Rate of soil‐aggregate formation under different organic matter amendments—a short‐term incubation experiment

• Published in: Journal of plant nutrition and soil science 2014-04, Vol.177 (2), p.297-306
• Main Authors: Andruschkewitsch, Rouven, Geisseler, Daniel, Dultz, Stefan, Joergensen, Rainer‐Georg, Ludwig, Bernard
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; bacteria; Biochemistry and biology; Biological and medical sciences; carbon dioxide; Chemical, physicochemical, biochemical and biological properties; ergosterol; evolution; Fundamental and applied biological sciences. Psychology; fungi; General agronomy. Plant production; microbial activity; microbial biomass; Microbiology; Organic matter; Other nutrients. Amendments. Solid and liquid wastes. Sludges and slurries; Physical properties; Physics, chemistry, biochemistry and biology of agricultural and forest soils; soil depth; soil organic carbon; soil respiration; Soil science; soil structure; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Structure, texture, density, mechanical behavior. Heat and gas exchanges; Triticum aestivum; water-stable aggregates; wheat straw
• ISSN: 1436-8730; 1522-2624
• DOI: 10.1002/jpln.201200628

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.