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 (NH 3 ) 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 NH 3 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 NH 3 losses over 9 d ranged from 0.8 to 9.5% of applied N. On both soils, NH 3 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 NH 3 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 NH 3 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