由于执行1983年联邦农田面积缩小计划,许多农民面临着这样一个问题,就是决定1984年他们的玉米要施多少氮肥。多数农民习惯于把玉米与大豆轮作或者玉米连作,而对于在前一年休闲或种过细粒谷物或豆科牧草的农地上种植玉米,则缺乏试验。由于土壤氮素的有效性在很大程度上受环境条件所制约,因此一旦改变了耕作制,就势必会影响氮素的矿化量, As a result of the implementation of the federal plan to reduce farmland in 1983, many farmers faced the problem of determining how much nitrogen fertilizer their corn would require in 1984. Most peasants are accustomed to cropping corn with soybeans or corn, and lacking experimentation with planting corn on farmland that was laid loose or planted with fine grain or legume pasture the previous year. Because the effectiveness of soil nitrogen is largely controlled by environmental conditions, once the tillage system is changed, it is bound to affect the amount of nitrogen mineralization,