Root Traits of Durum Wheat and Chickpea Vary with Soil Nitrogen Availability when Intercropped or Grown Alone in Mediterranean Conditions

Studies focusing on root traits of intercropped cereals and legumes measured under field conditions are scarce. In this study, we hypothesized that the presence of chickpea would impact soil N availability and modify durum wheat and chickpea root traits when intercropped compared with sole crops. We expected specific root length (SRL) and root length density (RLD) to increase in presence of chickpea while root tissue density (RTD) and root diameter (RD) would decrease.

The study was performed in 2017 at the INRA experimental station of Mauguio (France) in Mediterranean conditions. Durum wheat and chickpea were grown either alone or intercropped in an organic long-term field experiment. Each of the three cropping treatments occurred as 4 randomized plots (6 x 10 m²). Soil and roots were sampled at chickpea flowering stage with a hydraulic soil corer of 5 cm in diameter, at two soil depths (0-30 cm and 30-60 cm). Four cores centered on plant individuals were collected per horizon for each plot and for each crop species, leading to 64 samples by depth thus a total of 128 soil cores. Roots were washed, scanned and analyzed with WinRhizo^TM and for C, N and P concentrations. Twenty four additional soil cores were collected for soil C, N and P analyses.

Results showed that the total root biomass of both chickpea and wheat was the same for the sole crop and intercrop. The N content of chickpea roots tended to increase when intercropped. For chickpea, the RLD and RD decreased at each depth when intercropped, while the decrease was not significant for durum wheat. SRL and RTD did not vary for both species. Overall, durum wheat root traits were less affected by intercropping than those of chickpea indicating a better competitive behavior probably due to its fasciculate root system architecture.