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In areas under intensive livestock farming and with high application rates of animal manure, inorganic and organic phosphorus (P) may be leached from soils. Since the contribution of these P compounds to P leaching may differ, it is important to determine the speciation of P in these soils. We determined the effect of various fertilization regimes on the P speciation in NaOH–Na2EDTA (ethylenediaminetetraacetic acid) and water extracts of acidic sandy soil samples from the top 5 cm of grassland with wet chemical analysis and 31P nuclear magnetic resonance (NMR) spectroscopy. These soils had been treated for a period of 11 years with no fertilizer (control), N (no P application), N–P–K, or different animal manures. Inorganic P was highly elevated in the NaOH–Na2EDTA extracts of the soils amended with N–P–K or animal manures, while organic P increased only in the soil treated with pig slurry. Water-extractable P showed a similar trend. As indicated by 31P NMR, orthophosphate monoesters were the main organic P compounds in all soils. Our results suggest that long-term applications of large amounts of P fertilizer and animal manures caused an accumulation of inorganic P, resulting in an increase of the potential risk related to mobilization of inorganic P in the top 5 cm of these soils.

Nuclear magnetic resonance (NMR) was used to investigate the effects of changes in root temperature, of changes in the area of root in contact with culture solution and of day/night rhythm on the water balance of a cucumber and a gherkin plant. Results are discussed in terms of water potential, flow rate and resistance using a previously presented model of water balance. As long as water uptake alone is varied, flow rate and water content (or potential) will change in the same direction. In contrast, from that model it is predicted that changes in transpiration will affect flow rate and water content in opposite ways. An experimental verification of this prediction was given in the previous paper. Results obtained by the NMR method are compared to those determined using a dendrometer. The results demonstrate that the NMR method is a valuable tool to study plant water balance and that it can serve as a technique for discriminating between changes in plant water balance that are due to changes in water uptake by roots and those due to changes in transpiration.