Nitrogen acquisition and its relation to growth and yield in recent high-yielding cultivars of rice (Oryza sativa L.) in Japan

During the last two decades, high-yielding cultivars for multipurpose use of rice have been bred and released in Japan. Some of them have repeatedly recorded high yields of over 9 t ha(-1) of brown rice (about 1.1.25 t ha(-1) of rough rice). Here, characteristic features of nitrogen (N) acquisition and its relation to formation of yield components, dry matter production and grain yield at yield levels over 9 t ha(-1) of brown rice in recent high-yielding cultivars, a large grain type of japonica variety, "Akita 63," extra-panicle weight types of indica variety, "Takanari" and "Saikai 198," and a panicle weight type of japonica variety, "Fukuhibiki," are described as compared with those in the standard japonica cultivars, "Toyonishiki" and "Nipponbare." The grain yield of the recent high-yielding cultivars was 9.4 to 11.6 t ha(-1) of brown rice; that is 1.2-1.7 times greater than those of the standard cultivars. Sink capacity (1000-grain weight x spikelet number per unit land area) was 47-62% greater in the recent high-yielding cultivars, largely due to their 1.3-1.5 times greater N-use efficiency for sink formation (sink capacity per unit amount of total plant N in the aboveground part at maturity), although major component(s) responsible for their greater sink capacity differ among the cultivars. The ratio of grain yield to total dry matter was 1.1-1.4 times greater in the recent high-yielding cultivars than in the standard cultivars, indicating that the former efficiently translocate dry matter into spikelets during the grain-filling period. N-use efficiency for dry matter production (total dry matter per unit amount of total plant N) was comparable between "Akita 63," "Fukuhibiki" and "Toyonishiki," and slightly greater in "Takanari" and "Saikai 198" than in "Nipponbare." These results indicate that greater N-use efficiency for sink formation and efficient translocation of dry matter into spikelets contribute greatly to the high-yielding potential of the recent high-yielding cultivars.