Cover crops can increase ammonia volatilization and reduce the efficacy of urease inhibitors
Stephanie B. Kulesza, Alex Woodley, Kayleigh Heather, Grace Kilroy
Abstract
Abstract Surface application of urea can result in high nitrogen (N) losses through ammonia (NH 3 ) volatilization. While management practices aim to increase the efficiency of nutrient cycling and prevent N loss, it is unknown whether the combination of multiple practices will have a synergistic or antagonistic effect. Therefore, laboratory volatilization studies were conducted to determine the effect of five cover crop treatments (surface clover [ Trifolium incarnatum L.] and rye [ Secale cereale L.], incorporated clover and rye, and bare soil), three N application timings (2, 4, and 8 wk after cover crop addition), and two N sources (untreated and treated urea) on the effectiveness of a urease inhibitor. Soils were incubated according to N application timing treatment, amended with the appropriate N source, and placed in chambers which captured NH 3 over 7 d. There were significant interactions between cover crop treatment and N source and N source and N application timing on cumulative NH 3 loss, ranging from 29 to 174 kg N ha −1 . Losses were highest from treated urea when applied 2 wk after residue addition (75.9 kg N ha −1 ) or on top of surface residues (85.8 kg N ha −1 ). There was no significant effect of application timing on cumulative NH 3 loss from untreated urea. However, inhibitor effectiveness did increase when residue was applied eight weeks after residue addition (77%) as compared with 2 wk after residue addition (45%). Future research should focus on alternate dosing or application timing to overcome high residue scenarios in these systems.