Previous PageTable Of ContentsNext Page

Re-use of saline water on tomatoes: an approach to managing salinity and increasing profit

P.S. Cornish

NSW Agriculture, Horticultural Research and Advisory Station, PO Box 581, Gosford NSW 2250

One approach to managing salinity is to retain salt on-farm by re-using saline drainage or groundwater. Tomatoes may be a suitable crop for this purpose. They are relatively salt tolerant and about two-thirds of the tomato processing industry has ready access to saline water. Also, work at Gosford with table tomatoes grown in hydroponics has shown that mild salt stress increases the concentration of soluble solids (CSS) in fruit by up to 0.5 brix with no loss in yield (Cornish, unpublished data). As the price paid for processing tomatoes depends on CSS, the reuse of saline water on tomatoes may be sound both economically and environmentally. This paper reports on studies designed to establish the principles of plant management using saline water to irrigate processing tomatoes.

Methods

Six cultivars of processing tomatoes were compared at different degrees of salt stress in a nutrient film hydroponic system (1989/90) or in the field under a rainshelter (1990/91). In both experiments, plants were grown without saline stress until mid flowering. The electrical conductivity (EC) of nutrient solution in hydroponics was then raised from 2.0 mS/cm to 2 (control), 4, 6, 8, 10 or 12 mS/cm. In the field, plots were irrigated with water made saline with NaCI to an EC of 4 or 8 mS/cm, or they received non saline water (0.1 mS/cm) as a control. Soil solution EC, yield and CSS were measured.

The cultivar UC82B was grown in the field, under a rainshelter, without saline stress until treatments were imposed. Treatments comprised salinisation (8 mS/cm) from mid flowering, the end of flowering, or from 10 days after flowering. One treatment received water which increased in EC from 4 mS/cm at early flowering to 8 mS/cm by late flowering. The control received non saline irrigation water.

Results and discussion

There were no cultivar x EC interactions for either CSS or yield. In hydroponics CSS rose linearly with increasing solution EC (CSS = 4.4 + 0.102 EC, r2 = 0.90**), but yield declined linearly (Yield [kg/pot] = 12.59 - 0.23 EC, r2 = 0.74**). Similar results were obtained in the field. The decline in yield with rising CSS contrasts with earlier work with table tomatoes (see Introduction).

Salinisation with water at EC 8 from mid flowering reduced fruit number, fruit size and yield. In the treatment with rising salinity, effects on fruit size were offset by increases in fruit number. Yield was not significantly reduced (P<0.05), whilst CS S increased by 1.0 brix and solids yield increased from 2.52 to 2.91 t/ha.

The technique of irrigating with saline water clearly has potential, both economically and environmentally, but work is needed to develop reliable application strategies.

Acknowledgements

The Horticultural Research and Development Corporation and Tomato Processing Research Committee funded the work and John Heckenberg gave valued field assistance.

Previous PageTop Of PageNext Page