Review of environmental effects

Cultivation of bioenergy crops in arable land has flourished from the recent few decades because of the worldwide energy crisis and focusing on the sustainable energy sources with less environmental effects. But we should recognize that what kind of impact have on the environment and socio-economy because of the massive expansion of bioenergy crop cultivation in Sweden.

Energy is an essential criterion for development in any place in the world. If we compare with any fossil fuels, using bioenergy is most advantageous. The most benefit is to use biomass is the renewability of it. But due to its renewable characteristics, it has some severe environmental alteration process that may turn or change the environmental phenomenon. For this reason, it is completely interconnected with air, water, soil, and biodiversity in different ways. (Wu et al., 2018).

After 1970, the world's agricultural production has increased twice than before because of the sudden population growth and for the related requirements or food security. Also, for the worldwide fuel crisis, some country has started to cultivate the bioenergy crops in their fallen arable land. For this reason, about a quarter of the greenhouse gas has emitted from crop cultivation in 2010. (Bennetzen et al., 2016). From the previous discussion, we know that Sweden is the highest country using biomass energy crop cultivation in the world. In the world level, agriculture is contributing about 14% of anthropogenic greenhouse gas emissions, while 17% is happening for the changing of land use patterns. (Palut, 2007). So, finding out the greenhouse gas emissions for the bioenergy crop cultivation in arable land is an important issue.

Because of bioenergy crop cultivation in arable lands, the greenhouse gas emissions may reduce by three ways like a) reinstallation of carbon in mineral soils, b) less emission of carbon di oxide from the organic soils due to less ploughing of land, and c) less emission of nitrous oxide from the land due to less utilization of nitrogen or other fertilizers. (Börjesson, 1999).

Effects on Soil

The cultivation of bioenergy crops in arable land has many ethical impacts on the soil when if compare with the traditional agricultural crop cultivation. It saves the loss of soil humus and increased soil fertility. On the other hand, due to conventional agriculture crop cultivation, farmers need to do more intensive soil tillage, which is responsible for reducing soil fertility and loss of humus. (Bouwman, 1990). During the last 25 years of energy crop cultivation in Sweden, the humus level has increased on the topsoil about 1 percent. Increasing humus level means increasing fertility in the soils and the result of this is increasing the overall crop cultivation rate during the following years. The study has shown the harvesting of food crops has increased by at least 5%. (Gustafsson, 1987).). Whereas, physical and chemical properties were improved due to the high contents of humus level. (Andersson, 1990). Theoretically, about 47% of Swedish arable land has developed the humus level in mineral soils. The amount of collection for annual crops would be twice if the places were cultivated by the perennial energy crops (for example the Salix) previously for 25 years. But the amount may reduce according to the time and next criteria of cultivation. (Mattsson, 1996).

Also, after using the Salix plantations surrounding the food crop cultivation, wind erosion may reduce. Because of wind erosion plant blasting, roots uncovering, losing of organic matters and fine particles, seeds exploitation, and reducing soil fertility may happen. (Mattsson et al., 1996).

Some results from the previous study have shown that, if any area of annual cultivated crops surrounded by the perennial energy crops (for example the Salix), the wind erosion may reduce several times, and total production also be increased for this reason. (Jonsson, 1994).

To protect from the water erosion of soil, perennial energy crops (for example the Salix) have also good contribution. It may reduce the rill erosion especially from the clay and silty fields in hilly areas. But the water erosion may happen for low soil cover and extreme run-off in Salix plantations also. In Sweden, about 20% of arable land is exposed to rill erosion. If 5% of rill erosion happens about 500 kg/ha/year may loose from the topsoil. (Alstrom, 1991). So to save soil from water erosion, perennial energy crops (for example the Salix) cultivation to the surrounded area is an important way.

Carbon in mineral soils

For the reinstallation of carbon in land, it needs much amount of organic matter should be added, and less amount should be eroded at the same time from the soil. It happens when traditional food crops replace perennial energy crops because the rate of tillage would reduce.

Also, for the bioenergy crops, the input amount of organic matter remains high for the litter and roots. About 4.5-10-ton dry matter/ha/year may recirculate in established salix cultivation where nearly two-thirds have come from litter and one third by roots. (Sjödahl et al., 1994).

After harvesting the crops from the arable land, the abandoned materials of energy crops contain 60% of carbon also decomposed by the soil. (Reicosky et al., 1995). That affects the high enrichment of carbon in the topsoil. For example, several cultivations of salix in the same arable land within a few years increases the carbon content in the upper soil. Though the total carbon content remains unchanged, it may change after a long period. (Reicosky et al., 1995;

Makeschin, 1994). Even the cultivation of ley grass in arable land increases 30-40 tonne C per ha. Food crops need more than 30 years to get the same amount of carbon in topsoil. (Thyselius et al., 1992).

Soils have a close connection with other parts of the environment, like air and water. When soils also absorb three major greenhouse gases in its like Carbon dioxide (CO2), Methane (CH4) and Nitrous oxide (NO2). Even the vegetation of soil absorbs carbon and nitrogen through photosynthesis and nutrient up taking respectively. But after comparing with the size of traditional food crops, energy crops may absorb more carbon and nitrogen in their body.

Because if the stock of carbon and nitrogen be more inland than it is more favorable for the environment. (Höglund et al., 2013).

For the perennial crop, soils not cultivated regularly so the release of carbon not happened generally and the penetration of carbon increases through the roots. But for traditional annual crops, the possibility of carbon input is in little amount, and the carbon release is common.

Organic soil may grow 0.1 to 1 ton per hectare in the topsoil (30 cm of the above part of the soil) for the cultivation of perennial grasses. (Hillier et al., 2009). High rates of carbon accumulated in Nothern Sweden for the cultivation of reed canary grasses within the first three years. About 3 to 3.4 tons of carbon accumulated in the top 20 cm of soil per hectare. This amount is about seven times higher than the traditional agricultural food crops. (Xiong &

Kätterer, 2010).

Soil carbon sequestration had increased in Sweden for the cultivation of poplar and willow.

After calculating the 20- and 22-years harvesting cycle of willow and poplar based on the leaf litter observation and decay modeling, 2.81 and 3.51 tonnes of carbon per hectares produced for willow and poplar litter (leaf + fine roots litter) respectively. (Rytter, 2001; Rytter, 2012).

On the other side, the soil carbon accumulation is about 0.41 tons and 0.52 tons per hectares for willow and poplar, respectively. (Berg & Ekbohm, 1991).

The primary source of nitrous oxide (N2O) emissions for greenhouse gas is the agricultural sector. Even nitrous oxide emission is more harmful than carbon dioxide emissions. Because 1 kg of nitrous oxide (N2O) has 100 years of climatic impact, but to get the same kind of effects in the environment, we need about 300 kg of carbon dioxide (CO2). Sweden releases about 70% of nitrous oxide (N2O) from the agricultural sectors. (Kasimir, 2009). Though nitrous oxide (N2O) is more effective than carbon dioxide (CO2) but the source of nitrous oxide (N2O) emissions are not so much frequent like the carbon dioxide (CO2). It is mainly happened for the excessive use of nitrogen fertilizers in the agricultural fields when the utilization of nitrogen fertilizer for the forest growth and bioenergy crops are not so common (Nordin et al., 2008).

For example, in Northeastern Germany, emissions of nitrous oxide were half from salix and poplar comparison with annual crops (Hellebrand et al., 2010).

Carbon emmissions

Vegetation on the arable lands accumulate a huge amount of carbon, nitrogen and other minerals in different quantity. For this reason, the soil surface acts as a significant carbon and nitrogen reservoir, but due to the cultivation of crops, it becomes light and releases many organic matters and minerals. Among them, carbon dioxide (CO2), methane (CH4) and nitrogen oxide (N2O) are more critical because of quantity and impacts on the environment.

(Höglund et al., 2013).So, changing of land use pattern has a significant contribution to the emission of carbon. It's entirely depended on the soil and vegetation types. In this perspective, the accumulation of carbon rate is higher for traditional agricultural crops than the perennial energy crops because of frequent soil tillage. The rate is 2-3 cm per year for the carrots and potatoes. For the permanent pasture, the rate is 0.5 cm per year, in the same way, 1-2 cm for grain and 1 cm for ley. (Berglund, 1989). In the same way, perennial grass cultivation in arable land may increase the organic carbon at about 0.1-1 tons per hectare per year. High accumulation rates also happened for reed canary grass in three different growing stages. In the

upper 20 cm, the rate was 3-3.4 tonnes per hectare. In the second and third generations, the rate was more than the first growing season, and it was two to seven times higher than any other agricultural food crops. (Xiong & Kätterer, 2010). The accumulation rate for willow and poplar is higher than the other. Willow increases about 2.81 tons of carbon per hectare per year during their 22 years harvesting life cycle. While poplar accumulates 3.51 tons in the whole 20 years life cycle. This calculation was for total litter (leaf + fine root litter) (Rytter, 2012).

According to this, it is possible to do an estimation that, bioenergy crop cultivation in arable land rather than the agricultural crop cultivation may reduce the carbon from 2 to 1 cm per year.

It means about 7 tons of carbon reduces per hectare per year when the total content and density of carbon in Swedish organic soils were 200 kg/m3. (Berglund, 1989).

Nitrogen emmissions

The emission of nitrogen mainly happens because of the extra use of nitrogen fertilizers, whereas the requirement of nitrogen fertilizers is shallow or ignore able for bioenergy crop cultivation. On average, about 50 kg of nitrogen needs in a hectare for energy crop cultivation.

Beside this, due to have an extensive root system and more longer growing season, nitrogen loses from the topsoil of arable lands is negligible for the bioenergy crop. Another reason might be the low availability of nitrogen minerals in the topsoil of Sweden. (Börjesson, 1996). An estimation for the bioenergy crop cultivation may reduce the N2O emission at about 0.3 kg per hectare per year had established by the Bouwman and National Swedish Environmental Protection Board. (Bouwman 1990; National Swedish Environmental Protection Board, 1990).

Also from Ahlgren, the N2O emission rate is like, for ley grass 0.5, willow 2.1, ley crops 2.5, sugar beet 3.0, rapeseed 3.1, wheat 3.6, maize 3.7. All amounts are in kg per ha per year according to IPCC rate of 2006. (Ahlgren et al., 2010). So it means that, energy crops release less nitrogen than the agricultural food crops.

Wastewater Treatment

The wastewater treatment output depends on the nutrient contents of the water and the nutrient demand for energy crops — most of the cases the wastewater used as the supplement of fertilizers. Because the wastewater contains many organic and inorganic materials, those are important for bioenergy crop growth. (Perttu et al., 1994). After using the wastewater irrigation, the production of bioenergy crops may increase more than 2-3 times, compared without using the fertilizers. (Nielsen, 1994). Some studies have shown that, if the Nitrogen and Phosphorus

contain are 500-1000 mm/ha/yr, then about 75-95% of the elements are possible to remove by the cultivation of energy crops from arable lands. Even if the amounts are high like 2000-5000 mm/ha/yr, then still, it is possible to decrease 10-55%, according to the soil contents and vegetation types. (Perttu et al., 1994). During the summertime, the amount of Nitrogen contents in wastewater remains high because the utility rate of nitrogen per person in the municipality remains high. On average, the percentage of nitrogen utility is about 4kg/person/year. (National Swedish Environmental Protection Board, 1993). For 600 mm/ha/year of nitrogen in wastewater, mainly carrying 125 kg Nitrogen in solid condition. But this amount has not only long-term effects on the environment. (Perttu et al., 1994). Though, in some cases, Sweden uses some pretreatment to reduce the high nitrogen contents by cultivating other vegetation.

(Rosenqvist et al., 1997). It is possible to treat about 70% of the municipal waste of Sweden by bioenergy crops. Then it needs about 100,000 ha of arable land, which is equivalent to 3.6% of total arable land. (Statistics Sweden, 1996). Some energy crops have a high evapotranspiration rate than other traditional agricultural food, like salix and reed canary grasses. This kind of plant reduces the nutrient leaching to soil and groundwater levels. When leaching is the most significant effect for the wastewater about every 3-hectare size of energy crop cultivation can reduce 150g N per liter leaching from the topsoil. (Perttu & Aronsson, 2013).

So, if the wastewater used for bioenergy crop production, it saves water from some severe pollution of water. It also protects from excessive nutrient leaching to soils and underground water. But there has some little risk for discharging heavy metals from wastewater. Because the amount of released heavy metals from the municipality on the environment may become ignorable because of the low quantity, even the high concentration of heavy metals problem could be solved after the frequent cultivation of bioenergy crops in a specific area.

Effects on Biodiversity

Biodiversity is an important indicator to realize environmental stability because it indicates food production and about all kind of ecosystem services. (Qin et al., 2018). Initial land use condition, landscape configuration, and the types of bioenergy crops production profoundly affect biodiversity. Due to direct land-use changes and changes in the production system, biological abundance may affect seriously. This land-use conversion changes the plant kinds and locations that affect depended on biodiversity. If the direct replacement happens for changing the grassland to bioenergy crops that may help to increase the productivity of ecosystem functions. (Correa et al., 2017). Besides, many studies have shown that Miscanthus has a less negative impact on biodiversity comparison with traditional annual crops. Because

perennial crops give more stable habitation for the wildlife. (Rowe et al., 2009; Werling et al., 2014). In addition, energy crops cultivation in the grassland or abandoned land may change the landscape design. If better management may practice in the land that could reduce the risk of biodiversity loss. (Manning et al., 2015).

From the biodiversity perspective, bioenergy crops cultivation has a significant impact on arable land also. At first, it directly affects the soil organisms like on different bacteria and fungus, various decomposers, earthworms, carbides, woodlice, and harvestman. Also, the vegetation of bioenergy crops acts as the primary food source for the different types of primary consumers like rabbits, moose, and even for some insects in the surrounding food webs.

(Makeschin, 1994).

Bioenergy crops on the arable land act as a suitable and safest habitat for any small and micro-organisms. Because of the bioenergy crops cultivation, the farmers need a minimal amount of chemical pesticides (0.2 kg/ha) rather than other traditional agricultural food. For traditional agriculture crops production, the farmer needs to use about 1 kg chemical pesticides in a hectare. (Börjesson, 1996).

Some study has shown that, after the cultivation of salix crops, the production of pollinating insects like bees have increased. That has a positive effect on the production of other plants.

(Björklund et al., 1999). It has estimated that about twelve salix plants may help to an occurrence at least 125 species of vascular plants. (Gustafsson, 1987).

On the other hand, for the transition of wildlife, the short-rotation forest act as a heaven. Only in the summertime, about 25 species of birds make a habitat in the short rotation forest. It happens because of the maximum source of food from insects in the bioenergy cultivation.

Also, about seven species of wild animals have come to take their maximum meal. (Sage &

Robertson, 1994; Paine et al., 1996).

Though, massive cultivation of bioenergy crops has some adverse impact on the environment, it may increase the growth of different pests like fungus, insects, and herbivores. Those pests may spread to the other vegetation and may hamper the ecosystems (Christerssonet al., 1992).

Another big problem with the massive cultivation of bioenergy crops is genetic contamination.

If the bioenergy crops are cultivated on big arable land for an extended period, it may contaminate the genetic species diversity. (Official Report of the Swedish Government, 1992).