| Summary: | To determine the soil mechanism in root-zone caused by water saving and the production response to alternate drip irrigation (ADI), the present study investigated the effects of deficit ADI on tomato growth using the conventional surface drip irrigation (CDI) as a control. The interactions among the experimental treatments on root index, photosynthetic efficiency, biomass accumulation, yield, fruit quality and irrigation water use efficiency (<i>IWUE</i>) were assessed and the inner mechanism of root-soil effecting on tomato growth, photosynthate distribution, yield and quality was discussed. ADI significantly enhanced root-soil interaction, promoted soil nitrogen and phosphorus absorption by tomato and tomato growth. However, different soil moisture deficits significantly affected tomato photosynthate accumulation and distribution, as well as fruit quality. With irrigation amount of 50% field capacity (<i>F</i>), ADI significantly increased soluble sugar, total soluble solid and lycopene by 38.08%, 19.48% and 30.05%, respectively, compared to those of CDI, but decreased irrigation amounts by 29.86% in comparison with the CDI one. ADI of 70% <i>F</i> could significantly distribute more photosynthate to fruits, thus enhanced tomato yields by 24.6% and improved <i>IWUE</i> by 17.05% compared to that of CDI. In addition, ADI of 70% <i>F</i> improved tomato fruits quality, and in particular organic acid was decreased by 43.75% and sugar-acid ratio was increased by 97% compared to CDI. However, ADI of 60% <i>F</i> distributed more photosynthate to plant, showing no significant difference of yields in comparison with CDI and ADI of 70% <i>F</i>, but a higher <i>IWUE</i> by 19.54% than that of CDI. ADI of 60% <i>F</i> significantly enhanced soluble sugar, total soluble solid, soluble protein, lycopene and sugar-acid ratio in tomato fruits by 2.06, 1.26, 1.61, 1.4 and 3.2 times respectively compared to CDI. Therefore, ADI of 60% or 70% <i>F</i> can be overall recommended for tomato production in a greenhouse, plant growth, fruit yield and quality, and <i>IWUE</i>.
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