The interaction between types of cover crop residue and digestate application methods affects ammonia volatilization during maize cropping season.

Organic and mineral fertilizers are important sources of ammonia (NH3 ) emissions from agricultural fields. The objectives of this study were: (i) to evaluate how different cover crop (CC) residues (i.e. rye [Secale cereale L.], white mustard [Sinapis alba L.] plus bare soil as control) in combination with different application methods of digestate (surface broadcast vs. shallow injection) affect NH3 volatilization before planting maize (Zea mays L.); and (ii) to assess the residual effect of previous CCs on NH3 volatilization after urea top-dress application at the V5-V6 phonological stage of maize. Ammonia volatilization was measured using semi-static chambers for 14 days (335 h) after planting and for 6 days (150 h) at the V5-V6 stage. Overall, NH3 emissions decreased by 67-77% with digestate injection compared with surface broadcasting. However, the reduction in NH3 volatilization using the injection method was significantly lower with mustard residue (6.72 kg NH3 -N ha-1 ) than with rye residue (14.15 kg NH3 -N ha-1 ), which allowed for more volatilization by increasing the exposure of digestate to the air. Broadcast digestate method did not affect the cumulative NH3 -N losses obtained with different cover crop types. After urea top-dressing at the V5-V6 stage of maize, the cumulative losses of NH3 (during 150 h) were 2.99 kg NH3 -N ha-1 with rye as previous CC, and 2.49 kg NH3 -N ha-1 with mustard. Our study shows that digestate injection before maize planting and urea top-dressing application followed immediately by irrigation (15 mm) could be considered as useful strategies to mitigate NH3 volatilization and increase N use efficiency in maize. This article is protected by copyright. All rights reserved.