Low‐Disturbance Manure Incorporation Effects on Ammonia and Nitrate Loss
2012
Low‐disturbance manure application methods can provide the benefits of manure incorporation, including reducing ammonia (NH₃) emissions, in production systems where tillage is not possible. However, incorporation can exacerbate nitrate (NO₃⁻) leaching. We sought to assess the trade‐offs in NH₃ and NO₃⁻ losses caused by alternative manure application methods. Dairy slurry (2006–2007) and liquid swine manure (2008–2009) were applied to no‐till corn by (i) shallow (<10 cm) disk injection, (ii) surface banding with soil aeration, (iii) broadcasting, and (iv) broadcasting with tillage incorporation. Ammonia emissions were monitored for 72 h after application using ventilated chambers and passive diffusion samplers, and NO₃⁻ leaching to 80 cm was monitored with buried column lysimeters. The greatest NH₃ emissions occurred with broadcasting (35–63 kg NH₃–N ha⁻¹), and the lowest emissions were from unamended soil (<1 kg NH₃–N ha⁻¹). Injection decreased NH₃–N emissions by 91 to 99% compared with broadcasting and resulted in lower emissions than tillage incorporation 1 h after broadcasting. Ammonia‐nitrogen emissions from banding manure with aeration were inconsistent between years, averaging 0 to 71% that of broadcasting. Annual NO₃⁻ leaching losses were small (<25 kg NO₃–N ha⁻¹) and similar between treatments, except for the first winter when NO₃⁻ leaching was fivefold greater with injection. Because NO₃⁻ leaching with injection was substantially lower over subsequent seasons, we hypothesize that the elevated losses during the first winter were through preferential flow paths inadvertently created during lysimeter installation. Overall, shallow disk injection yielded the lowest NH₃ emissions without consistently increasing NO₃⁻ leaching, whereas manure banding with soil aeration conserved inconsistent amounts of N.
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