Phosphate regime of sod-podzolic soil in natural and agrophytocenoses

The phosphate regime of sod-podzolic soil (heavy loam) of Cis-Urals under natural phytocenoses (mixed forest, cereal-grass meadow) and agrophytocenoses was studied. The influence of agricultural use of arable land on phosphate regime was evaluated in the long-term stationary experiment (year of establishment - 1978) and the eastern galega (Galega orientalis L.) (year of sowing - 1988). The total content of phosphorus in soil, quantity of its organic, mineral and plant available forms were studied, the fractional composition of mineral phosphates was considered (using Ginzburg-Lebedeva method). The total content of phosphorus in the upper soil layer in all studied objects varied from 1 030 to 1 350 mg/kg. Mineral phosphorus forms prevailed over organic ones in the soil. It was found that the fractional composition of mineral phosphates was 40-62% represented by iron phosphates and 31-48% by calcium phosphates, which is due to the characteristic features of the soil-forming rock - yellow-brown non-carbonate silt drape. Aluminum phosphates amounted to 8-12%. Long-term cultivation of crops during five cycles of the eight-field crop rotation led to a significant decrease in the content of organic phosphorus in the soil. The lower content of iron phosphates (1.6-1.8 times) and the higher content (1.3-2.0 times) of calcium phosphates, available for plants, were observed in the soil of long-term experiment when compared with natural phytocenoses. The content of plant available phosphorus in soil gradually decreased from 239 to 164 mg/kg from the moment of experiment establishment to the fifth rotation. Prolonged fertilizer application (N60P60K60) resulted in the significant increase in mineral and plant available phosphorus forms content in the soil. The residual phosphorus of fertilizers was noted in the Fe-P, Ca-PI and Ca-PII fractions. Under the eastern galega the quantitative and qualitative indicators of the phosphate regime of the soil did not differ significantly from their natural analogues.