Ammonia volatilization in gemmiparous and early seedling stages from direct seeding rice fields with different nitrogen management strategies: A pots experiment

Ammonia volatilization (AV) from direct seeding rice (DSR) fields in gemmiparous and early seedling stages was measured to reveal the effect of nitrogen (N) fertilizer management by pots experiment, and compared with those from traditional transplant rice paddies. There were three N fertilizer types, urea (U), ammonium bicarbonate (AB), and control released urea (CRU), which were applied through surface broadcasting (S) or 5 cm depth placement (D). The cumulative AV losses within four weeks after sowing from DSR pots were 35.8, 23.6, 17.6, 27.0, 18.4 and 16.3 kg N ha−1 for the treatments of AB + S, U + S, CRU + S, AB + D, U + D, and CRU + D, respectively, accounting for 59.7, 39.3, 29.3, 45.1, 30.6 and 27.6% of N application for each treatment. The lowest AV losses incurred with the combined CRU + D treatment. The absence of crop uptake and canopy shelter, the very low ponding water depth during gemmiparous and seedling stages in DSR fields favored the AV process, and resulted in much higher AV losses than in traditional transplanting rice fields. The N fertilizer type was the predominant factor that caused AV loss in DSR fields. AB resulted in much higher AV losses from the DSR fields than U and CRU. The 5 cm deep placement of N reduced AV rates and lagged the AV process. The suitable N fertilizer type and application method for basal fertilizer in DSR fields were CRU and deep placement, respectively. Dividing the basal fertilizer into two splits, and fertilizing with proper N fertilizer types and methods should be the efficient measures to mitigate the AV losses from DSR paddies.

► NH3 volatilization from direct seeding rice pots was observed with different N regimes.
► Direct seeding led to higher NH3 volatilization than transplant cultivation.
► The N fertilizer type was the predominant factor that caused AV loss in DSR pots.
► CRU and deep placement are the suitable type and method for basal N application.