Rainfall after urea application can reduce rice yield
Ammonia volatilization from surface-applied urea is the nitrogen loss pathway of primary concern in direct-seeded, delayed-flood rice (Oryza sativa L.). Rainfall following urea application but before floodwater covers the soil may reduce ammonia loss but its effect on rice recovery of urea-nitrogen is unknown. A recently published paper in the January - February 2017 issue of Agronomy Journal discusses the effects of post-urea application rainfall amount and urease inhibitor rate on nitrogen uptake and yield of rice.
Ammonia volatilization from urea declined as the amount of simulated rainfall after urea application increased. However, the yield of rice fertilized with urea and flooded 7 to 12 days later tended to decrease as simulated rainfall amount increased indicating nitrogen was being lost via another pathway, probably denitrification. Use of a urease inhibitor [N-(n-butyl) thiophosphoric triamide] reduced ammonia volatilization across simulated rainfall amounts and prevented the yield loss observed with urea at the greatest simulated rainfall amounts.
This study indicates rainfall between urea application and flooding can be detrimental to fertilizer-N recovery and rice yield. The urease inhibitor appears to reduce nitrogen loss from ammonia volatilization and denitrification and should be considered a best management practice regardless of field moisture conditions when urea is applied.
Read the full article in Agronomy Journal. Free preview April 7 - April 14