Effect of microbial nitrogen immobilization during the growth period on the availability of nitrogen fertilizer for winter cereals |
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Authors: | K Blankenau H-W Olfs H Kuhlmann |
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Institution: | (1) Centre for Plant Nutrition and Environmental Research Hanninghof, Hanninghof 35, 48249 Dülmen, Germany e-mail: klaus.blankenau@hydro.com Tel.: +49-2594-798242 Fax: +49-2594-7455, DE;(2) Hydro Agri Deutschland, Hanninghof 35, 48249 Dülmen, Germany, DE |
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Abstract: | Pot and field experiments were conducted to determine microbial immobilization of N fertilizer during growth periods of winter
wheat and winter barley. In a pot experiment with winter wheat, Ca(15NO3)2 was applied at tillering Zadok's growth stage (GS) 25)], stem elongation (GS 31) and ear emergence (GS 49). Rates of 100 mg
N pot–1, 200 mg N pot–1 or 300 mg N pot–1 were applied at each N application date. At crop maturity, 15N-labelled fertilizer N immobilization was highest at the highest N rate (3×300 mg N pot–1). For each N-rate treatment about 50% of the total immobilized fertilizer N was immobilized from the first N dressing, and
30% and 20% of the total 15N immobilized was derived from the second and third applications, respectively. In field trials with winter wheat (three sites)
and winter barley (one site) N was applied at the same growth stages as for the pot trial. N was also applied to fallow plots,
but only at GS 25. N which was not recovered (neither in crops nor in soil mineral N pools) was considered to represent net
immobilized N. A clear effect of N rate (51–255 kg N ha–1) on net N immobilization was not found. The highest net N immobilization was found for the period between GS 25 (March) and
GS 31 (late April) which amounted to 54–97% of the total net N immobilized at harvest (July/August). At GS 31, non-recovered
N was found to be of similar magnitude for cropped and fallow plots, indicating that C from roots did not affect net N immobilization.
Microbial biomass N (Nmic) was determined for cropped plots at GS 31. Although Nmic tended to be higher in fertilized than in unfertilized plots, fertilizer-induced increases in Nmic and net N immobilization were poorly correlated. It can be concluded that microbial immobilization of fertilizer N is particularly
high after the first N application when crop growth and N uptake are low.
Received: 6 July 1999 |
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Keywords: | Nitrogen immobilization Nitrogen recovery Cereals Fallow Microbial biomass nitrogen |
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