INTERACTIONS BETWEEN ROOT AND SHOOT ENVIRONMENTAL FACTORS ON CROP YIELD AND QUALITY

     In order to improve both the yield and quality of glasshouse crop in a saline environment, the interactions between the environmental factors on both shoot and root have to be well defined. For the glasshouse tomato production, the yield is reduced linearly with moderate EC mainly due to a reduction in individual fruit size. The basic effect of EC on tomato fruit growth is on its accumulation of water and nutrients, rather than photoassimilate. The benefit in higher fruit dry matter content is quite limited, since the yield reduction is only acceptable when it is compensated by the premium in the market. However, the fruit weight under the same EC can be improved by reducing the crop transpiration rate on fruit water relations and by CO₂ enrichment on photoassimilate supply and on raising the salt tolerance level. Apart from selecting the acceptable EC range for tomato production, the application of instant EC adjustment based on micro-climate of the glasshouse or diurnal EC fluctuation in the root zone has not been successful. Apart from fruit weight reduction, high EC also increases the incidence of blossom-end rot (BER) caused by local Ca deficiency in the fast growing fruit. The severity of BER at high EC can be reduced by adjusting the nutrient composition of the feed (lower nitrate and ammonia nitrate), or by reducing the temperature-enhanced fruit growth. However, the application of split-root system appears to sustain the benefit of higher fruit dry matter content, while both the yield reduction and the incidence of BER is lessen. In glasshouse tomato production, the application of moderate EC in conjunction with fruit growth regulation by the supply of photoassimilate and water/nutrient can be beneficial for both crop yield and quality.

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