Organic Tomatoes: Increasing Quality and Taste by Reducing Irrigation

Product quality and taste are important in the marketing of organic produce. From 2002 to 2005, Dutch organic greenhouse farmers have cooperated in the research and farm development project "Biokas". Part of the research was directed to quality and taste of tomatoes.

It was found that a minor decrease in irrigation may cause an increase in taste by reducing the vegetative character and improving the generative character of the crop, or by creating a higher Electro Conductivity (EC). Growers will not always reduce irrigation because of the risk of yield reduction. Reduced irrigation, however, might lead to less leaching and thus a higher nutrient efficiency. A model for irrigation was developed, as well as a model for nitrogen availability during the growing season.

In one glasshouse, two blocks, one with reduced irrigation ("dry"), and one with normal irrigation ("control") were monitored. From April to September 2005, probes were gathered and analysed by means of:
1. the PPO Taste model (six probes);
2. biocristallisations (five probes) and
3. professional taste panel (August and September probes only). The last four probes were gathered and analysed in duplo.

The results: All three measurement methods indicated that the taste (model, panel) and the inner quality (biocristallisations) were improved by the reduced irrigation. The taste model, being the only quantitative method out of these three, gave an average increase of 4.7 points, from June to September. Differences of 2-3 points are considered to be relevant from a consumers' perspective. The yield decreased about 2.2 %, being EUR 1.50 m². To compensate for this loss (by obtaining a higher price for better taste and quality), the average farmers' price should have been EUR 1.54 as opposed to EUR 1.5, the price received in 2005.

Conclusion: Quality and taste of tomatoes can be improved by reducing irrigation. The effect of this may be reduced leaching and improved nutrient efficiency. In 2006, again taste and yield measurements will take place under reduced irrigation and compared with ‘normal’ irrigation. Together with measurements of soil water content, soil water EC and the use of an irrigation advisory model, a better understanding of the role of irrigation in taste improvement will be achieved.

Growers will strive towards a higher quality and taste only if they are paid for it.
So far, this has not been the case in Holland. Trade companies are important partners for incorporating quality and taste parameters in the communication to consumers and in the price they pay farmers for a better product.

The results of the project are available in reports in Dutch with an English summary.
For further information please contact the author: G.J. van der Burgt on email: g.vanderburgt@louisbolk.nl.

This article has been edited from the original available at www.organicfqhresearch.org/downloads/newsletter/fqh_news_feb2006.pdf