Process rates of nitrogen cycle in uppermost topsoil after harvesting in no-tilled and ploughed agricultural clay soil

No-till is considered an agricultural practice beneficial for the environment as soil erosion is decreased compared to ploughed soils. For on overall evaluation of the benefits and disadvantages of this crop production method, understanding the soil nutrient cycle is also of importance. The study was designed to obtain information about gross soil nitrogen (N) process rates in boreal no-tilled and mouldboard ploughed spring barley (Hordeum vulgare L.) fields after autumn harvesting. In situ soil gross N transformation process rates were quantified for the 5 cm topsoil in 9 days' incubation experiment using N-15 pool dilution and tracing techniques and a numerical N-15 tracing model. Gross N mineralization into ammonium (NH4+) and NH4+ immobilization were the most important N transformation processes in the soils. The gross mineralization rate was 14% and NH4+ immobilization rate 64% higher in no-till than in ploughing. Regardless of the faster mineralization, the gross rate of NH4+ oxidation into nitrate (NO3-) in no-till was one order of magnitude lower compared the ploughing. The results indicate that the no-tilled soils have the potential to decrease the risk for NO3- leaching due to slower NH4+ oxidation.