Soil NH_4~+ Fixation and Fertilizer N Recovery as Affected by Soil Moisture and Fertilizer Application Methods

摘要

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 glassshelter, respectively, by using ammonium bicarbonate (NH_4HCO_3). The laboratory closed incubation box experiment was conducted using the Luvisol to study NH_4~+ fixation rate at soil moisture levels of 10.1%, 22.7% and 35.3% water filled pore space (WFPS). The fixed NH_4~+-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 NH_4~+ fixation rates at all moisture levels could help prevent NH_4~+ losses from ammonia volatilization fn 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% of the added N fertilizer was recovered 26 days after application to the Luvisol, while only 61 4% could be recovered from the Entisol, due to higher NH_4~+ fixation capacity of the Luvisol. The amount of fixed NH_4~+ decreased with increasing WFPS. The amount of fixed NH_4~+ in the incorporated fertilizer treatment was, on average, 10% higher than that in the banded treatment. Higher NH_4~+ fixation rates could prevent N loss and thus increase N recovery. The results from the Luvisol showed lower nitrogen recovery as soil moisture level increased, which could be explained by the fact that most of the fixed NH_4~+ was still not released when the soil moisture level was low. When the fertilizer was incorporated into the soil, the recoveryof N increased, compared with the banded treatment, by an average of 26.2% in the Luvisol and 11.2% in the Entisol, which implied that when farmers applied fertilizer, it would be best to mix it well with the soil.