Incorporation of urea in puddled rice soils as affected by tillage implements

Banding of Urea Increased Ammonia Volatilization in a Dry Acidic Soil

“…Incorporation of NH 4 ‐N sources usually reduces NH 3 volatilization by decreasing NH 4 + availability through increased adsorption on soil particles and increasing resistance to NH 3 diffusion to the atmosphere (Sommer et al, 2004). Accordingly, reductions in NH 3 –N loss of 8 to 20% were observed when urea was mixed in a variety of soils (du Preez and Burger, 1987; Padilla et al, 1990; Blaise et al, 1996). Broadcast urea hydrolysis occurred more rapidly after application when granules were incorporated due to higher soil water content at depth compared to the soil surface.…”

“…Therefore it is difficult to evaluate if these experiments properly simulated the soil conditions around banded urea in the field. Furthermore, field studies looking at volatilization and plant N uptake using different application methods were performed in cropping systems such as rice or cereals that use narrow row spacing (Sen and Bandyopadhyay, 1986; Padilla et al, 1990; Malhi et al, 1996). In crops such as maize, rows are farther apart and urea is concentrated in fewer bands; thereby increasing urea concentration and the potential for large NH 3 –N loss to the atmosphere.…”

Nitrogen Transformations in Submerged Soils

“…These estimates of denitrifi cation ranged up to about 50% of the applied urea N, leading to speculation that NH 3 volatilization and denitrifi cation were concurrent, complementary loss mechanisms (De Datt a and Freney et al, 1990). In such case the management of urea to reduce NH 3 volatilization would lead to concurrent increases in denitrifi cation, resulting in litt le or no reduction in total loss of fertilizer N. A high variance and uncertainty is, however, associated with indirect estimates of denitrifi cation by diff erence, and indirectly estimated denitrifi cation rates ranging up to 50% of the applied urea N would require much higher nitrifi cation rates than the maximum reported for submerged rice soils (Buresh and De Datt a, 1990). An underestimation of NH 3 loss, particularly with the simplifi ed bulk aerodynamic method, might have contributed to overestimation of denitrifi cation loss, and high indirect estimates of denitrifi cation have never been substantiated by direct measurements using the 15 N tracer technique.…”

“…Tillage to incorporate fertilizer is, however, typically more energy demanding in the absence of fl oodwater. Implements available to Asian rice farmers are moreover only partially eff ective in reducing the buildup of ammoniacal N and ρNH 3 in fl oodwater (Padilla et al, 1990), and N losses from incorporated urea can still remain substantial under farmers' practices. The crop requirement for fertilizer N is small in the 2 to 3 wk following transplanting or sowing rice, and Asian rice farmers were reluctant to adopt the incorporation of fertilizer N before transplanting or sowing rice (Fujisaka, 1994).…”

“…However, even when accounting for entrapment of formed N 2 O and N 2 and preferential transport of formed N 2 O and N 2 through the rice canopy, the con-version of applied urea N to N 2 O and N 2 was small in puddled soils that remained saturated or submerged. Therefore, it was concluded that NH 3 volatilization and not emission of N 2 O and N 2 was the dominant mechanism for loss of applied urea N, representing >90% of the lost urea N in the investigated rice soils (Buresh and De Datt a, 1990).…”