长期不施肥条件下几种典型土壤全磷和Olsen-P的变化

研究了11个不同气候条件、不同耕作制度、典型土壤类型长期定位试验不施肥处理土壤全磷和Olsen-P变化及其影响因素。结果表明，在长期不施肥条件下耕作，土壤Olsen-P含量下降比全磷的明显；在试验进行5年左右，土壤全磷含量都有所降低，以后各点表现不尽相同，新疆灰漠土、长沙水稻土和郑州潮土全磷含量随时间延长呈显著直线下降，其它试验点全磷的变化不明显；作物携出磷与土壤全磷下降之间，无论绝对含量或相对含量都不成比例。土壤Olsen磷下降率比全磷高几倍。Olsen-P下降趋势与起始土壤Olsen磷含量有关:起始土壤Olsen-P磷大于20 mg/kg时，25年内一直呈现明显下降趋势，降低40.5 mg/kg，特别是前5年下降更快，降低30 mg/kg；起始土壤Olsen-P为10～20 mg/kg时，下降趋势比前者缓慢，15年内一直呈明显下降趋势，下降19 mg/kg, 前5年下降15 mg/kg，15年后几乎不变；起始土壤Olsen-P小于10 mg/kg时，25年内无明显变化。Olsen-P下降量与起始Olsen-P占全磷的比例成显著直线关系。

Total-P and Olsen-P dynamics of long-term experiment without fertilization

Dynamics of total phosphorus and Olsen-P of soils without fertilization were studied with long-term experiment on eleven typical soils. The results indicated that changes of Olsen-P were more significant than that of total P over time in all soils. Soil total P decreased linearly with time for gray desert soil, paddy soil and fluvo-aquic soil, but did not change significantly for other soils. Decreases in soil total P was not significantly correlated with crop P uptake. Tendency of soil Olsen-P decrease differed with initial Olsen-P content in the soils. When initial Olsen-P was greater than 20 mg/kg, it decreased quickly and reduced 30 mg/kg in 5 years and reduced 40.5 mg/kg in 25 years. When initial Olsen- P was between 10 mg/kg and 20 mg/kg, they decreased slowly and reduced 15 mg/kg in 5 years and 19 mg/kg in 15 years. When initial Olsen-P was less than 10 mg/kg, there was no obvious change over time. The ratios of Olsen-P to total-P and avail-N to Olsen-P were two important factors influencing Olsen-P change. Olsen-P decreased linearly with ratio of Olsen-P to total-P.