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Ammonia poses a risk to human health and terrestrial and aquatic ecosystems. In Spain in 2022, the agricultural sector was responsible for 97% of ammonia emissions to the atmosphere, with the application of animal manure as fertilizer accounting for 24.4% of these emissions. The search for effective mitigation strategies in the application of animal manures is imperative to support the implementation of policies that contribute to the sustainability of the agricultural sector. The aim of this study is to evaluate three digestate application techniques, namely, acidification, open disc injection, and fertigation, in a wheat–maize rotation and compare them to traditional trail hose application. In spring wheat topdressing, acidification is the most efficient method for reducing ammonia emissions, followed by disc injection and, finally, fertigation. In the summer base dressing to maize, acidification is the best method, with more than 70% reduction compared with trail hoses. In terms of both base dressing and side-dressing fertilization, the most efficient method is fertigation, with a 70% reduction, followed by acidification and disc injection (>25%). Although the three methods reduce ammonia emissions, they have certain drawbacks: fertigation requires previous solid/liquid separation, acidification requires ad hoc equipment, and disc injection requires high mechanical traction. Full article

Easy and inexpensive methods for measuring ammonia emissions in multi-plot field trials allow the comparison of several treatments with liquid manure application. One approach that might be suitable under these conditions is the dynamic tube method (DTM). Applying the DTM, a mobile chamber system is placed on the soil surface, and the air volume within is exchanged at a constant rate for approx. 90 s. with an automated pump. This procedure is assumed to achieve an equilibrium ammonia concentration within the system. Subsequently, a measurement is performed using an ammonia-sensitive detector tube. Ammonia fluxes are calculated based on an empirical model that also takes into account the background ammonia concentration measured on unfertilized control plots. Between measurements on different plots, the chamber system is flushed with ambient air and cleaned with paper towels to minimize contamination with ammonia. The aim of this study was to determine important prerequisites and boundary conditions for the application of the DTM. We conducted a laboratory experiment to test if the ammonia concentration remains stable while performing a measurement. Furthermore, we investigated the cleaning procedure and the effect of potential ammonia carryover on cumulated emissions under field conditions following liquid manure application. The laboratory experiment indicated that the premeasurement phase to ensure a constant ammonia concentration is not sufficient. The concentration only stabilized after performing more than 100 pump strokes, with 20 pump strokes (lasting approximately 90 s) being the recommendation. However, the duration of performing a measurement can vary substantially, and linear conversion accounts for those differences, so a stable concentration is mandatory. Further experiments showed that the cleaning procedure is not sufficient under field conditions. Thirty minutes after performing measurements on high emitting plots, which resulted in an ammonia concentration of approx. 10 ppm in the chamber, we detected a residual concentration of 2 ppm. This contamination may affect measurements on plots with liquid manure application as well as on untreated control plots. In a field experiment with trailing hose application of liquid manure, we subsequently demonstrated that the calculation of cumulative ammonia emissions can vary by a factor of three, depending on the degree of chamber system contamination when measuring control plots. When the ammonia background values were determined by an uncontaminated chamber system that was used to measure only control plots, cumulative ammonia emissions were approximately 9 kg NH₃-N ha⁻¹. However, when ammonia background values were determined using the contaminated chamber system that was also used to measure on plots with liquid manure application, the calculation of cumulative ammonia losses indicated approximately 3 kg NH₃-N ha⁻¹. Based on these results, it can be concluded that a new empirical DTM calibration is needed for multi-plot field experiments with high-emitting treatments. Full article

Ammonia emissions following liquid manure application impair human health and threaten natural ecosystems. In growing arable crops, where immediate soil incorporation of the applied liquid manure is not possible, best-available application techniques are required in order to decrease ammonia losses. We determined ammonia emission, crop yield and nitrogen uptake of winter wheat in eight experimental sites across Germany. Each individual experiment consisted of an unfertilized control (N0), broadcast calcium ammonium nitrate (CAN) application as well as four different techniques to apply cattle slurry (CS) and biogas digestate (BD). Fertilizer was applied to growing winter wheat at a total rate of 170 kg N ha⁻¹ split into two equal dressings. The following application techniques were tested for both liquid manure types: (i) trailing hose (TH) application using untreated and (ii) acidified (~pH 6) liquid manure (+A), as well as (iii) a combination of open slot injection (SI) for the first dressing and trailing shoe (TS) application for the second dressing without and (iv) with the addition of a nitrification inhibitor (NI) for the first dressing. The highest ammonia emissions (on average 30 kg N ha⁻¹) occurred following TH application of BD. TH application of CS led to significantly lower emissions (on average 19 kg N ha⁻¹). Overall, acidification reduced ammonia emissions by 64% compared to TH application without acidification for both types of liquid manures. On average, the combination of SI and TS application resulted in 23% lower NH₃ emissions in comparison to TH application (25% for the first application by SI and 20% for the second application by TS). Supplementing an NI did not affect ammonia emissions. However, decreasing ammonia emissions by acidification or SI did not increase winter wheat yield and nitrogen uptake. All organically fertilized treatments led to similar crop yield (approx. 7 t ha⁻¹ grain dry matter yield) and above-ground biomass nitrogen uptake (approx. 150 kg ha⁻¹). Yield (8 t ha⁻¹) and nitrogen uptake (approx. 190 kg ha⁻¹) were significantly higher for the CAN treatment; while for the control, yield (approx. 4.5 t ha⁻¹) and above-ground biomass nitrogen uptake (approx. 90 kg ha⁻¹) were significantly lower. Overall, our results show that reducing NH₃ emissions following liquid manure application to growing crops is possible by using different mitigation techniques. For our field trial series, acidification was the technique with the greatest NH₃ mitigation potential. Full article

Ammonia (NH₃) emissions resulting from the field application of livestock slurry has both negative human health and environmental impacts. However, decreasing the exposed surface area (ESA) of slurry upon application can reduce NH₃ volatilization by limiting its atmospheric exposure. In the present study, three strategies for depositing slurry within a growing crop were studied, including: 1. standard trailing hoses (SA_hose), 2. trailing shoes (SA_shoes), and 3. the combination of rigid tines and trailing shoes (SA_tines+shoes). Application methods interact with the soil to varying degrees and were evaluated within the context of contemporary weed management practices, namely in cereals receiving inter-row hoeing. SA_hose, SA_shoes, and SA_tines+shoes were compared in three coinciding experiments that assessed slurry ESA, NH₃ emissions, and crop and weed effects. SA_tines+shoes resulted in smallest ESA, 70–72% and 61–66% less than SA_hose and SA_shoes, respectively. However, in only one of three site–years did SA_shoes and SA_tines+shoes reduce NH₃ emissions compared to SA_hose, by 46% and 29%, respectively. Crop yields, nitrogen (N) accumulation in crop biomass, and intra-row weed biomass were unaffected by the placement method. In heavily crusted soils, the SA_tines+shoes prototype worked well; however, the functional differences among placement strategies were not great enough to detect crop and NH₃ effects. Full article

Field application of organic slurries contributes considerably to emissions of ammonia (NH₃) which causes sever environmental damage and can result in lower nitrogen (N) fertilizer efficiency. In recent years, field acidification systems have been introduced to reduce such NH₃ emissions. However, combined field data on ammonia emissions and N use efficiency of acidified slurries, in particular by practical acidification systems, are scarce. Here, we present for the first time a simultaneous in situ assessment of the effects of acidification of five different organic slurries with a commercial acidifications system combined with different application techniques. The analysis was performed in randomized plot trials in winter wheat and spring barley after two applications to each crop (before tillering and after flag leave emergence) in year 2014 in Denmark. Slurry types included cattle slurry, mink slurry, pig slurry, anaerobic digestate, and the liquid phase of anaerobic digestate. Tested application techniques were trail hose application with and without slurry acidification in winter wheat and slurry injection and incorporation compared to trail hose application with and without acidification in spring barley. Slurries were applied on 9 m × 9 m plots separated by buffer areas of the same dimension. Ammonia emission was determined by a combination of semi-quantitative acid traps scaled by absolute emissions obtained from Draeger Tube Method dynamic chamber measurements. Experimental results were analysed by mixed effects models and HSD post hoc test (p < 0.05). Significant and almost quantitative NH₃ emission reduction compared to trail hose application was observed in the barley trial by slurry incorporation of acidified slurry (89% reduction) and closed slot injection (96% reduction), while incorporation alone decreased emissions by 60%. In the two applications to winter wheat, compared to trail hose application of non-acidified slurry, acidification reduced NH₃ emissions by 61% and 67% in cattle slurry, in anaerobic digestate by 45% and 57% and liquid phase of anaerobic digestate by 58%, respectively. Similar effects but on a lower emission level were observed in mink slurry, while acidification showed almost no effect in pig slurry. Acidifying animal manure with a commercial system was confirmed to consistently reduce NH₃ emissions of most slurry types, and emission reductions were similar as from experimental acidification systems. However, failure to reduce ammonia emissions in pig slurry hint to technical limitations of such systems. Winter wheat and spring barley yields were only partly significantly increased by use of ammonia emission mitigation measures, while there were significant positive effects on apparent nitrogen use efficiency (+17–28%). The assessment of the agronomic effects of acidification requires further investigations. Full article