Effect of tillage practices and hay straw on ammonia volatilization from nitrogen fertilizer solutions

Abstract

Urea (U) fertilizer solutions applied on soil surface lose nitrogen through ammonia (NH3) volatilization, and such losses may be influenced by tillage practices and by the presence of crop residues. Ammonia measurements in corn (Zea mays L.) fields were initiated and continued for 9 d in July 1988 and 1989 to assess the effects of three tillage practices used in corn production (conventional, CT; reduced, RT; and zero tillage, ZT) and urea-ammonium nitrate (UAN) formulations on the volatilization of NH3 from UAN solutions. The UAN formulations were 33% U — 67% ammonium nitrate (AN) and 50% U — 50% AN. These UAN formulations indicate proportion, as percentage, of total N derived from U and AN, respectively. The experiments were conducted on two agricultural soils of Quebec [Macdonald sandy loam (Humic Gleysol), and St. Benoit sandy loam (Eutric Brunisol)]. Cumulative NH3 losses over 9 d ranged from 0.8 to 9.5% of applied N. On both soils, NH3 losses from 50–50 UAN were higher than the 33–67 UAN by 13.5, 14.6 and 23.9% on CT, RT, and ZT, respectively. Reduced NH3 loss with CT was attributed in part to lower crop residues than with ZT treatments. In a separate experiment to evaluate the effect of plant residues on NH3 loss, chopped timothy hay (Phleum pratense L.) was used to provide a greater surface cover and a uniform spreading of residues. Hay straw surface-applied to a conventionally tilled St. Benoit soil had to reach a threshold level somewhere between 750 and 1500 kg ha−1 to increase N losses compared to no added hay treatment. Key words: UAN solution, ammonia volatilization, tillage, hay straw