在推广甘薯良种过程中,常遇到二个问题。一是种源少,于由繁殖倍数低,一个新品种大面积发展起来,一般都要几年时间。往往因为时间长,新品种的“青春期”常常在小面积繁殖阶段中渡过,待到大面积使用,它的优良品性也往往开始退化。二是大量调运,除了浪费大量物力人力外,还容易带来病害或造成混杂。因此,在少引的基础上加快繁殖,是迅速实现甘薯良种化的有效途径。我县群众创造的“四级育苗五级到田”,就是根据种薯和秧苗发芽生长所需要的温、光、水、肥、气条件,人为地给它创造一个有利的环境,提前排种育苗,多次剪苗,以苗繁苗,加大繁苗系数的方法。一般繁殖系数在千倍左右,高的可达2,000倍之多。1976年我县从徐州地区农科所引进具有“三高一好”(即高产、高干、高抗烂根病和品质好)的徐薯18号秧苗100棵,1977年采用了“四级育苗五级到田”的方法,仅三年时间,全县徐薯18号面积就发展到31万5千亩,加上用同样办法繁殖的宁薯2号等其它良种,全县良种面积已达42.8万亩,实现了全县甘薯良种化,同时还支援省内外徐薯18号种薯1,200万斤,薯苗7,200万株。我县三堡公社,1978年全社以24,000斤薯种分到大队大搞“四 In the promotion of sweet potato varieties, often encounter two problems. First, less provenance, due to the low multiplication, a large area of ​​new varieties developed, generally have a few years time. Often, because of the long time, the “adolescent” of the new breed often passes through the small-scale breeding stage. When it is used in a large area, its good character often begins to degenerate. Second, a large number of transport, in addition to a lot of material and human waste of human resources, but also easy to bring disease or mixed. Therefore, to speed up the breeding on the basis of less cited, is an effective way to realize the sweet potato seedling quickly. The “four-level nursery up to five levels” created by the masses in our county is to artificially create a favorable environment for seed germination and growth according to the temperature, light, water, fertilizer and gas conditions required for germination and growth of seed potatoes and seedlings. Nursery, repeatedly cut seedlings, seedlings and seedlings to increase the number of Fanmiao method. The general breeding coefficient in a thousand times, up to 2,000 times as high. In 1976, the county introduced 100 seedlings of Xushu 18 with “three highs and one good” (that is, high yield, high dryness, high root rot resistance and good quality) from the Agricultural Science Department of Xuzhou District. In 1977, Nursery five to the field “approach, only three years, the county Xushu 18 area to 315,000 acres, coupled with the same method of reproduction of the other varieties of Ningshu 2, the county has a good area Up to 428,000 mu, realizing the good variety of sweet potatoes in the whole county, and also supporting 12 million kilos of seedlings of Xushu 18 and 72 million of potato seedlings in and outside the province. Sanbao commune in our county, in 1978 the whole society to 24,000 jin of potato species assigned to brigade engage in ”four