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要进一步提高籽粒产量,就需要了解以往已获得的增产知识。本文分析了美国大平原(涉及7个州)和玉米带(涉及4个州)自1954年以来有关技术与冬小麦产量变化的关系,试图弄清产量变化的主要原因。在所涉及的11个州的每个州,均单独估算了有关技术、遗传改良以及由于施用氮肥引致的产量变化。另外,还分析了其他因素的产量贡献,最后综合为地区性增产水平。1954—1979年,大平原小麦年增产率为30k g/ha,玉米带小麦年增产率为43kg/ha。在大平原地区,遗传改良,施用氮肥和其他因素的增产比重分别为43%,22%和35%;而在玉米带,其相应的增产比重分别为74%,22%和2%。假若将内布拉斯加州、堪萨斯州和俄克拉何马州的分析年度延伸至1984年,可以看到年增产率基本未变,但遗传改良、施用氮肥和其他因素的增产比例却从1954—1979年间的45%,25%和30%变化为61%,27%和13%。实验表明,在玉米带,1954—1979年期间,遗传改良和施用氮肥的增产贡献几乎相当于总的增产贡献;而在大平原地区,其他因素(灌溉、病虫防治,耕作措施等)的增产贡献却等于总增产贡献的1/3。在廿世纪八十年代期间,有关技术使小麦的年增产量保持不变。但与1954—1979年间相比,八十年代期间,遗传改良的增产贡献更要大一些。
To further increase the grain yield, we need to know the production knowledge that has been obtained in the past. This paper analyzes the relationship between technology and winter wheat yield changes in the Great Plains (involving seven states) and corn belt (involving four states) since 1954 in an attempt to understand the main causes of changes in production. In each of the 11 states involved, the technology, genetic improvement, and changes in production due to the application of nitrogen fertilizer are separately estimated. In addition, the output contribution of other factors is also analyzed, and finally, it is integrated into the regional increase of production. From 1954 to 1979, the annual yield of wheat in the Great Plains was 30 kg / ha and that of corn was 43 kg / ha. In the Great Plains, genetic improvement, nitrogenous fertilizer application and other factors increased yields by 43%, 22% and 35% respectively, while those in maize belts were 74%, 22% and 2% respectively. If the years of analysis for Nebraska, Kansas and Oklahoma were extended to 1984, the annual rate of increase is almost unchanged, but the rate of increase in genetic improvement, application of nitrogen fertilization, and other factors, Between 1979, 45%, 25% and 30% changed to 61%, 27% and 13% respectively. Experiments have shown that in the corn belt, the contribution to the increase of yields from genetic improvement and application of nitrogen fertilizers is almost equivalent to the total increase in production between 1954 and 1979; in the Great Plains, the increase of other factors (irrigation, pest control, tillage measures, etc.) Contribution is equal to 1/3 of the total production contribution. During the 1980s, the technology kept the annual increase in wheat output unchanged. However, compared with 1954-1979, during the 1980s, the contribution of genetic improvement increased more.