Effects of repeated fertilizer and cattle slurry applications over 38 years on N dynamics in a temperate grassland soil
The effects of repeated synthetic fertilizer or cattle slurry applications at annual rates of 50, 100 or 200 m 3 ha −1 yr −1 over a 38 year period were investigated with respect to herbage yield, N uptake and gross soil N dynamics at a permanent grassland site. While synthetic fertilizer had a susta...
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Veröffentlicht in: | Soil biology & biochemistry 2011-06, Vol.43 (6), p.1362-1371 |
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Zusammenfassung: | The effects of repeated synthetic fertilizer or cattle slurry applications at annual rates of 50, 100 or 200
m
3
ha
−1
yr
−1 over a 38 year period were investigated with respect to herbage yield, N uptake and gross soil N dynamics at a permanent grassland site. While synthetic fertilizer had a sustained and constant effect on herbage yield and N uptake, increasing cattle slurry application rates increased the herbage yield and N uptake linearly over the entire observation period. Cattle slurry applications, two and four times the recommended rate (50
m
3
ha
−1
yr
−1, 170
kg
N
ha
−1), increased N uptake by 46 and 78%, respectively after 38 years. To explain the long-term effect, a
15N tracing study was carried out to identify the potential change in N dynamics under the various treatments. The analysis model evaluated process-specific rates, such as mineralization, from two organic-N pools, as well as nitrification from NH
4
+ and organic-N oxidation. Total mineralization was similar in all treatments. However, while in an unfertilized control treatment more than 90% of NH
4
+ production was related to mineralization of recalcitrant organic-N, a shift occurred toward a predominance of mineralization from labile organic-N in the cattle slurry treatments and this proportion increased with the increase in slurry application rate. Furthermore, the oxidation of recalcitrant organic-N shifted from a predominant NH
4
+ production in the control treatment, toward a predominant NO
3
− production (heterotrophic nitrification) in the cattle slurry treatments. The concomitant increase in heterotrophic nitrification and NH
4
+ oxidation with increasing cattle slurry application rate was mainly responsible for the increase in net NO
3
− production rate. Thus the increase in N uptake and herbage yield on the cattle slurry treatments could be related to NO
3
− rather than NH
4
+ production. The
15N tracing study was successful in revealing process-specific changes in the N cycle in relationship to long-term repeated amendments.
► Repeated N applications over 38 years affect N uptake and N dynamics. ► Changes in the N dynamics were evaluated via a
15N tracing study. ► Applications of slurry shift mineralization from recalcitrant to labile organic matter. ► Increasing cattle slurry applications promote oxidation of NH
4
+ and organic-N. ► Individual gross N rates are affected by the application rate. |
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ISSN: | 0038-0717 1879-3428 |
DOI: | 10.1016/j.soilbio.2011.03.014 |