In agriculture, maintaining and increasing soil C stocks is an important aspect of sustainable soil management. Below ground C inputs by crops into soil, i.e. root biomass and C rhizodeposition, are a major source of soil C in agro-ecosystems. To predict long-term C storage in soil or estimate C turnover dynamics, soil C models include root biomass (e.g. CENTURY, Yasso07) and often also C rhizodeposition (e.g. RothC, ICBM) as explanatory variables. As root data are scarce, below ground C inputs are mostly estimated from above ground C production or crop yield, which postulates proportionality of below and above ground C allocation of a given crop. However, yields can vary widely between sites and agricultural systems but little is known about crop response to agricultural intensity below ground.
We, therefore, aim at (i) quantifying root biomass and C rhizodeposition of agricultural crops in two fields and (ii) evaluating the effect of agricultural intensity on below ground C inputs and below / above ground C ratios. The study is conducted on the Swiss long-term field trials “DOK” (Therwil, BL) and “ZOFE” (Zurich), including seven agricultural systems with increasing intensities from 0 to 1.4 according to fertilizer inputs relative to Swiss recommendations. To quantify crop root-derived C, individual plants (maize) or sub-populations (wheat, rapeseed) are grown in microplots and repeatedly pulse-labelled with 13C-CO2 during the entire growth period (figure 1). At physiological maturity, plants are harvested, soil and roots are sampled and separated, and all pools are analysed for their 13C concentrations by IRMS. The results will help to better understand the role of agricultural intensity in crop C allocation below ground and to re-parameterize soil C models.
National Research Program NRP68 – Soil as a resource (SNSF)
Figure 1: Labelling chambers setup in the field