Abstract
Rice plants, variety 'Mubo-Aikoku', were grown in experimental paddy fields at the University of Tokyo under different application conditions of nitrogen fertilizer: as basal dressing only; as both basal and top dressing applied once, twice, or four times between the tillering stage and the heading period. The total amount of nitrogen supplied was 8 kg per 10 ares in each case. The number of primary roots and the density of formation of thick secondary roots on the superficial roots increased as the number of applications of top dressing increased. Observation of additional lateral roots on superficial roots revealed the development of tertiary roots in the fields receiving basal dressing, of fourth roots in the field reseiving one application of top dressing, and of fifth roots in the fields receiving two or four applications of top dressing.
