PROFILE DISTRIBUTION OF THE FORMS OF SOIL -PHOSPHORUS IN DEPENDENCE ON THE DEGREE OF ANTHROPOGENIC EFFECT

The phosphorus distribution and its individual forms in the soil profi le are influenced by a number of factors, among whose is soil type, cl imatic conditions, vegetation cover, and anthropogenic activities. The aim, of the study was to extend the knowledge concerning the composit ion and phosphorus content in soil profile in dependence on the degree of agricultural farming. Single sampling was carried out in the autum n of 1988 on intensively cultivated field, fallow (the field ceased to be cultivated in 1985), on the meadow and in forest (deciduous with p revalence of oak) to the depth of 50 cm. The soil is Cambisol in all s ites (characteristics is presented in Tab. 1). The total phosphorus wa s determined after mineralization of the sample by perchloric acid (S o m m e r s , N e l s o n , 1972), organic phosphorus by gradual extra ction of soil by sulphuric acid and sodium hydroxide (B o w m a n , 19 89), phosphorus in soil microbial biomass by fumigation extraction met hod (B r o o k e s et al., 1982). Available, mobile, water-soluble pho sphorus and the rate of phosphorus release were determined by cation-e xchange method (M a c h a c e k , 1986). Individual forms of phosphoru s were determined by the procedure with ammonium molybdate and ascorbi c acid (M u r p h y , R i l e y , 1962; W a t a n a b e, O l s e n, 19 65). Average total phosphorus content (P(celk)) in the layer of 0 to 5 0 cm (Tab. II) was higher in the field and on fallow compared with the meadow and forest. This increase of P(celk) was manifested in the fie ld solely in topsoil, while P(celk) content in fallow was high in the whole soil profile. P(celk) content on the meadow and in forest was co ntinuously falling from the surface layer to 50 cm. Average mineral ph osphorus content (P(min) like P(celk) content was higher in the field and on fallow than on the meadow and in forest (Tab. II). This differe nce was again manifested in the topsoil influenced by phosphorus ferti lizing, while on fallow in the whole soil profile (Tab. III).The propo rtion of P(min) in P(celk) increased in the layer of 40 to 50 cm compa red with the layer of 0 to 5 cm by 13 % in the field, by 14 % on fallo w, by 18 % on meadow and by 20 % in forest. Average organic phosphorus content (P(org) was the highest in the field (Tab. II) and was fallin g in the following sequence: fallow, meadow, forest. Its proportion in P(celk) ranged in all sites in the layer of 0 to 50 cm between 12 % ( fallow) and 19 % (field) and was falling with the depth of soil profil e. An amount of phosphorus bound in microbial biomass (P(mic)) was the highest in the surface layer to 5 cm(Tab. II) which was occupied the Most by microorganisms and over-rooted. P(mic) content on average part icipated in P(org) by 12 % in the field, 14 % on fallow, 33 % on meado w, and 27 % in forest. Average available phosphorus content (P(v) + P( k)) in the whole soil profile was higher in the field and fallow than on meadow and in forest (Tab. II). While in the field and fallow P(v) + P(k) formed 9.2 and 4.1 % of P(celk), m meadow and in forest it was only 1.5 and 1.8 %. The same trend appeared in water-soluble phosphoru s content (P(v)). An average higher mte of phosphorus release is assoc iated with higher availability of phosphorus in the field. The average rate of release of available phosphorus (R(v) + R(k)) found in the wh ole soil profile in the field was higher almost 20 times compared with that on meadow and in forest. This rate was 10 times higher on fallow . The margin between topsoil and subsoil layers was markedly manifeste d in all studied characteristics in the soil profile in the field. Thi s difference disappeared on fallow after finishing the cultivation, th ough the average values of parameters under study of the whole soil pr ofile show the effect of the previous cultivation. The proportion of P (mic) in P(org) and all parameters of soil phorphorus regime reflected the most sensitively the different intensity of anthropogenic effect on studied sites.