Sub-Theme 2 | Improvement of Cultural Practicies for the New High-yielding Rice Varieties
The modern techniques of rice cultural practices were systematically established with hand transplanting after the foundation of the first public organization of agricultural research station in Korea in the early 20th century (1906), and has developed into the present scientific system after the Liberation from Japan in 1945 along with the intensive research works. Particularly, the technology of rice cultural practices has been greatly advanced by the cultivation of Tongil type rice varieties since the early 1970’s because of some different ecological responses from japonica varieties. Tongil type rice varieties showed the relatively longer basic vegetative growth with more or less neutral response to photoperiod as compared with traditional temperate japonica, and needed relatively higher temperature during the growth stage of grain ripening in the Korean situations of climates.
The history of the development in cultural practice technologies for high yield in Korea can be mainly classified as before and after 1970. Between 1950 and 1960s, although high yield techniques for Japonica rice with tall height had been substantially improved, a limit was presented in terms of increasing the actual yield performance in farmers field, resulted in increasing the yield potential of 5 ton per ha when it was first released, which was compared to 3.5 ton per ha of the best japonica.
In phenotypic perspective, Tongil-type rice had an advantage of being close to the ideotype for rice which is counted as an important trait for high yield potential; short-statured and erected-leaf type with heavy-panicle weight, better responses to high nitrogen fertilizer and dense planting, which is securing the number of spikelets per unit area as sink for increasing yield. However, Tongil-type rice carried several disadvantages mainly due to its cold sensitivity derived from Indica germplasm in physiology aspect, as well. These flaws in Tongil-type rice caused discoloration in seedling nursery, growth retard of root age and growth at the early stage of paddy field, and increased infertility caused by spikelet-sterility type cold injury outbreak after a reduction in the division stage, poor ripening from excess number of spikelets in the late ripening stage. In addition, there were difficulties in increasing the yield from the low soil fertility level on the Korean paddy soil. To improve and make up the downsides, the research projects practiced to maximize the four yield components, such as the number of panicles per area, the number of spikelets per panicle, the percentage of ripened grains and 1000 grain weight of brown rice in a balanced manner.
In order to secure the sufficient number of panicles per unit area, it fostered healthy seeding; transplanted proper density; facilitated tillering by applying both basal fertilizer and topdressing at tillering stage; secured the sufficient number of effective tillering to avoid non-productive tiller at the early stage by mid-summer drainage in paddy fields. The technique by which ear manuring and top dressing were applied to paddy fields in a timely manner was developed to increase the percentage of ripened grains for the effective number of grains per panicle. Also, manure, silicate, soil dressing, and deep plowing were applied to enhance the fertility and physical structure of paddy soil. Rice was planted based on a region specific weather condition at a right moment to reduce the risks at natural disasters such as outbreak of disease and insects, lodging, and freezing, since those may occur frequently under the high fertilization and dense planting condition.
By successful disseminating this high yield techniques, from 1973 to 1987, for 15 years, the national average yield on rice for Tongil-type rice surpassed that of Japonica by 17%, 4.71 ton per ha and 4.03 ton per ha respectively. The high yield farm’s productivity (8.94 ton) increased by 2.22 times compared to that of Japonica (4.03 ton), and by 1.9 times higher than that of Tongil-type rice.