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.