Nitrate availability in Brazilian soils under effect of liming and sourcesand amounts of nitrogen

The aim of this work was to evaluate the effect of liming and sources and d oses of nitrogen on nitrate availability in Brazilian soils. Two experiment s were carried out: one with five soils from Bahia State and the other with five soils from Minas Gerais State. Soil samples were previously moistened and incubated at 26 degreesC in order to activate the microorganism popula tion. Soil samples from Bahia State were incubated with 50, 100, 150 e 200 mg of N per kg of soil as ammonium sulfate or urea and in the Minas Gerais soils it was evaluated the effect of liming on nitrification. Soil samples were incubated at 26 degreesC during 15 days. Urea nitrified faster than am monium sulfate. The sandy soil did not exhibit net nitrification following ammonium application, but nitrification in this soil was significantly high er under urea. The nitrate availability increases with the liming of Minas Gerais soils. Nitrification rate showed to be highly correlated with base s aturation whereas urea hydrolysis was correlated with organic matter conten t.