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

Laine, Merjo, Rütting, Tobias, Alakukku, Laura, Palojärvi, Ansa, Strömmer, Rauni
Nutrient cycling in agroecosystems 2018 v.110 no.1 pp. 39-49
Hordeum vulgare, ammonium, autumn, clay soils, crop production, harvesting, leaching, mineralization, models, nitrates, nitrogen, nitrogen cycle, no-tillage, oxidation, plowing, risk, soil erosion, soil nutrients, spring barley, stable isotopes, topsoil
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 ¹⁵N pool dilution and tracing techniques and a numerical ¹⁵N 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.