ISHS Acta Horticulturae 507: III International Workshop on Models for Plant Growth and Control of the Shoot and Root Environments in Greenhouses
ADSORPTION AND ACCUMULATION OF NA IN RECIRCULATING CROPPING SYSTEMS |
| Authors: | M. Heinen, P. de Willigen |
| Keywords: | cation exchange capacity, CEC, Gapon exchange, rockwool, simulation model, sodium |
| Abstract:
When the water used for irrigation or fertigation in glasshouse horticulture is contaminated with NaCl, one may expect accumulation of Na and Cl in recirculating cropping systems, as Na and Cl are not taken up in large quantities. We determined to what extent Na accumulates in a recirculating rockwool cropping system. We used a simulation model that describes water movement and solute transport in porous media. The model was extended to include exchange of cations at the adsorption complex. We considered the specific case of Ca and Na exchange according to the Gapon exchange equation. This equation states that a divalent cation (Ca) will occupy preferentially the adsorption complex in relation to a monovalent (Na) cation. For the case of Na accumulation in a recirculating rockwool cropping system, we used a nutrient solution in which both Na and Ca are present. The level of the nutrient solution in the supply tank is kept constant by replenishing the amount of water that was used by evapotranspiration with NaCl contaminated water. Na accumulates in the nutrient solution more or less linearly, and only a very small effect of CEC of the root zone was observed. Since all cations present in the nutrient solution are preferentially adsorbed relative to Na, we conclude that in studies of Na accumulation in recirculating cropping systems, adsorption of Na does not need to be considered. | |
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