抄録
In continuance to the previous studies, the authors investigated the seasonal change in inorganic elements, especially N, P and K in rice plant leaves grown with different fertilizer treatments in 1952 dnd '53, the results being as follows: N content in dry leaf blade decreased as the plant grew, but at the stage of young ear formation it stopped decreasing, and after heading stage it decreased again gradually. Such dropping of N percentage, being especially marked in the plots without N fertilizing, i. e. PK, P, K and Nil plots, seemed to be caused by N translocation from leaf blades to young ears. Consequently, N content at that stage may be taken as an index of want of the plant for N dressing. P or K status of the plant was indicated well in P or K percentage in the leaf sheath respectively. P or K was proved deficient in the leaf sheath, especially in that of the lower leaf in the plot without P or K respectively. As to NPK inter-relation, composition of NPK units in L. B. and L. S. is shown in Table 1. Ratios of % values of N, P and K to the N+P+K value were found nearly constant in top leaves, physiologically active ones, during the growth period, except the stage of young ear formation, and as the lower leaves got older, N decreased and K increased, till they gradually died. In N, P and K plots, N, P or K ratio respectively to N+P+K was found higher than that in the NPK plot during vegetative growth period, but at later reproductive stages such was not the case. Conse quently, leaf analysis could serve well for indicating fertilizer condition during vegeta tive stages of rice plant. but in later stages it could do no more.
