SALINITY EFFECTS ON FRUIT YIELD IN VEGETABLE CROPS: A SIMULATION STUDY
Salinity can reduce crop growth and yield through its impact on plant water relations by: (1) increased fruit dry matter content, (2) reduced leaf expansion and (3) stomatal closure. In this simulation study the tomato model TOMSIM was used to predict salinity impact on fruit fresh yield, based on single or combined effects through plant water relations. The following influences were tested: Increase in fruit dry matter content (5% at EC=2 dS m -1 ) by 0.2% per dS m -1 ; decrease in specific
... f area (SLA) by 8% per dS m -1 starting from a threshold of 3 or 6 dS m -1 ; increase in stomatal resistance (r s ) by a factor 2 or 4 over the range 1 to 10 dS m -1 . Simulations showed threshold salinity levels of 2.9-4.4 dS m -1 , except when only r s or only SLA was affected (higher threshold). Impact of r s was small as total resistance for CO 2 import is determined by a series of resistances in which r s is rather small, under non-stressed conditions. Yield decline in % per dS m -1 varied between 1.9 and 17.8. When only an effect of salinity on r s was simulated this decline was lowest, whereas a salinity effect on SLA from EC=3 dS m -1 onwards, gave the strongest decline per unit rise in EC. Simulations showed that delayed leaf picking or increased plant density mitigate the negative effect of salinity via leaf expansion, as average leaf area index increases. For example, at EC=7 dS m -1 one week delay in leaf picking resulted in 10% yield increase (24.2 instead of 22.0 kg m -2 ), whereas at EC=9 dS m -1 this was 25% (14.7 instead of 11.8 kg m -2 ). Applicability of these results, if confirmed by targeted experiments, would not be limited to tomato as the processes described in the model are general.