Yamauchi (2020) Morphological and histological differences among three types of component roots and their differential contribution to water uptake in the rice root system,

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.

In the rice growing area of Kenya’s highlands, the development of a water-saving rice cultivation system is a key strategy because the shortage of irrigation water is a frequently occurring problem. The purpose of this study was to investigate the effect of alternate wetting and drying (AWD) on the growth and yield of rice under the unique cultivation environment of tropical highlands. Field experiments were performed over a period of four years (2014–2017) in a paddy field. Dry matter production of a lowland variety, Basmati 370, was greater under continuous flooding (CF) than under AWD. In years with low minimum temperature (less than 15 °C) during the reproductive and ripening stages, filled grain ratios were significantly higher under AWD than under CF. Accordingly, higher dry matter production under CF did not contribute to grain yield. In the years when rice was not exposed to low minimum temperature during the reproductive and ripening stages, filled grain ratio did not decrease even under CF. Therefore, there was no difference between filled grain ratio under AWD and CF. Our results indicated that AWD could mitigate the decline in grain filling, induced by low minimum temperature during the reproductive and ripening stages in Basmati 370, under the cultivation conditions in tropical highlands. Although AWD may reduce the above-ground biomass, its mitigation effect on grain filling could outweigh this drawback and can still be beneficial to rice farmers in the tropical highlands.