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Above- and belowground nitrogen distribution of a red clover-perennial ryegrass sward along a soil nutrient availability gradient established by organic and conventional cropping systems

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Abstract

Aims

Belowground legume nitrogen (N) composed of roots and rhizodeposition is an important N input to soils, but published data of belowground N vary broadly, probably due to extrapolation from short-term experiments and dissimilar growing conditions. We quantified belowground N inputs of red clover (Trifolium pratense L.) during two consecutive years in a clover-grass sward along a soil nutrient availability gradient.

Methods

We established a red clover-perennial ryegrass (Lolium perenne L.) model sward in microplots located in field plots of the DOK experiment, which has a 33-year history of organic and conventional cropping, resulting in a soil nutrient availability gradient. Four treatments were examined: the zero fertilisation control, bio-organic with half and full dose manure application, and the conventional system with mineral fertilisation at full dose. We studied the development of clover aboveground and belowground N using multiple pulse 15N urea leaf labelling.

Results

Belowground clover N increased over time and with rising nutrient availability and was proportional to aboveground clover N at all times. Belowground clover N amounted to 40% of aboveground clover N during two consecutive years, irrespective of the nutrient availability status. Belowground clover N development was initially dominated by fast root growth, followed by enhanced root turnover during the second year. Potassium availability limited clover growth and total N accumulation in treatments with low nutrient availability.

Conclusions

Belowground red clover N inputs could be estimated from aboveground N by a constant factor of 0.4, regardless of the nutrient availability and cultivation time. Root turnover led to a distinct absolute increase of N rhizodeposition over time. Hence, N rhizodeposition, with an 80% share of belowground N, was the predominant N pool at the end of the second year.

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Abbreviations

AGN:

Aboveground N

BGN:

Belowground N, comprising physically recoverable root N at the time of excavation plus NdfR

BIOORG1:

Bio-organic treatment of the DOK experiment with half dose fertilisation

BIOORG2:

Bio-organic treatment of the DOK experiment with full dose fertilisation

CONMIN2:

Conventional treatment of the DOK experiment with full dose sole mineral fertilisation

CFE:

Chloroform fumigation extraction

DOK:

Long-term experiment comparing Bio-Dynamic, Bio-Organic, and conventional (K) cropping systems

EAF:

Excess atom fraction

LMP(t):

Labelled microplot, delimiting the 15N labelled plant-soil system (excavated after t months of sward cultivation)

NdfR:

Nitrogen derived from rhizodeposition

NOFERT:

Unfertilised control treatment of the DOK experiment

RMP(t):

Reference microplot, delimiting the unlabelled plant-soil system (excavated after t months of sward cultivation)

t:

Time from planting of red clover and perennial ryegrass until microplot excavation in months

References

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Acknowledgments

We warmly thank the Agroscope field team, especially their head Ernst Brack, Lucie Gunst and Monika Schnider from Agroscope for their versatile help in the DOK experiment and in the lab, the FiBL field team for their help in the DOK experiment, Stephano Bernasconi from the Geological Institute at ETH Zurich for isotopic analysis, Claude Renaux from the statistical consulting service of the seminar of statistics at the ETH Zürich, and Juliane Hirte from Agroscope for the final internal review of the manuscript. The work was funded by the Swiss National Science Foundation Grant 205321_132770 / 1.

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Correspondence to Jochen Mayer.

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Responsible Editor: Richard J. Simpson.

Andreas Hammelehle is currently affiliated at Landesbetrieb Landwirtschaft Hessen, Fachinformation Pflanzenbau, 61169 Friedberg, Germany.

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Hammelehle, A., Oberson, A., Lüscher, A. et al. Above- and belowground nitrogen distribution of a red clover-perennial ryegrass sward along a soil nutrient availability gradient established by organic and conventional cropping systems. Plant Soil 425, 507–525 (2018). https://doi.org/10.1007/s11104-018-3559-z

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  • DOI: https://doi.org/10.1007/s11104-018-3559-z

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