Carbon input and balance in soils is regarded as the main criterion of agricultural sustainability. Generally, carbon dynamic depends not only on the carbon input and its decomposition rate, but it is also influenced by various agronomic practices. Therefore, changes in organic carbon stock and humic substances quality were evaluated in two different agricultural management systems (permanent grassland and intensive crop sequences). Haplic Cambisol (Czech-Moravian Highland, locality Vatín, Czech Republic) was sampled twice a year (spring and autumn) in the depth 0-20 cm during the period 2010-2016. Soil was sandy-loam textured, with middle organic carbon content and very low humic substances quality. Results showed that crop management practices directly influenced soil cumulative potential, quality of humic substances, soil reaction and amount of nutrients. Statistically significant differences were found

Gabriela Barančíková

Jiří Jandák

Ladislav Menšík

Lubica Pospíšilová

Magdalena Hábová

Vítězslav Vlček

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Agriculturae Conspectus Scientifi cus . Vol 83 (2018) No 1 (25-30)ORIGINAL SCIENTIFIC PAPERSummaryCarbon input and balance in soils is regarded as the main criterion of agricultural sustainability. Generally, carbon dynamic depends not only on the carbon input and its decomposition rate, but it is also infl uenced by various agronomic practices. Th erefore, changes in organic carbon stock and humic substances quality were evaluated in two diff erent agricultural management systems (permanent grassland and intensive crop sequences). Haplic Cambisol (Czech-Moravian Highland, locality Vatín, Czech Republic) was sampled twice a year (spring and autumn) in the depth 0-20 cm during the period 2010-2016. Soil was sandy-loam textured, with middle organic carbon content and very low humic substances quality. Results showed that crop management practices directly infl uenced soil cumulative potential, quality of humic substances, soil reaction and amount of nutrients. Statistically signifi cant diff erences were found.Key wordscarbon forms, arable soil, permanent grasslandCarbon Dynamic aft er Conversion of Permanent Grassland into Arable Soil Lubica POSPÍŠILOVÁ 1( )Magdalena HÁBOVÁ 1Vítězslav VLČEK 1Jiří JANDÁK 1Ladislav MENŠÍK 2Gabriela BARANČÍKOVÁ 31 Faculty of AgriScience Mendel University in Brno, Department of Agro chemistry, Soil Science, Microbiology and Plant Nutrition, Zemědělská 1, 613 00 Brno, Czech Republic e-mail: lubica.pospisilova@mendelu.cz2 Crop Research Institute, Division of Crop Management Systems, Drnovská 507/73, 161 06 Praha 6 - Ruzyně, Czech Republic3 National Agriculture and Food Centre, SSCRI Bratislava, External working place Prešov, Raymannova 1, 080 01 Prešov, SlovakiaReceived: June ,  . Accepted: September , ACKNOWLEDGEMENTS Financial support from the National Agricultural Agency of the project QJ1210263, QJ1510179, MZE RO0417, OP VaVpl CZ.1.05/4.1.00/04.0135 project Mendel University in Brno, Czech Republic and the Slovak Research and Development Agency (APVV-0243-11 and APVV-14-0087) is highly acknowledged.Agric. conspec. sci. Vol 83 (2018) No 1 Lubica POSPÍŠILOVÁ, Magdalena HÁBOVÁ, Vítězslav VLČEK, Jiří JANDÁK, Ladislav MENŠÍK, Gabriela BARANČÍKOVÁIntroductionSoil carbon, specifi cally in the form of soil organic matter, plays a key role in the functioning of soils to produce a wide range of vital environmental functions. Loss of soil carbon degrades these services, resulting in decreased of crop yields, environmental and market value of soil. Land management can also enhance soil carbon by optimal crop rotation and fallow cover crops, organic matter addition, and optimal fertilization systems tillage systems (Banwart et al., 2015). Soil organic carbon forms could be divided into stable and labile. Stable carbon forms are represented by humic acids (HA), fulvic acids (FA) and humins. Because of relatively long period of time that stable carbon spends with the soil and is thereby withheld from the atmosphere, it is oft en referred to as being sequestered. Carbon sequestration depends on soil capac-ity to store resistant plant residues and protects and accumulates the stable humic substances (HS). Th e degree of resistance of HA and FA is attributed to their chemical composition, especially the absence of labile (hydrolysable) linkages, and to the lack of regu-larly repeating units. Humin is generally considered to be a com-ponent of HS although some of its units may not have undergone the biological transformation (Swift , 1999 and 2001). Labile carbon forms are mainly introduced by dissolved organic carbon (DOC) and by carbon of microbial biomass (Cmic) as quoted Leinweber et al. (1995) and Degens and Sparling (1996). DOC is supposed to be very active in carbon pool and its chemical composition and mo-bility (the smaller and more polar an organic molecule) directly aff ect biological soil properties. Relationship between DOC and soil was studied by Zsolnay (2003) and Pospíšilová et al. (2011). Th ey concluded that DOC content is controlled by its content in soil. Instead of complicated determination of DOC determination of water extractable organic carbon (WEOC) is frequently used as quoted Šestauberová and Novák (2011). Stability or lability of any organic carbon fraction could be due to either chemical compo-sition or protection within the soil aggregates. It is supposed that chemical properties of HS are integrally linked to the soil s´ behav-ior in nutrient cycling and supply, water retention, soil structure and soil biological parameters (Filep and Rekasi, 2011).Many diff erent mathematical models were proposed to charac-terized soil organic carbon stock (Coleman and Jenkinson, 2005; Smith et al., 2005; 2007; De Li Liu et al., 2016). Th ey showed that the amount of soil organic carbon that is attained under agricul-ture largely depends upon the carbon input and its decomposition rate under various agronomic practices. Whether soils are a sink or source of carbon depends on the actual organic carbon stock, agricultural practices over time, soil properties (e.g. clay content, soil depth, content and quality of plant input, organic fertilizer input etc.), and climatic conditions.Th e aim of our research was to evaluate dynamic of stabile and labile carbon forms and humic substances quality in two diff erent agricultural management systems (permanent grassland and intensive crop sequences) during the period 2010-2016.Material and methodsHaplic Cambisol (locality Vatín, Czech-Moravian Upland, 530 m a.s.l.) belongs to the potatoes growing area. Average annual temperature is 6.9 °C. Average annual precipitation 621 mm. Soil was sampled twice a year (spring and autumn) in 0-20 cm depth. Native grassland (Sanguisorba-Festucetum comutatae) was ploughed and intensive crop sequences involved 50 % of cereals, 16.6 % of root crops, and 33.4 % of technical crops. Nutrients were applied at ratios (N-P-K, kg/ha/year): 130–40–80 (winter wheat) and 60–35–80 (spring barley). Soil reaction was determined by potentiometric method in distilled water and in 1M KCl solution (1:2.5). Particle size analysis was determined by pipette method (Zbíral et al., 2010). Total organic carbon content (TOC) was determined by oxidimetric titration method (Nelson and Sommers, 1982). Fractional composition of HS was determined according to Kononova and Beltchikova method (1963) as follows: 5g of air dried soil sample, sieved at mesh size of 1mm and extracted by a mixture (1:1; 0.1M NaOH + 0.1M Na4P2O7) for 24h. Th e sediment was separated by centrifugation at 2800g for 10min, washed with mixture and centrifuge again. Two individual washings were unifi ed with original supernatant. Sum of HS and HA was determined by oxidimetric titration method in aliquot volumes. FA content was calculated as a diff erence between HS and HA. WEOC was determined as follows: 1 g of soil sample was suspended into 100 ml demineralized distilled water and shaking for 30 min. Th en the samples were centrifuged (15 min at 3000 rpm) and fi ltrated through membranes fi lter S-PAK ™ Millipore (0.45 μm). Content of WEOC was determined according to ČSN EN 1484 and ČSN EN 12260 using high temperature (720 °C) catalytic combustion with chemo- luminescent detection of fl ue gases (carbon and oxygen) and spectrometric detection of CO2 in infrared spectral region using analyser Shimadzu TOC-VCSH with auto sampler ASI-5000 (Shimadzu, Kyoto, Japan). Cmic carbon was determined by fumigation-extraction method in fresh soil samples, sieved through 5 mm according to Vance et al. (1987). Statistical analysis, including graphical outputs, was carried out using STATISTICA 12.0 (Stat-Soft  Inc., Tulsa USA, StatSoft  ČR s.r.o., 2014). Statistical data processing Exploratory Data Analysis /EDA/, ANOVA - Tukey test /HSD-test/ a Fisher test /LSD test/, Principal Component Analysis (PCA) for data evaluation was applied (Meloun and Militký, 2011). PCA was used for interpreting the parameters of soil organic matter (TOC, HS, HA, FA etc.) and physico-chemical properties of soil (pH, con-tent of phosphorus and potassium, etc.). Selected measured charac-teristics were used as predictors (factors); they were chosen on the basis of an eigenvalue graph. Variables with impaired assumption of normality were converted using logarithmic transformation. As part of step 1, PCA was carried out with all the variables to com-pute the most important variables. Step 2 involved selecting active and supplementary variables for better interpretation. Th is stepwise analysis signifi cantly improves the outcome of the PCA analysis in case of a smaller number of samples. PCA was used for calculat-ing a component weight for the investigated variables (Meloun and Militký, 2011). Based on correlations and contributions in convinc-ing factors each of the characteristics was subsequently judged for relevance to explain the multidimensional dependencies (correla-tions) in the factorial plane. Statistical signifi cance was assessed at a signifi cance level of P = 0.05.Results and discussion Studied soil was sandy-loam textured, with acid soil reaction, and low cation exchange capacity. Humus content was middle but its quality was very low. Prevalence of FA was determined and HA/FA ratio was less than 1. Humifi cation degree was middle (30-40 Agric. conspec. sci. Vol 83 (2018) No 1Carbon Dynamic after Conversion of Permanent Grassland into Arable Soil%). Statistical evaluation of studied soil parameters is showed in Table 1. Comparison of diff erent carbon forms in arable soil and permanent grassland showed higher content of stable carbon form (TOC, HS, HA, FA) in grassland (Figure 1). Also labile carbon forms (WEOC, Cmic) content was higher in grassland to compare with arable soil (Figure 1). On the other hand, amount of nutri-ents and more favourable soil reaction was reached in arable soil. Permanent grassland was more acid and had lower nutrients con-tent. Our observation also showed that in spite of lower content of HS, HA, and FA in arable soil we reached more favourable HA/FA ratio here soil to compare with grassland. We can say that in spite of lower content of HS their quality is higher than quality of HS in permanent grassland. Similar results were published by Tesařová et al. (2006) and Petrášová et al. (2009). Th ey stressed that decreas-ing of total carbon content is evident mainly the fi rst two-three years aft er ploughing and then the new, and lower equilibrium of total carbon content in arable soil took place. Th is eff ect is gener-ally called priming eff ect. Further the ordination diagram (Figure 2) is showing the results of PCA analysis. Two diff erent categories (permanent grassland and arable soil) are evident. Statistically signifi cant separation into two categories according to balanced TOC, potassium and phosphorus content and the soil pH is evi-dent. Total variability (PC1, PC2 and PC3) of studied parameters is higher than 94 %. On axis PC1 potassium content is in strong positive relationship with phosphorus content (r=0.90). Medium positive relationship (r=0.80–0.85) between soil reaction and po-tassium and phosphorus content was determined. We can also con-clude that on the axis PC1, TOC is in positive relationship with FA (r=0.74) and HA (r=0.68) – see Figure 2. No signifi cant correla-tion on PC2 axis was found. Th e PC2 axis lacks considerable cor-relation; rather, directions are characterised, depending on HA/FA ratio (Figure 2). In conclude it should be stress that diff erences in quantity and quality of soil organic matter are directly infl u-ence by crop sequence and plant species, fertilizing system (min-eral and organic), tillage system and by intensity of agricultural exploitation as well. Because of depending of labile carbon forms onto total organic carbon amount regulation of carbon balance in sustainable agronomical practices is possible due to appropriate agricultural management system.ConclusionLand use and management practices are directly infl uence stabile and labile carbon forms in soil. Very high carbon accu-mulation potential was confi rmed under permanent grassland. Accumulation potential of arable soil is depending on intensity of agriculture and management system with respect to soil type and climatic conditions. Table 1. Statistical evaluation of studied soil parameters in Arable land and Permanent grassland Characteristic Site HSD Test* LSD Test** Arable land Permanent grassland Arable land Permanent grassland TOC Arable land x 0.000177 x 0.000010 Permanent grassland 0.000177 x 0.000010 x HS Arable land x 0.000172 x 0.000000 Permanent grassland 0.000172 x 0.000000 x HA Arable land x 0.004722 x 0.004559 Permanent grassland 0.004722 x 0.004559 x FA Arable land x 0.000218 x 0.000060 Permanent grassland 0.000218 x 0.000060 x HA/FA ratio Arable land x 0.323781 x 0.323656 Permanent grassland 0.323781 x 0.323656 x DH I Arable land x 0.602599 x 0.602452 Permanent grassland 0.602599 x 0.602452 x DH II Arable land x 0.261271 x 0.261137 Permanent grassland 0.261271 x 0.261137 x pH Arable land x 0.000262 x 0.000108 Permanent grassland 0.000262 x 0.000108 x Cwe Arable land x 0.003794 x 0.003638 Permanent grassland 0.003794 x 0.003638 x Cmic Arable land x 0.002175 x 0.002034 Permanent grassland 0.002175 x 0.002034 x K Arable land x 0.000172 x 0.000000 Permanent grassland 0.000172 x 0.000000 x P Arable land x 0.000172 x 0.000001 Permanent grassland 0.000172 x 0.000001 x Ca Arable land x 0.051929 x 0.051790 Permanent grassland 0.051929 x 0.051790 x Mg Arable land x 0.002702 x 0.002546 Permanent grassland 0.002702 x 0.002546 x Note: n = 7; * Tukey test ; ** Fisher test; P = 0,05   Agric. conspec. sci. Vol 83 (2018) No 1 Lubica POSPÍŠILOVÁ, Magdalena HÁBOVÁ, Vítězslav VLČEK, Jiří JANDÁK, Ladislav MENŠÍK, Gabriela BARANČÍKOVÁFigure 1. Content of different carbon forms and degree of humification in Arable land and Permanent grasslandAgric. conspec. sci. Vol 83 (2018) No 1Carbon Dynamic after Conversion of Permanent Grassland into Arable SoilFigure 2. Multivariate statistical PCA of studied soil parameters in Arable land and Permanent grasslandAgric. conspec. sci. Vol 83 (2018) No 1 Lubica POSPÍŠILOVÁ, Magdalena HÁBOVÁ, Vítězslav VLČEK, Jiří JANDÁK, Ladislav MENŠÍK, Gabriela BARANČÍKOVÁ ReferencesBanwart A. S., Noellemeyer E., Milne E. (2015): Th e Global Challenge for Soil Carbon. Science, Management and Policy for Multiple benefi ts SCOPE Series volume 71: 1-10.Coleman K., Jenkinson D.S. (2005): ROTHC-26.3. A model for the turnover of carbon in soil. 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Carbon Dynamic after Conversion of Permanent Grassland into Arable Soil

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