A lysimeter study of the fate of fertilizer nitrogen in spring barley crops grown on a shallow soil overlying Chalk: denitrification losses and the nitrogen balance |
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| Authors: | R J DOWDELL C P WEBSTER |
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| Institution: | Agricultural Research Council Letcombe Laboratory, Wantage, Oxon OX 12 9JT |
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| Abstract: | Four successive spring barley crops were grown in monoliths of a shallow soil overlying Chalk, contained in lysimeters. After harvest of the fourth crop, 25% of the nitrogen-15 labelled fertilizer applied 4 years earlier was found remaining in the roots and soil. Of this, 73% was present in the upper 30cm of the profile. From the amounts of fertilizer derived nitrogen that remained at the beginning of each cropping season we estimate that 5–6% of the residual nitrogen-15 turned over each year, representing a net release of 20% of the labelled nitrogen contained in the microbial biomass. Mineralization of the total biomass at the same fractional rate would release 120 kg N ha?1 a?1. This estimate is supported by the difference between input and outputs of total nitrogen during the experiment of 76–94 kg N ha?1 a?1 in fertilized lysimeters and 129kg N ha?1 a?1 in unfertilized control lysimeters. The total recovery of the applied labelled nitrogen was 81–87%. The nitrogen not accounted for was taken to be lost by denitrification of nitrate to dinitrogen, as no nitrous oxide emissions were detected during the experiment. Laboratory studies in aerobic and anaerobic conditions in presence of acetylene confirmed that 10–20% of the applied nitrogen-15 could have been transformed to dinitrogen. |
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