Seedling Quality and Temperature Responses of Sparsely Sown Rice in Nursery Boxes in the Tohoku Region

Abstract

The characteristics and temperature responses of sparsely sown rice seedlings were investigated using leading rice cultivars in the Tohoku region. In experiment 1, ‘Akitakomachi’ seedlings were investigated under three sowing conditions: sparse (60 g box^-1 of dry seed), standard (120 g box^-1), and dense (240 g box^-1), at Iwate University in 2020. Compared to the standard and dense sowing conditions, the sparse sowing condition produced seedlings with more vigorous leaf age development and higher dry matter weight with increasing accumulated soil temperature. In addition, sparsely sown seedlings had higher dry matter weight per plant length than those sown under other densities. In experiment 2, the seedling quality of leading cultivars such as ‘Masshigura’, ‘Akitakomachi’, ‘Ginganoshizuku’, ‘Haenuki’, ‘Hitomebore’ and ‘Tennotsubu’ was investigated at each experimental site in the Tohoku region in 2023 and 2024 under sparse sowing (65–80 g box^-1) and standard sowing conditions (120–160 g box^-1). The sparsely sown seedlings had higher dry matter weight and more seedling vigor than standard seedlings under an accumulated air temperature range of 400–700°C-day, regardless of the experimental site and cultivar. This is attributed to the larger dry matter per unit air temperature of the sparsely sown seedlings. Sparse sowing can maintain superior seedling quality over a wide temperature range; therefore, it is not only beneficial for large-scale operations with long transplanting periods but also helps to prevent the decline of seedling quality under the global warming environmental situation.