Organic carbon content in grassland soil in Poland

11 The aim of the study is to evaluate the content of organic carbon (C org ) in the soils of Polish grasslands (GL). The 12 Tiurin's method (mineral soils) and the mass loss method (soil of organic origin) were used. It was found that: /i/ 13 the average C org content of mineral soils is 2.44% and of organic soils – 10.42%; /ii/ according to the Polish criteria, 14 about 84% of GL mineral soils are classified as classes with high and very high C org content, and over 15% and 15 1% – in classes with medium and low C org content, respectively; more than 99% of organic soils belong to two 16 classes with the highest C org content and less than 1% to the class with an average content; /iii/ according to the 17 European Soil Bureau, the share of GL mineral soils with a high C org content is slightly over 4%, medium – slightly 18 over 47%, and low and very low – around 50%; for organic soils they are 67%, 29%, and 4%, respectively; /iv/ 19 the reserves of organic carbon in the 0 – 30 cm layer on the entire surface of GL soils amount to 412.7 million tons 20 of C org . There are opportunities to increase the C org stock in meadow soils.


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Grassland soils are characterized by a high content of organic matter (SOM), which provides 27 plants with nutrients, increases soil aggregation and reduces soil erosion, as well as increases cation 28 exchange and water retention capacity [1]. The reserves of organic matter in permanent grassland soils 29 are usually much greater than in cultivated soils. In the Dutch conditions, it was found in this respect 30 that the multiplicity of the SOM level between the mentioned soil types may be from 2 to 5 [2]. The 31 formation of large amounts of organic matter in GL soils is favored by their permanent plant cover, due 32 to the fact that it is characterized by a high ability to accumulate CO2 from the atmosphere (in the process 33 of photosynthesis), which translates into the level of biomass production and the amount of plant 34 residues formed from it returning to the soil, and the turf process (as a result, the topsoil is enriched with 35 organic matter) [3]. Looking from a different point of view, the greater accumulation of organic matter 36 in GL soils as compared to arable land is favored by the fact that they are generally not subject to Possibilities of using this potential are created, in particular, by activities aimed at increasing yields from 48 GLs through the use of fertilizers and irrigation, improving the species composition of sward (using 49 high-yield and legume mixtures), and activities involving the rehabilitation of degraded meadows and 50 pastures, as well as minimizing the negative effects of grazing [12][13][14]. 51 Permanent GLs in Poland cover over 3.1 million ha, i.e. 21.3% of the agricultural land area [15]. 52 Their soils constitute a very large reservoir of organic carbon, and there are significant opportunities to 53 increase it through GL renovation, due to the fact that, as it is estimated, over 50% of them are degraded 54 (which results in low yields) [16]. In the near future, an important impulse to increase organic carbon in 55 grassland soils may be the 'Farm to Fork' strategy adopted by the European Commission as part of the 56 European Green Deal which, among others, supports and recommends the development of carbon 57 dioxide-absorbing crops as a new business model for farmers [17]. 58 The problem of storing and shaping organic carbon in the soils of grasslands in Poland is not 59 sufficiently recognized in quantitative terms. Given the importance of grassland in mitigating climate 60 change and the practical challenges it poses it needs further investigation. This work fits within these 61 needs. Its purpose is to determine the content and abundance of organic carbon in grassland soils in 62 Poland. 63

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The research on the content of organic matter and organic carbon in the soils of GLs in Poland 67 was carried out as part of the soil and water monitoring system conducted by the National Chemical-68 Agricultural Station (KSChR) and regional chemical and agricultural stations, in cooperation with the 69 Institute of Technology and Life Sciences (ITP) [18,19]. Soil samples for research were taken from a 70 depth of 30 cm from 860 permanent monitoring points of grassland soils throughout Poland, of which 71 703 were located on mineral soils and 157 on organic soilstable 1. Soil material for laboratory analyzes 72 was obtained mainly in 2008 and a small part in the next few years. OMthe content of organic matter in the soil, %. 113

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The obtained results were also statistically processed. In this regard: 115  descriptive statistics of the sets of results for determination of organic carbon content in soil 116 samples were performed, calculating their arithmetic means and coefficients of variation -CV; 117  an analysis of the r-Pearson correlation between the average Corg content in the soil and the cattle 118 density in the voivodships was carried out; 119  the significance of differences between the average Corg contents in various categories of mineral 120 soils was determined using the Kruskal-Wallis test.   the European Database on Soils, only in slightly more than 4% of mineral soils of GL in Poland the Corg 167 content is high, while in more than 47% it is average, and in approx. 50% very low or low. The highest Corg content in GL mineral soils was recorded in Podlaskie Voivodeship, which is 201 the most developed in Poland in terms of milk production. It was found that there are directly 202 proportional positive relationships between the Corg state of soil accumulation, at the NUTS 2 level, and 203 the number of cows and cattle per 100 ha of agricultural land - Fig. 1 and 2, and that they are statistically 204 significant - Table 11. Correlation relationships between the factors mentioned correspond to the 205 findings of Hewins et al. [30], which shows that on a regional scale, long-term grazing of livestock of 206 moderate intensity may increase the Corg content in the 0-30 layer of mineral soil.

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Among the distinguished categories of GL mineral soils, the Corg content was higher in very 215 light soils (loose, slightly loamy sands) and light (loamy sands) than in medium soils (sandy and light 216 loams), as well as heavy soils (medium and heavy loams, loams)table 4. However, the differences in 217 organic carbon content between particular types of soilas shown by the results of the Kruskal-Wallis 218 testwere not statistically significanttable 12. It should also be noted that the obtained data on the 219 level of Corg in various soil categories do not coincide with the existing knowledge, that grassland soils 220 rich in clay and dusty fractions generally have a higher SOM content than sandy soils [31, 32], or that 221 fine-grained soils usually have a greater ability to retain SOC, and therefore contain more SOC than 222 coarse-grained soils [33]. 223 224 [   serious deficiencies of available forms of phosphorus (the share of GL soils with very low and 265 low P abundance is over 59%; the classes with the highest abundance, i.e. 'high' and 'very 266 high', include slightly more than 30% of soils); 267  very large deficiencies of assimilable forms of potassium (about 78% of GL soils are 'low' or 268 'very low' rich in K, including 97% of organic soils of GL; soils in the 'high' and 'very high' 269 fertility classes are only 13.2%). According to Nyc and Pokładek [45], these needs concern 2,186.9 thous. ha GL.                                                      Source: own study based on the KSChR results.     Notes: complex Bincludes slightly and moderately rotten soils on deep, poorly and moderately decomposed peats; BCincludes medium and slightly rotten soils on slightly shallower, moderately decomposed peat; Cincludes shallow and medium-deep peat-muck soils as well as mineral-muck, muck and black earth soils. Figure 1 The The relationship between the cattle stock per 100 ha of arable land and the content of organic carbon in mineral soils of grasslands; explanations as for g. 1. Source: own study

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