Get on your boots: estimating root biomass and rhizodeposition of peas under field conditions reveals the necessity of field experiments.

Aims: More sustainable agricultural systems, which contribute to C sequestration and biological N fixation, require accurate quantification of plant C and N inputs into soils. This has to be conducted under field conditions, as there are serious shortcomings to pot-based experiments, which have dominated studies on rhizodeposition estimation in the past. Therefore, amounts of below-ground plant C, N, and especially the rhizodeposition of peas were quantified in the field more accurately, with particular emphasis on their transfer into different soil compartments during vegetation. Methods: Pea (Pisum sativum L.) plants were labelled with multiple pulses of 13C-glucose and 15N urea using the cotton wick method. Plants were harvested at four dates depending on plant development. Representative soil samples were taken at harvest with a special drilling tool, considering the spatial distribution of pea roots. Results: Our results indicate that the quantity of C and N rhizodeposition did not change between flowering and maturity. About one third of the C and N rhizodeposits were present in microbial biomass and extractable C or the inorganic N pool of soil. When comparing this field study to a former pot experiment, a higher root-to-shoot ratio was detected; also the rhizodeposition-to-root ratio was altered in the field, questioning the assumption that results from pot experiments can be transferred to field conditions. Conclusions: Due to a higher below-ground C (BGC) and N (BGN) input compared to pot experiments, studies aiming at quantifying BGC and BGN input will have to be conducted under field conditions. [ABSTRACT FROM AUTHOR]