Characterization of soil nitrogen and nitrogen uptake by grass following a two-year fallow of potted soils receiving mineral and organic sources of nitrogen

• Published in: Soil biology & biochemistry 1994-10, Vol.26 (10), p.1299-1304
• Main Authors: Olfs, H.-W., Werner, W.
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Nitrogen fertilization; Nitrogen, phosphorus, potassium fertilizations; Soil-plant relationships. Soil fertility. Fertilization. Amendments
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/0038-0717(94)90210-0

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, 15N-labelled fertilizer was used. After 2yr 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 (Nmin) and readily extractable organic N compounds (Norg) were determined. Changes in the Nnmin 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 Norg 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 contents were smaller and the amount of added nitrogen had a pronounced effect. Increase or decrease of the Norg contents were not related to a reverse change in the Nmin content. Total N uptake was significantly related to Nmin content in the soil at the end of the fallow, i.e. prior to sowing (r2 = 0.98∗∗). The relationship was less close between Norg and N uptake during the following growth period (r2 = 0.48∗–0.56∗). The results of the 15N 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.