磷肥在热带土壤中的转化规律及残效

TRANSFORMATION AND RESIDUAL EFFECTS OF PHOSPHATE FERTILIZERS IN TROPICAL SOILS

采用海南岛6类土壤,进行不同施磷量盆栽试验,应用土壤无机磷分级方法,研究水溶性磷肥在砖红壤中转化的情况。盆栽试验历时5年。其结果表明:(1)过磷酸钙与土壤充分混合,连续盆栽作物5年中均有明显效应。(2)施磷肥处理所增加的有效磷比例和盆栽后土壤有效磷量逐年下降幅度因土壤类型不同而差异很大。(3)水溶性磷肥在土壤中很快转化为各种形态的无机磷,但其形态比例、变化趋向和速度也因土壤类型不同而异。玄武岩(铁质)砖红壤以Fe—P(磷酸铁盐)为主,浅海沉积物(硅铝质)砖红壤以Al—P(磷酸铝盐)为主,花岗岩和云母片岩(铝质)砖红壤的Al—P含量略高于Fe—P。在盆栽过程中各类土壤的Al—P含量逐年降低,而Fe—P的含量除了在玄武岩砖红壤中是逐年降低外,在其他类型的土壤中则逐年提高,施肥后,Ca—P(磷酸钙盐)的含量在各类土壤中都比盆栽前提高,但变化幅度很微小。(4)不同施磷量处理间土壤中O—P(闭蓄态磷酸铁)的含量差异不显著,盆栽过程头3年没有明显变化,而盆找后第5年比前3年有所增长,但只有玄武岩砖红壤的增长量达到显著水平。(5)无机磷转化的次序,似乎存在Al—P→Fe—P→O—P转化的趋向,因此,Al—P的有效性>Fe—P。

Transformation patterns of water soluble phosphate fertilizers in laterites were investigated with soil inorganic phosphorous classification method throught pot culture on 6 types of soil supplied with various rates of P fertilizers. The results obtained for five consecutive years indicated that thorough mixing of calcium superphosphate with soil could give marked positive effects. The increase in available P due to P fertilizer application and the yearly decrease in available P after pot culture varied greatly with soil types.Water-soluble P fertilizers transformed rapidly into different forms of inorganic phosphorus but the proportion of each form, tendency and time for the transformation also differed with soil types. This is demonstrated by principally Fe-P in basalt-derived laterite, Al--P in coastal deposit-derived laterite, while Al--P content somewhat higher than that of Fe--P in granite and mica-gneiss derived laterite. Yearly decrease in Al--P content in all soil types was found over the course of pot culture. However, yearly increase in Fe--P content in all soil types except basalt-derived laterite was also observed. Minor increase in Ca--P content due to fertilizer application was noted in all soil types as compared with pre-culture. No noticeable difference was recorded in O-P(occluded phosphate)content between P fertilizer application treatments, which showed no evident changes during the first three years of pot culture but increased a little bit at fifth year after pot culture with significance only in basalt-derived lateritc. The sequence of inorganic phosphorous transformation seemed to be Al--P→Fe--P→O--P. It is therefore considered that the availability of Al--P is larger than Fe—P.