Fosfaat moet de kringloop weer in

Niet alleen olie raakt op, ook zoet water, fosfaat en landbouwgrond zijn niet grenzeloos beschikbaar. Met een uitdijende wereldbevolking groeien echter de aanspraken op grondstoffen en andere natuurlijke hulpbronnen. In die concurrentiestrijd zijn duurzame oplossingen nodig als besparing, denken in kringlopen en eerlijk delen. ‘Nederland gaat nu onverantwoordelijk om met fosfaat.

Strategies to increase nitrogen use efficiency and reduce nitrate leaching in vegetable production in the Netherlands

Environmental concern and legislation of fertilization requires strategies to increase nitrogen use efficiency and reduce nitrate leaching. Strategies can be fertilizer choice, timing of N availability and fertilizer placement. Rainfall in the experimental year 2007 was moderate and different strategies were therefore not seriously tested. However, for crops that allow regular fertilization, it is questionable whether special fertilizers can do better than calcium ammonium nitrate (CAN) when fertilizers are applied according to good practice (i.e., row application, side dressing and split applications). Specific application of small amounts of N near planted endive showed increased initial growth, even at high levels of soil mineral N, and was found to lead in one of two plantings to increased yield at harvest. Substitution of broadcast N before planting by a starter application close to the plants followed by side dressing maintains maximum production while leaching risk is reduced

The fate of nitrogen from crop residues of broccoli, leek and sugar beet

Environmental concern has lead to legislation on fertilization to reduce nutrient losses to the environment. Reducing N input may be inadequate for crops that have a high N content in their residues. Reducing N input will negatively affect yield, but the residues remain. Management of crop residues may then be a more effective strategy to reduce N losses, notably nitrate leaching. Two experiments were carried out in 2006-07 and 2007-08 to study all emission routes of N from crop residues of broccoli, leek and sugar beet, and to determine the contribution of N from the residues to nitrate in groundwater. Crop residues were surface applied or rototilled, and compared with a blank and application of fertilizer N. About 11 to 16% of the N-content was lost to the air. Total N-losses to the air as ammonia and through denitrification were little affected by tillage, but partitioning was. When residues were left on the soil surface, most N was lost as ammonia, when the residues were rototilled, most N was lost through denitrification. Year strongly affected N leaching from crop residues, and the fraction of N from crop residues that was leached was twice as high in 2006-07 than in 2007-08. Tillage increased N leaching from broccoli, but had little effect with leek or sugar beet. Between 20 and 60% of the N content of residues of leek and broccoli was leached. Removal of residues after harvest will therefore contribute to reduce N leaching. However, options for treatment and re-use of the residues need to be studied as well as the effects on nitrate leaching and gaseous losses to assess the effects of the system as a whol

N-Behoefte Zantedeschia op basis van een nieuwe analyse

De N-behoefte van Zantedeschia is niet eenduidigaf te leiden. Er zijn indicaties dat de gebruiksnorm van 110 kg/ha voldoende lijkt op goed ingemeste percelen maar een onderbouwing daarvan ontbreekt omdat in zowel de praktijkgegevens als de oude proefgegevens de historisch toegediende hoeveelheden organische mest onbekend zijn. Het belang van organische bemesting is groter geworden omdat in het huidige gebruiksnormenstelsel ook de hoeveelheid N uit organische mest moet worden meegerekend

Aspects of the ontogenesis of the avian columella auris

Observations on embryological material from Spheniscus demersus, Acridotheres tristis, Geopelia cuneata and Gallus domesticus strongly suggest that the avian stapes represents part of an infrapharyngohyal while the rest of the pharyngohyal material (supra- plus infrapharyngohyal) together with the epihyal and a secondary laterohyal component form the extracolumella. The latter structure bears three so-called processes: the supracolumellar arcade or process (de Beer's lateral prong) whose inner limb is derived from the suprapharyngohyal and the outer limb (comprising at least part of the intercalary) from the laterohyal blasteme; the tympanic process (extracolumellar process) also derived from laterohyal blasteme; and the infracolumellar process (formed by the distal tip of the epihyal and a composite interhyal) which is continuous with the ceratohyal in most birds. Our investigation suggests that the supposed great variation in the development of the columella among birds is a fallacy.Waarnemings op embriologiese preparate van Spheniscus demersus, Acridotheres tristis, Geopelia cuneata en Gallus domesticus dui sterk daarop dat die stapes by voSIs deel van 'n infrafaringohiale verteenwoordig terwyl die res van die faringohiale materiaal (supra- plus infrafaringohiale) saam met die epihihiale en 'n sekonddre laterohiale komponent die ekstrakolumella vorm. Laasgenoemde struktuur dra drie sogenaamde uitsteeksels: die suprakolumellaar-uitsteeksel of -arkade (‘lateral prong’ van de Beer) waarvan die ‘binnebeen’ van die suprafaringohiale afkomstig is en die ‘buitebeen’ (wat minstens 'n deel van die interkalare insluit) deur die laterohiale blasteem bygedra word; die timpaniese uitsteeksel of ekstrakolumellaar-uitsteeksel wat ook van die laterohiale blasteem afkomstig is; en die infrakolumellaar-uitsteeksel (gevorm deur die distale punt van die epihiale enn saamgestelde interhiale) wat by meeste vo荤is aaneenlopend met die keratohiale voorkom. Ons ondersoek dui daarop dat die vermeende groot variasie wat ten opsigte van die ontwikkeling van die kolumella by vofils sou bestaan, 'n dwaling is

Effect of ammonium nutrition on uptake and metabolism of nitrate in wheat.

Wheat plants 1 month old grown in nitrate culture were exposed for 2 days to media containing 4 meq NO3 and 0-4 meq NH4/l. Where solutions contained both forms of N the uptake of NH4 exceeded that of NO3 even at the lowest NH4 level. NH4 metabolism predominated over NO3 assimilation and resulted in a higher free amino acid content, a lower carboxylate content and lower nitrate reductase activity in the tops than with NO3 alone. NH4 inhibited nitrate reductase activity whereas amino acids did not. The fall in activity of this enzyme in wheat tops caused by NH4 nutrition could not be related to the low level of tissue NH4 and it was suggested that changes in the redox situation in the cells might be involved. (Abstract retrieved from CAB Abstracts by CABI’s permission

The morphogenesis of the avian Columella auris with special reference to Struthio camelus

The columella auris of the ostrich is derived as in the crocodile from three sources; the two upper segments of the hyoid arch (pharyngohyal and epihyal) and a laterohyal component. The latter contributes the homologue of the crocodilian suprastapedial (or lacertilian intercalary) as well as the tympanic process and the material of the lateral limb (which is not lacking as stated in the literature) of the lateral prong (supracolumellar arcade). Conditions in Struthio camelus confirm the views expressed by the authors in their paper on Crocodilus niloticus regarding the homologies of the columellar processes. The avian infracolumellar process represents the crocodilian infrastapedial plus the interhyal which in addition to primary arch material, includes a secondary subepidermal part. The ceratohyal (usually called stylohyal in the literature) remains attached to the columella through the infracolumellar process

Safety and Effectiveness of Struvite from Black Water and Urine as a Phosphorus Fertilizer

To ensure food supply, phosphorus must be recycled, for which an appealing method is using struvite fertilizer from human excreta. One struvite from black water and another from urine were assessed for safety under Dutch regulations, and for effectiveness as P fertilizer in a maize field experiment and a literature review. Both struvites contained 12% P, 12% Mg, 6% N, and 0.5-1.5% of several micronutrients. Struvites did not exceed Dutch regulations for heavy metals or pathogens, and based on literature, organic toxins should be far below regulatory limits. In this study and 18 others, struvite appears to have similar effectiveness to soluble fertilizer. Early in the season, 200 kg P2O5 ha-1 of black water struvite and soluble phosphorus improved maize performance (

Vleselijke lusten belasten de natuur

De auteurs betogen in dit hoofdstuk dat (1) verduurzaming van de landbouw veel meer omvat dan het vergroten van economische en milieutechnische efficiënties, (2) intensivering en schaalvergroting behalve voordelen ook nadelen kennen, waaraan in de praktijk veel te gemakkelijk voorbij wordt gegaan, (3) frequent als 'oplossingen' aangedragen voorstellen geen echte oplossingen blijken te zijn en (4) Wageningen UR met een opener vizier zou moeten opereren