Hemp (Cannabis Sativa L.), native to the Himalayas, has spread to India and the Far East since the Neolithic, and China is the country where it is cultivated for the longest time. Its introduction in Europe probably dates back to the second millennium BC. In Italy, it is reported in the first century BC, and was found in many Etruscan findings. Later, it was used by the Roman Empire for the construction of sails, nets and ropes, but saw a broader diffusion only in the Middle Ages especially in the Po Valley. In the following centuries, the cultivation extended in great part of Central Italy up to Campania and Basilicata. In the twentieth century, after having recorded a progressive increase in the cultivated area up to 90,000 ha, from the 1940s throughout the 1960s, it experienced a decline and almost disappeared due to the introduction of synthetic fibers and especially due to Italy’s adhesion to the Protocol on the Single Convention on Narcotic Drugs proposed by the United Nations, signed in New York on 30th March 1961 and subsequently to the Protocol of Amendment adopted in Geneva on 25 March 1972. This amendment was transformed by Italian Government in law through the publication in the Official Journal number 236 of 10 September 1974.
Only since the beginning of the twenty-first century, the interest for hemp has revived thanks to the Community Legislation and especially the Council Regulation 1251/1999/EC of 17/05/1999 which established a support scheme for producers of certain arable crops, including industrial hemp, and was followed by subsequent implementing regulations, the 2316/1999 and 327/2002, of the European Commission and the Regulation 953/2006 of the European Council on the introduction of aid for the processing of flax and hemp grown for fiber. But only with the Regulation (EU) No. 1307/2013 of the European Parliament and the Council of 17 December 2013 (last reform of the CAP 2014–2020), hemp cultivation was included among those eligible for CAP payments on the condition that the seed used for the cultivation are from registered varieties in the European catalog with a content of Δ9‐tetrahydrocannabinol (THC) less than 0.2%. In Italy, the application of the Community Regulations on the cultivation of industrial hemp has precise legislative reference (Law 242, 2016), valid from January 2017, which has among its purposes: "Support and promotion of the hemp sector (Cannabis sativa L.) as a crop capable of reducing environmental impact in agriculture, reducing land consumption and desertification and loss of biodiversity, and as a crop to be used as a possible substitute for surplus crops and as a rotational crop." The same law also provides an exemption of liability for the farmers in case that the THC content is more than 0.2%, but less than 0.6%, and also encourages the development of certain sectors such as green building, food and textiles. But it does not regulate the possible use of inflorescences for the pharmaceutical and parapharmaceutical sectors.
Importance of hemp cultivation for environment and agriculture
All of us who work in the field and ordinary citizens can begin to argue about the topical of this ancient culture starting with a simple question: Why today we need to encourage the cultivation of hemp in the world? The answer is because hemp acts positively both on ecosystem and human health, thus promoting the many ecological and biological mechanisms that govern the conservation and evolution of life itself.
In fact, its ecological profile is perfectly oriented in the containment directions of the so-called Planetary Boundaries that are the limits of sustainable ecological development proposed by the 'Earth System and Environmental Scientist led by Johan Rockström from the Stockholm Resilience Center and Will Steffen from Australian National University for Planet Earth (2009). The Stockholm Resilience Center for Planet Earth is an international study center that deals with the sustainable development of the planet earth based on the use of natural resources. The "planetary limits" traced in 2009 by the Swedish researcher define the boundaries within which we human beings can operate safely, without harming the balance of the planet.
Three of these limits have already been largely exceeded and are at a point of no return. The ecological processes that can positively interfere with some of these limits are those in which the cultivation of hemp can generate great benefits to environment. The first concern is that the CO2 concentration is currently standing at 450 parts per million (ppm) in the atmosphere, much more compared to the pre-industrial value of 280 ppm. Hemp acts positively on the concentration of CO2 in the atmosphere because it is a culture ΔCO2 negative. It means that this crop is capable in the carbon cycle of removing more CO2 from the ambient than it emits. The high ability to sequester CO2 from the atmosphere is a trait common to many agricultural species, especially woody ones, but this feature is particularly evident in hemp which has a very rapid growth compared to other herbaceous crops. For example, hemp compared to other fiber crops such as cotton and flax which have a longer growth cycle produces about 8 and 3 times more biomass, respectively. It should be noted that the CO2 values absorbed by 1 hectare of hemp vary considerably according to the agronomic practices adopted and the biomass produced per hectare. Melosini (2017) for a production of biomass produced between 8 and 12 tons report values of CO2 seized between 10 and 15 tons per hectare. Adesina et al. (2020) instead have related the increase in dry matter of the stem (where 80% of atmospheric carbon is sequestered and stored) as a function of nitrogen fertilization for nitrogen values between 0 and 120 kg/ha with the possibility of sequester up to 22 tons of CO2 per hectare. This great variability of hemp to sequester carbon depends on the fact that the increase in the stem per unit of nitrogen cannot be accurately determined from the literature data due to the different methods used and the cultivation environment. In addition, recent agronomic research has shown that hemp can also have a beneficial effect on the reduction of agricultural greenhouse gases through the mechanisms that govern its nitrogenous nutrition. In fact, it has recently been shown that hemp cultivation has a better vegetative development and better seed quality if slow release fertilizers such as UREA are used compared to synthetic fertilizers such as ammonium nitrate (NH4NO3) (Tedeschi et al. 2020).
The ammonium nitrate also compared with UREA, has favored, during most of the vegetative cycle of hemp, a greater emission of greenhouse gases in the atmosphere such as nitrous oxide (N2O) which is extremely dangerous because it heats 297 times more than CO2 and alone it accounts for 7% of total Italian emissions (IPCC Report 2018).
The low efficiency in the use of nitric nitrogen is an eco-physiological characteristic of this crop when compared with other interesting species from the point of view of the bioeconomy such as cotton and kenaf. In fact, it has been shown that photosynthetic metabolism of hemp in relation to the foliar nitrogen content is more efficient at low nitrogen levels (< 2 g N/m2) than cotton and kenaf; while above this threshold value, it is lower compared to the other two species (Tang et al. 2017). The consequence is that the slow absorption of nitric nitrogen can favor both the leaching processes with pollution of the groundwater and denitrification with a consequent increase in the emission of the greenhouse gas N2O into the atmosphere. For these two combined effects, namely the seizure of atmospheric CO2 in its own biomass and lower N2O emissions into the atmosphere due to the favorable use of slow release nitrogen fertilizers, hemp can reasonably be considered a climate-friendly crop, namely to combat climate change.
Finally, hemp also has positive effects on the containment of biodiversity loss, another parameter of the Planetary Boundaries (number of extinct species /million species/year) whose limit has also exceeded the point of no return and which is currently > 100. The proposed value to counter biodiversity loss should be around 10. The increase in plant biodiversity linked to the cultivation of hemp depends on the fact that, thanks to the strong emission of terpenic essences from its inflorescences, hemp attracts pollinating insects. The crop is also itself a source of biodiversity because its pollen carried by the wind can reach a considerable distance of 3 km (Campiglia 2020).
Moreover, thanks to its high size and the fact that it is not weeded, it creates a microclimate near the inflorescences that is favorable to pollinating insects. A very recent research conducted in the USA has highlighted that hemp, thanks to its flowering cycle that occurs at a different time compared to other species and also to the abundant pollen produced, has favored the nutrition of various species of bees, increasing their biodiversity. Thanks to the increase in pollination with other crops in the area, the biodiversity of the entire agro-ecosystem under study has also been increased (Flicker et al. 2020). The beneficial effects of hemp on the environment are shown in Fig. 1.
Moreover, territorial researches in the last 20 years have identified some indices of prediction of the desertification processes in existence and it has been demonstrated that 41% of the soils of Southern Italy are currently subject to desertification phenomena (Perini et al. 2008). In many of these areas, new cultivation systems are being studied with the introduction of industrial non-food crops to try to maintain productive agricultural soils otherwise subject to abandonment and desertification.
The hemp fiber together with other industrial crops has been tested in the last 15 years in salinized soils of the Volturno Plain in the North of the Campania Region (Sorrentino et al. 2014). This area was once a fertile alluvial plain and gave rise to almost all the fruit and vegetable production of imperial Rome whereas today is subject to high soil desertification due to the combined effect of climate change and human activities. The reduction of rainfall caused by climate change has led to greater exploitation of the groundwater by local farmers who begin to find, given the proximity to the coast, increasingly saline water and unsuitable for irrigation (Pagliuca 2004). In this context, from a productive comparison between fiber hemp and maize on saline soil with a high electrical conductivity (Ece), it was found that, at a value of 8 ds/m Ece, maize showed a reduction in grain production by 50%, while fiber hemp at the same value of Ece showed a reduction of the fiber produced less, equal to 25% (Tedeschi et al. 2003). These production reductions were calculated and normalized in accordance with the Maas and Hoffmann report (1977) which measured the loss of agricultural production in tons per hectare (Ton/Ha) in relation to the degree of salinization of the soil (Ece) compared to the maximum achievable in non-salinized soils. Even at more moderate values of soil electrical conductivity equal to 4.5 ds/m, fiber hemp was more productive than other renewal crops such as sunflower, containing the reduction within 10% compared to 15% of sunflower (Sorrentino et al. 2000). Figure 2 shows an experimental plot of fiber hemp (a) and comparison on a highly salinized soil between maize and two varieties of fiber hemp (Carmagnola and Fibranova × Carmagnola).
We can, therefore, conclude that hemp is very important for the protection of the environment and agriculture because it can combat climate change and desertification processes in a positive and balanced manner. For these reasons, hemp can play a very important role in agriculture in the near future and be, especially in the current process of green transition, an active player in the green economy considering that the agro-industrial sectors that it can activate are already naturally "green oriented" (Sorrentino et al. 2019).