Effects of lanthanum on nitrification and ammonification in three Chinese soils

The effects of lanthanum on nitrification and ammonification in three Chinese soils were evaluated through an incubation experiment. Soils were collected from experimental plots under rice/rape rotation in Yingtan, Jiangxi province (red soil), under rice/wheat rotation in Wuxi, Jiangsu province (paddy soil), and under corn/wheat rotation in Fengqiu, Henan province (Fluvo-aquic soil). Soil nitrification was stimulated slightly by La at lower concentrations, and the stimulation rate reached about 20% in red soil at 150 mg La kg(-1) dry soil, and 14% in fluvo-aquic soil at 300 mg La kg(-1) dry soil. When more La was added in soils, nitrification was inhibited, with a maximum inhibition rate of 42, 44 and 66% in red soil, fluvo-aquic soil, and paddy soil, respectively. Soil ammonification was not significantly different between control and up to 600 mg La kg(-1) dry soil in red soil, but it was significantly reduced in doses of 900 and 1200 mg La kg(-1) dry soil. Significant reduction in soil ammonification was also found in doses from 60 to 1200 mg La kg(-1) dry soil except for 600 mg La kg(-1) dry soil in fluvo-aquic soil. In contrast the ammonification in paddy soil was strongly stimulated by La, reaching about 25 times that of control at 900 mg La kg(-1) dry soil. We assumed that application of La accelerates the transformation of nitrogen in soils at low dosage, and the currently applied dosage in agriculture in China cannot inhibit soil nitrification and ammonification even after long term successive application.