The effect of manuring on cereal and pulse amino acid delta N-15 values

Amino acid delta N-15 values of barley (Hordeum vulgare) and bread wheat (Triticum aestivum) grains and rachis and broad bean (Vicia faba) and pea (Pisum sativum) seeds, grown in manured and unmanured soil at the experimental farm stations of Rothamsted, UK and Bad Lauchstadt, Germany, were determined by GC-C-IRMS. Manuring was found to result in a consistent N-15-enrichment of cereal grain amino acid delta N-15 values, indicating that manuring did not affect the metabolic routing of nitrogen (N) into cereal grain amino acids. The increase in cereal grain delta N-15 values with manuring is therefore due to a N-15-enrichment in the delta N-15 value of assimilated inorganic-N. Greater variation was observed in the N-15-enrichment of rachis amino acids with manuring, possibly due to enhanced sensitivity to changes in growing conditions and higher turnover of N in rachis cells compared to cereal grains. Total amino acid delta N-15 values of manured and unmanured broad beans and peas were very similar, indicating that the legumes assimilated N-2 from the atmosphere rather than N from the soil, since there was no evidence for routing of N-15-enriched manure N into any of the pulse amino acids. Crop amino acid delta N-15 values thus provide insights into the sources of N assimilated by non N-2-fixing and N-2-fixing crops grown on manured and unmanured soils, and reveal an effect of manure on N metabolism in different crop species and plant parts. (C) 2014 Published by Elsevier Ltd.