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Wat zijn de consequenties als je afwijkt van basisrecepten voor de voeding of een hoger drainpercentage aanhoudt? Bijvoorbeeld als je een deel van het nitraat vervangt door chloor of sulfaat. Of een hoger drainpercentage prefereert dan de standaard 33%. Dit is deel 4 van een serie over bemesting.

Soil properties of importance are dry bulk density, organic matter content, nutrient content and waterholding 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 relevantproperties using methods users are familiar with.Special attention is needed to interpret total nutrients, extracted nutrients and organic matter content.

Landbouwkundig ingenieur Chris Blok, als onderzoeker werkzaam bij Wageningen UR ontvangt redactielid Ad Alblas voor een gesprek over Maatschappelijk Verantwoord Ondernemen (MVO).

Since the expansion of soil-less culture in the Netherlands in the mid-eighties of the previous century, emission of nutrients and plant protection products (PPP’s) used in the root environment was considered as a huge problem. Eventually, the government and growers organisations reached an agreement which aimed at reducing the N, P and PPP emissions. For soil-less culture, reuse of drain water or closed growing systems became obligatory. Recently, the regulation changed by shifting the focus on reaching emission targets for N rather reaching 100 % closure of the systems. Yet, recirculation is still the key issue for reaching the goal of zero emission by 2027. These closed systems will potentially lead to substantial reduction of mineral leaching to the environment, however, they require adequate water quality and nutrient management. Moreover, satisfactory disinfection to control root diseases and removal of organic components is needed. In practice, substantial loss of water and minerals still occurs occasionally, when growers decide to flush the system and drainage water is partially discharged to the surface water or sewage system, causing emission of nutrients and PPP’s. There are several reasons for growers to discharge e.g. accumulation of Na, mismanagement in EC or pH or nutrient supply, and serious problems with soil borne diseases or growth inhibition. This paper will give an overview of the state of the art of systems for nutrient solution recycling, and the requirements for water treatment, water quality and nutrient supply and strategies to obtain the highest efficiencies for nutrient and water use.

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Summary Chrysanthemum is an important greenhouse crop in Holland and is still cultivated in soil. To prevent the emission of nutrients and crop protecting agents, an emission:free cropping system should be developed. This experiment was conducted to that purpose. The objectives of this experiment were: (1) to compare the plant growth performance among six closed systems and thereby evaluate the priority of each system; (2) to investigate the impact of some indexes associated with rhizosphere on plant growth and thereby optimize the corresponding system. Six candidate systems were deep soil system (S1), sand bed (S2), peat bed (S3), lily crate (S4), cassette bed (S5) and cassette box system (S6). In S5 and S6, substrate volume, anti root barrier, foil and irrigation regime were varied as factors of possible influence on the rhizosphere. Growing period, above ground growth parameters (including fresh weight, dry weight, plant height and leaf number) and root performance were recorded and used to evaluate plant growth performance. The results showed that the latter four high:tech systems could shorten the growing period by about 12 d in comparison to S1 and S2. After in depth discussion, however, four systems including S1, S2, S3 and S5 were suggested for next round trial. The results also showed fresh weight and dry weight advantage for the S5 system combined with 10 cm height of substrate, an anti:root fabric and a sprinkling irrigation or normal sub irrigation. Plants in S6 showed a lower fresh weight yield and a slightly lower dry weight yield as the amount of water and nutrients supplied was just not enough to meet the plant demands. Consequently for S6, plants grown in substrate wrapped with complete foil gave the best performance as the foil reduced water loss due to evaporation.