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Conservation farming (CF), involving basin tillage, residue retention and crop rotation, combined with biochar may help to mitigate negative impacts of conventional agriculture. In this study, the effects of CF on the amount and quality of soil organic matter (SOM) and potential nitrogen (N) mineralization were investigated in a maize-soya-maize rotation in an Acrisol in Zambia. A large field was run under CF for 7 years and in the subsequent three growing seasons (2015–2018), four management practices were introduced to study effects on soil characteristics and crop yield. We tested i) a continuation of regular CF (CF-NORM) ii) CF without residue retention (CF-NO-RES); iii) Conventional (CONV), with full tillage and removal of residues; and iv) CF with 4 ton ha-1 pigeon pea biochar inside basins and residue retention (CF-BC). The experiment involved the addition of fertilizer only to maize, while soya received none. Soya yield was significantly higher in CF systems than in CONV. Maize yields were not affected by the different management practices probably due to the ample fertilizer addition. CF-NORM had a higher stock of soil organic carbon (SOC), higher N mineralization rates, more hot-water extractable carbon (HWEC; labile SOC) and particulate organic matter (POM) inside basins compared to the surrounding soil (outside basins). Our results suggest that the input of roots inside basins are more effective increasing SOM and N mineralization, than the crop residues that are placed outside basins. CONV reduced both quality and quantity of SOM and N mineralization as compared to CF inside basins. CF-BC increased the amount of SOC as compared with CF-NORM, whereas N mineralization rate and HWEC remained unaffected. The results suggest benefits on yield of CF and none of biochar; larger impact of root biomass on the build-up of SOM than crop residues; and high stability of biochar in soil. [ABSTRACT FROM AUTHOR]

Relationships between soil C and N stocks and soil formation, climate, and vegetation were investigated in a gridded database connected to the National Forest Inventory in Norway. For mineral soil orders, C and N stocks were estimated to be 11.1-19.3 kg C·m−2 and 0.41-0.78 kg N·m−2, respectively, declining in the following order: Gleysols > Podzols > Brunisols > Regosols. Organic peat-type soils stored, on average, 31.3 kg C·m−2 and 1.10 kg N·m−2, whereas shallow Organic folisols stored, on average, 10.2 kg C·m−2 and 0.34 kg N·m−2. For Norway's 120 000 km2 of forest, the total of soil C stocks was estimated to be 1.83 Gt C, with a 95% CI of 1.71-1.95 Gt C. Podzolic soils comprise the largest soil group and store approximately 50% of the forest soil C. Sixty percent of the soil C stock in Podzolic soils was stored in the mineral soil, increasing with temperature and precipitation. Poorly drained soil types store approximately 47% of the total forest soil C in Norway. Soils with water saturation have large C stocks mainly in the forest floor, suggesting that they are more susceptible to forest management and environmental change. Soil C stocks under pine and spruce forests were similar, although pine forests had larger C stocks in the forest floor, while spruce forests had the highest C stocks in the mineral soil compartment. C stocks in the forest floor increase from dry to moist ground vegetation, while ground vegetation nutrient classes reflect better the C and N stocks in the mineral soil. [ABSTRACT FROM AUTHOR]

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Soil organic matter (SOM) in arctic and boreal soils is the largest terrestrial reservoir of carbon. Increased SOM mineralisation under increased temperature has the potential to induce a massive release of CO2. Precise parameterisation of the response of arctic soils to increased temperatures is therefore crucial for correctly simulating our future climate. Here, we investigated the temperature response of SOM mineralisation in eight arctic soil profiles of Norway, Svalbard and Russia. Samples were collected at two depths from both mineral and organic soils, which were affected or not by permafrost and were incubated for 91 days at 4, 8, 12, and 16 °C. Temperature response was investigated through two parameters derived from a simple exponential model: the intensity of mineralisation, α, and the temperature sensitivity, Q10. For each sample, SOM quality was investigated by 13C-NMR, whereas bacterial and fungal community structure was characterised by T-RFLP and ARISA fingerprints, respectively. When estimated from the whole incubation period, α proved to be higher in deep permafrost samples than in shallow active layer ones due to the presence transient flushes of mineralisation in deep permafrost affected soils. At the end of the incubation period, after mineralization flushes had passed, neither α nor Q10 (averaging 1.28 ± 0.07) seemed to be affected by soil type (organic vs mineral soil), site, depth or permafrost. SOM composition and microbial community structure on the contrary where affected by site and soil type. Our results suggest that deep samples of permafrost affected soil contain a small pool of fast cycling carbon, which is quickly depleted after thawing. Once the mineralization flush had passed, the temperature response of permafrost affected soil proved to be relatively homogenous among sample types, suggesting that the use of a single temperature sensitivity parameter in land surface models for SOM decomposition in permafrost-affected soils is justified. [ABSTRACT FROM AUTHOR]

Abstract: Dissolved organic matter (DOM) plays an essential role in many biogeochemical processes in soil and water, and the retention of DOM in soils influences the amount and composition of DOM exported from terrestrial to aquatic ecosystems. Adsorption in soil mineral horizons is considered a main mechanism by which DOM is retained and stabilised in soils, and podzol soils have received attention due to their capacity to retain DOM in the mineral B horizon. With the projected increase in temperature and precipitation at higher latitudes, the transport of organic matter is expected to increase, but few studies have investigated the adsorption of DOM in poorly podzolised soils at higher latitudes. In this study, we used batch equilibrium experiments to investigate the potential for DOM adsorption in the B horizon of poorly podzolised soils from a confined area in Neiden, northern Norway. We used the Initial Mass (IM) isotherm to describe the amount of dissolved organic carbon (DOC) removed from or released to solution by the soil as a linear function of the amount of DOC added to the soil–water suspension. Our results suggest that the affinity for DOC of B horizons in poorly podzolised high-latitude soils is largely determined by the content of amorphous Fe and Al oxides, where adsorption is limited by the saturation of amorphous Fe and Al with organic matter. The B horizons show a relatively large variation in DOC sorption characteristics, with an overall low potential to adsorb added DOC at field relevant DOC concentrations. Six out of twelve B horizons show a net DOC desorption over the whole range of added DOC (0–480mgCkg−1 soil). These findings indicate a limited potential for retention and stabilisation of DOM in poorly podzolised soils at higher latitudes in a warmer and wetter climate. [Copyright &y& Elsevier]