Effect of grazing in Norwegian outfields related to the quantity and quality of soil organic carbon and other soil properties

Abstract

Utilization of the outfield for grazing have long traditions in Norway. Not only as a pasture, but also mowed to provide food for the winter (Rekdal & Angeloff, 2021). From 1949 to 1999, grazing in Norway changed from being dominated by livestock to being equally grazed between wild herbivore and livestock (Austrheim et al., 2011). This change in usage has led several of the semi-natural habitat types to end up on the red list of the Norwegian Biodiversity Information Centre, such as Semi-natural meadow and Hayfields (Hovstad, 2018). Therefore, grazing in outfield areas in Norway are desired as a way of keeping the cultural landscape. Resent years events particularly, in addition to a growing concern about the world’s food situation has increased the interest for local food production. The latest analysis of grazing and the outfield suitable of such, indicates that Norway’s unused potential in outfield is about 55% (Rekdal & Angeloff, 2021).

In addition to recent years events, the world is facing changes in climate. Still debated on how extensive and where the greatest changes will appear, a change in food production are required to undergo adjustments. Knowledge of management and “best practice” models are therefore crucial. Also in Norway, information on how the soil in outfields are affected by grazing is as important than ever.

In this thesis five locations who differs in climate and vegetation are sampled. All these locations are grazed during the summer season by suckler cows which is a part of the Norwegian meat production. Throughout this thesis grazing was not found to significantly affect the SOC-stock, SOC concentration or the thickness of the organic layer. While grazing was found to significantly decrease the HWEC-stock in all mineral layers and the CN-ratio in the organic layer.

The decrease in the HWEC-stock is suggested caused by removal of organic matter by grazers. The basis for this assumption is partly the combination of the significant decline in HWECstocks and difference between grazed and non-grazed site in the thickness of the organic layer mean values (not significant). In addition, the CN ratio was found to significantly decrease under grazing in the organic layer.

The HWEC-stock is viewed as a measure of the labile fraction (Dong et al., 2021), and is a useful indicator of the soil quality in soil-plant ecosystems (Ghani et al., 2003). The form and behaviour of the SOM and SOC is fully reliant on microbial mass (Bhattacharyya et al., 2022), and a decrease of the HWEC might therefor be a sign that a decline of microbial biomass pool (Ghani et al., 2003) are taking place. Since a significant decrease were found between the grazed site and the control sites (non-grazed) it might be an early indicator of degradation of the soil structure.

A significant increase in bulk density between sites in the two top layers (the organic layer, mineral 0-10 cm) were found for all locations. In accordance with other studies on grazing effects (Byrnes et al., 2018; Martinsen et al., 2012; Piñeiro et al., 2010), it was concluded that the pastures were influenced by the grazing animals.

On the background of different utilizing periods and grazer densities, the management of the pastures is suggested to might be influencing the HWEC-stock. Amongst the tested factors related to geography and effect on the SOC-stock, only MAT were found significant. Precipitation and content of fine texture quantity were not found to significantly effect SOCstocks. Therefore, geography was found somewhat related to the SOC-stock. Only Mg-stock had a significant difference between sites. Grazing was not found to significantly affect the soil’s pH. No plausible explanation for this significant result was found. The other macronutrient stocks were not found to significantly change with grazing.

Beiting i utmark har lange tradisjoner i Norge. Ikke bare er utmarka benyttet som beite, men ble før også slått for å skaffe dyrene mat til vinteren (Rekdal & Angeloff, 2021). Fra 1949 til 1999 endret beite i Norge seg fra å være dominert av husdyr til å bli likt beitet mellom ville dyr og husdyr (Austrheim et al., 2011). Denne bruksendringen har ført til at flere av de semi-naturlige naturtypene har havnet på rødlista til Artsdatabanken, som for eksempel Semi-naturlig eng og slåttemark (Hovstad, 2018). Beiting som en måte å opprettholde kulturlandskapet er en av grunnene til at beiting i den norske utmarka er ønsket. Med tanke på de siste årenes begivenheter, i tillegg til en økende bekymring for verdens matsituasjon har interessen for lokal matproduksjon økt. Den siste analysen utført på beitebruk og utmarkas egnethet for dette, indikerer at Norges ubrukte potensial i utmark er om lag 55 % (Rekdal & Angeloff, 2021). Verden står i tillegg til de siste årenes hendelser på trappene av klimaendringer. Omfang og område for hvor været vil endres mest drastisk er usikkert, men matproduksjonen vil mest sannsynlig uansett måtte omstilles og berede seg på disse endringene. Kunnskap om forvalting og «best practice»-modeller er derfor avgjørende. Kanskje viktigere enn noen gang, også i Norge, er informasjon om hvordan jorda i utmark påvirkes av beiting. I denne oppgaven er fem lokasjoner som er forskjellige i klima og vegetasjon prøvetatt. Alle disse lokalitetene beites i sommersesongen av ammekyr som er en del av den norske kjøttproduksjonen. Gjennom denne oppgaven ble det ikke beiting funnet til å signifikant påvirke det organiske karbonet i jorda (SOC-stock), konsentrasjonen av organisk karbon (SOC%) eller tykkelsen på det organiske sjiktet. I motsetning ble beiting funnet å signifikant redusere hot water extractable carbon (HWEC) signifikant i alle mineralsjikt og CN-forholdet (karbon:nitrogen) i det organiske sjiktet.