Rate of soil‐aggregate formation under different organic matter amendments—a short‐term incubation experiment |
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| Authors: | Rouven Andruschkewitsch Daniel Geisseler Stefan Dultz Rainer‐Georg Joergensen Bernard Ludwig |
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| Institution: | 1. Department of Environmental Chemistry, University of Kassel, Nordbahnhofstra?e 1a, 37213 Witzenhausen, Germany;2. Institute of Soil Science, Leibniz University of Hannover, Herrenh?user Stra?e 2, 30419 Hannover, Germany;3. Department of Soil Biology and Plant Nutrition, University of Kassel, Nordbahnhofstra?e 1a, 37213 Witzenhausen, Germany |
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| Abstract: | To improve soil structure and take advantage of several accompanying ecological benefits, it is necessary to understand the underlying processes of aggregate dynamics in soils. Our objective was to quantify macroaggregate (> 250 μm) rebuilding in soils from loess (Haplic Luvisol) with different initial soil organic C (SOC) contents and different amendments of organic matter (OM) in a short term incubation experiment. Two soils differing in C content and sampled at 0–5 and 5–25 cm soil depths were incubated after macroaggregate destruction. The following treatments were applied: (1) control (without any addition), (2) OM1 (addition of OM: preincubated wheat straw < 10 mm, C : N 40.6] at a rate of 4.1 g C kg soil]–1), and (3) OM2 (same as (2) at a rate of 8.2 g C kg soil]–1). Evolution of CO2 released from the treatments was measured continuously, and contents of different water‐stable aggregate‐size classes (> 250 μm, 250–53 μm, < 53 μm), microbial biomass, and ergosterol were determined after 7 and 28 d of incubation. Highest microbial activity was observed in the first 3 d after the OM application. With one exception, > 50% of the rebuilt macroaggregates were formed within the first 7 d after rewetting and addition of OM. However, the amount of organic C within the new macroaggregates was ≈ 2‐ to 3‐fold higher than in the original soil. The process of aggregate formation was still proceeding after 7 d of incubation, however at a lower rate. Contents of organic C within macroaggregates were decreased markedly after 28 d of incubation in the OM1 and OM2 treatments, suggesting that the microbial biomass (bacteria and fungi) used organic C within the newly built macroaggregates. Overall, the results confirmed for all treatments that macroaggregate formation is a rapid process and highly connected with the amount of OM added and microbial activity. However, the time of maximum aggregation after C addition depends on the soil and substrate investigated. Moreover, the results suggest that the primary macroaggregates, formed within the first 7 d, are still unstable and oversaturated with OM and therefore act as C source for microbial decomposition processes. |
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| Keywords: | ergosterol water‐stable aggregates microbial biomass soil respiration |
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