Effects of acidification and injection of pasture applied cattle slurry on ammonia losses, N 2 O emissions and crop N uptake

Abstract

Abstract Surface application of cattle slurry on grassland is characterized by a high risk of ammonia (NH 3 ) losses. Different techniques and measures to lower these emissions are available, but reported abatement efficiencies vary substantially among studies. Therefore, a direct comparison of five different slurry application techniques was conducted in a two year field trial (2012–2013) on perennial grassland in Southern Denmark (sandy soil) and Northern Germany (marsh, clay soil). The techniques included open slot injection of cattle slurry with different distances between double disc injectors (0.166 m injection close, IC; 0.33 m injection wide, IW) and bandspreading of cattle slurry acidified to pH 6.5 (acid low, AL) and 6.0 (acid high, AH) as well as band spreading as reference (BS). For evaluation of N efficiency of slurry treatments, mineral fertilizer equivalents (MFE) were derived by comparison with a mineral N yield response curve. NH 3 emissions were measured with the combination of passive flux sampling and a dynamic chamber method. Nitrous oxide (N 2 O) emissions were determined with a static chamber method at the marsh site. Grass dry matter yield and N yield were determined in all treatments. Ammonia losses were significantly reduced compared to BS treatment by 31, 61, 42 and 79% by IC, IW, AL and AH, respectively. Slurry application techniques had no significant effect on dry matter yield at both study sites. Only treatment AH resulted in higher N uptake among slurry treatments on sandy soil (2012) or clay soil (2013). Except for AH with highest MFE values at Waygaard, MFE values of slurry treatments were higher at sandy soil (53–62%) than at clay soil (39–88%). N 2 O emissions were at a low level in 2012 (0.12–0.38% of N total ) and showed no significant differences among application methods. In 2013, N 2 O emissions were higher (0.07–0.75% of N total ) compared to 2012 and IW resulted in significantly higher emissions than BS. Treatment AH (acidification to pH 6.0) showed lowest NH 3 losses, highest yields while N 2 O emissions were not-significantly increased. Acidification and injection methods proved to reduce NH 3 losses reliably but trade-offs like increased N 2 O emissions from IW and high acid requirement from AH of 4.8 l t −1 slurry have to be taken into consideration.