Long-term changes of the δ¹⁵N natural abundance of plants and soil in a temperate grassland

• Published in: Plant and soil 2009, Vol.325 (1-2), p.157-169
• Main Authors: Kriszan, Melanie, Amelung, Wulf, Schellberg, Jürgen, Gebbing, Thomas, Kühbauch, Walter
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Animal, plant and microbial ecology; Biological and medical sciences; Biomedical and Life Sciences; Ecology; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Life Sciences; Nitrogen fertilization; Nitrogen, phosphorus, potassium fertilizations; Plant Physiology; Plant Sciences; Regular Article; Soil science; Soil Science & Conservation; Soil-plant relationships. Soil fertility; Soil-plant relationships. Soil fertility. Fertilization. Amendments
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/s11104-009-9965-5

Tracing back the N use efficiency of long-term fertilizer trials is important for future management recommendations. Here we tested the changes in natural N-isotope composition as an indicator for N- management within a long-term fertilization lysimeter experiment in a low mountain range pasture ecosystem at Rengen (Eifel Mountains), Germany. Cattle slurry (δ¹⁵N = 8.9 ± 0.5‰) and mineral fertilizers (calcium ammonium nitrate; δ¹⁵N = −1.0 ± 0.2‰) were applied at a rate between 0 and 480 kg N ha⁻¹ yr⁻¹ throughout 20 years from 1985 onwards. In 2006, samples were taken from different grass species, coarse and fine particulate soil organic matter, bulk soil and leachates. Total soil N content hardly changed during fertilization experiment. As also N leaching has been small within the stagnant water regime, most N was lost through the gaseous phase beside plant uptake and cutting. Unlike N uptake by plants, the process of N volatilization resulted in strong discrimination against the ¹⁵N isotope. As a consequence, the δ¹⁵N values of top soil samples increased from 1.8 ± 0.4‰ to 6.0 ± 0.4‰ and that of the plants from −1.2 ± 1.3‰ to 4.8 ± 1.2‰ with increasing N fertilizer rate. Samples receiving organic fertilizer were most enriched in δ¹⁵N. The results suggest that parts of the fertilizer N signal was preserved in soils and even discovered in soil organic matter pools with slow N turnover. However, a ¹⁵N/¹⁴N isotope fractionation of up to 1.5‰ added to the δ¹⁵N values recovered in soils and plants, rendering the increase in δ¹⁵N value a powerful indicator to long-term inefficient N usage and past N management in the terrestrial environment.