Characterization of soil nitrogen and nitrogen uptake by grass following a two-year fallow of potted soils receiving mineral and organic sources of nitrogen
1994
Olfs, H.W. | Werner, W.
Nitrogen turnover in fertilized soils with or without a supply of decomposable organic matter and the time-dependent remineralization of immobilized nitrogen were studied in a 3-year pot experiment. In three treatments, (15)N-labelled fertilizer was used. After 2 yr of fallow the soils were planted with ryegrass and N uptake was measured. Soil samples were taken during the fallow and the following period of plant growth and contents of mineral nitrogen (N(min)) and readily extractable organic N compounds (N(org)) were determined. Changes in the N(min) content during the 2-yr fallow became differentiated according to (1) the amount of applied mineral N and (2) the C-to-N ratio that was established. Even 2 yr after C incorporation N was immobilized in some treatments. Changes of N(org) values during the first 4 weeks of the fallow depended primarily on the amount of added carbon. In the 3rd experimental yr differentiation of N(org) contents were smaller and the amount of added nitrogen had a pronounced effect. Increase or decrease of the N(org) contents were not related to a reverse change in the N(min) content. Total N uptake was significantly related to N(min) content in the soil at the end of the fallow, i.e. prior to sowing (r(2) = 0.98**). The relationship was less close between N(org) and N uptake during the following growth period (r(2) = 0.48*-0.56*). The results of the (15)N treatments proved that application of fertilizer N enhanced N uptake from the native soil pool. Production of stabilized N compounds seemed to depend on the amount of microbial usable carbon, the C-to-N ratio of the added substrate and the number of turnover cycles.
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