Phosphorus distribution after three decades of different soil management and cover crops in subtropical region

The no-tillage system combining winter cover crops and crop rotation may increase the efficiency use of soil P and phosphate fertilizer, The objective of this study was to evaluate the effect of three decades of different soil management systems and winter cover crops on the fractions of P in a clayey Oxisol of Parana State, Brazil. The bi-factorial experiment with three replicates was established in 1986. The main plots consisted of seven winter cover crops. In the subplots, two tillage systems were used: no-tillage and conventional tillage. The soil was sampled in the 0-10 cm soil layer in each plot in the post-harvest of the corn (March 2015), the flowering of the winter cover crops (September 2015) and at soybean flowering (February 2016). Samples from a native forest adjacent to the experimental area were also taken for comparison. The different pools of P were evaluated. Results indicated that after 30 years of no-till with phosphate fertilizers addition, the amount of P organic pools and type of P organic compound were very similar to those observed in the natural biome. The no-tillage guaranteed higher inorganic and organic P, both rapid and moderately available, in comparison to the conventional tillage system. However, in the conventional tillage (40 years - 80 plows + 160 harrows), despite the addition of 3 Mg ha(-1) of P2O5, the available and moderately labile P content in soil surface were very similar to soil under natural forest. In the natural biome, the amount of P stored in soil microbial biomass was stable in the time showing a homeostatic equilibrium. Nevertheless, in cultivated soil and fertilized with inorganic phosphate, there was a synchronism between plant demand and storage in soil microbial biomass. Except for P stored in soil microbial biomass, the other P pools, regardless its nature (organic or inorganic) or degree of bioavailability, had despicable or absent effect of winter cover plants, compared to winter fallow.