| Abstract | Tijekom posljednjih nekoliko desetljeća, rastom globalne populacije raste i životni standard, a time i kumulativna razina emisije stakleničkih plinova. Upravo sve veće emisije stakleničkih plinova uzrokovane ljudskim aktivnostima, kao posljedica njihovog ispuštanja iz nekih od sektora, kao što su energetika, industrija i poljoprivreda, dovode do njihove akumulacije u atmosferi, što rezultira promjenama u atmosferi, kopnu i oceanima. Od mnogih stakleničkih plinova, ugljikov dioksid (CO2) predstavlja jedan od najvažnijih spojeva koji utječu na procese globalnog zagrijavanja te se smatra pokretačem globalnih klimatskih promjena. Kruženje ugljika u prirodi nezamislivo je bez tla kao bitne sastavnice okoliša, što potvrđuje da su tlo i klima oduvijek bili usko povezani. Stoga je bitno naglasiti kako je jedan od glavnih čimbenika u borbi protiv klimatskih promjena upravo tlo. S dvostruko većim sadržajem ugljika od atmosfere, ono značajno pridonosi bilanci ugljika. Upravo iz tog razloga, važno je pravilno upravljati tlom, usporavajući tempo klimatskih promjena kroz prakse poput smanjene obrade, pravilne gnojidbe te optimiziranog plodoreda u poljoprivredi. Cilj ove disertacije bio je terenskim mjerenjima utvrditi ovisnost C-CO2 emisije tla o tipu gnojidbe (I.-kontrola; II.- N250 + P + K + 40 t/ha organskog krutog stajskog miješanog gnoja; III.-N300 + P + K; IV.-crni ugar - obrada bez sjetve) u tri vegetacijske godine (2016., 2017. i 2018.) za tri vrste usjeva (ozima pšenica, kukuruz i soja), te provesti bilanciranje odnosno utvrditi prilive i odlive ugljika iz tla na svim istraživanim tretmanima i utvrditi ovisnost o emisiji C-CO2 iz tla. U vegetaciji ozime pšenice, prosječna godišnja emisija C-CO2 iz tla iznosila je 17,96 kg ha-1 dan-1, u vegetaciji kukuruza 11,19 kg ha-1 dan-1, te u vegetaciji soje 13,17 kg ha-1 dan-1. Iz dobivenih rezultata, može se vidjeti kako se prosječna godišnja emisija C-CO2 smanjivala redom ozima pšenica > soja > kukuruz. U sve tri godine istraživanja, prosječne mjesečne emisije C-CO2 iz tla bile su znatno više u razdoblju kada je vegetacijski pokrov bio prisutan u odnosu na razdoblje bez njegove prisutnosti. Također, najniže prosječne godišnje vrijednosti emisije C-CO2 zabilježene su na tretmanu s crnim ugarom tijekom sve tri godine istraživanja. Primijenjena mineralna gnojidba pokazala je najveći prosječni kumulativni godišnji gubitak emisijom u atmosferu (19,6 t C ha-1), dok je tretman s primijenjenom organskom gnojidbom pokazao najveću srednju vrijednost sadržaja ugljika u tlu (64,7 t C ha-1). S obzirom na dobivene rezultate, bitno je još jednom naglasiti važnost usvajanja održivih poljoprivrednih praksi kojima će se podići razine ugljika u tlu te smanjiti gubitci kroz emisije CO2 u atmosferu. |
| Abstract (english) | In recent, as the world's population has grown, the standard of living has risen and with it the cumulative level of greenhouse gas emissions. It is precisely the increasing emissions of greenhouse gasses caused by human activities that, through their release from the energy, industrial and agricultural sectors, lead to their accumulation in the atmosphere and to climate warming, resulting in changes in the atmosphere, on land and in the oceans. Among the numerous greenhouse gasses, carbon dioxide (CO2) is one of the most important compounds affecting global warming and is considered to be the driving force of global climate change. The carbon cycle in nature is inconceivable without soil as an essential component of the environment, confirming that soil and climate have always been closely linked. It is therefore important to emphasize that one of the most important factors in the fight against climate change is precisely the soil respectively human activity on the soil. With a carbon content multiple as high as in the atmosphere, it contributes significantly to the global carbon balance. In terrestrial ecosystems, soil respiration is therefore the key proces linking the below-above-ground carbon cycle. As the second largest global component of carbon flux in terrestrial ecosystems, soil respiration contributes significantly to the greenhouse effect. This is precisely why it is important to manage the soil properly and slow down the pace of climate change through practices such as reduced tillage, proper fertilization and optimized crop rotations in agriculture. In addition to the mentioned practices, soil temperature, soil water content, soil C:N, amount of organic matter, microorganisms, presence and type of vegetation, soil pH and other factors also contribute to soil CO2 emissions. It is also important to emphasize that the process of CO2 formation in the soil is directly related to climatic factors such as air temperature and relative humidity, which affect soil temperature and relative soil moisture and thus carbon emission and sequestration.
Soil fertilization is considered as one of the most important agricultural measures for increasing productivity and yield. The application of fertilizers is of great importance for CO2 emissions from the soil, which can vary by changing the amount and chemical composition of the fertilizer. High nitrogen concentrations in the soil, especially after mineral N fertilization, can stimulate microbial decomposition of soil organic matter, so that any transformation of organic matter results in emissions to the environment. In addition, greenhouse gas emissions caused by the application of fertilizers represent one of the more important sources of total agricultural emissions.
The motivation for the research in this doctoral thesis lies in the scientific interest to determine the impact of the carbon dioxide amount that is emitted into the atmosphere as a greenhouse gas from the soil, as a result of the agricultural practices, especially through different forms of fertilization. These findings will be the basis for planning sustainable soil management in the study region, and also in other areas with the same or similar pedological and climatic characteristics. Precisely for this reason, the research conducted in this dissertation is based on the hypothesis that: a) the C-CO2 emission from agricultural soil will depend on the type of fertilization, b) the C-CO2 emission from agricultural soil will depend on the type of crop, c) the C-CO2 emission from agricultural soil will depend on the carbon content of the soil. To prove the established hypotheses, the following objectives were set for this study: a) using field measurements, determine the dependence of soil C-CO2 emissions on the fertilization type in three years with three different arable crops, b) carry out a balance, i.e. determine the inflows and outflows of carbon from the soil for all treatments studied and determine the dependence on the C-CO2 emissions from the soil.
The research was conducted on the arable land on the Jelenščak plot, in the village Potok near Popovača, and included 10 different treatments, four of which were selected for the purposes of this dissertation. Four different treatments included: I.- control – no fertilization; II.- N250 + P + K + 40 t/ha organic solid mixed manure; III.- N300 + P + K; IV.- black fallow – cultivation without sowing. The cover crop at the experimental field in the investigated 2016 was winter wheat (Triticum aestivum L.), in 2017 corn (Zea mays L.) and in 2018 soybean (Glycine max L.). The measurement of the carbon dioxide concentration on the soil surface was carried out based on the static chamber method, and measured with a portable infrared detector of carbon dioxide GasAlerMicro5 IR (2011). Temperature (°C), electrical conductivity (dS/m) and soil moisture content (%) were measured using the IMKO HD2 instrument (Trime – Pico64 probe, 2011) at a depth of 10 cm in the vicinity of each chamber, during each CO2 concentration measurement. Air temperature (°C), relative humidity (%) and air pressure (hPa) (Testo 610, 2011 and Testo 511, 2011) were measured at each arrival and departure from the experimental field. During the research period, a total of 24 measurements of concentration and calculation of C-CO2 emissions from the soil and agroecological factors were done.
The results demonstrate a descending pattern in average annual C-CO2 emissions: winter wheat > soybean > corn. The C-CO2 emission during corn cultivation was 37,7 % lower than the emission observed during winter wheat growth, while during soybean cultivation, the emissions were 26,7 % lower compared to winter wheat vegetation and 15,0 % lower compared to corn vegetation. These results suggest variations in carbon dioxide emissions across different crops, indicating potential differences in soil carbon dynamics influenced by crop characteristics including root structure, residue composition, and overall biomass. Likewise, in all three research years, C-CO2 emissions from the soil were higher in the period when the vegetation cover was present compared to the period without its presence. The average annual values of C-CO2 emissions from the soil according to fertilization treatments were the lowest on the treatment with black fallow during all three years, and the highest on the treatments with applied organic (2016) or mineral fertilization (2017 and 2018). These results indicate that the reduction in C-CO2 emissions in the black fallow treatment can be attributed to a lack of organic matter input due to the absence of crops, and mineral and organic fertilization, which implies a reduced availability of organic materials for decomposition, consequently leading to lower CO2 emissions. During winter wheat vegetation, C-CO2 emissions varied between 1,91 kg ha-1 day-1 (black fallow) and 54,33 kg ha-1 day-1 (mineral fertilization). For corn, emissions ranged from 0,76 kg ha-1 day-1 (organic fertilization) to 38,21 kg ha-1 day-1 (mineral fertilization). In soybean cultivation, emissions varied between 2,26 kg ha-1 day-1 (black fallow) and 37,89 kg ha-1 day-1 (mineral fertilization). The applied mineral fertilization showed the highest cumulative annual loss by emission to the atmosphere (19,6 t C ha-1), followed by the organic fertilization treatment (18,4 t C ha-1), the control treatment (14,3 t C ha-1) and the black fallow treatment (9,4 t C ha-1). The organic fertilization had the highest mean soil carbon content (64,7 t C ha-1), and the highest percentage reduction in total soil carbon content was recorded in the control treatment (55,6 %). Based on the obtained results, it was determined that the emission of C-CO2 depends on a various of interdependent factors within the agricultural system. On the studied soil of limited fertility, it was evident that every aspect within the agroecosystem, including agrotechnical practices and crop selection, is important and crucial in mitigating climate change, while simultaneously preserving and achieving good agricultural production. |
