The influence of long term fertilization on available inorganic P forms, total P and fractionation of P of Siberian soils were studied by the Machigin, Chirikov and Franzison procedures, Mehta procedure, and Chang and Jackson procedure modification, respectively (A.V. Sokolov (ed.) Agrochemical Methods of Soil Analises. 1975. Nauka, Moscow). The samples (0-20 cm depth) of the 3 arable soils different in physical and chemical properties, cultivation history and climatic conditions were used. These soils is typically moderate frozen or long storage of frozen (up to August).

The temperature below zero achieve the deep of about 1.1-1.6 m. The unfrozen period did not lasts more then 80-105 days. In acid sandy podzoluvisol (FAO classification) of Southern West Siberia taiga the summarized amount of three most soluble fractions of soil P (extracted with 1% (NH4)2SO4 + 0.25% (NH4)2MoO4, pH 4.8; NH4OAc + 0.25% (NH4)2MoO4, pH 4.3; and 0.5N NH4F) is 24.4 mg P/kg soil. After 37 years application of mineral fertilizers (34.3, 15, and 28.5 kg/ha'year of N, P and K, respectively) or the same quantity of mineral fertlizers plus organic fertilizer at the rate 5.7 t/ha'year the summarized amount of these three P fractions was increased by 68-82 %. The contribution of these three more soluble fractions to sum of inorganic P fractions did not exceed 11 % in the unfertilized plot and 16-18 % in fertilized plots.

In heavy-textured greyzems of East Siberia forest-steppe the summarized amount of three most soluble fractions of soil P was 69.3 mg/kg. During 20 years of crop cultivation without fertilizer these soluble P was decreased by 21 %. Long-term application of mineral fertilizers (60, 25, and 52 kg/ha'year of N, P and K, respectively) or the same quantity of N, P, and K derived from organic fertilizer allowed to increase accumulation of these soluble P in the soil by 40-50 %.

The amount of available inorganic P forms in chernozems of Altay forest steppe was closely related with fertilizers rate. The 13 years application of high rate of mineral fertilizers (67.5, 36, and 68.4 kg/ha'year of N, P and K, respectively) enlarged the amount of 0.5 N HAc-extractable inorganic P from 92 to 144 mg/kg, of 1% (NH4)2CO3-extractable P from 3.0 to 10.9 mg/kg, and sum of three more soluble P fractions from 24.4 to 62.3 mg/kg as compared to the low rate of mineral fertilizers (22.5, 12, and 22.8 kg/ha'year of N, P and K, respectively).

The content of total P and organic P of studied soils were ranged from 449 to 1334 and from 174 to 523 mg/kg, respectively. Long-term fertilization allowed to increase the amount of these P forms by 8-18 % and by 20-40 %, respectively.

Rimma P. Makarikova
The Institute of Soil Science and Agrochemistry,
Siberian Branch of Russian Academy of Sciences
Sovetskaya Str. 18, Novosibirsk 99
630099, Russia
Tel: (3832) 225 088
Fax: (3832) 225 665
E-Mail: root@issa.nsk.su