The effects of irrigation method and seedling age at transplanting on the growth and yield of rice grown on heterogeneous saline soils

We investigated the effect of transplanting young seedlings and intermittent irrigation on the growth and yield of rice on the soil with three profiles of salinity. Fifteen-liter pots were filled with non-saline soil (non-saline plot), with the soil to which 45 g of salt was applied to all layers of the soil (homogeneous saline plot), and with the soil to which 45 g of salt was applied to the lower half layer (heterogeneous saline plot). Younger and older seedlings of paddy rice Nipponbare, at leaf ages of 2.5 and 4.7, respectively were transplanted to these pots, one seedling per pot. Then plants were subjected to continuously submerged soil conditions, or intermittent irrigation. In the non-saline plot, growth of young and older seedlings was poorer in intermittent irrigation than in submerged soil conditions. In the homogenous saline plot, young seedlings died soon after the transplanting and older seedlings survived longer under submerged soil conditions. Salinity distribution was not changed much in submerged soil conditions, but salinity moved up under intermittent irrigation regardless of initial salinity distribution. We concluded that transplanting young seedlings was not acceptable in saline soil because their salinity tolerance was low. Intermittent irrigation was not preferable, because it promoted the accumulation of salt in the upper soil layer. On the other hand, low salinity in the upper soil layer improved seedling survival and early growth. The results suggest that the upper layer should be low in salinity, and the plants should be grown under submerged soil conditions to produce healthy rice plants.