Summary Immobilization of nitrogen (N) in decomposing straw varies between soils, and the objective of this study was to identify the mechanisms responsible. Internode segments of wheat straw were incubated in Denmark and in Scotland in arable soils fertilized with NH4NO3, labelled with 15N, for periods up to 1 year. Straw was recovered from the soils periodically and analysed for microbial biomass and different forms of N using chemical methods and CPMAS 15N NMR spectroscopy. The total N content of the straw increased, as long as the soil was not too wet, such that there was overall immobilization. This was accompanied by a rapid increase in the content of amino acid N and to a lesser extent of glucosamine N and a concomitant decrease in the carbohydrate content of the straw. Using direct and plate counts for bacterial and ergosterol content for fungal estimation, we found that fungal biomass was much greater than that of bacteria. This correlated with the forms of N in the straw as determined by CPMAS 15N NMR, which showed spectra that were more typical of fungi than of bacteria. It seems that immobilization of N is primarily caused by fungi as they decompose the straw.

Two disbudded, potted chrysanthemum cultivars were subirrigated with 9.25, 12.3, and 18.5 mM N during vegetative, but not reproductive growth. At commercial harvest, visible symptoms of N deficiency or differences in plant/inflorescence quality were minimal, whereas N uptake efficiency was dramatically improved at 9.25 and 12.3 mM N.

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Clear sand adsorbs 15-35% total phosphorus (P) from septic tank effluent, but P is mobilized when low-P effluent is applied. Amorphous P compounds formed by alkali aluminate chemical addition may also be subject to leaching. Crystalline mineralization is the desired end effect that isolates P thoroughly from the water resource. Using new low-energy iron electrochemistry (EC-P process), dissolved ferrous iron reacts with sewage phosphate ions (PO) and precipitates onto filtration medium as vivianite [Fe(PO)·8HO], as identified by scanning electron microscopy and X-ray diffraction and predicted from Eh-pH-aHPO phase relations. Removal rates of 90-99% in sand, soil and synthetic foam filters are obtained. The precipitation of vivianite demonstrates that P can be immobilized quickly and without intermediary adsorption phases, as with Fe-rich soils. Vitreous silicate material (VSM) or rockwool that traps and precipitates mineral P after EC-P treatment was investigated as a means of P reuse as a fertilizing soil amendment. Comparative soil leaching and growth studies using corn plants demonstrate that the VSM alone reduces P losses from soils, and that VSM which has received EC-P effluent is equivalent to or better than commercial superphosphate fertilizer.

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