Soil Phosphorus Distribution Under No-Till Crop Production in Southern Brazil.

Phosphorus (P) is an important nutrient to crop prodution and it is a constraint to obtain high crop yields in tropical soils. Soil P distribution in soil profile can minimize yield loss during dry conditions to allow plants uptake P in deeper soil layers. No-till tend to increase soil P in surface soil layers mainly when P is added via surface broadcast. We aimed to investigate soil P distribution in soil profile affected by P rates in three Oxisol from Southern Brazil under no till applied via surface broadcast. On-farm research were conducted to evaluate P crops response in three locations under oxisol in Southern Brazil (Ijui, Cruz Alta and Vacaria). Phosphorus doses applied in Ijui (Rio Grande do Sul state) were zero, 30, 60,  120, 240 and 450 kg/ha of P2O5. In cruz Alta and Vacaria were zero, 40, 60, 120, 170 and 225 kg/ha of P2O5. Differences among doses P in each soils was due the planter limitations to add fertilizers in high ammounts. In all locations P was applied via surface broadcast. Soil P amounts increased in soil surface layers of 0-5 and 5-10 in all soils. We observe that even soils were in the critical level of P, doses similar to P uptake reposition can increase soil P in 0-5 cm to values up to 5-fold the critical level and it might increase the risk of P losses via surface runnoff. In subsurface layers we did not observe differences on soil P concentrations. Studies with P overtime are necessary to verify the soil P movement in the soil profile affected by P applied in surface broadscast.