Slurry acidification outperformed injection as an ammonia emission-reducing technique in boreal grass cultivation

Nutr Cycl Agroecosyst https://doi.org/10.1007/s10705-021-10190-1 (0123456789().,-volV) ( 01234567 89().,-volV) ORIGINAL ARTICLE Slurry acidification outperformed injection as an ammonia emission-reducing technique in boreal grass cultivation Riikka Keskinen Mari Räty . Maarit Termonen . Tapio Salo . Sari Luostarinen . Received: 16 July 2021 / Accepted: 17 December 2021 © The Author(s) 2022 Abstract Ammonia (NH3) constitutes the single largest loss of manure nitrogen (N), making measures targeted at reducing its emissions meaningful for the environment and the overall efficiency of manure N use. In this study, the performance of two emissionreducing techniques, acidification and injection, were studied in a field experiment with grass ley over two growing seasons. Emissions of NH3, crop growth, and N use efficiency were determined from plots fertilized with cattle slurry either band spread, injected or band spread after acidification. The approximate cumulative NH3 losses from the plots with band-spread untreated slurry amounted to about 22 kg NH3-N ha−1 over the observation periods in 2017 and 10 kg NH3-N ha−1 in 2018. The injection and acidification reduced the estimated cumulative NH3 emissions by 43 and 95% respectively in 2018, and both by 97% in 2017. In 2017, the emissionreducing techniques had no impacts on crop growth, but in 2018, acidification increased dry matter yield Supplementary Information The online version contains supplementary material available at https://doi.org/10.1007/s10705-021-10190-1. R. Keskinen (&) · T. Salo · S. Luostarinen Natural Resources Institute Finland (Luke), Tietotie 4, 31600 Jokioinen, Finland e-mail: M. Termonen · M. Räty Natural Resources Institute Finland (Luke), Halolantie 31 A, 71750 Maaninka, Finland by 29% and apparent N recovery by 65% compared with band-spread untreated slurry. According to the current results, acidification consistently produced the lowest NH3 emissions and a discernible positive yield effect. It can therefore be recommended instead of injection for reducing NH3 emissions in boreal grass cultivation. Keywords Band spreading · Cattle slurry · Grass yield · Nitrogen · Sulfur · Sulfuric acid Introduction Despite decades of efforts to improve nitrogen (N) use efficiency in agriculture, a major reservoir of N excreted in livestock manures remains underutilized (Bouwman et al. 2009; Leip et al. 2011; Liu et al. 2017). At best, roughly half of the manure N supply is used by crops, while the rest is lost to the environment in different forms (Oenema et al. 2007; McCrakin et al. 2018). Leached nitrate (NO−3 ) causes eutrophication of surface waters and pollution of groundwaters, volatilized ammonia (NH3) induces the acidification and eutrophication of wider ecosystems, whereas nitrous oxide (N2O) acts as a greenhouse gas (Webb et al. 2013). In addition to the environmental hazards, leakages of reactive N are not economically sensible. Reducing the losses of manure N requires systemic action comprised of ways to ensure sufficient field area for manure 123 Nutr Cycl Agroecosyst application in relation to stock density, to identify alternative management strategies for direct land spreading, and to optimize animal diets, housing, manure storage, and application technologies (Rotz 2004; Sims et al. 2005; Liu et al. 2017). Losses of manure N over storage and during and directly after soil application are dominated by NH3 volatilization (Webb et al. 2013). According to the modeling of Oenema et al. (2007), an average of 19% of the N excreted in animal housing volatilized as NH3 during storage, and another 19% following soil application. The relative proportions of NH3 and its non-volatile conjugate acid ammonium (NH? 4) depend on pH and temperature, so that the presence of NH3 increases with an increase in these variables (Hartung and Phillips 1994; Martinelle and Häggström 1997). In fresh animal excreta, N occurs as mainly organically bound (Bristow et al. 1992; Kirchmann and Witter 1992). The organic N compounds are mineralized at various rates to an inorganic form as NH? 4 , the urea in urine being a major rapidly degradable source of N (Van Kessel et al. 2000). Marked NH3 release can be expected at pH levels above 7, which are typically reached in manures (Sommer and Hutchings 2001). Due to the dominance of NH3 in N losses, measures targeted at reducing its emissions are meaningful in increasing the overall efficiency of manure N use. Lowering the slurry pH to 4.5–6.5 by the addition of acid can be used to increase the ratio of NH? 4 to NH3 and thus minimize NH3 volatilization (Ndegwa et al. 2008). This acidification practice with strong sulfuric acid (H2SO4) has already become established in Denmark (e.g. Fangueiro et al. 2015). Its effectiveness varies, but in field applications, decreases of up to 80% in NH3 emissions and several dozen kg of conserved N ha−1 have been reported (e.g. Pain et al. 1994; Kai et al. 2008; Fangueiro et al. 2015). Although there are safety risks in handling H2SO4, its high efficacy in comparison to weaker acids and high accessory sulfur (S) content can be considered advantages, especially in conditions where there is a concern of sufficient S supply due to decreased atmospheric deposition and low S fertilization (Keskinen et al. 2016; Michalovicz et al. 2021). An alternative to acidification with acids in preventing NH3 volatilization is to quickly cover the manure with soil following application to minimize the surface area of slurry exposed to the 123 atmosphere (Sommer and Hutchings 2001; Webb et al. 2013). In comparison to the conventional surface broadcasting method, emissions of NH3 can be roughly halved by band spreading, and reduced by up to ca. 90% by slurry injection or incorporation below the soil surface (Webb et al. 2005). To make the most of the injection technique in NH3 emission reduction, application rates need to be adjusted to the slot volume so that it can hold the amount of slurry applied (Webb et al. 2013). Increasing the volume of the slots decreases NH3 losses but increases the demand for energy due to the soil’s penetration resistance (Hansen et al. 2003). In this study, the effects of applying cattle slurry with acidification and injection on NH3 emissions, crop growth, and N use efficiency were studied in boreal grass cultivation during two growing seasons. It was hypothesized that the N conserved from volatilization increased the amount of N available for crop uptake and was thus reflected as increased yields. However, a successful reduction of emissions has not always resulted in significant increases in crop N uptake (Webb et al. 2010). This may be related to difficulties in measuring small changes against large background variations caused by the heterogeneity in manure composition, soil fertility, and/or weather conditions or that N has not been the growth limiting factor. On the other hand, the tested methods may have other than N- (...truncated)