Phosphorus fraction in the topsoils of some main soil types of Slovakia

In top soils of 9 Slovakia soil types there were determined easily and hardly soluble fractions of organic soil phosphorus fixed to iron and aluminium (fractions P-FeAl) and calcium (fractions P-Ca) and organic phosphorus. The topics were studied based on pot trials. From the pot trials two topsoil groups with various soil reaction values were used: pHKCl 7.7-7.3 (A group: Calcaric Fluvisol, Phaeosol Chernozem, Orthic Luvisol) and topsoil with pHKCl range 5.9-4.3 (B group: Albo-gleyic Luvisol, Luvisols Pseudogley, Pseudogleyic Cambisol, Cambisol acid). Phosphorus was monitored in two fertilization variants: 0 zero fertilization, and treatment NPK = a single dressing of 80 kg N + 600 kg P + 1200 kg K per ha. Fertilizer contact with soil lasted for three years. Both fertilizer treatments were seeded on the first year by spring barley, in the second year tillage only, and in the third year by lupin. For phosphorus fertilizer powdered superphosphate was used. The results are presented in means for the A and B topsoil groups. Easily and hardly soluble organic phosphorus (fractions P-FeAl and P-Ca) were determined by Scharafat method (1970) and total organic phosphorus by the Dean method (Black, 1965). After three-year action of high phosphorus fertilizer (600 kg P per ha) in topsoil, there was detected an increased level of easily soluble P-FeAl fraction on average by 24 mg P.kg** (-1) (A topsoil group) and 57 mg.kg** (-1) (B group). Easily soluble fraction P-Ca rose by 37 mg P.kg** (-1) (A) and 65 mg P.kg** (-1) (B). In the third year after fertilization there appeared an increase in phosphorus also in the hardly soluble inthe fraction P-FeAl to 43 mg P and fraction P-Ca of 123 mg P.kg** (-1) (A) or P-FeAl by 135 mg P and P-Ca by 47 mg P.kg** (-1) (B topsoil group). Results confirmed that in topsoil with alcalic to neutral reaction (A) applied phosphorus overwhelmingly predominates over easily and heavily soluble phosphorus fixated with iron and aluminium (in fraction P-Ca), and to the contrary, in topsoil with weak acid reaction, iron and aluminium fixated fractions of inorganic phosphorus (P-FeAl) dominate. The overwhelming part (about 80-90 %) is included in hardly soluble fractions P-FeAl and P-Ca. Ratio of easily soluble fractions P-FeAl:P-Ca was in non-fertilized and in fertilized topsoil about 2:1 (A) and 8-10:1 (B). A hardly soluble fractions P-FeAl:P-Ca were substantially less than easily soluble - 0.15-0.22:1 (A), or 1.4-1.9:1 (B). The great share of total soil phosphorus falls to organically fixed phosphorus. Its higher content was determined in topsoil with higher humus and organic substance contents (A) - on average 36 % (variants 0) to 45 % (NPK variants). In topsoil with a lower humus content (B) organic phosphorus contents were on average only 22 % (0 variants) and 29 % (NPK variants)