Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Gevolgen nieuw mestbeleid voor Koeien & Kansen-bedrijven in 2005
    Vermeij, I. ; Haan, M.H.A. de; Meerkerk, B. - \ 2007
    Lelystad : Animal Sciences Group (Koeien & kansen rapport 37) - 13
    mestgiften - melkveehouderij - agrarische bedrijfsvoering - stikstofbalans - stikstofmeststoffen - mineralenboekhouding - stikstofverliezen - dressings - dairy farming - farm management - nitrogen balance - nitrogen fertilizers - nutrient accounting system - nitrogen losses
    Vijftien Koeien&Kansen-bedrijven hebben in 2004 plannen opgesteld om in te spelen op het nieuwe mestbeleid. Deze bedrijven lopen voor de muziek uit en voeren de normen uit het mestbeleid al eerder toe dan verplicht is. Omdat tijdens het opstellen van de plannen het nieuwe mestbeleid nog niet volledig uitgewerkt was, dienden de in 2004 opgestelde plannen later bijgesteld te worden. De wijziging van het mestbeleid van MINAS naar gebruiksnorm dwingt de meeste bedrijven tot aanpassingen. Tien van de vijftien bedrijven moesten hun bedrijfsvoering aanpassen om een inkomensdaling te voorkomen. De meest voorkomende maatregelen waren mestafvoer en verlagen van het stikstofbemestingsniveau. Opvallend is dat verlaging van stikstof en fosfaat uit dierlijke mest veelal gecompenseerd wordt door een hogere kunstmestgift. Om in aanmerking te komen voor derogatie (250 kg N/ha i.p.v. 170 kg) had een derde deel van de bedrijven het plan om minder maïs te telen. De bedrijfspecifieke excretienorm wordt gezien als potentieel middel om mestafzet te kunnen verlagen. Recentelijk is de gerealiseerde situatie in 2005 vergeleken met de opgestelde plannen
    Stikstof mineralisatie op melkveebedrijf "De Marke" : analyse van waarnemingen en van hun betekenis voor het management
    Verloop, J. ; Hilhorst, G.J. ; Oenema, J. - \ 2007
    Lelystad : Animal Sciences Group (Rapport / Plant Research International 132) - 66
    bodemchemie - mineralisatie - stikstofgehalte - agrarische bedrijfsvoering - monitoring - stikstofbalans - zandgronden - melkveehouderij - bodemmonitoring - achterhoek - soil chemistry - mineralization - nitrogen content - farm management - monitoring - nitrogen balance - sandy soils - dairy farming - soil monitoring - achterhoek
    Om verschillen in mineralisatiesnelheid gedurende een seizoen te onderzoeken, is de mineralisatie per maand geanalyseerd. Bovendien is de cumulatieve mineralisatie op jaarbasis en de variabiliteit daarvan onderzocht. Het onderzoek omvat de periode 1993-2005.
    Het lot van stikstof uit gewasresten
    Ruijter, F.J. de; Smit, A.L. - \ 2007
    Wageningen : Plant Research International (Rapport / Plant Research International 133) - 34
    agrarische afvalstoffen - stikstof - uitspoelen - stikstofbalans - nederland - agricultural wastes - nitrogen - leaching - nitrogen balance - netherlands
    Het voorliggende rapport beschrijft de resultaten van een literatuurstudie rondom de vraag 'Welk deel van N uit gewasresten spoelt uit naar grondwater?' Hierbij zijn de volgende aspecten bekeken: mineralisatie van N uit gewasresten en beïnvloedende factoren (o.a. eigenschappen gewasresten, temperatuur, tijdstip van inwerken, deeltjesgrootte), humusvorming, ammoniakvervluchtiging en denitrificatie
    Uit de mest- en mineralenprogramma's : Sturen op Nitraat; ontwikkeling en toetsing van nitraatindicatoren
    Boels, D. - \ 2006
    Wageningen : Alterra (Informatieblad / Alterra 398.107) - 2
    nitraat - stikstofbalans - stikstof - waterkwaliteit - landbouw - agrarische bedrijfsvoering - monitoring - indicatoren - nitraatuitspoeling - grondwaterkwaliteit - mestbeleid - mineralenboekhouding - nitrate - nitrogen balance - nitrogen - water quality - agriculture - farm management - monitoring - indicators - nitrate leaching - groundwater quality - manure policy - nutrient accounting system
    Nederland moet aan de doelstelling van EU-Nitraat Richtlijn voldoen en ondermeer een grondwaterkwaliteit realiseren die overeenkomt met een nitraatgehalte <50 mg/l. Er is een traject ingezet om N-verliezen te beperken, maar desondanks zouden vanaf 2003 voor de droge zandgronden mogelijk aanvullende maatregelen nodig zijn. Maatwerk werd voorzien, en daarom werd een systematiek bepleit om effecten van maatregelen af te meten aan verandering van het nitraatgehalte van het grondwater. Daarvan werd een verbeterde grondslag verwacht voorverder N-beleid, zouden individuele boeren op bedrijfsniveau locatiespecifieke maatregelen kunnen ontwikkelen, zouden drinkwaterbedrijven en regionale overheden op basis van metingen afspraken met boeren kunnen maken over maatregelen en zou informatie worden verkregen voor evaluatie van gebiedsgericht mestbeleid, als aanvulling op het landelijk meetnet mestbeleid. Het project Sturen op Nitraat werd gestart in 2000 om de mogelijkheden en bruikbaarheid te onderzoeken van methoden voor het bepalen van het nitraatgehalte. In dit Infoblad wordt ingegaan op de ontwikkeling van indicatoren en hun bruikbaarheid
    Enkele afrondende notities uit Sturen op Nitraat
    Berge, H.F.M. ten - \ 2006
    Wageningen : Plant Research International (Reeks sturen op nitraat 17) - 38
    nitraten - verontreiniging - uitspoelen - stikstofbalans - kunstmeststoffen - bemesting - nitrates - pollution - leaching - nitrogen balance - fertilizers - fertilizer application
    Het project 'Sturen op nitraat' was gericht op het vaststellen van indicatoren voor de nitraatconcentratie in het bovenste grondwater in de Nederlandse zandgebieden. Over het project is gerapporteerd in 12 rapporten. Over enkele afgeleide vraagstukken werden korte interne notities geschreven die nu in dit rapport gebundeld zijn. Het betreft de volgende onderwerpen: 1. nitraat in het bodemprofiel als respons-variabele 2. De invloed van enkele gewaskenmerken op Nminnitraat in de bodem, en op de nitraatconcentratie in het bovenste grondwater 3. Discussie over het intercept in de relatie tussen Nminnitraat en de nitraatconcentratie in grondwater 4. Mogelijkheden om de nitraatnorm te halen
    N management in agrosystems in relation to the water framework directive : proceedings of the 14th N Workshop, October 2005, Maastricht, the Netherlands
    Schröder, J.J. ; Neeteson, J.J. - \ 2006
    Wageningen : Plant Research International (Report / Plant Research International 116) - 434
    stikstof - nitraten - uitspoelen - waterverontreiniging - stikstofbalans - bodemchemie - agrarische bedrijfsvoering - begroeide stroken - agro-ecosystemen - bufferzones - soil chemistry - nitrogen - nitrates - leaching - water pollution - nitrogen balance - farm management - vegetated strips - agroecosystems - buffer zones
    Nitrogen management in agrosystems in relation to the water framework directive was the overall theme for the 14th Nitrogen Workshop. This report is a synthesis of the contributions from this workshop, drawn from oral and poster presentations and from the discussions in the various working groups. This book is divided in eight main sections: 1) N flows at the regional level: policy implications of the Water Framework Drective. 2) N flows at the farm level: indicators and tools for improved N management. 3) Manure quality: can it be manipulated and what are the effects on whole-farm N efficiency. 4) Grassland renovation: prudent or risky? 5) Buffer strips and catch crops: cosmetic or beneficial? 6) Crop-related indicators: is the crop able to tell farmers what to do? 7) Soil-related indicators: ex ante hints or ex-post evaluation? 8) N turnover and losses at the plot scale: are detailed studies still informative?
    Ontwikkeling van geleide bemestingssystemen in de open teelten
    Radersma, S. - \ 2005
    Kennisakker.nl 2005 (2005)15 feb.
    stikstofmeststoffen - landbouw - stikstofgehalte - stikstofbalans - gewasopbrengst - bemesting - vollegrondsteelt - akkerbouw - nitrogen fertilizers - agriculture - nitrogen content - nitrogen balance - crop yield - fertilizer application - outdoor cropping - arable farming
    De bemesting in de Nederlandse landbouw staat onder grote druk, vooral als het om de stikstofbemesting gaat. De Nederlandse teler zal minder stikstof moeten gaan gebruiken. Er is onderzoek uitgevoerd dat zowel was gericht op de maximale productie te halen als op verkleinen van de verliezen van stikstof naar vooral het grondwater. Geleide bemestingssystemen helpen om bij krappere stikstofnormen de stikstof zo te verdelen over ruimte en tijd dat in de meeste gevallen toch de maximale productie kan worden gehaald. Zo kon bij gebruik van geleide bemestingssystemen in zetmeelaaardappelen de stikstofgift verlaagd worden zonder dat de opbrengst afnam. Bij bloembollen kon de bemesting ook gereduceerd worden zonder dat het ten koste ging van de opbrengst.
    N-mineraal in bodem indicator voor nitraat in grondwater
    Hoving, I.E. - \ 2005
    V-focus (2005)april 2005. - ISSN 1574-1575 - p. 14 - 15.
    rundveeteelt - grondwater - dierlijke meststoffen - mineralen - boekhouding - nitraat - stikstof - stikstofbalans - bemonsteren - agrarische bedrijfsvoering - zandgronden - mineralenboekhouding - cattle farming - groundwater - animal manures - minerals - accounting - nitrate - nitrogen - nitrogen balance - sampling - sandy soils - farm management - nutrient accounting system
    Gesteld wordt dat op droge zandgrond de hoeveelheid N-mineraal in de bodem in het najaar de beste indicatie is om de nitraatconcentratie in het grondwater te voorspellen voor het voorjaar daarop. Met de Nmin-meting kunnen boeren zien waar de stikstofverliezen zullen optreden
    Effect of operational variables on nitrogen transformations in duckweed stabilization ponds
    Caicedo Bejarano, J.R. - \ 2005
    Wageningen University. Promotor(en): H.J. Gijzen, co-promotor(en): N.P. van der Steen. - [S.l.] : S.n. - ISBN 9789085041627 - 163
    spirodela polyrhiza - stikstof - stikstofbalans - nitrificatie - anaërobe behandeling - algen - bezinkingsvijvers - spirodela polyrhiza - nitrogen - nitrogen balance - nitrification - anaerobic treatment - algae - stabilization ponds
    There is a diversity of conventional technologies available for removal of pollutants from wastewater. Most of these technologies are aerobic alternatives with high construction cost and high energy consumption and require skilled personal for operation and maintenance. As a consequence, only countries with a high gross national product (GNP) can afford these options. Where these technologies were introduced in developing countries, in most cases these could not be operated sustainably, leading to loss of investments and continued water resource contamination. Extensive investments in wastewater treatment plants world-wide during the last decades have greatly reduced the organic loading of receiving water bodies in high GNP countries. Only recently, many of these plants were appropriated to remove nitrogen and phosphorus. The increasing use of chemical fertilizer may cause high levels of eutrophication in water bodies, which may induce algae blooms resulting in strong fluctuations in oxygen concentration. Oxygen depletion causes fish kill as well as odor problems.

    The situation in countries with a low GNP is worse than in the developed world. The unequal expansion of water supply coverage compared to the expansion in wastewater and sanitation services leads to increased contamination of surface and ground waters. The general trend is to use conventional WWT systems for big cities, but for medium and small sized cities non-conventional systems are often considered. Therefore, there is an urgent need to develop and improve low cost technologies for wastewater treatment that are within the economic and technological capabilities of developing countries. In countries like Colombia it is very common that the regulation controls mainly the removals of organic matter and suspended solids. Other parameters like nitrogen, phosphorus, pathogens, micro-contaminants are also crucial and need to be addressed. This makes a response via conventional technologies very expensive, and for developing regions in fact unachievable. It would be ideal if new technologies can provide besides the removal of organic matter and solids, resource recovery like the generation of biogas (energy production) or high quality biomass (animal fodder). At the moment, no technological packages appear to be readily available.

    Experience has shown that no single technology can offer an optimum treatment for the different components to be treated in wastewater or to recover them as valuable resources. Therefore an adequate combination of different technologies in an integrated system could convert a wastewater treatment into an attractive sustainable system. For example UASB reactor and duckweed ponds are relatively low cost technologies and their combination offers several advantages. Firstly, anaerobic treatment will reduce considerably the organic matter in the wastewater and convert it into methane, which can be used as a source of renewable energy. Secondly, the effluents of anaerobic treatment could be post-treated to meet discharge standards in duckweed ponds for nutrient recovery in the form of high quality biomass.At this point three valuable products can be listed: biogas for use as an energy source, biomass that can be used for aquaculture or animal feed and treated effluent that can be re-used in irrigation. A system that generates such by-products increases the feasibility and sustainability of pollution control programs. Furthermore, the products may help to address the increasing need for food production in the world. 

    The development of duckweed pond technology has been concentrated on the study of the processes occurring within the ponds, with respect to organic matter, nitrogen, phosphorus and pathogen removal and the corresponding mechanisms. Further research is needed in order to have a good control of effluent nitrogen levels. There are still important questions to be answer like how to maximize nitrogen recovery via duckweed production, how to get good effluent levels depending on effluent reuse. If the effluent is going to be used in crop irrigation, to reduce nitrogen effluent concentration to 15-20 mg l -1 will be enough. If the effluent is going to be discharge in surface waters the nitrogen level would have to be reduced as much as possible. Therefore it is important to study how the design and combination of technologies could generate the required nitrogen effluent levels. The present work was focus on the study of the effect of different operational variables, like the effect of anaerobic pre-treatment, the combination of algae and duckweed ponds, the effect of pond depth on nitrogen transformation and removals.

    The effect of anaerobic pre-treatment on environmental and physicochemical characteristics of duckweed stabilization ponds was studied in Chapter 2 .The environmental and physicochemical conditions affect both plant growth and microbiological treatment processes in the system. Two series of continuous-flow pilot plants, composed of seven ponds in series each, were operated side by side. One system received artificial sewage with anaerobic pre-treatment, while the other system received the same wastewater without anaerobic pretreatment. pH, temperature, dissolved oxygen, alkalinity, conductivity, biochemical oxygen demand, total and ammonium nitrogen, nitrites and nitrates, and phosphorus were monitored under steady state conditions. It was found that pH levels were very stable in both systems with and without anaerobic pretreatment. Vertical temperature gradients were present during daytime but not as strong as they may occur in conventional stabilization ponds. Oxygen levels were significantly higher in the duckweed system with anaerobic pretreatment, especially in the top layer. (up to 2 mg O 2 l -1 ) than in the system without pretreatment (up to 1.2 mg O 2 l -1 ). Nevertheless, aeration rates were low in both systems. Both systems were efficient in removing organic matter. The system without pretreatment obtained 98% of BOD 5 removal in pond 4, so 12 days of retention time will be sufficient to reach high organic matter removal. The system with pretreatment obtained also 98% BOD 5 removal (92% in UASB reactor). In this case the duckweed ponds will serve as a polishing step for remaining organic matter. Nutrient removals were 37-48% for nitrogen and 45-50 % for phosphorus in the lines with and without pretreatment respectively.

    The main form of nitrogen in anaerobic effluent is ammonium. This is the preferred nitrogen source for duckweed, but at high levels it may become inhibitory to the plant. Renewal fed batch experiments at laboratory scale were performed (Chapter 3 ) to assess the effect of total ammonia (NH 3 + NH 4+ ) nitrogen and pH on the growth rate of the duckweed Spirodela polyrrhiza. The experiments were performed at different total ammonia nitrogen concentrations, different pH ranges and in three different growth media. The inhibition of duckweed growth by ammonium was found to be due to a combined effect of ammonium ions (NH 4+ ) and ammonia (NH 3 ), the relative importance of each one depending on pH.

    The effect of anaerobic pre-treatment on the performance of a duckweed stabilization pond system was assessed in a pilot plant located in the Ginebra Research Station-Colombia (Chapter 4). The pilot plant consisted of two lines of seven duckweed ponds in series. One line received de-gritted domestic wastewater and the other received effluent of a 250 m 3 Up-flow Anaerobic Sludge Blanket (UASB) reactor, treating the same wastewater. Both lines were operated at a total hydraulic retention time of 21 days.The systems were monitored for temperature, pH, oxygen, biochemical oxygen demand, chemical oxygen demand, total suspended solids, total phosphorus, biomass production, and different forms of nitrogen. No effect of anaerobic pretreatment was observed on pH and temperature in the two systems. Oxygen concentrations were higher in the system with UASB reactor. Although both systems complied with the Colombian regulation for BOD removal (> 85%)pretreatment with UASB reactor may contribute to the reduction of area requirement for the stabilization ponds. Effluent quality in terms of total suspended solids was excellent, i.e. 9 ± 2 and 4 ± 1 mg l -1 in the system with and without pre-treatment, respectively. Total nitrogen removals were 63 % and 68% and phosphorus removals were 24% and 29% in the system with and without pre-treatment, respectively. The differences between the two systems were found not to be significant. Duckweed biomass production was in the range of 54-90 g m -2 -d -1 (fresh weight) in the system with pre-treatment and 36-84 g m -2 -d -1 in the system without pre-treatment. Total biomass productions were significantly different at 92% level of confidence. Protein content was 35.1% and 36.6% for the system with and without pre-treatment, respectively.Nitrogen removal is nowadays one of the most important effluent treatment objectives because of the serious pollution problems it causes to the environment. How nitrogen is transformed and removed in duckweed ponds was studied and nitrogen balances were established (Chapter 5). The experimental system was the same as in the previous chapter. Ammonia volatilization was found to be not an important removal mechanism in duckweed ponds (less than 1%). Removal by sedimentation was also low at 2.1% and 4.7% for the systems with and without anaerobic pre-treatment, respectively. Instead, denitrification was found to be the most important removal mechanism (42% and 48%), followed by duckweed biomass up-take (15.6% and 15.1%). Average nitrogen biomass up-take rates were 199 mg N m -2 d -1 and 193 mg N m -2 d -1 for the system with and without pre-treatment, respectively. Nitrification rates were in the range of112 - 1190 mg N m -2d -1 and 58-1123 mg N m -2 d -1 for the system with and without anaerobic pretreatment respectively. Denitrification rates were in the range of 112 - 937 mg N m -2 d -1 and 59 - 1039 mg N m -2 d -1 for the system with and without pre-treatment respectively. The configuration of the system, in particular the down and up flow pattern seemed to have an important stimulating effect on denitrification rates, probably by causing alternative exposure of the pond water to aerobic and anoxic conditions.Although the potential of duckweed ponds for removing carbonaceous and suspended material from wastewater has been demonstrated, the system could be further optimized for nitrogen removal. The effect of introducing algae-ponds (aerobic zones) into a series of duckweed stabilization ponds on nitrification and denitrification (Chapter 6 ) was studied in two consecutive phases. During the first phase, the seven ponds of the pilot plant were fully covered with duckweed (Spirodela polyrrhiza). Before the start of the second phase, the duckweed cover was removed from ponds 1 and 3, with a view to allow algae growth in the 'open' ponds. The feed of the duckweed pond system consisted of the effluent of a real scale UASB reactor, which treated domestic wastewater from Ginebra-Colombia. The system was operated with a continuous flow to produce a hydraulic retention time (HRT) of 3 days per pond and a total HRT of 21 days. Effluent total nitrogen was significantly different in the two phases, with 13.8± 2.9 mg TN l -1 (63 % removal) and 3.7±1.5 mg TN l -1 (90%) for first and second phase, respectively.Denitrification was the most important removal mechanism during both phases, and amounted to 43.5 % and 76.2 % of influent nitrogen, in first and second phase, respectively. Ammonia volatilization and sedimentation were insignificant processes for nitrogen removal in both phases. Nitrification played an important role in nitrogen transformations in the duckweed systems and it was favored by the introduction of aerobic zones in ponds 1 and 3. Denitrification also played a key role in nitrogen transformations and removal. Despite the presence of oxygen in the water column, denitrification occurred, probably due to the anaerobic microenvironment of system biofilms. Higher nitrogen removal might be obtained in duckweed pond systems through the introduction of aerobic zones in early stages of the system. Where effluents cannot be reused for crop irrigation, strict nitrogen effluent criteria can be met using hybrid duckweed-algal ponds at considerably shorter hydraulic retention time compared to fully duckweed covered systems.

    The effect of pond depth on nitrogen removal in duckweed stabilization ponds was studied in Chapter 7. The pilot plant consisted of two lines with seven duckweed ponds in series, with different depths and fed with effluent of a laboratory scale UASB reactor. Three experimental conditions were studied: DSP1 with pond depth 0.7 m and HRT= 21 days, DSP2 with pond depth 0.4 m and HRT = 12 days, and DSP3 with pond depth 0.4 m and HRT = 21 days. The systems were monitored for pH, temperature and oxygen profiles, organic matter removal (BOD 5 ), nitrogen transformations, biomass production and biomass nitrogen content. Average total nitrogen removal rates were 598 mg N m -2 d -1 for DSP 1, 589 mg N m -2 d -1 for DSP 2 and 482 mg N m -2 d -1 for DSP 3. In spite of the lower nitrogen removal rate in DSP 3, it had higher removal efficiency (44 %, 43 % and 62 % for DSP 1, 2 and 3 respectively) due to the lower surface loading rate in this system. This shows that using the percentage of removal as a parameter for comparison should be done with care and the operational parameters of the compared systems should be taken into account. Denitrification was the most important nitrogen removal mechanism for the three DSPs. Nitrogen removal via biomass production was the second most important removal mechanism for the three experiments. Pond depth does not seem to determine nitrification or denitrification. Nitrification seems to be related to surface organic loading rate, while denitrification was related to BOD availability. The comparison between two pond systems with different depth, but operated at the same hydraulic surface loading rate (DSP 1 and 2) showed similar nitrogen removals in the shallower system as in the deeper system. This suggests that duckweed pond system could be designed with shallow depth without affecting surface loading and nitrogen removal efficiency. Nitrogen removal appeared to be governed by surface loading rate rather than by hydraulic retention time.

    Most of the research so far has been performed at laboratory or pilot scale. In the process of technology-development it is important to test findings at full scale. In Chapter 8 , the performance of a full scale duckweed pond was compared with a full scale algae pond treating effluent of a UASB reactor operated under similar conditions of climate, configuration, wastewater composition and loading rate. The real scale experimental system was composed of two continuous flow channels. One operated as an algae pond and the other as a duckweed pond ( Spirodela polyrrhiza and Lemna minor . ) . The volume of each channel was 225 m 3 , an average surface area of 322 m 2 , L/W ratio= 13.1 and depth of 0.7 m. The wastewater flow was 19.7 m 3 d -1 , for each system and the theoretical hydraulic retention time was 11.5 days. The ponds were monitored for the following parameters: Organic matter (BOD 5 ), total suspended solids (TSS), ammonium nitrogen (NH 4+ -N), total Kjeldahl nitrogen (TKN), nitrite nitrogen (NO 2 -N), nitrate nitrogen (NO 3 -N), total phosphorous (TP) and faecal coliform (FC). The duckweed pond developed different environmental conditions in terms of pH, temperature and oxygen, compared to the algae pond. The duckweed pond was more efficient in removing organic matter and the algae pond was more efficient in nitrogen removal. Denitrification accounted for most of the nitrogen removal in the algae and duckweed ponds. The second most important mechanism for nitrogen removal was ammonia volatilization for the algae pond and plant up-take for the duckweed pond. In the design of duckweed pond systems special attention should be paid to the reactor configuration and flow pattern in order to obtain good contact between water column and the duckweed cover and to reduce hydraulic problems.

    Practical applications.

    Wastewater treatment can be converted into an attractive, feasible and sustainable alternative by combining anaerobic pretreatment, duckweed ponds, and algae ponds. The integrated system UASB reactor, algae pond and duckweed pond offers the possibility to remove the various unwanted component in wastewater and to recover part of the valuable material present in the wastewater in the form of biomass or biogas The effluents may be suitable for discharge or for irrigation depending on the removal efficiencies of the system. The design and operation of this integrated system may have two different approaches. Firstly, one could optimize nitrogen recovery by duckweed uptake and effluent irrigation. Secondly, one could maximize nitrogen removal in order to protect the receiving water resources. 

    If the objective of the treatment is recovery of nitrogen then the stimulation of duckweed incorporation and the reduction of effluent nitrogen to a suitable range for irrigation would be the best option. The configuration of an efficient anaerobic pre-treatment followed by a series of ponds completely covered with duckweed would be recommendable. Influent ammonium nitrogen concentration below 50 mg l -1 and pH below 8 would be desirable to avoid biomass growth inhibition. The comparison between two pond systems with different depths and the same hydraulic surface loading rate showed similar nitrogen removals in the shallower system as in the deeper system. This means that duckweed pond system could be designed with the shallower depth without affecting nitrogen removal efficiency. Shallow ponds are easier to build, to operate and to maintain and in the case of duckweed covered ponds, they can be regarded as a crop production system.

    If the objective of the treatment is nitrogen removal due to disposal regulations, a strategy to enhance denitrification should be adopted. Higher nitrogen removals may be obtained in duckweed pond systems through the introduction of aerobic zones in early stages of the system, which allows a considerable reduction of the hydraulic retention time. Strict nitrogen effluent criteria can therefore be met at relatively short hydraulic retention times. The configuration of the system, in particular the down and up flow pattern seems to have an important positive effect on denitrification rates. Compartmentalization of the treatment system improves the pond performance. In the design of pond systems special attention should be paid to the reactor configuration and hydraulic flow pattern, good contact water-biomass and to avoidance of short circuiting and dead zones. In the process of technology development the following studies are envisaged and recommended for further research: Future studies should be focused on shallow ponds with the views to enhance nitrogen removal via its recovery in the form of duckweed biomass. Shallow ponds will also reduce construction cost of the treatment systems.

    Alternative uses of treated effluent and produced biomass should be investigated.In the case of effluent reuse on irrigation, the reduction of nitrogen concentrations in the treatment system to 15-25 mg l -1 will be enough. The use of vegetable biomass as a food complement on the diet of fish and pork is an alternative that has been preliminary explored in the area of research. Further studies are necessary to determine its feasibility.For safe discharge of effluent to open water bodies, effluent nitrogen concentration should be low. In this case nitrogen removal processes may be influence by affecting growth conditions of nitrifiers/dentrifiers like oxygen levels or availability of area for bacterial attachment. It is important to performed studies in order to find the best combination of duckweed and algae ponds for nitrogen removal. The introduction of baffles on the treatment channels will increase the availability of area for biomass growth and will improved the hydraulic characteristics of the treatment systems. The appropriated number and distribution of baffles should be investigated. Recycling of final aerobic effluent to the UASB reactor or to the entrance of the duckweed pond could be an interesting option to stimulate denitrification. Pathogen removal will be affected by the use of low pond depths, the presence of aerobic zones and compartmentalization in the treatment system. These effects should be researched in order to optimizedalso the removal of pathogenic microorganisms.
    CNGRAS : A dynamic simulation model for grassland management and C and N flows at field scale
    Conijn, J.G. - \ 2005
    Wageningen : Plant Research International (Rapport / Plant Research International 107) - 58
    graslandbeheer - voedingsstoffenbalans - stikstofbalans - simulatiemodellen - nederland - grassland management - nutrient balance - nitrogen balance - simulation models - netherlands
    Beschrijving van het graslandmodel CNGRAS dat uit 5 componenten bestaat: grasproductie, graslandbeheer, organische bodemkoolstof en -stikstof, inorganische bodemstikstof en bodemwaterbalans
    Efficiënt gebruik van stikstof noodzakelijk
    Dijk, W. van; Schoot, J.R. van der; Smit, A.L. - \ 2005
    Boerderij 2005 (2005)13. - ISSN 0006-5617 - p. 18 - 19.
    dierlijke meststoffen - normen - mineralen - mestbehoeftebepaling - stikstofbalans - toedieningshoeveelheden - akkerbouw - zandgronden - landbouwbeleid - animal manures - standards - minerals - fertilizer requirement determination - nitrogen balance - application rates - arable farming - sandy soils - agricultural policy
    Vanaf 1 januari 2006 wordt Minas vervangen door een gebruiksnormenstelsel. Er komt een gebruiksnorm voor zowel stikstof (N) als fosfaat. De N-gebruiksnorm is gewasspecifiek en gebaseerd op het bemestingsadvies. Voor zandgronden wordt echter vanaf 2007 de gebruiksnorm verlaagd naar 95 procent van het advies, omdat stikstof op zand makkelijk uitspoelt. Via een scherpe bemestingsstrategie kan opbrengstderving grotendeels worden voorkomen. De kosten stijgen wel
    Eindrapportage van de milieuresultaten behaald in de nitraatprojecten (1999-2003). Deel II: Resultaten per project
    Berge, H.F.M. ten; Hack-ten Broeke, M.J.D. - \ 2005
    Wageningen : Plant Research International (Rapport / Plant Research International 75B) - 275
    nitraten - stikstofbalans - waterverontreiniging - verontreinigingsbeheersing - nederland - bodemchemie - uitspoelen - nitrates - soil chemistry - leaching - nitrogen balance - water pollution - pollution control - netherlands
    Met dit rapport wordt beoogd de milieu-resultaten samen te vatten die behaald zijn in de projecten welke in de periode 1999-2003 in Nederland zijn uitgevoerd in het kader van het Actieplan Nitraatprojecten, en die hier kortweg worden aangeduid als ‘de Nitraatprojecten’. Deze synthesestudie maakt deel uit van zowel de Evaluatie Actieplan Nitraatprojecten, alsook van de Evaluatie Meststoffenwet 2004, en bestaat uit twee delen. Het voorliggende Deel I brengt de belangrijkste milieuresultaten uit de Nitraatprojecten samen. Daarbij is gepoogd om overeenkomsten en verschillen te benoemen. Dit deel bevat ook een opsomming van de belangrijkste conclusies uit de projecten. Deel II omvat een serie hoofdstukken, waarin telkens per nitraatproject de milieuresultaten behandeld worden. Die hoofdstukken zijn opgesteld door de projectleiders of andere direct betrokkenen in de respectievelijke projecten, en vormen het basismateriaal waaruit dit Deel I is ‘gedistilleerd’
    Crop Systems Dynamics: an ecophysiological simulation model for genotype-by-environment interactions
    Yin, X. ; Laar, H.H. van - \ 2005
    Wageningen : Wageningen Academic Publishers - ISBN 9789076998558 - 155
    gewasproductie - gewasopbrengst - simulatiemodellen - wiskundige modellen - plantenfysiologie - plant-water relaties - stikstofbalans - source-sink relaties - wortel spruit ratio - groeianalyse - agro-ecologie - ecofysiologie - crop production - crop yield - simulation models - mathematical models - plant physiology - plant water relations - nitrogen balance - source sink relations - root shoot ratio - growth analysis - agroecology - ecophysiology
    This book presents a generic process-based crop growth model, GECROS (Genotype-by-Environment interaction on CROp growth Simulator), developed in Wageningen. The model uses robust yet simple algorithms to summarize the current knowledge of individual physiological processes and their interactions and feedback mechanisms. It was structured from the basics of whole-crop systems dynamics to embody the physiological causes rather than descriptive algorithms of the emergent consequences. It also attempts to model each process at a consistent level of detail, so that no area is overemphasized and similarly no area is treated in a trivial manner. Main attention has been paid to interactive aspects in crop growth such as photosynthesis-transpiration coupling via stomatal conductance, carbon-nitrogen interaction on leaf area index, functional balance between shoot and root activities, and interplay between source supply and sink demand on reserve formation and remobilization. GECROS is presented here in an open style, rather than as a ‘black-box’. Model theories are described in individual chapters, and their supporting texts (notably model derivations) are given in Appendices. The model source code, written in the simulation language FST (FORTRAN Simulation Translator), and the definition of variables are provided.
    Geleide bemesting in de open teelten: ontwikkeling van systemen
    Radersma, S. ; Geel, W.C.A. van; Grashoff, C. ; Molema, G.J. ; Wees, N.S. van - \ 2004
    Wageningen : PPO (PPO 334) - 31
    kunstmeststoffen - voedingsstoffenbalans - voedingsstoffenopname (planten) - stikstofmeststoffen - stikstofbalans - akkerbouw - nederland - bemesting - fertilizers - nutrient balance - nutrient uptake - nitrogen fertilizers - nitrogen balance - arable farming - netherlands - fertilizer application
    Een geleid bemestingssysteem is een combinatie van technieken die het mogelijk maken om stikstof meststof toe te dienen zodanig dat het N-aanbod zo goed mogelijk in overeenstemming is met de N-opname en de N-behoefte van het gewas. Het doel van geleide bemestingsystemen is om te komen tot lagere N-giften en N-verliezen bij gelijkblijvende opbrengst (kwantitatief en kwalitatief) ten opzichte van de huidige standaard bemestingssystemen. Uit de proeven bleek bepaalde combinaties van verschillende systemen of aanvullingen op onderdelen van systemen nog tot een duidelijke bespring van N-gift zouden kunnen leiden, zonder negatieve effecten op de opbrengst.
    Variatie van stikstofoverschotten en nitraatconcentraties binnen een bedrijfssysteem : verkenning op grond van gegevens van de De Marke
    Verloop, J. ; Oenema, J. ; Sebek, L.B.J. ; Hilhorst, G.J. - \ 2004
    Wageningen : Plant Research International (Rapport / Project De Marke 47) - 34
    stikstofbalans - nitraat - uitspoelen - bedrijfssystemen - teeltsystemen - kunstmeststoffen - bemesting - nitrogen balance - nitrate - leaching - farming systems - cropping systems - fertilizers - fertilizer application
    Stikstofstromen op het kernbedrijf Meterik : modelberekeningen met FUSSIM2 en MOTOR
    Assinck, F.B.T. ; Willigen, P. de - \ 2004
    Wageningen : Plant Research International (Telen met toekomst OV0405) - 42
    stikstofkringloop - stikstofbalans - simulatiemodellen - systeemanalyse - uitspoelen - nitraat - waterverontreiniging - groenbemesters - oogstresten - akkerbouw - nederland - nitrogen cycle - nitrogen balance - simulation models - systems analysis - leaching - nitrate - water pollution - green manures - crop residues - arable farming - netherlands
    MiNiAC, a model to simulate mineral nitrogen dynamics in arable crop rotations : model description and verification of version 1.00
    Postma, J. ; Pronk, A.A. - \ 2004
    Wageningen : Plant Research International (Report / Plant Research International 81) - 26
    rotaties - teeltsystemen - stikstofbalans - nitraat - akkerbouw - simulatiemodellen - nederland - rotations - cropping systems - nitrogen balance - nitrate - arable farming - simulation models - netherlands
    Aanvoer en overschot van stikstof als indicatoren voor nitraatuitspoeling : resultaten uit "Koeien en Kansen" 1997 - 2003
    Oenema, J. ; Berge, H.F.M. ten - \ 2004
    Wageningen : Animal Sciences Group (Rapport / Plant Research International nr. 91) - 46
    bodemchemie - nitraten - stikstofbalans - verontreinigingsbeheersing - melkveehouderij - bemesting - soil chemistry - nitrates - nitrogen balance - pollution control - dairy farming - fertilizer application
    Dit rapport doet verslag van de ontwikkelingen van stikstofoverschotten en stikstofaanvoer op verschillende niveaus over de periode 1997 – 2002, en van de nitraatconcentratie van het bovenste grondwater over de periode 2000 – 2002. Resultaten over 2003 zijn in een bijlage opgenomen. Doel van het project was om versneld de MINAS norm op de 17 voorbeeldbedrijven te halen.
    Afvoer van gewasresten ter beperking van stikstofverliezen: bureaustudie naar de effecten op de stikstofbalans, mineralisatie en organische stof
    Ruijter, F.J. de; Postma, R. - \ 2004
    Wageningen : Plant Research International (Telen met toekomst OV0412) - 40
    oogstresten - stoppel - stikstofbalans - stikstof - mineralisatie - organisch bodemmateriaal - verontreiniging - groenteteelt - crop residues - stubble - nitrogen balance - nitrogen - mineralization - soil organic matter - pollution - vegetable growing
    In deze bureaustudie is gekeken naar het effect van afvoeren van gewasresten op organische stof, stikstofmineralisatie en bemesting. Als maat voor de stikstofverliezen naar het milieu wordt het stikstofoverschot op de balans gebruikt. Aan de hand van een voorbeeldbedrijf met de gewassen sla, spinazie en prei is het effect van de afvoer van preiresten bekeken
    Quick scan van de milieukundige effecten van een aantal voorstellen voor gebruiksnormen; rapportage in het kader van de evaluatie meststoffenwet 2004
    Schoumans, O.F. ; Berg, R. van den - \ 2004
    Wageningen : Alterra (Alterra-rapport 730.6) - 69
    bodemchemie - voedingsstoffen - nitraten - fosfaten - uitspoelen - waterverontreiniging - milieuwetgeving - stikstofbalans - modellen - Nederland - soil chemistry - nutrients - nitrogen balance - nitrates - phosphates - leaching - water pollution - models - environmental legislation - Netherlands
    Voor de nadere uitwerking van de Mestwetgeving, die vanaf 2006 zal worden ingevoerd en welke is gebaseerd op de invoering van gebruiksnormen, is in opdracht van de rijksoverheid in het kader van de evaluatie van de Meststoffenwet 2004 een ex-ante milieu-evaluatie uitgevoerd, waarbij is nagegaan wat de gevolgen zijn van verschillende niveaus in fosfaat- en stikstofgebruiksnormen op de nutriëntenemissies naar het grond- en oppervlaktewater vanuit landbouwgronden. De beoordeelde stikstofnormen leiden tot een verbetering van de grond- en oppervlaktewaterkwaliteit, echter in alle gevallen treedt op een deel van het areaal (20-25%) nog een overschrijding van de grondwaterkwaliteitdoelstellingen op. De stikstofemissies naar het oppervlaktewater dalen met ca. 20% ten opzichte van de situatie eind jaren negentig. De beoordeelde fosfaatnormen leiden nog steeds tot een toename van de fosfaatophoping in de bodem. Verwacht wordt dat in eerste instantie de fosfaatuitspoeling in 2030 vermindert met 10 tot 15 %, maar dat door de toename van de fosfaatophoping in de bodem, en daarmee de mate van fosfaatverzadiging van de landbouwgronden, op langere termijn (eind 21e eeuw) de situatie weer verslechtert tot het niveau van 2000.
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