Browsing by Author "Girz, Andrei"

In agricultural soils, Nitrogen (N) is an essential nutrient in crop production, and its supply comes from various pools. Understanding the N pools in soil could help farmers make better decisions about N fertilisation, increase productivity, reduce costs, and decrease environmental impacts. N is a challenging element to track in soil due to its seven oxidation states that are large-ly cycled and intermediated by soil organisms between various organic, mineral, and gaseous forms. This thesis aims to find whether C farming practices accumulate N in soil through investi-gating the size of soil N pools and how they relate to each other through a literature survey and data from a four-year carbon (C) farming experiment. The thesis also investigates whether meas-uring the fast-cycling N pools and including them in fertilisation recommendation calculations results in financial savings from N fertiliser cuts. Twenty different Finnish farms were investigated, split between six C farming practices: subsoil-ing, undersown cover crops, ley farming, soil organic amendments, planned grazing, diverse grasses lay. Soil samples were collected at two different depths (0-17 and 17-30 cm) and ana-lysed for total N and C (Total N, Total C), mineral N, Illinois Soil N Test (ISNT N), autoclave citrate extractable protein N (ACE-Protein N), water extractable organic N and C (WSON and WSOC), and microbial activity derived N (PMN) from CO2 burst after rewetting of dry soil (Resp C).The analysis recovered on average 25% of total N, while 75% remained in the non-recovered pool. Clay%, C% and C:Clay explained the variation in Total N (r2=0.90), ISNT N (r2=0.90), pro-tein N (r2=0.93) and the non-recovered N (r2=0.83), but it did not for WSON (r2=0.50), PMN (r2=0.21) and inorganic N (r2=0.20). Four-year C farming management did not result in statisti-cally significant differences in the N pools, even though PMN and WSON were 19% and 11.6% higher in treatment than in control, respectively. The variation was high for both (SD=48 and 42), explaining the non-significance. Strong correlations (Spearman rho, ρ) were observed between Total N - ISNT N, Residual N, and WSON, indicating their predictive capability for total N, while protein N showed weaker correlations. PMN correlated strongly with bacterial respiration C (ρ = 0.94) and WSON (ρ = 0.75) and had a negative strong correlation with the WSOC:WSON ratio (ρ = -0.73). In conclusion, soil's non-recovered N fraction, likely associated with the mineral surfaces and undecomposed particulate organic matter (POM), is the largest portion of total N. Clay%, C% and C:Clay explains the variation in the slow-cycling N pools but not in the fast-cycling ones. The quality of soil organic matter (SOM) is better assessed using WSON, PMN, and the WSOC:WSON ratio. Utilising PMN as a predictor of N release from SOM results in lower N ferti-liser recommendations, leading to cost savings for farmers. This research shows that four years of C farming do not increase the N stock in soil. Further research is needed to determine if C farming practices in a long-term experiment would increase the soil N stocks, significantly affect soil N pool relationships and result in financial savings for farmers.