Browsing by Subject "maan hiilensidonta"

Declining trend of carbon content in croplands has been reported in Finland as well as globally and at the same time soil degradation has risen to a significant threat for food production. Increasing soil carbon content for example with carbon rich fertilizers may improve soil water retention properties, soil structure, and increase soil carbon sink. The aim of this thesis was to study if the usage of carbon-rich fertilizers (pulp mill sludge, liquid vinasse, bone meal and biowaste compost with biochar) increase soil carbon content, soil water retention and water stable aggregates compared to usage of inorganic fertilizers or unfertilized control in a four-year time period (2016-2019). Material for water retention curve and water stable aggregate measurements was collected in HYKERRYS-project field experiment after harvest in august 2019. Existing data were utilized for determination of soil total carbon content, which had been collected every year after harvest in the topsoil (0-20 cm). The total carbon content was determined with Variomax CN-analyser in 2016-2018 and with LECO CN-analyzer in 2019. Water retention curve was determined by underpressure method in sandbox (for pF 1,5, 1,8 and 2,0) and overpressure method in pressure plate extractor (for pF 2,7, 3,4 ja 4,2) using undisturbed and disturbed (pF 4,2) soil samples collected in topsoil. Water-stability of aggregates was determined with wet sieving method for aggregate size fraction 2-5 mm. Before wet sieving, samples were dry sieved on fraction classes > 5 mm, 2-5 mm and < 2 mm. Soil carbon content (soil C) in the composted pulp mill sludge treatment was by +0,5 % statistically significant (p < 0,05) higher than that in the mineral fertilizer treatment in 2019. Statistically significant regression between added C and measured soil C content supported the view that added C increased soil C contents also in other treatments even if no significant differences between these treatments were detected. None of the treatments significantly improved the water retention or water stable aggregates (p > 0,05). The results of this thesis indicated that adding composted pulp mill sludge over 22 000 kg DM ha 1 (8000 kg C ha-1) in four years is enough to significantly raise the carbon content of a humic clay loam soil, but it is not enough to improve soil water retention properties or the water stability of soil aggregates.