Changes on P availability under different soil management

The volcanic ash soils in the IX Region has a high P retention capacity and due to the high cost of fertilizers in the agricultural production, it's necessary to realize researches in order to study the availability of nutrients in soils to optimize their efficiency. A trial was carried out under two management systems: no tillage without burning crop residues (NT-B) and no tillage burning crop residues (NT+B), during three years with two crop rotation; Lupine-wheat-oat (S1)and Wheat-lupine-wheat (S2). The objective of this experiment was to evaluate and predict the influence of the management system used over the bioavailable P through time. It was used conventional and isotopic techniques (Fardeau, 1997). At the beginning of the experiment, the exchangeable isotopic values showed a low bioavailable P in the soil under both tillage management system. At the end of the experiment, the soil presented a positive behavior under the NT-B system, shoving a high value for the bioavailable P, whilst the P retention capacity tend to decrease. With this system it was observed a P redistribution in different pools, with a better available P for the crops through the time, which doesn't observed in the other system wit burning residues (author)