Aggregation and organic matter in subarctic Andosols under different grassland management
Lehtinen, T. ; Gisladottir, G. ; Lair, G.J. ; Leeuwen, J.P. van; Blum, W.E.H. ; Bloem, J. ; Steffens, M. ; Ragnarsdottir, K.V. - \ 2015
Acta Agriculturae Scandinavica Section B-Soil and Plant Science 65 (2015)3. - ISSN 0906-4710 - p. 246 - 263.
c-13 nmr-spectroscopy - soil microbial biomass - mediterranean conditions - structural stability - cultivated soils - farming systems - volcanic soils - carbon stocks - land-use - tillage
Quantity and quality of soil organic matter (SOM) affect physical, chemical, and biological soil properties, and are pivotal to productive and healthy grasslands. Thus, we analyzed the distribution of soil aggregates and assessed quality, quantity, and distribution of SOM in two unimproved and improved (two organic and two conventional) grasslands in subarctic Iceland, in Haplic and Histic Andosols. We also evaluated principal physicochemical and biological soil properties, which influence soil aggregation and SOM dynamics. Macroaggregates (>250 µm) in topsoils were most prominent in unimproved (62–77%) and organically (58–69%) managed sites, whereas 20–250 µm aggregates were the most prominent in conventionally managed sites (51–53%). Macroaggregate stability in topsoils, measured as mean weight diameter, was approximately twice as high in organically managed (12–20 mm) compared with the conventionally managed (5–8 mm) sites, possibly due to higher organic inputs (e.g., manure, compost, and cattle urine). In unimproved grasslands and one organic site, macroaggregates contributed between 40% and 70% of soil organic carbon (SOC) and nitrogen to bulk soil, whereas in high SOM concentration sites free particulate organic matter contributed up to 70% of the SOC and nitrogen to bulk soil. Aggregate hierarchy in Haplic Andosols was confirmed by different stabilizing mechanisms of micro- and macroaggregates, however, somewhat diminished by oxides (pyrophosphate-, oxalate-, and dithionite-extractable Fe, Al, and Mn) acting as binding agents for macroaggregates. In Histic Andosols, no aggregate hierarchy was observed. The higher macroaggregate stability in organic farming practice compared with conventional farming is of interest due to the importance of macroaggregates in protecting SOM and soils from erosion, which is a prerequisite for soil functions in grasslands that are envisaged for food production in the future.
Nitrogen losses from two grassland soils with different fungal biomass
Vries, F.T. de; Groenigen, J.W. van; Hoffland, E. ; Bloem, J. - \ 2011
Soil Biology and Biochemistry 43 (2011)5. - ISSN 0038-0717 - p. 997 - 1005.
arbuscular mycorrhizal fungi - organic-matter - microbial communities - carbon sequestration - upland grasslands - cultivated soils - food webs - mineralization - ecosystems - management
Nitrogen losses from agricultural grasslands cause eutrophication of ground- and surface water and contribute to global warming and atmospheric pollution. It is widely assumed that soils with a higher fungal biomass have lower N losses, but this relationship has never been experimentally confirmed. With the increased interest in soil-based ecosystem services and sustainable management of soils, such a relationship would be relevant for agricultural management. Here we present a first attempt to test this relationship experimentally. We used intact soil columns from two plots from a field experiment that had consistent differences in fungal biomass (68 ± 8 vs. 111 ± 9 µg C g-1) as a result of different fertilizer history (80 vs. 40 kg N ha-1 y-1 as farm yard manure), while other soil properties were very similar. We performed two greenhouse experiments: in the main experiment the columns received either mineral fertilizer N or no N (control). We measured N leaching, N2O emission and denitrification from the columns during 4 weeks, after which we analyzed fungal and bacterial biomass and soil N pools. In the additional 15N experiment we traced added N in leachates, soil, plants and microbial biomass. We found that in the main experiment, N2O emission and denitrification were lower in the high fungal biomass soil, irrespective of the addition of fertilizer N. Higher 15N recovery in the high fungal biomass soil also indicated lower N losses through dentrification. In the main experiment, N leaching after fertilizer addition showed a 3-fold increase compared to the control in low fungal biomass soil (11.9 ± 1.0 and 3.9 ± 1.0 kg N ha-1, respectively), but did not increase in high fungal biomass soil (6.4 ± 0.9 after N addition vs. 4.5 ± 0.8 kg N ha-1 in the control). Thus, in the high fungal biomass soil more N was immobilized. However, the 15N experiment did not confirm these results; N leaching was higher in high fungal biomass soil, even though this soil showed higher immobilization of 15N into microbial biomass. However, only 3% of total 15N was found in the microbial biomass 2 weeks after the mineral fertilization. Most of the recovered 15N was found in plants (approximately 25%) and soil organic matter (approximately 15%), and these amounts did not differ between the high and the low fungal biomass soil. Our main experiment confirmed the assumption of lower N losses in a soil with higher fungal biomass. The additional 15N experiment showed that higher fungal biomass is probably not the direct cause of higher N retention, but rather the result of low nitrogen availability. Both experiments confirmed that higher fungal biomass can be considered as an indicator of higher nitrogen retention in soils
Increased Litter Build Up and Soil Organic Matter Stabilization in a Poplar Plantation After 6 Years of atmospheric CO2 Enrichment (FACE): Final Results of POP-EuroFace Compared to Other Forest FACE Experiments
Hoosbeek, M.R. ; Scarascia-Mugnozza, G. - \ 2009
Ecosystems 12 (2009)2. - ISSN 1432-9840 - p. 220 - 239.
nitrogen-use efficiency - elevated co2 - carbon storage - mineral soil - terrestrial ecosystems - biomass production - cultivated soils - tropospheric o-3 - deciduous forest - n-fertilization
Free air CO2 enrichment (FACE) experiments in aggrading temperate forests and plantations have been initiated to test whether temperate forest ecosystems act as sinks for anthropogenic emissions of CO2. These FACE experiments have demonstrated increases in net primary production and carbon (C) storage in forest vegetation due to increased atmospheric CO2 concentrations. However, the fate of this extra biomass in the forest floor or mineral soil is less clear. After 6 years of FACE treatment in a short-rotation poplar plantation, we observed an additional sink of 32 g C m¿2 y¿1 in the forest floor. Mineral soil C content increased equally under ambient and increased CO2 treatment during the 6-year experiment. However, during the first half of the experiment the increase in soil C was suppressed under FACE due to a priming effect, that is, the additional labile C increased the mineralization of older SOM, whereas during the second half of the experiment the increase in soil C was larger under FACE. An additional sink of 54 g C m¿2 y¿1 in the top 10 cm of the mineral soil was created under FACE during the second half of the experiment. Although, this FACE effect was not significant due to a combination of soil spatial variability and the low number of replicates that are inherent to the present generation of forest stand FACE experiments. Physical fractionation by wet sieving revealed an increase in the C and nitrogen (N) content of macro-aggregates due to FACE. Further fractionation by density showed that FACE increased C and N contents of the light iPOM and mineral associated intra-macro-aggregate fractions. Isolation of micro-aggregates from macro-aggregates and subsequent fractionation by density revealed that FACE increased C and N contents of the light iPOM, C content of the fine iPOM and C and N contents of the mineral associated intra-micro-aggregate fractions. From this we infer that the amount of stabilized C and N increased under FACE treatment. We compared our data with published results of other forest FACE experiments and infer that the type of vegetation and soil base saturation, as a proxy for bioturbation, are important factors related to the size of the additional C sinks of the forest floor¿soil system under FACE.
Effects of free atmospheric CO2 enrichment (FACE), N fertilization and poplar genotype on the physical protection of carbon in the mineral soil of a poplar plantation after five years
Hoosbeek, M.R. ; Vos, J.M. ; Bakker, E.J. ; Scarascia-Mugnozza, G. - \ 2006
Biogeosciences 3 (2006)4. - ISSN 1726-4170 - p. 479 - 487.
organic-matter dynamics - elevated co2 - biomass production - cultivated soils - c sequestration - forest - turnover - aggregate - storage - rotation
Free air CO2 enrichment (FACE) experiments in aggrading forests and plantations have demonstrated significant increases in net primary production (NPP) and C storage in forest vegetation. The extra C uptake may also be stored in forest floor litter and in forest soil. After five years of FACE treatment at the EuroFACE short rotation poplar plantation, the increase of total soil C% was larger under elevated than under ambient CO2. However, the fate of this additional C allocated belowground remains unclear. The stability of soil organic matter is controlled by the chemical structure of the organic matter and the formation of micro-aggregates (within macro-aggregates) in which organic matter is stabilized and protected. FACE and N-fertilization treatment did not affect the micro- and macro-aggregate weight, C or N fractions obtained by wet sieving. However, Populus euramericana increased the small macro-aggregate and free micro-aggregate weight and C fractions. The obtained macro-aggregates were broken up in order to isolate recently formed micro-aggregates within macro-aggregates (iM-micro-aggregates). FACE increased the iM-micro-aggregate weight and C fractions, although not significantly. This study reveals that FACE did not affect the formation of aggregates. We did, however, observe a trend of increased stabilization and protection of soil C in micro-aggregates formed within macro-aggregates under FACE. Moreover, the largest effect on aggregate formation was due to differences in species, i.e. poplar genotype. P. euramericana increased the formation of free micro-aggregates which means that more newly incorporated soil C was stabilized and protected. The choice of species in a plantation, or the effect of global change on species diversity, may therefore affect the stabilization and protection of C in soils.
Earthworms and management affect organic matter incorporation and microaggregate formation in agricultural soils
Pulleman, M.M. ; Six, J. ; Uyl, A. ; Marinissen, J.C.Y. ; Jongmans, A.G. - \ 2005
Applied Soil Ecology 29 (2005)1. - ISSN 0929-1393 - p. 1 - 15.
no-tillage agroecosystems - silt loam - cultivated soils - casts - carbon - aggregation - dynamics - pasture - systems - megascolecidae
Through their feeding activities and cast production, earthworms influence both aggregate turnover and soil organic matter (SOM) dynamics. We studied the impact of earthworm activity on soil macro- and microaggregation and SOM incorporation in different farming systems. Dry-sieved aggregates (4¿12.5 mm) of a permanent pasture (PP), a conventional arable field (CA) and an organic arable field (OA) (0¿10 and 10¿20 cm depth) were separated into different aggregate fractions, which were analyzed for organic C and N. The separation was based on macromorphological characteristics that reflect the dominant process of aggregate formation and the degree of degradation. We distinguished: two classes of biogenic macroaggregates (fresh casts and welded casts); one class of physicogenic macroaggregates (angular to subangular blocky macroaggregates); and an intermediate fraction (rounded to subrounded macroaggregates). The structural arrangement of mineral particles and organic matter and the quantitative contribution of particulate organic matter (POM) and microaggregates were studied in thin sections. Total organic C contents tended to be higher in biogenic than in physicogenic macroaggregates of the PP and OA soils, whereas the reverse was found for the CA soil. Comparison of the different macroaggregate types in thin sections revealed that the worm-made macroaggregates of the PP soil were considerably enriched in fine POM and microaggregates, in which large amounts of organic matter were intimately mixed with fine mineral material. By contrast, worm casts of the CA and OA soils were hardly enriched in POM and microaggregates. Our study demonstrated that earthworms can directly initiate the formation of microaggregates, which in turn affects the physical protection of SOM against microbial decay. Farming practices that stimulate earthworm activity may thus constitute an important aspect of sustainable agricultural management. However, the much smaller amounts of POM and microaggregates present in worm casts of CA and OA than PP indicate a different impact of earthworms on C stabilization depending on land use. Further research is needed to elucidate the exact management conditions that favour the beneficial effects of earthworms on soil microstructure and associated SOM dynamics. In this respect, the use of micromorphological techniques in addition to chemical and physical analyses was shown to be very valuable