Effect of soil organic carbon loss on the stability and structure of microaggregates: First insights from an organic carbon depletion field trial in a loess soil

<p>Soil microaggregates are considered to play an important role in soil functioning and soil organic carbon (SOC) is of great importance for the formation and stabilization of these aggregates. The loss of SOC can occur, for example, after a change in land use and may lead to a decreased aggregate stability, which makes soils vulnerable to various threats, such as erosion or compaction. It is therefore important to shed light on the effect of SOC loss on aggregate stability in order to better understand and preserve the functioning of healthy soils.</p><p>We sampled two adjacent plots from a loess soil in Selhausen (Germany) and measured aggregate stability and architecture of soil microaggregates. One plot was kept free from vegetation by the application of herbicides and by tillage (to a depth of 5 cm) from 2005 on (organic matter depletion, OMD), while the other plot was used for agriculture using conventional tillage (control). Over the course of 14 years, the SOC concentration in the bulk soil has been reduced from 12.2 to 10.1 g SOC kg-1 soil. It was, however, unclear whether a loss of SOC had also taken place in microaggregates (since they are known to have very long turnover times). We took 10 undisturbed soil cores from two depths of each plot (Ap and Bt horizons).</p><p>The stability of aggregates against hydraulic and mechanical stresses was tested using wet sieving  (mesh sizes of 0.25 to 8 mm) and a crushing test in a load frame adapted to the microaggregate scale. For the latter test, microaggregates were isolated from the bulk soil using a newly developed dry crushing approach. To shed light on the effect of a decreased SOC content on microaggregate structure, we scanned several microaggregates with a computed tomography scanner at sub-micron resolution and analysed the features of their pore systems. SOC losses had also occurred in large  microaggregates (250-53 µm) in the Ap horizon: SOC contents in this fraction were 16.3 g SOC kg⁻¹ (control) and 12.8 g SOC kg⁻¹ (OMD). While wet sieving indicated a lower stability of macroaggregates from the Ap horizon in the OMD plot (geometric mean diameter: 1.54 mm (control) vs 0.43 mm (OMD)), an effect on the tensile strength of large microaggregates could not be found. Total porosity and pore connectivity, derived from Euler characteristic, as well as several pore skeleton traits (number of branches, junctions, etc.) were lower in aggregates from the OMD treatment. However, the difference was also present or even stronger in the Bt horizon than in the Ap horizon, so the supposed treatment effect might have been due to other effects like spatial heterogeneity of texture. Thus, the observed SOC losses may not have been large enough to substantially influence struture or stability of large microaggregates.</p>

Soil organic carbon content: decreases partly attributed to dilution by increased depth of cultivation in southern Ontario

Soil organic carbon contents and depths of Ap horizons (i.e., cultivated topsoil) from Ontario soil survey reports were reviewed, analyzed, and compared from 1950 to 2019. Organic carbon concentrations have declined from 2.85% to 2.34% in Ap horizons, whereas depths have increased by 40%. Considering the entire Ap horizon depth, we show that soil carbon stocks (kg C·ha−1) may be constant or increasing. Losses of organic carbon due to cultivation should not be discounted; however, dilution of organic carbon within a deeper plow layer may contribute significantly to observed decreases in organic carbon concentrations in topsoil.

Model of the pression transfer apply on an alfisol from Tabuleiros Costeiros

The cohesive subsurface horizon of the Arfisol of Tabuleiros Costeiros, reduces the effective depth of these soils, compromising the yield and longevity of the perennial crops. This pedogenetic limitation can be potentiated when the pressure applied on the surface of the Ap horizon, during the traffic of agricultural machinery is transmitted to deeper horizons, AB or Bt, at higher levels the load-bearing capacity of these layers. The objective of this research was to mathematically model the transfer of pressures applied to the surface of the Ap horizon of an Alfisol for subsurface layers, relating the pressure applied to the soil profile moisture. With the experiment developed in the Laboratory of Soils and Plant Nutrition of Embrapa Tabuleiros Costeiros, it was concluded that moisture has a damping effect on the pressure transmitted from upper layers to subsurface. The pressure transmitted to the subsurface shows an exponential function with negative correlation as a function of depth, independent of the applied pressure on the surface. The increase in the contact area for the application of pressures on the soil surface, attenuates the transmission of pressure to lower layers when compared to the same pressure applied in smaller areas

Identifikasi Fraksi Fe, Al, dan Si Amorf pada Beberapa Ordo Tanah di Lahan Kering Aceh Besar dengan Ekstraksi Ammonium Oksalat

Abstrak: Hasil penelitian menunjukkan bahwa kandungan Fe, Al, dan Si amorf pada tanah ordo Andisol di lahan kering Aceh Besar berkisar dari 0,61 – 0,65%, kandungan Fe amorf tertinggi terdapat pada horizon Ap sebesar 0,65%, sedangkan kandungan terendah terdapat pada horizon Bw 0,61%. Untuk kandungan Al amorf berkisar dari 5,20 – 3,02%, kandungan Al tertinggi terdapat pada horizon AB sebesar 5,20% sedangkan kandungan terendah terdapat pada horizon Ap 3,02%. Untuk kandungan Si amorf berkisar dari 6,81 – 5,92%, untuk kandungan Si tertinggi terdapat pada horizon Ap sebesar 6,81%, untuk kandungan terendah terdapat pada horizon Bw dengan kandungan 5,92%. Pola distribusi Fe, Al, dan Si amorf pada ordo Andisol di lahan kering Aceh Besar, kandungan Fe pada kedalaman 20 - 60 cm relatif stabil, untuk kandungan Al cenderung naik dari kedalaman 20 - 60 cm, kemudian untuk pola Si juga terjadi penurunan dari kedalaman 20 - 60 cm. Untuk kandungan Fe, Al, dan Si amorf pada ordo Oxisol berkisar dari 0,16 - 9,03%. Kandungan Fe berkisar dari 0,19 – 1,65% kandungan Fe tertinggi pada Oxisol terdapat pada horizon BA yaitu 1,65% dan kandungan terendah terdapat pada horizon Bo1 yaitu 0,16%, untuk kandungan Al berkisar dari 3,48 – 6,44% kandungan Al tertinggi terdapat pada horizon A yaitu 6,44% dan kandungan terendah terdapat pada horizon Bo1 yaitu 3,48%. Pada Si kandungannya berkisar dari 6,37 – 9,03%, kandungan Si tertinggi pada Oxisol terdapat pada horizon Bo1 yaitu 9,03% dan kandungan terendah terdapat pada horizon A yaitu 6,37%. Pola distribusi Fe, Al, da Si Oxisol di lahan kering Kabupaten Aceh Besar, kandungan Fe terjadi penurunan dari kedalaman 10 cm sampai kedalaman 104 cm, dan pada kandungan Al terjadi penurunan dari kedalaman 10 cm sampai kedalaman 104 cm. Kemudian untuk kandungan Si kandungannya relatif tetap.Fe, Al, and Si Amorf in Andisol and in the Seulawah Valley Dryland, Aceh Besar DistrictAbstrac: The results showed that the content of Fe, Al, and Si amorphous in the Andisol order in dry land in Aceh Besar ranged from 0.61 to 0.65%, the highest amorphous Fe content was found in the Ap horizon of 0.65%, while the lowest content was at the Bw horizon of 0.61%. For the amorphous Al content ranges from 5.20 - 3.02%, the highest Al content is in the AB horizon of 5.20% while the lowest content is in the Ap 3.02% horizon. For the amorphous Si content ranges from 6.81 - 5.92%, for the highest Si content is in the Ap horizon of 6.81%, for the lowest content is found in the Bw horizon with 5.92% content. Amorphous Fe, Al, and Si distribution patterns in the Andisol order in Aceh Besar drylands, Fe content at a depth of 20 - 60 cm is relatively stable, for Al content tends to rise from a depth of 20 - 60 cm, then for the Si pattern there is also a decrease from a depth of 20 - 60 cm. For the content of Fe, Al, and Si amorphous in the Oxisol order ranges from 0.16 to 9.03%. The Fe content ranges from 0.19 - 1.65%, the highest Fe content in Oxisol is found on the BA horizon, which is 1.65% and the lowest content is on the Bo1 horizon, 0.16%, for Al content ranges from 3.48 - 6, 44% of the highest Al content is on the A horizon which is 6.44% and the lowest content is on the Bo1 horizon which is 3.48%. In Si content ranges from 6.37 - 9.03%, the highest Si content in Oxisol is in the Bo1 horizon which is 9.03% and the lowest content is in horizon A which is 6.37%. The distribution pattern of Fe, Al, and Si Si Oxisol in Aceh Besar Dryland District, Fe content decreased from a depth of 10 cm to depth 104 cm, and in the Al content decreased from a depth of 10 cm to a depth of 104 cm. Then for the womb the content is relatively fixed.

Impact of land use change on organic carbon sequestration in Arenosol

Conversion of arable soils into other land uses can stabilize and increase accumulation of soil organic carbon (SOC) and in addition prevent deterioration in its properties. The data has shown changes in SOC sequestration in Ap horizon after arable land conversion (1995–2015) into managed grassland, abandoned and pine afforested. SOC in Arenosol topsoil was positively affected by long term fallow and conversion into grassland. Abandoned land and fertilised managed grassland accumulated significantly more SOC, 48% and 38% respectively compared with arable land. In unfertilised managed grassland SOC stocks decreased 2.3% during 21 years, but losses were lower than in fertilised arable land. Pine afforestation of loamy sand helped to reduce the intensity of SOM mineralization compared to arable land. The Ap horizon thickness in pine forest soil increased from 28 to 31 cm during 21 years period. However, SOC stock decreased by 1% due to reduction in carbon concentration.

Pedogenic Carbonates and Radiocarbon Isotopes of Organic Carbon at Depth in the Russian Chernozem

Conversion of native grasslands to agricultural sites has resulted in remarkable changes in soil carbon at depth, but its impact on soil diagnostic horizons is unknown. This study was conducted to radiocarbon date the soil organic carbon (SOC) and quantify pedogenic carbonates in the Russian Chernozem at depth at three sites: a native grassland field (not cultivated for at least 300 years), an adjacent 50-year continuous fallow field in the V.V. Alekhin Central-Chernozem Biosphere State Reserve in the Kursk region of Russia (UNESCO—MAB Biosphere Reserve), and a cropland in the Experimental Station of the Kursk Institute of Agronomy and Soil Erosion Control. All sampled soils were classified as Fine-silty, mixed, frigid Pachic Hapludolls (Haplic Chernozem). The radiocarbon age (14C date, y BP) of SOC was highly variable: in the native grassland field, it varied from post-bomb (A-horizon) to 8011 ± 54 y BP (C-horizon); in the continuous fallow, it varied from 1569 ± 41 y BP (Ap-horizon) to 11,380 ± 180 y BP (C1-horizon); and in the cropland, it varied from 1055 ± 38 y BP (Ap-horizon) to 11,805 ± 68 y BP (Ck-horizon). Cultivation resulted in morphological/diagnostic changes in the soil profile (conversion of A to Ap; conversion of Bw to Bk horizon) over a 50-year period. These changes are supported by radiocarbon dating of SOC and pedogenic carbonate distribution within the soil profile. The proportion of pedogenic carbonates was highly variable: in the native grassland, it was 27% (C-horizon); in the continuous fallow, it varied from 53% (Bk1-horizon) to 72% (C2-horizon); and in the cropland, it varied from 85% (A-horizon) to 10% (Ck-horizon). The radiocarbon age differences with depth among the soils reflect changes in the soil carbon dynamics resulting from cultivation.

Soil Quality Assessment of Phaeozems and Luvisols from the Kujawy Region (Central Poland) / Ocena cech użytkowych czarnych ziem i gleb płowych rejonu Kujaw

To assess the soil quality of Phaeozems and Luvisols from Kujawy region (Kujawy-Pomerania Province, Poland), the soil quality indicators such as: content of organic matter and nutrients, as well as bulk density were used. The soils showed similar inherent properties (soil texture, depth to parent material, type of clay) and management practices (tillage, crop rotation, nutrient application). The following properties were determined: bulk density, grain size composition, exchangeable acidity, concentration of available forms of potassium, phosphorus and magnesium, and the content of total organic carbon (TOC) and nitrogen (Nt). The amounts of dissolved organic carbon (DOC) and dissolved nitrogen (DN) were measured in the solution obtained after extraction with 0.004 M CaCl2. The stock of TOCs, Nts and DOCs, and DNs were calculated. The total organic carbon content in surface horizon of Phaeozems was significant higher (13.9-20.1 g·kg-1) than in Ap horizon of Luvisols (8.3-11.0 g·kg-1), which is a consequence of their origin. The stock of organic carbon in Ap horizon fell within 5.89 to 8.49 kg·m2 in Phaeozems and 3.80 to 4.81 kg·m2 in Luvisols. Although Phaeozems demonstrated a significant higher content of TOC, as compared with Luvisols, the amount of dissolved organic carbon was similar in both soil types, which points to a higher share of DOC in the total organic carbon content in Luvisols (up to 17.5% in Et horizon). The amounts of dissolved organic carbon and dissolved nitrogen and their stock do not depend on the type of soils if the management practices are similar.

The changes of enzymatic activity of soil under eastern galega (Galega orientalis Lam.) after NPKCa fertilization

Changes in the enzymatic activity of soil variably fertilized with NPKCa were investigated in a field experiment carried out in 2005–2010. The study was conducted with a legume plant, i.e. eastern galega (Galega orientalis Lam.). The experiment was completely randomized and carried out in three replications with the following mineral fertilization: control, N, P, K, NPK, NP, NK, PK, NPKCa, PKCa, Ca, NKCa, and NPCa. Mineral fertilization was applied in kg/ha: (N-20, P-50, K-160, Ca-150). The soil samples collected from the Ap horizon (0–30 cm) of the rhizosphere in spring after the 1^st, 2^nd and 3^rd swathing had a pH_KCl in range from 6.55 to 6.93. The activity of acid phosphatase and alkaline phosphatase was at a low level. The highest activity of urease was recorded in the soil fertilized with NPK, whereas the highest activity of dehydrogenases was in the soil fertilized with PKCa.

Wpływ Wapnowania i Nawożenia Mineralnego na Zawartość Rozpuszczalnych Form Pierwiastków Śladowych W Glebie Płowej / The Influence of Liming and Mineral Fertilization on the Content of Trace Elements Soluble Forms in Haplic Luvisols Formed from Loess

The research was carried out on a permanent fertilization field in the area of the Rzeszow Foothills Region, with Haplic Luvisols formed from loess. The following plants were cultivated in a 4-year cropping system: pasture sunflower, winter wheat, potatoes and spring barley. Various mineral fertilizers NPK + Mg constans and various mineral fertilization NPK + Mg Ca constans were applied in the experiment. Liming was applied in the form of CaO (at the dose of 2.86 t Ca × ha.1). The experiment included 14 fertilizer objects, in 4 replications according to the method of random sub-blocks. Analysis of variance (ANOVA) was applied in statistic processing for a double classification: liming (A) and mineral fertilization (B) . independently of liming. As a result of the testing, it was found that liming raised the content of Cr in Ap and Bt horizons. Mineral fertilization raised the content of Co and Cr in Ap and Bt horizons and Cd and Pb in Bt horizon. The combined effect of liming and mineral fertilization decreased the content of Ni and Co in Ap horizon and Cd in Bt horizon and raised the content of Cr in Ap and Bt horizons and Pb in Bt horizon.