Componenten van het fosfaat in de grond welke betrokken zijn bij de fosfaatvoorziening van de plant

The phosphate supply of a plant largely depends on the amount of phosphate which can be released from phosphate reserves into the soil solution. The behaviour of exchangeable soil phosphate and the best method of estimating the isotopically exchangeable fraction was studied in pot experiments with oats and experiments with soil suspensions.The kinetics of phosphate ions in soil suspensions were discussed. The results of the experiments indicated the course of the exchange of phosphate ions between the solution and the solid reserve. The isotopically exchangeable soil phosphate appeared to be heterogeneous in composition.The quantity of isotopically exchangeable soil phosphate (L- and E-values) was calculated on the assumption that isotopic balance had been reached in the experiments at least for a certain part of the soil phosphate. For the L-value (determined in pot experiments) the consequences were studied of a lack of equilibrium.Finally the quantities of phosphate absorbed by oat plants were compared with those withdrawn by ion exchangers from soil suspensions (of a soil with the same phosphate reserve)

Soil Dynamic Models: Predicting the Behavior of Fertilizers in the Soil

This chapter provides an overview of the most dominant processes for the situation where organic biobased derivatives are added to the soil, with emphasis on decomposition, production of mineral nutrients, and losses to the environment. Organic compounds in the soil (organic matter, organic fertilizers, biobased derivatives, soil biomass) are subject to microbiological conversion reaction. Decomposition of organic matter usually occurs relatively quickly as long as enough molecular oxygen is present. Two major models can be distinguished in modeling mineralization of organic matter: multi‐pool models with a constant decomposition rate factor and models with a time‐dependent decomposition rate factor. Leaching is the loss of nutrients via draining of water as a result of excess rainfall or irrigation. It is of environmental concern as it contributes to the contamination of the groundwater and surface‐water systems. The chapter presents an overview of processes for some selected soil dynamic models.<br/

Phylogeny and biogeography of pholadid bivalve Barnea (Anchomasa) with considerations on the phylogeny of Pholadoidea

The paper examines the systematics, phylogeny and biogeographical history of Barnea (Anchomasa), which is one of the most abundant and diversified of modern pholadid bivalves. The range of morphology of its distinctive characters and comparisons with other pholadoidean taxa are described in detail. An extensive cladistic analysis based on morphological characters at genus and subgenus levels allowed the inclusion of B. (Anchomasa) into the phylogeny of Pholadoidea and the establishment of its most appropriate taxonomic position. The analysis confirms that Barnea s.s. and B. (Umitakea) are its closest relatives and that the morphological similarities to other taxa are mainly due to plesiomorphies. The fossil record and the data on the present 12day distribution contributed to trace the biogeographical history of B. (Anchomasa). The present 12day biogeography is marked by the disjunct distribution of species. Species are distributed mainly either along the Atlantic and Pacific coasts of the American continent (American group) or in the Indo 12West Pacific region (Indo 12West Pacific group). Both these groups have distinct morphological features and biogeographical structures. The fossil record and the known geodynamic scenario suggest a relationship of direct derivation between the Indo 12West Pacific group and a stock of north 12eastern Atlantic to Paratethyan species. This reflects a vicariant event related to the closure of the connection between western Tethys and the Indian Ocean in the middle Miocene. The American group presumably arose from the European stock during the Late Pliocene by dispersal towards the eastern coasts of North America and rapid southward diffusion. A relative differentiation within the American group is probably related to the last phases of emergence of the Panama Isthmus. The cladistic analysis also gives suggestions for the reconstruction of the phylogeny of the superfamily Pholadoidea. It confirms the interpretation of several characters sustained by previous authors. However, it also shows remarkable differences to the previous taxonomic arrangements. Pholadinae includes only taxa having the protoplax and it appears to be the sister 12group of a major clade composed mainly of two groups, namely Martesiinae\u2013Jouannetiinae and Xylophagainae\u2013Teredinidae. The Martesiinae are paraphyletic whereas the obligate wood 12boring Xylophagainae and Teredinidae form a well 12supported monophyletic group