Since 1962, varietal development and dissemination for summer upland crops have been actively initiated by the Crop Experiment Station, Office of Rural Development, Suweon, Korea. The major breeding objectives of soybeans have been to develop varieties which are early maturing, disease resistant, and adaptable to late planting for after-barley cropping. Development of eleven new soybean varieties including Hwangkeumkong, Jangyeobkong, Danyeobkong, and Kwangkyo has greatly increased the soybean yield throughout country. For com, after development of Hwangok #2, a synthetic, in early 1960's, nine corn hybrids-single crosses, double-crosses, and three-way crosses-such as Jecheon-ok, Hoengseong-ok, Kwangok, Suweon #19, etc., have been disseminated mainly to Kangweon province, a major corn producing area in Korea, and drew up the yield over 4 tons per hectare. The major breeding objectives of sweet potato have been to develop varieties which have high starch content and root yield. Hwangmi, Hongmi, and Shinmi are three sweet potato varieties developed and disseminated by the Crop Experiment Station, Office of Rural Development and are grown most widely in Korea. Most of researches on cultural practices of upland crops have begun on a full scale from early 1960's. In soybeans, for example, no fertilizer but for barley was applied although the effects of phosphate and potassium fertilizers were great on soybeans in after-barley soybean croppings. The effects of heavy application of phosphate and calcium fertilizers on soybeans in newly reclaimed soils were recognized. Recently a mixed fertilizer for soybean (N; 40, P:70, K:60 kg/㏊) was developed and sold for soybean growers. The optimum planting densities of 220, 000 plants/ha in full-season cropping and 330, 000 pts/ha in after-barley cropping of soybeans were known from repeated experiments. For higher yield, a means of cultural practices such as transplanting-pinching, direct planting-pinching, and hilling-up, etc., were developed along with barley-stubble planting with no tillage and integrated herbicide application for labour savings. For sweet potato, cultural practices for planting date, harvesting date, fertilizer, and planting density were fully established. For early marketing, a technique of vinyl-mulching on sweet potato has also fully developed. For com, planting density of 37, 000 pts/ha in early 1960's has been changed to 55, 000 pts/ha for grain production and 67, 000 pts/ha for silage. The amounts of fertilizers have also been changed from 120-120-120kg/ha (N-P-K) in early 1960s to 180-150-150 kg/ha. These increases in number of plants per unit area and fertilizer levels have resulted in greater production for both grain and silage. At the same time, the production techniques of F1 seeds have also improved.
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