een korte meedruppelproef met tomaat zijn verschillende concentraties vrij chloor (0, 4, 8, 20 ppm) gedoseerd aan het voedingswater. Er werd geen gewasschade gevonden of negatief effect op de wortelkolonisatie van Trianum door de geringe chloorwaardes (vrij en totaal) die na vier weken bij de druppelaar werden teruggemeten. Testen met gewasbehandelingen laten zien dat éénmalige behandelingen tot 300 ppm geen gewasschade geven. Bij meerdere toepassingen is groeiremming te voorkomen door lagere concentraties te gebruiken of blootstellingstijd te beperken. Electrolysewater kan een veilig en bruikbaar alternatief bij het terugdringen van het fungicidegebruik.

International Symposium on Growing Media, 2008

For routine toxicity testing of composts and growing media, two different types of assays are usu... more For routine toxicity testing of composts and growing media, two different types of assays are usually applied. One approach is the use of growing trials in pots with various mixtures of the material. In extract-based tests, seeds are germinated in petri dishes and exposed to an exudate from the material to be tested. In this study, one of these methods, the Phytotoxkit microbiotest, was compared to the standard phytotoxicity test with Lactuca sativa as used by the RHP foundation. The Phytotoxkit test was performed in transparent test containers which allow for direct observation and length measurements of the seedlings by means of image analysis. Two dicotyles (Lepidium sativum and Sinapis alba) and one monocotyle (Sorghum saccharatum) were used. When measuring a presumably phytotoxic bark, in comparison with a reference bark, the Phytotoxkit showed a seedling length inhibition of 60-80% for the dicotyles and less than 20% for the monocotyle after three days. The RHP growing trial showed 30% weight inhibition of the lettuce after two weeks of plant growth when comparing the same barks in mixtures. This preliminary comparison showed that the Phytotoxkit microbiotest is a quick and practical bioassay with a high resolution which has a potential to become an international standard.

Bioresource Technology, 2010

In a Plant Microbial Fuel Cell (P-MFC) three plants were tested for concurrent biomass and bio-el... more In a Plant Microbial Fuel Cell (P-MFC) three plants were tested for concurrent biomass and bio-electricity production and maximization of power output. Spartina anglica and Arundinella anomala concurrently produced biomass and bio-electricity for six months consecutively. Average power production of the P-MFC with S. anglica during 13 weeks was 16% of the theoretical maximum power and 8% during 7 weeks for A. anomala. The P-MFC with Arundo donax, did not produce electricity with a stable output, due to break down of the system. The highest obtained power density in a P-MFC was 222 mW/m 2 membrane surface area with S. anglica, over twice as high as the highest reported power density in a P-MFC. High biomass yields were obtained in all P-MFC's, with a high root:shoot ratio, probably caused nutrient availability and anaerobia in the soil. Power output maximization via adjusting load on the system lead to unstable performance of the P-MFC.

This report decribes experiments with anaerobic digestation of champost and organic rest products... more This report decribes experiments with anaerobic digestation of champost and organic rest products for re-use in mushroom casing. The digestates will reduce the emission of carbon dioxide by peat use for casing and will reduce the number of transport movements. Both reductions serve the mushroom sector. Wageningen UR Greenhouse Horticulture is measuring the quality aspects of the digestates with standard methods used in the potting soil industry such as texture, organic matter and nutrient and ash content. In this report a literature review and measurements of digestates and casings are combined. The literature review lists critical values for amongst others salt, water and air content. It is argued values per unit volume are more informative on water and air distribution than values per unit weight. Extract indicate nutrient levels but only deliver an indirect indication of how plants or mushrooms experience their environment. Measurements indicate it is necessary to wash digestates...

The area of crops like tomato and peppers and roses grown on rooting media is worldwide increasin... more The area of crops like tomato and peppers and roses grown on rooting media is worldwide increasing. The driving force seems the combination of higher yield levels and the possibility to avoid diseases while still mono cropping. Increasingly the possibilities to avoid emissions of crop protectants and nutrients become important too. Finally the need to increase the efficiency with which irrigation water is turned into marketable products is becoming urgent in many parts of the world, including southern Europe. It is therefore a safe assumption that the area of substrate grown crops in the world will remain increasing for a very long time to come. Eventually the area of plants grown on substrates in the field may surpass the area of plants grown on substrates in greenhouses.

De werking is getest van een flexibel geautomatiseerd meet- en regelsysteem voor de ammoniumgift ... more De werking is getest van een flexibel geautomatiseerd meet- en regelsysteem voor de ammoniumgift (afhankelijk van de pH van de drain). Het effect is van de verhoogde ammoniumgift op de pH, de gewassamenstelling en gewasproductie is gemeten.

Soil properties of importance are dry bulk density, organic matter content, nutrient content and ... more Soil properties of importance are dry bulk density, organic matter content, nutrient content and water holding capacity. Rooting media properties of importance are pH, EC, water retention, water uptake rate, porosity, stability, shrinkage and nitrogen fixation. Miscommunication between producers and user groups can be avoided by measuring the relevant properties using methods users are familiar with. Special attention is needed to interpret total nutrients, extracted nutrients and organic matter content.

In the Netherlands most crops grown in greenhouses reuse drain water. However, in the cultivation... more In the Netherlands most crops grown in greenhouses reuse drain water. However, in the cultivation of amaryllis cut flowers (Hippeastrum) little drainage water is being reused so far because of strong suspicions of inhibitory substances in the drainage water. To reduce the emission of nutrients to the environment an experiment was started on request of the amaryllis growers. In a greenhouse experiment drainage water of amaryllis was treated with advanced oxidation and reused. This was compared with the reuse of drainage water treated with an UV disinfector and a control treatment without the reuse of drainage water. In three years of cultivation, there was no difference in production and no adverse effects were seen in crop growth. This research was funded by the Dutch amaryllis growers, the ‘Topsector Tuinbouw en Uitgangsmaterialen’, the Product Board for Horticulture, the project ‘Samenwerken aan Vaardigheden’ and Koppert.In the Netherlands most crops grown in greenhouses reuse dra...

De doelstelling van het CocoMix project is het ontwikkelen van een substraat waarin geen veen mee... more De doelstelling van het CocoMix project is het ontwikkelen van een substraat waarin geen veen meer is verwerkt. Positief is dat de markt al behoorlijk in beweging is om veen te vervangen. De markt heeft tot op heden een aantal positieve resultaten behaald met verschillende ‘veenvervangers’ (Blok & Verhagen, 2009). Toch blijkt dat altijd nog een percentage veen nodig is om problemen met wortelgroei in de propagationfase te voorkomen. IntroVation is door de SBIR van het ministerie van LNV in staat gesteld een substraat te ontwikkelen dat voor 100% veenvrij is. Kokos is een substraat met een aantal gunstige eigenschappen. Doordat kokos weinig nutrienten bevat (lage EC-waarde) kan de teler de voedingstoffen goed controleren. Daarnaast heeft kokos een gunstig water en luchthuishoudingen kan het na indroging weer makkelijk vocht opnemen. Kokos mist echter een hechtende eigenschap, dit maakt het moeilijk om zwartveen te vervangen. Bovendien is de pH van kokos te hoog en te instabiel. In de...

Hydroponic production systems are challenged by root diseases, but can be made less susceptible t... more Hydroponic production systems are challenged by root diseases, but can be made less susceptible to infection. While the systems are mostly unchallenged by nematodes, pathogens that can live and spread though water still cause loss of yield. Common diseases would be Phytophthora, Pythium, Fusarium and bacteria such as Erwinias and Pseudomonads. Since horticulture cannot be performed in a sterile environment on a commercial scale, insight in population dynamics of pathogens in aquatic systems as well as plants' resilience need to be understood to lower the risk of infection. This paper addresses a number of biological principles in aquatic ecology that could be used in improving system design processes as well as providing the first data on the population dynamics in chrysanthemum production on deep flow systems in The Netherlands using next generation sequencing (NGS). It was observed that free colonisation of the water leads to highly diverse bacterial populations, while inocula...

Acta Horticulturae, 2019

Phalaenopsis is the top-selling ornamental pot plant in the Netherlands, and the area under its p... more Phalaenopsis is the top-selling ornamental pot plant in the Netherlands, and the area under its production was 242 ha in 2014. Previously, production systems of Phalaenopsis (open or free to drain systems) resulted in high emission of nutrients to the ground and surface water, approximately 1500 kg N ha-1 year-1 , in the Netherlands. Little is known of the response of Phalaenopsis to water reuse systems, as orchids have been exempt from recirculation obligations owing to their salt sensitivity. Regulations aimed to reduce nitrogen (N) emissions to a maximum of 150 kg ha-1 year-1 in 2018, with the ultimate goal being 0 kg ha-1 year-1 , in 2027. Wageningen University and the Research Business Unit Greenhouse Horticulture were commissioned by the government as well as the Phalaenopsis grower association of the Netherlands to develop a system that could achieve the current goal of a maximum of 150 kg N ha-1 year-1. A recirculation system with UV disinfection and the reuse of drain water was utilized at the experimental site in Bleiswijk. Two recirculation treatments were tested with the aim to maintain the current production and quality levels while also lowering the emissions to the standard of 2018, with the possibility of further improvements to achieve the desired standards for 2027. The aim of the first reuse treatment was to discard small amounts of drain water to keep sodium at a maximum of 1.2 mmol L-1. In the second treatment, as much drain water was reused as possible. Emissions of N were reduced to 182 and 60 kg ha-1 year-1 , respectively. Plant growth parameters including leaf number, total leaf area, and number of spikes and flowers, showed no significant differences. In this experiment reuse of drain water reduced emissions considerably without any adverse effects on plant growth or disease incidence.

Acta Horticulturae, 2019

Competition for freshwater resources, and legal restrictions on discharge of agrochemicals (plant... more Competition for freshwater resources, and legal restrictions on discharge of agrochemicals (plant protection products and fertilisers) increase pressure on agricultural practice to improve water-use-efficiency of crop production globally. Zero-discharge greenhouse crop production can be an effective solution to both problems. Preliminary results of experiments with cucumber and sweet pepper on stone wool substrate in two greenhouse compartments showed that productivity did not significantly differ in zero-discharge growing compared to standard growing strategies. In this paper we present the final evaluation of the sweet pepper trial (December 2014-November 2015). In the reference compartment a total amount of 465 m 3 ha-1 y-1 (169.3kg N) was discharged. In the zero-discharge compartment there was no discharge during cropping. The nutrient composition of irrigation and drain water was analysed weekly (compared to two-weekly in reference) and nutrient stock composition was changed accordingly. Drain water was filtered with a flatbed filter (no rinsing water) and upon changes in fertigation, the new fertigation solution was first distributed throughout the entire irrigation system by a circulation pump, before application. An irrigation strategy was developed for the end of the cropping season, aiming to drain substrate slabs and to empty drain tanks as much as possible and reduce the amount of remaining nutrients in the slabs, without compromising productivity. Water-use-efficiency of the zero-liquid discharge strategy was lower than in de reference strategy, due to a more vegetative crop growth.

IV International Symposium on Irrigation of Horticultural Crops, 2004

Measurements of crop transpiration have been carried out by the Applied Plant Research station in... more Measurements of crop transpiration have been carried out by the Applied Plant Research station in Naaldwijk for many years with increasingly better weighing equipment. Ultimately a weighing gutter system has been developed that operates well under practical conditions and is a useful tool in crop management. The APR-Naaldwijk weighable gutter system monitors the water management of greenhouse crops and offers information for checking and automatically regulating the water supply. The collected data offer additional information on climate control and fresh weight growth of the crop. The system and results from testing are presented in this paper.

International Symposium on Growing Media 2007, 2009

The aim of the study was to get accurate data on the effects of mixing container media components... more The aim of the study was to get accurate data on the effects of mixing container media components and to match these data against models for mixing container media. It was accepted that the mixing of two container media components was related linearly to the amounts of material mixed, for parameters such as degradability. For other parameters the extra material necessary to compensate for the effect of interstitial filling had to be taken into account. Four different two component mixes were measured for 36 different ratios in all. Moisture content, air content, shrinkage, density and EC and pH were measured for each mixture. A formula based on measured densities of the components and the mix was used to predict moisture/air content in the mixes. It is concluded that the formula and the underlying method underestimate the water content in relatively wet materials such as peat-coir products and overrate the moisture content for relatively dry materials such as peat and flax straw mixes. The increase in density of the mix may be calculated either by measuring the volume loss or the density increase of one or more test mixes, from modelling a simplified particle size distribution, or from an empirically calculated relationship with particle size distribution parameters.

International Symposium on Growing Media and Soilless Cultivation, 2014

Recycling of the nutrient solution during cultivation of greenhouse crops reduces the total input... more Recycling of the nutrient solution during cultivation of greenhouse crops reduces the total input of water and fertilizers and decreases emission of nutrients to the environment. However growers fear accumulation of harmful substances in the drain water. For this reason drain water in practice is regularly discharged into the environment. In this study drain water from a commercial rose grower in The Netherlands was tested with a phytotoxicity test (Phytotoxkit) during a period of one year. The Phytotoxkit was used to assess growth response of drain water without disinfection; drain water disinfected with UV; drain water disinfected with UV and peroxide. In this phytotoxicity test, garden cress (Lepidium sativum) and mustard (Sinapis alba) are grown in a Phytotoxkit container on a filter paper moistened with the drain water under analysis. After incubation for three days in a climate-controlled cabinet, root length is measured. The Phytotoxkit showed growth decrease caused by untreated drain water disappeared when using a UV disinfection of 100 MJ.cm-2 or UV disinfection of 100 MJ.cm-2 combined with 10-25 ppm peroxide. Untreated drain water caused growth responses of-20% root length in only 3 out of 10 sample moments. Control of drain water with the Phytotoxkit provides the grower information about the presence of phytotoxic substances in the drain water and the effectiveness of treatments. The Phytotoxkit thus can prevent unnecessary discharge of drain water to the environment.

Dit onderzoek had als doel om de werking van electrolysewater te verbinden met de chemische eigen... more Dit onderzoek had als doel om de werking van electrolysewater te verbinden met de chemische eigenschappen en op zoek te gaan naar veilige toepassingen als gewasbehandeling voor de glastuinbouwsector. Vijf producenten hebben voor dit onderzoek de gewenste samenstelling van electrolysewater aangeleverd. Alle producten met daarin 36-65 ppm vrij chloor waren binnen vijf minuten 100% effectief tegen de bacterie, Erwinia chrysanthemi en de schimmel, Botrytis cinerea. De grenzen van gewasschade in de kiemplantentest werden sterker bepaald door de hoeveelheid natriumzout en EC gehalte van de electrolysevloeistof dan de hoeveelheid vrij chloor. In een korte meedruppelproef met tomaat zijn verschillende concentraties vrij chloor (0, 4, 8, 20 ppm) gedoseerd aan het voedingswater. Er werd geen gewasschade gevonden of negatief effect op de wortelkolonisatie van Trianum door de geringe chloorwaardes (vrij en totaal) die na vier weken bij de druppelaar werden teruggemeten. Testen met gewasbehandelingen laten zien dat éénmalige behandelingen tot 300 ppm geen gewasschade geven. Bij meerdere toepassingen is groeiremming te voorkomen door lagere concentraties te gebruiken of blootstellingstijd te beperken. Electrolysewater kan een veilig en bruikbaar alternatief bij het terugdringen van het fungicidegebruik.

International Symposium on Growing Media, 2008

For routine toxicity testing of composts and growing media, two different types of assays are usu... more For routine toxicity testing of composts and growing media, two different types of assays are usually applied. One approach is the use of growing trials in pots with various mixtures of the material. In extract-based tests, seeds are germinated in petri dishes and exposed to an exudate from the material to be tested. In this study, one of these methods, the Phytotoxkit microbiotest, was compared to the standard phytotoxicity test with Lactuca sativa as used by the RHP foundation. The Phytotoxkit test was performed in transparent test containers which allow for direct observation and length measurements of the seedlings by means of image analysis. Two dicotyles (Lepidium sativum and Sinapis alba) and one monocotyle (Sorghum saccharatum) were used. When measuring a presumably phytotoxic bark, in comparison with a reference bark, the Phytotoxkit showed a seedling length inhibition of 60-80% for the dicotyles and less than 20% for the monocotyle after three days. The RHP growing trial showed 30% weight inhibition of the lettuce after two weeks of plant growth when comparing the same barks in mixtures. This preliminary comparison showed that the Phytotoxkit microbiotest is a quick and practical bioassay with a high resolution which has a potential to become an international standard.

Bioresource Technology, 2010

In a Plant Microbial Fuel Cell (P-MFC) three plants were tested for concurrent biomass and bio-el... more In a Plant Microbial Fuel Cell (P-MFC) three plants were tested for concurrent biomass and bio-electricity production and maximization of power output. Spartina anglica and Arundinella anomala concurrently produced biomass and bio-electricity for six months consecutively. Average power production of the P-MFC with S. anglica during 13 weeks was 16% of the theoretical maximum power and 8% during 7 weeks for A. anomala. The P-MFC with Arundo donax, did not produce electricity with a stable output, due to break down of the system. The highest obtained power density in a P-MFC was 222 mW/m 2 membrane surface area with S. anglica, over twice as high as the highest reported power density in a P-MFC. High biomass yields were obtained in all P-MFC's, with a high root:shoot ratio, probably caused nutrient availability and anaerobia in the soil. Power output maximization via adjusting load on the system lead to unstable performance of the P-MFC.

This report decribes experiments with anaerobic digestation of champost and organic rest products... more This report decribes experiments with anaerobic digestation of champost and organic rest products for re-use in mushroom casing. The digestates will reduce the emission of carbon dioxide by peat use for casing and will reduce the number of transport movements. Both reductions serve the mushroom sector. Wageningen UR Greenhouse Horticulture is measuring the quality aspects of the digestates with standard methods used in the potting soil industry such as texture, organic matter and nutrient and ash content. In this report a literature review and measurements of digestates and casings are combined. The literature review lists critical values for amongst others salt, water and air content. It is argued values per unit volume are more informative on water and air distribution than values per unit weight. Extract indicate nutrient levels but only deliver an indirect indication of how plants or mushrooms experience their environment. Measurements indicate it is necessary to wash digestates...

The area of crops like tomato and peppers and roses grown on rooting media is worldwide increasin... more The area of crops like tomato and peppers and roses grown on rooting media is worldwide increasing. The driving force seems the combination of higher yield levels and the possibility to avoid diseases while still mono cropping. Increasingly the possibilities to avoid emissions of crop protectants and nutrients become important too. Finally the need to increase the efficiency with which irrigation water is turned into marketable products is becoming urgent in many parts of the world, including southern Europe. It is therefore a safe assumption that the area of substrate grown crops in the world will remain increasing for a very long time to come. Eventually the area of plants grown on substrates in the field may surpass the area of plants grown on substrates in greenhouses.

De werking is getest van een flexibel geautomatiseerd meet- en regelsysteem voor de ammoniumgift ... more De werking is getest van een flexibel geautomatiseerd meet- en regelsysteem voor de ammoniumgift (afhankelijk van de pH van de drain). Het effect is van de verhoogde ammoniumgift op de pH, de gewassamenstelling en gewasproductie is gemeten.