Monitoring and modeling root-uptake salinity reduction factors of a tomato crop under non-uniform soil salinity distribution

This study has investigated the possibility for monitoring simultaneously and continuously the relationship between
the macroscopic crop response and the evolution of water content, electrical conductivity and root density along the
soil profile during the whole growing season of a tomato crop under different salinity treatments. Water storages
measured by TDR sensors were used for calculating directly the actual water uptake by the root system along the
whole soil profile under the different salinity levels imposed during the experiments. It was observed that during
irrigation with saline water the salt content increased along the whole profile but that it tended to accumulate quite
uniformly below the 20 cm in the case of the 4 dSm-1 treatment and at depth between 15 and 25 cm in the case of the
8dSm-1 salinity treatment. Compared to the reference freshwater treatment, the evapotranspiration under salinity
treatments started to decrease at a threshold value of the time-depth average electrical conductivity (EC) of soil water
of about 3dSm-1. Based on the results of soil and plant monitoring, the root uptake process was simulated by using a
model for water and solute flow in the soil-plant-atmosphere continuum. This way, the root activity reduction at each
depth-node was calculated as a function of the salinity (and eventually water) stress. This enabled relating the
distribution of higher/lower activity of root uptake along the soil profile in response to the actual distribution of salts.