Effect of tube depth of moistube-irrigation under plastic film mulching on soil water and salt transports of greenhouse tomato

In order to verify the effect of moistube-irrigation under plastic film mulching on water and salt transport in tomato in slight alkaline soils under greenhouse conditions, three buried depths (10 cm, 15 cm, 20 cm) of moistubes of moistube- irrigation under plastic film mulching were designed and the effects of the moistube depths on water content and salinity of soils under (in tomato planting row) and between (between tomato rows) plastic films investigated. The results showed that the change trends in soil water content and salinity were consistent for different moistube depths under and between the plastic films. Under plastic film, soil water content increased initially and then decreased, whereas salinity decreased with time. Between plastic films, soil water content and salinity increased over time. The soil water content between plastic films was less than that under plastic film. With increasing soil depth, the difference in soil water content between under-film and between-films reduced. The difference of soil water content between under-film and between-films was maximal in surface soil. In 5060 cm soil layer, water contents under plastic film and between plastic films were tend to be consistent. The deeper the moistube was, the higher the soil water content was. At fruiting stage of tomato, soil water contents were 23.31%, 24.46% and 22.42% for moistube depths of 20 cm, 15 cm and 10 cm, respectively. The difference in soil water content between under-film and between-films for 10 cm depth of moistube was less those for 15 cm and 20 cm depths of moistubes. Soil salinity under plastic film was less than that between plastic films, and with the increase of buried depth of moistube, the difference between under-film and between-films increased. In 040 cm layer under plastic film, soil was desalinated during the whole growth period of tomato, though the relative desalination rate decreased with increasing soil depth. Also in 040 cm soil layer, the nearer to the moistube, the more obvious the effect of desalination. The soil layer of 4060 cm was in slight salification due to less soil water content and salinity. The 1020 cm soil layer had maximal soil water content, minimum salinity and highest salt desalination rate. However, between plastic films, the soil with depth of 060 cm was in salt deposition state, and the salt deposition rate decreased with the increase of soil depth. Salt deposition rate was highest for the 020 cm soil depth. At fruiting stage of tomato, average maximal desalination rates of 1020 soil layer under plastic film were 24.66%, 32.28% and 14.71% for moistube depths of 20 cm, 15 cm and 10 cm. At seedling and last fruiting stages of tomato, the desalination rates of 1020 soil layer were also highest for 15 cm moistube depth among three buried depths, which were 27.42% and 24.67%. The results showed a significant effect of tube depth of moistube-irrigation under plastic film mulching on salt-leaching of soil in tomato root area. In summary, the buried depth of 15 cm of moistube had the highest average desalination rate of 26.05% and the highest average soil water content of 25.1%, which created an appropriate soil water-salt environment for tomato growth. 15 cm was the best moistube depth of moistube-irrigation under plastic film mulching.