6Barak P, Jobe B O, KruegerA R, et al. Effects of long- term soilacidification due to nitrogen fertilizer inputs in Wisconsin[J].Plantand Soil,1997(197):61-69.
7Poss R, Smith C J, Dunin F X, et al. Rate of soil acidification underwheat in a semi- arid environment[J].Plant and Soil,1995(177):85-100.
