Abstract
In the present work, it was hypothesized that through modelling it is possible to overcome the constraints that arise in the quantification of N pollution swapping associated to slurry application practices when using individual experimental data. For this, environmental N losses were assessed under two methods of dairy slurry application to a double cropping system (rainfed oats (Avena strigosa)/irrigated maize (Zea mays)) in two different soils. An integrated experimentation and modelling approach was applied using the RZWQM2 model. The model was first tested using four years of experimental data concerning N fluxes to/from different environmental compartments (soil mineralization, N gas emissions, and N leaching). The model estimated emissions with overall efficiencies of ~70% and r2 ~ 0.75. Total N losses were higher for surface band application (95.4 and 40.2 kg ha−1 for the sandy and sandy loam soils, respectively). However, when slurry was injected, nitrate leaching considerably increased (by 107 and 64% for the sandy and sandy loam soils, respectively), even though gas emissions were minimized. This N swapping among path losses requires targeting of the N mitigation measures to the environmental compartment showing the highest vulnerability. Generally, the estimated emission factors (EFs) were lower than or equal to (slurry injection in the sandy loam soil) the IPCC default. The values showed high variability, reinforcing the need to use agricultural system specific EFs. The methodologies used in this study, focused on scenario analysis, can support policy as they can be used to set up integral strategies to decrease N emissions from livestock farming systems, taking into account possible synergies and antagonisms produced by the measures among NH3 and N2O emissions and NO3− leaching.
Highlights
Agriculture intensification and the consequent increase in nitrogen (N) fertilizer usage, together with the industrialization of livestock production, have generated large amounts of N-rich manures, namely slurry (Ilea, 2009; Malek et al, 2018)
Excessive nitrate emissions to water bodies are still occurring throughout Europe despite the large set of legislation (Bouraoui and Grizzetti, 2014), e.g. the Water Framework Directive (WFD) (2000/60/EC) and the Nitrate Directive (ND) (Council Directive 1991/676/EEC)
The parameters that most influence the N2O emissions fall into the soil properties group and N2O rate coefficients group (Fig. SM1)
Summary
Agriculture intensification and the consequent increase in nitrogen (N) fertilizer usage, together with the industrialization of livestock production, have generated large amounts of N-rich manures, namely slurry (Ilea, 2009; Malek et al, 2018) This has led to considerable N surpluses and mineral N accumulation in soils, contributing to increased losses to the different environmental compartments - such as water bodies contamination with nitrate (NO3−) and N emissions to the atmosphere, including ammonia volatilization (NH3) and direct and indirect nitrous oxide (N2O) emissions (Oenema et al, 2011; Chadwick et al, 2011; Bittman et al, 2014; FAO, 2017). For the same period, Portugal had increases of 9 and 11% for the total number of cattle and pigs, respectively, suggesting an increase in the areas amended with slurry since the last national survey (2009)
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