Daigger等的工作曾表明在休闲地上施肥4个月后,100%的N量可计算出来。但是,种植植物以后,可计算的数值就有所下降。Ferman和Allen发现玉米生长的第6到第9星期内,可计算的N量从100%减少到85%左右。其它研究者也指出禾本科作物总N累积在抽穗期前后最高,随后即下降,成熟期总N含量只是抽穗期的60—80%。对此,曾认为在未能计算出的N Daigger et al.’s work has shown that 100% of the N content can be calculated after four months of fertilization in fallow land. However, after planting the plant, the value that can be calculated drops somewhat. Ferman and Allen found that within the 6th to 9th weeks of maize growth, the calculable N decreased from 100% to about 85%. Other researchers also pointed out that the total N accumulation in gramineous crops was highest before and after heading stage, and then decreased. The total N content in mature stage was only 60-80% of heading stage. In this regard, I thought I could not figure out N