Soil NH4~+ Fixation and Fertilizer N Recovery as Affected by Soil Moisture and Fertilizer Application Methods

Ammonium fixation and the effects of soil moisture and application methods on fertilizer N recovery were investigated in two soils of Shaanxi Province, China, a Luvisol and an Entisol, through two experiments performed in the laboratory and in a glass shelter, respectively, by using ammonium bicarbonate (NH4HCO3). The laboratory closed incubation box experiment was conducted using the Luvisol to study NH4+ fixation rate at soil moisture levels of 10.1%, 22.7% and 35.3% water filled pore space (WFPS). The fixed NH4+-N increased dramatically to 51% and 66%, 67% and 74%, and 82% and 85% 1, 2 and 36 h after fertilizer incorporation at moisture levels of 10.1% and 22.7% WFPS and 35.3% WFPS, respectively. The rapid NH4+ fixation rates at all moisture levels could help prevent NH4+ losses from ammonia volatilization. In the glass shelter pot experiment, N fertilizer was applied by either banding (in a concentrated strip) or incorporating (thoroughly mixing) with the Entisol and the Luvisol. An average of 74.2%