Soil Carbon Sequestration Under Bioenergy Crops in Poland

Our dependence on soil, and our curiosity about it, is leading to the investigation of changes within soil processes. Furthermore, the diversity and dynamics of soil are enabling new discoveries and insights, which help us to understand the variations in soil processes. Consequently, this permits us to take the necessary measures for soil protection, thus promoting soil health. This book aims to provide an up-to-date account of the current state of knowledge in recent practices and assessments in soil science. Moreover, it presents a comprehensive evaluation of the effect of residue/waste application on soil properties and, further, on the mechanism of plant adaptation and plant growth. Interesting examples of simulation using various models dealing with carbon sequestration, ecosystem respiration, and soil landscape, etc. are demonstrated. The book also includes chapters on the analysis of areal data and geostatistics using different assessment methods. More recent developments in analytical techniques used to obtain answers to the various physical mechanisms, chemical, and biological processes in soil are also present.


Introduction
Agriculture practices have an important role to play in mitigating climate change due to atmospheric enrichment of carbon dioxide, and other greenhouse gases (GHG). Land management can strongly influence soil carbon stocks and careful management can be used to sequestered soil carbon. It is important to propose contemporary management practises to farming, like the conversion from a tillage system to no-tillage, incorporation of cover crops and forages in the crop rotation, use of crop residues and biosolids e.g. mulch, implementation of biocrops, as well as integrated nutrient management which including compost/manures as well as the precision use of fertilizers and integrated pest management. Sustainable management in agriculture should reduce and avoid the introduction of carbon dioxide (CO 2 ) to the atmosphere, which is one of three most prevalent GHGs directly emitted by human activity. CO 2 is the most important anthropogenic GHG, and according to IPCC Fourth Assessment Report (2007), anthropogenic CO 2 emissions grew by about 80% between 1970 and 2004. Carbon sequestration is a process through which agricultural and forestry practices remove carbon dioxide (CO 2 ) from the atmosphere into a form that does not affect atmospheric chemistry (Lal, 2004a). A natural way to trap atmospheric CO 2 is by photosynthesis, where carbon dioxide is absorbed by plants and turned into carbon compounds, stored or fixed C as soil organic carbon (SOC). The SOC pool consist litter, humads and humus, which it is comprised of mixtures of plant and animal residues at various stages of decomposition along with microbial by-products (Lal, 2004a). Agriculture is responsible for 13.5% of global anthropogenic GHG emissions (IPCC, 2007), but if sustainable land management practices are implemented, agricultural soils could become a carbon sink (Dumanski et al., 1998). There are five principal global carbon pools. The oceanic pool (38 Gt) is the largest, followed by the geologic (5 Gt), pedologic (2.5 Gt), biotic (0.56 Gt), and the atmospheric pool (0.76 Gt). The soils beneath the oceans are the most important reservoir of carbon in the terrestrial biosphere and contain three times the amount as compared with those that are found in vegetation (Lal, 2004b;SEC, 2009). Soils contain more than twice the carbon that can be found in the atmosphere and the loss of carbon from soils can have a significant effect on atmospheric CO 2 concentrations, which can influence the climate (Smith, 2008). Many studies have examined the sequestration potential in agriculture and forestry in Europe (Smith et al., 1997;Smith et al., 2000;Vleeshouwers & Verhagen, 2002;Freibauer et al., 2004; of 0.5-10% with an average of 2.2%. According to the division used in Polish soil with low humus content (<1%) account for approximately 6% of agricultural land, the average (1.1-2.0%), approximately 50% of the area, but about the content > 2% of approximately 33%. The global balance of organic matter in Polish soils is negative in all regions (-0.06 to -1.05 t C/ha/y), with the average for the country of -0.47 t C/ ha/y. This means that in large areas of Poland we note the CO 2 emissions from soil to the atmosphere (Terelak et al., 2001;Stuczynski et al., 2007). In the years 2000-2004, a preliminary analysis of soil humus content trends were carried out under repeated testing of standard profiles. Studies have shown a significant decline in humus, mainly in soils initially rich in organic matter. A decline in soil organic matter is associated with the change of soil water relations, i.e. more intensive use and drainage. In contrast, a large part of the light soils of the last 30 years recorded an increase of humus content associated with an increased level of fertilization and increase in quantity of crop residues (Stuczynski et al., 2007). Based on measurements taken in the years 1968-1983 and in 2003, the changes in soil organic matter and humus loss risk were able to be calculated. The results presented in figure 1 show both accumulation and humus loss in soil as well as soil organic matter balance. The highest losses of soil organic matter were calculated for the Kujawsko-pomorskie voivodeship, whilst the lowest was in the Malopolskie voivodeship. Voivodeships of the North Western part of the country have the lowest soil organic balance, and this indicates a greater share of soils with a higher risk of loss of function due to mineralisation of soil humus.

The soils organic matter balance based on coefficients
The amount of organic matter in soils is a key indicator for the quality, and is significant for their physicochemical properties such as sorption. Maintaining high humus content in soil is important because of its impact on soil carbon sequestration. Increasingly popular intensive use of soils, combined with a simplified crop rotation, increased predominance of cereal plants with reduced amounts of livestock, leads to a reduction in the amount of organic residues entering the soil, which in turn leads to reduced carbon sequestration in soil. The basic principle of good farm management is to maintain a positive, or at least a sustainable balance of soil organic matter. This balance can be obtained by the selection of species of cultivation plants, their participation in the crop structure, and the quantity of manure and organic. The various species of crops leave different amounts of crop residue. The soil carbon in cropland can be increased by planting more forages, and increasing residue inputs from plants with high biomass potential. Approximately, it can be concluded that the weight of cereal crop residues is about 3-fold greater than the root, and legumes with grasses, by up to 6-fold. In addition, a different duration and degree of shading the soil surface and the number of tillage performed and care, which affects the mineralisation of humus. The cultivated plants can be separated in three groups depending of the impact on the balance of humus in the soil. The first group includes plants with a potential in enriching the soil with organic matter. Among them are primarily long-term forage legumes and their mixtures with grasses and grasses grown in the field as well as crops grown for energy sources like tall grasses, fast growing trees. In addition, legumes and intercrops ploughed as green fertilizers have little positive effect on the balance of humus. The reproduction rate of soil for this group of plants ranges from 0.21 to 2.10, depending on the type of soil they are grown on (Fotyma & Mercik, 1992).  Stuczynski et al., (2007) The second group includes plants with a potential in degrading the soil organic matter. This group includes mainly root crops, root vegetables and corn. The characteristics for this group of crops is very little crop residue, seeded in wide rows, intercrops, heavy maintenance, and the short canopy (cover spacing) increases the distribution of humus resulting in increased erosion. The soil degradation rate for this group of plants ranges from -0.12 to -1.54, and is dependent on the type of soil they are grown on (Fotyma & Mercik, 1992). The mineralisation for these types of plants per year is about 1.0-1.5 t/ha of humus. To compensate for this loss about 15-16 t/ha manure should be used. The third group include plants with a small negative or neutral impact on soil organic matter. This group of plants includes cereals and oilseeds. Cereals previously were treated as plants degrading the soil organic matter, but changes in agricultural techniques (density of straw, shortening of straw), and combine harvester collection, leaves a lot of crop residue that significantly reduces their negative impact on the balance of soil organic matter. It should be emphasized that the quality of cereal crop residues is worse due to the unfavourable ratio of carbon to nitrogen. The soil degradation rate for this group of plants ranging from -0.49 to -0.56, is dependent on the type of soil they are grown on (Fotyma & Mercik, 1992). The coefficients values determine the amount of soil organic matter t/ha can enriched or depleted by following a one-year cultivation of the plants or through the application of 1t/ha dry matter of different natural and organic fertilizers. Using these coefficients can be simplified way to determine the soil organic matter balance for a farm, region or country. A positive result indicates a normal economy and organic matter, thus ensuring the long-term stabilisation of humus content at an optimum level. If the balance is negative then changes are necessary. This can be achieved by changing the crop structure (introduction of plants with positive coefficient), or increasing the dosage of organic fertilizers (ploughed straw) or intercrops cultivation for ploughing. Throughout the calculations the following formula was used (see Equation 1): The numerator is the sum of the ratio (the share of particular groups or species of plants in the crop structure multiplied by the coefficients for these species), while the denominator is the percentage of a sown area (where taking into account all the sown land as 100%). Based on those coefficients following the agricultural use of arable land, allows us to calculate the decreases in the soil organic matter amount by 0.39 to 0.66 t/ha for particular voivodeships and approximately 0.53 tonnes per one ha per year in Poland (Kus et al., 2006). Figure 2 presents carto-diagram which shows spatial differentiation, presented by standard deviation methods. The best situation of soil organic matter was calculated for the voivodeships of Warminskomazurskie, Podlaskie followed by the Malopolskie, and their positive situation is associated with a high share of legumes or their mixtures with grasses. An adverse situation appears in the Dolnoslaskie and Opolskie voivodeships, where there is a large share of root crops and maize. To offset this loss, approximately six tons of manure should be applied on every hectare of arable land used. The calculations (Kus et al., 2006) show that the national average production of natural fertilizers (manure) was approximately 7.3 t/ha of sowing area (Fig. 3). The highest amount of manure was produced in the Podlaskie voivodeship due to high livestock and low sowing area. This led to a significant surplus of soil organic matter in the Podlaskie voivodeship. The lowest production of manure was in the Dolnosląskie and Zachodniopomorskie voivodeships where the sowing area is high and livestock low.
In some voivodeships with a negative value of SOM, a balance can be best achieved through ploughing the straw. Particularly large quantities of straw can be ploughed in four voivodeships, (0.9 -1.0 t/ha in Opolskie and Lubuskie, about 1.2 t/ha in Zachodniopomorskie and to 1.9 t/ha Dolnoslaskie (Fig. 4). However, in some voivodeships www.intechopen.com such as Lubelskie, only 0.2 tons of the straw per 1 ha of arable land can be ploughed. In total, across the country three million tonnes of straw, which is less than 12% of the collected straw, could be allocated for ploughing.

Assessment of C organic balances
As indicators for determining a positive, neutral or negative balance of carbon in the soil the scale developed by Korschens et al., (2004) can be used -presented in the table 1. The presented scale has a range between below -200 kg/ha/y and values above 300 kg/ha/y. Comparing the results with this scale allows judging the impact on soil functions and potential yield performance of plants. It is important to emphasize that the carbon balance of more than 300 increases high emissions of nitrogen. Therefore, soil carbon sequestration cannot be considered in isolation from the nitrogen emissions.

The potential land use change for sequestering carbon in soils
Land use change significantly affects soil carbon stock (Guo & Gifford, 2002). Most longterm research shows significant changes in SOC (Smith, 2008). Land use change can play a positive or negative role in mitigating global warming by sequestering carbon from the atmosphere into vegetation and soils. Many land use activities generate carbon sequestration and thus counteract the impact of emissions made in a different place. There are two components of estimated emissions from land use change: decomposition of vegetation and mineralisation/oxidation of humus or SOC (Lal, 2004b). The conversion of arable land to woodland may result in a substantial increase in soil carbon sequestration from 0.3 to 0.6 t C/ha/y. The conversion of arable land to grassland may result in a substantial increase in soil C sequestration from 1.2 to 1.7 t C/ha/y. The potential carbon sequestration rate in the conversion of woodland to arable land was -0.6 t C/ha/y, while the conversion of grassland to arable land was at a rate of between -1.0 and -1.7 t C/ha/y (Freibauer et al., 2004). In addition, Guo & Gifford (2002) in a long-term experiment had shown that a conversion of forestland or grassland to arable land caused a significant loss of SOC, whereas a conversion of forestry to grassland did not result in a loss for all cases. The largest potential decrease of SOC loss is in land use change on highly organic soil (Gronlund et al., 2008). Drainage and cultivation of peat soils stimulates soil organic matter (SOM) mineralisation, which substantially increases CO 2 emissions from soils. Because of this, the Directive 2009/28/EC prohibits the use of land with high carbon stock (i.e. wetlands, continuously forested areas, and peat land) for the production of biofuels.

Potential of management change for sequestering carbon in soils
Correct agricultural practices of the soil can have a significant influence for carbon sequestration. A change in conventional cultivation practises has an important role in improving the soil's structure. Implementing modern practises like reduced tillage, no tillage or conservation tillage can significantly improve the soil's organic matter. Conventional tillage is defined as the mechanical manipulation (ploughing, disking and harrowing) of the top soil that leaves no more than 15% of the ground cover with crop residues. Such tillaging tends to disrupt the soil structure, accelerating the decomposition of soil organic matter, and making the bared topsoil vulnerable to erosion by rain and wind (Hillel & Rosenzweig, 2009). The alternative for conventional tillage is conservation tillage. The European Conservation Agriculture Federation (ECAF) defines conservation tillage as soil management practices, which minimise the disruption of the soil's structure, composition and natural biodiversity, thereby also minimising erosion and degradation, and water contamination (ECAF, 2002). By avoiding deep ploughing, this can increase the sequestration rate by 1.4 to 4.1 t C/ha/y. There is a growing interest in the impact of conservation tillage practices on carbon sequestration in recent years. According to Holland (2004), agriculture can act both as a sink and a source of CO2 emission and the use of conservation practices by agriculture could decrease this emission. The coverage of the soil surface with straw and cover crops, increases biomass productivity and turns the soil into a tremendous carbon sink. Reducing the intensity of soil cultivation lowers energy consumption and the emission of carbon dioxide, while carbon sequestration is raised through the increase of soil organic matter (Holland, 2002). On the basis of long-term experiments, West & Post (2002) concluded that conversion of conventional tillage to no-till sequesters an average of 0.57±0.14 t C/ha/y. Long-term field experiments are the most reliable source information about GHG emissions from different agricultural systems. However, they are difficult to manage and limited by time and costs (Li et al., 2009). Reduced tillage, enhanced crop residue incorporation, and farmyard manure application each increased soil C-sequestration, increased N2O emissions, and had little effect on CH4 uptake. Over 20 years, increases in N2O emissions, which were converted into CO2equivalent emissions with 100-year global warming potential multipliers, offset 75-310% of the carbon sequestered, depending on the scenario (Li et al., 2005). Simulation models provide an alternative method of assessment of agricultural practices effects (Farge et al., 2007). Many models have been developed to describe the responses of crop growth, soil water dynamics and soil biogeochemistry such as Roth C (Groenigen et al., 2010) for organic carbon turnover, CENTURY (Grant et al., 2004) or DNDC (Li et al., 1992;Giltrap et al., 2010) for carbon and nitrogen cycles.

Potential of cultivation energy plants for sequestering carbon in soils
The soil carbon in croplands can be increased by planting more forages, and increasing residue inputs from plants with a high biomass potential. Hopes for increased soil carbon sequestration are associated with an increase in large-scale energetic crops cultivation. Energy crops are characterised by rapid growth and large amount of biomass produced and consequently a very large amount of crop residue left at the field. Annually about 30% of the senescent leaves and post harvest remnants are entering the soil . One factor that is highly important for the amount of carbon sequestration in soil is that these perennial plants are grown for about 20 years on one field. The cultivation of energy crops is associated with greenhouse gas emissions (burning fuel, the production of fertilizers, crop protection). The assumption is that carbon sequestration of around 0.25 t C/ha/y resulting from energetic crops cultivation, allows biomass combustion to be neutral in terms of greenhouse gas emissions (Volk et al., 2004). Nevertheless, different authors found that the carbon sequestration rates for these cultivars are different. Bradley and King (2004), determined the carbon sequestration in forests and willows cultivations at 0.15-0.22 t C/ha/y, whereas in Miscanthus cultivation it was at 0.13-0.20 t C/ha/y. According to Matthews and Grogan (2001), carbon sequestration in the surface layer of the soil (0-23 cm) was at 0.31 for forests, and 0.41 for the cultivation of willow, whereas for Miscanthus it was measured at 0.93 t C/ha/y. Freibauer et al., (2004) and Smith (2004), determined the carbon sequestration in cultivations of energy crops at appropriately 0.60 and 0.62 t C/ha/y. Unfortunately for the carbon sequestration the liquidation of biocrops plantations causes large losses of accumulated carbon. This topic is not yet completely understood and requires further work from researchers.

Materials and methods
As mentioned before Poland has a temperate climate on the Western side of the Vistula River with larger influence of maritime climate than on the Eastern side of the river that has a larger influence of continental climate. For research on soil carbon sequestration dependant on the climate, we have divided Poland along the Vistula River into two regions of climatic influence. We have selected randomly ten experimental positions with available climate data from the MARS Database elaborated by the Joint Research Centre European Commission -5 grids cells (

Results and discussion
The results have shown that the significant difference in yield of Miscanthus grown under two different climate influences, as well as organic matter input, while soil organic matter did not denote a statistically significant difference. In comparing the case of willow, the yield was not significantly different, but the input of organic matter and soil organic matter was significantly different. This might be explained as the temperature had an impact in the case of Miscanthus but it did not influence willow plants. The opposite situation was found in the effect of precipitation. Borzęcka-Walker et al., (2008), did not find any significant differences between the yields of willow clones. The yield of willow grown in two different localisations, ranged from 11.1 -13.7 t/ha/y. There were lower simulated yields for willow cultivations (13.8-18.1 t/ha/y) located on very good soils of Eastern Europe (Fischer et al., 2005). It can be assumed that the limited water influenced the experimental yield of willow. The dry matter yield of Miscanthus genotypes was significantly different within an average of 10.2 -20.7 t/ha/y at both localisations. The yield for the first year of the experiment was low; this could be because it was the second year of cultivation when the plants are still not mature enough to obtain an economic yield (Clifton-Brown & Lewandowski 2000). In the second year of the experiment, the yield witnessed a high increase. In the third year of experiment this was characterised with very bad weather conditions, including a late spring ground-frost and long summer draught. The yields were approaching the presupposed simulated yields for Miscanthus cultivations (17.7-21.8 t/ha/y) located on very good soils of Eastern Europe (Fischer et al., 2005). It can be assumed with a high probability that the limited water in 2005 did not influence the experimental Miscanthus yield, but there was an influence from weather condition in 2006 (Borzecka-Walker et al., 2008).

Miscanthus
Willow maritime continental Maritime continental yield t C/ha/y 4.8 5.1 4.8 5.0 organic matter input t C/ha/y 5.4 6.1 2.9 3.5 soil organic carbon t C/ha/y 1.5 1.7 0.71 0.85 The aboveground biomass has a high influence on the amount of carbon sequestration, which enters the soil usually in the form of senescent leaf mass and postharvest remnants. Kahle (2001) measured in Germany that about 3.0-7.5 t/ha/y aboveground biomass full to soil. Matthews and Grogan (2001) in Great Britain estimated the inflow of the organic matter at a level of 7.5 t/ha/y, while for Poland it was calculated at from 2.63 to 6.58 t/ha/y (Borzecka-Walker et al., 2008). The organic matter input table 2 shows a greater potential for carbon mitigation for Miscanthus than for willow. Despite the very different movement of C into the soil plantations of willow and Miscanthus, most of this element accumulates in the litter. This is labile to C fraction, which in total will be mineralised and released as CO 2 in a short time after the restoration of conventional land use. Moderately stable fractions of carbon in the form of living organisms (humads) is the second largest fraction of sequestrated carbon. In almost all cases it will be transformed into humus after a change of use in the plantation.  (2004), who have determined the carbon sequestration in forests and willows cultivations at 0.15-0.22 t C/ha/y, whereas in Miscanthus cultivations they were at 0.13-0.20 t C/ha/y. According to , carbon sequestration in the surface layer of the soil (0-23 cm) was at 0.31 for forests, and 0.41 for the cultivation of willow, whereas for Miscanthus it was measured at 0.93 t C/ha/y. The net soil carbon sequestration in Miscanthus crops was around 0.38-0.95 t C/ha/y and 0.22-0.39 t C/ha/y for coppice willow (Borzecka-Walker et al., 2008). Freibauer et al., (2004) and Smith (2004) have determined the carbon sequestration in cultivations of energy crops appropriately at 0.60 and 0.62 t C/ha/y. Much of the carbon mitigation potential associated with the use of SRC willow and Miscanthus as bioenergy crops arises from their indefinite capacities as 'carbon neutral' alternatives to fossil fuel combustion . The assumption is that carbon sequestration of around 0.25 t C/ha/y resulting from energy crops cultivation makes biomass combustion neutral in terms of greenhouse gas emissions (Volk et al., 2004). The new cultivations will result in changes in fossil-fuel use, agricultural inputs, and carbon emissions with fossil fuels and other inputs. Management practices that alter crop yields and land productivity can affect the amount of land use crop production with further significant implications for both emissions and sequestration potential (West & Marlnd, 2003;Schneider & Mccarl, 2003

Conclusion
Agriculture practices have an important role to play in mitigating climate change due to atmospheric enrichment of CO 2 and other greenhouse gases. To improve the negative balance of soil carbon sequestration in Poland, corrective action should be taken. Land management can strongly influence soil carbon stocks and careful management can be used to increase soil carbon sequestration. It is important to propose contemporary management practises to farming like the conversion from tillage to no tillage systems, incorporation of cover crops, forages in crop rotation, as well as a liberal use of crop residues and biosolids like mulch. Special care should be taken of integrated nutrient management including compost/manures and precision use of fertilizers and integrated pest management. A very important role can be played by the implementation of biocrops which are characterised with very high potential of carbon sequestration and much lower GHG emission during the cultivation.
When considering carbon sequestration it should be mandatory to combine these analyses with nitrogen (N) as carbon and nitrogen move through terrestrial ecosystems coupled with biogeochemical cycles, and increasing C stocks in soils and vegetation which have an impact on the N cycle.

Acknowledgment
The work was done based on the results obtained within the research projects N N315 759240 and N N313 436839, funded by the Ministry of Science and Higher Education.