**3. Results**

The estimated greenhouse gas (GHG) emissions from fertilizer and irrigation inputs are displayed in Table 1. The results showed that the main GHG emissions from the silvopastoral system was nitric oxide and ammonia, and from the organic systems, it was mainly nitric oxide. The main contribution of the traditional agroforestry system was CO2 and the largest emission was from irrigation, which was only applied in the traditional agroforestry production system.


**Table 1.** Estimations of estimated greenhouse gas (GHG) emissions from four agroforestry systems in Italy and two production systems in Denmark. CFE: combined food and energy system.

In the combined food and energy production system in Denmark, GHG emissions emanated mainly from nitrogen (N) from the applied manure, with a small contribution from direct NO2-N dinitrogen monoxide (N2O). Much larger GHG contributions were recorded for conventional wheat production systems due to chemical fertilizer application.

The production system impacts on the environment are displayed in Table 2. In Italy, the highest global warming potential (GWP) was contributed by the traditional production systems, while silvopastoral systems exhibited the lowest GWP. The highest acidification and eutrophication effects originated in the silvopastoral system, whereas the lowest effects were recorded in the traditional system. In Denmark, GWP, acidification, and eutrophication were higher in the conventional wheat system than the combined food and energy system.

**Table 2.** Environmental impacts of the production systems. Greenhouse gas emissions from the Italian production systems are provided per weight (kg) of olive yield, while the unit of income (\$) is used for the Danish production systems. GWP: global warming potential (GWP100a).


Evident from Figure 3, the conventional and tradition production systems in Italy exhibited the highest adverse impacts on the environment due to fertilization. Silvopastoral and organic systems emissions mainly emanated from machinery use. GHG emissions due to orchard establishment were high on acidification and eutrophication impact categories in the silvopastoral system.

**Figure 3.** Percentage contribution from fertilizer, machinery use, irrigation, and orchard establishment on environmental impacts categories of global warming potential (GWP), acidification, and eutrophication for four Italian production systems.

Figure 4 shows that the application of fertilizer and manure had the greatest GHG emission contribution on GWP, acidification, and eutrophication for the conventional wheat and the combined food and energy system in Denmark. The second largest contributor to the GWP comes from machinery use, while seeding operation resulted in the second highest contribution to acidification and eutrophication in both production systems.

**Figure 4.** Percentage contribution from fertilizer, machinery use, and seeding on the environmental impact categories of global warming potential (GWP), acidification, and eutrophication for agroforestry and conventional production systems in Denmark.

The income from the diversity of produce in the combined food and energy systems in Denmark is presented in Table 3. Clover contributed to 49.1% of the total income, followed by wheat (30.5%) and barley (19.3%). The sale of willow woodchips amounted to only 1% of the total income.

**Table 3.** Income from the produce in the conventional wheat and combined food and energy production systems in Denmark.


The environmental impacts of the two production systems in Denmark were estimated based on the income from each production system (Table 4). The combined food and energy system had a lower GWP, acidification, and eutrophication impact compared to the conventional wheat production system.

**Table 4.** Environmental impacts of the conventional wheat and combined food and energy production systems in Denmark. GWP: global warming potential (GWP100a).


From the yield ha −1 (kg ha−1) and area (ha) for each of the Italian production systems, and from the income per farm (\$ farm−1), yield per area and price of wheat (0.49 \$ kg−1) for the Danish production systems, the GHG emission ha−<sup>1</sup> (Table 5) was calculated based on the results presented in Table 2.

**Table 5.** GHG emissions ha−<sup>1</sup> in production systems in Italy and Denmark. CFE: combined food and energy system.

