Phosphate state of soils of the slope agricultural landscape in the south-east of Western Siberia

Aim. To carry out a comparative assessment of the phosphate state of highly humus soils in the upper part of the erosion-dangerous slope (altitude is 280 - 310 m a.s.l.) and moderately humus soils in the middle and lower parts of the slope (an altitude is 190 - 280 m a.s.l.). The studied soils are located on a plot of arable land with square of 225 hectares and 4 km in length in the forest-steppe zone of the south-east of Western Siberia (55˚02´20˝N, 83˚50´00˝E) on the territory of the Cis-Salair drained plain. Methods. Soils (0 - 30 cm) were analyzed by humus content in sulfur-chromium mixture according to the Tyurin’s method; total (P_tot), organic (P_org) and mineral (P_min) phosphorus - by dry ashing according to Sanders and William’s methods; available phosphorus by two methods - according to Chirikov (P_A1) in 0,5 M CH₃COOH and according to Nikolov (P_A2) in 0,1 M C₄H₄O₅(NH₄)₂; easily available phosphorus (P_EA) - according to Karpinsky-Zamyatin in 0,015 M K₂SO₄. Phosphorus in plants (P_plant) was determined by the wet ashing in a mixture of acids according to Ginzburg’s method. Results. In soils of the slope, total phosphorus are consists of 66 - 44% of P_org and 34 - 56% of P_min. On the upper part of the slope in the highly humus soils was determined the most content of P_tot and P_org - 2282 и 1510 mg Р₂О₅/kg. In the middle and lower parts of the slope, the content of P_tot (2119 → 2002 → 1826 mg Р₂О₅/kg) and P_org (1033 → 923 → 809 mg Р₂О₅/kg) was gradually reduced in the follow of series of soils: agrochernozems → agro-dark-gray → agro-gray soils. The higher content of the mineral phosphorus and its available forms, on the contrary, was fixed in moderately humus soils. No differences in the above-ground phytomass reserves of the oat-pea mixture on highly and moderately humus soils were identified. Amount of the P_plant averaged was near 0,60 - 0,92% Р₂О₅, which corresponds to the optimal level. Main conclusions. The phosphate state of highly and moderately humus soils located at the different altitude steps of an erosion dangerous slope are differ. It is advisable to determine the P_A2 or P_EA for the rapid diagnosis of phosphorus nutrition of plants on the Cis-Salair drained plain soils.

phosphorus (total, organic, mineral, available, easily available), humus, altitude steps, phosphorus in plants, Novosibirsk region