Main soil nutrients dynamics in sod-dressing intercropped orchard

The study aimed to estimate seasonal dynamics of soil nitrogen, phosphorus and potassium under the influence of sod grasses in a sod-dressing intercropped orchard. The trial was conducted in a Welsey apple 1987-year orchard. Trees were planted at 8×6 m, cultivar seedlings used as rootstock. Red clover and meadow timothy in variant shares were used for interrow sodding. The cereal—legume intercropping was done in 2015, preceded by a 180 kg/ha active substance phosphorus-potassium dressing in reserve. Nitrogen was applied annually prior to growing season at 34.4 kg/ha active substance. Grass biomass in first hay cutting was the highest and comprised 45.3-49.9 % total mass. A total four cuttings dry mass was 3.36-7.10 t/ha depending on scheme. The maximum biomass was registered for the schemes with red clover and meadow timothy at ratios 1:1 and 7:3 (6.52 and 7.10 t/ha). In the growing period, grass depleted soil for 111.1—219.9 kg/ha nitrogen, 21.5-42.7 kg/ha phosphorus and 209.3—380.8 kg/ha potassium. Such consumptions suggest a serious competition for soil nutrients between grass vegetation and fruit trees. The available phosphorus and potassium content was independent of interrow dressing schemes. Inter-scheme differences did not exceed experimental bias due to presowing phosphorus and potassium application in reserve before trial. By first cutting, the nitrate nitrogen soil content in sodding schemes was 1.5-2-fold less vs. bare fallow, i.e. more nitrogen is used by vegetating grass, and its available forms recover slower than being consumed.

Crop sequence effects on energy efficiency and land demand in a long-term fertilisation trial

The effect of crop sequences (CR – continuous winter rye; CropR – three-field crop rotation of winter rye-spring barley-bare fallow) and fertilisation systems (unfertilised control, mineral fertiliser (NPK), farmyard manure (FYM)) on crop yield, energy efficiency indicators and land demand were analysed in a long-term experiment under Pannonian climate conditions. Due to lower fuel consumption in the bare fallow, the total fuel consumption for CropR was 27% lower than in CR. It was for NPK and FYM fertilisation by 29% and 42% higher than in the control. Although the energy output was lower in CropR than CR, the energy use efficiency for grain production increased by 35% and for above-ground biomass production by 20%. Overall crop sequences, the NPK treatment had higher crop yields, energy outputs and net-energy output with a lower energy use efficiency than the unfertilised control. CropR increased the land demand just by 20% in comparison to CR, although one-third of the land was not used for crop production. The land demand could be decreased with fertilisation by 50% (NPK) or 48% (FYM). A bare fallow year in the crop rotation decreased the crop yield, energy input and increased the energy use efficiency and land demand.

Impact of the Legume Catch Crop Serradella on Subsequent Growth and P Mobilization under Barley in Different Fertilization Treatments

Legume catch crops can enhance soil fertility and promote the N and P supply of the subsequent main crop, especially with low mineral fertilizer use. However, the specific impact of catch crops on arbuscular mycorrhiza formation of the following main crop is unknown. Therefore, the impact of serradella (Ornithopus sativus) vs. bare fallow was tested on mycorrhiza formation, potential soil enzyme activities and plant-available P under subsequently grown barley (Hordeum vulgare) and different fertilization treatments (P-unfertilized—P0; triple superphosphate—TSP; compost—COM; combined—COM + TSP) in a long-term field experiment in northeastern Germany. Catch cropping significantly increased mycorrhiza formation of barley up to 14% compared to bare fallow. The impact of serradella on mycorrhiza formation exceeded that of the fertilization treatment. Serradella led to increased phosphodiesterase activities and decreased ß-glucosidase activities in soil. Plant availability of P was not significantly affected by serradella. These findings provide initial evidence that even serradella as a non-host crop of mycorrhizal fungi can promote the mycorrhiza formation of the subsequent crop and P mobilization in soil. We conclude that the prolonged vegetation cover of arable soils by the use of catch crops can promote P mobilization and transfer from P pools to the following main crops.

The direct and legacy effects of drying-rewetting cycles on active and relatively resistant soil carbon decomposition

Global climate change is expected to increase the frequency of drought and heavy precipitation, which could create more frequent drying-rewetting cycles (DWC) in the soils. Although DWC effects on SOC decomposition has been widely studied, the effect of DWC and the subsequent legacy effect on the decomposition of different SOC pools is still unclear. We conducted a 128-d laboratory incubation to investigate the DWC effects by using soils from old-field for 15 years (OF, representing active SOC), bare-fallow for 15 years (BF), and bare-fallow for 23 years plus extra 815-d incubation (BF+, representing relatively resistant SOC). The experiment included nine 10-d DWC of three treatments: 1) constant-moisture at 60% WHC, 2) mild DWC with 10-d drying to 40% WHC and rewetting to 80% WHC, and 3) strong DWC with 10-d drying to 20% WHC and rewetting to 100% WHC. Following DWC period, there was a 10-d stabilization period (adjusting all treatments to 60% WHC), and then a 28-d extended incubation. During DWC period, the strong DWC had strong effect on CO2 release compared with the constant-moisture control, reducing the SOC decomposition from OF by 8% and BF by 10%, while increasing the SOC decomposition of BF+ by 16%. During extended period, both mild and strong DWC significantly increased SOC mineralization of OF, but decreased that of BF and BF+. This legacy effect compensated the changes in CO2 release during DWC period, resulting in the minor response of SOC decomposition of OF and BF+ to the DWC during the entire incubation.

Long-Term Bare Fallow Soil Reveals The Temperature Sensitivity of Priming Effect of The Relatively Stabilized Soil Organic Matter

Priming plays an important role in modifying the decomposition of soil organic matter (SOM), but there are large uncertainties in the temperature effect on priming mainly due to the variation in SOM stability. Long-term bare fallow offers a unique opportunity to isolate the relatively stabilized SOM pool and study its properties. We tested the temperature effect on priming of the relatively stabilized SOM pool by incubating soil samples collected from a bare fallow (representing the relatively stabilized SOM) and its adjacent old field (containing both stabilized SOM and labile SOM) at 10 and 20°C for 815 days. We amended the soil samples with C4 maize leaves to distinguish the CO2 source released from the soils (formed under C3 vegetation) and the substrate added (i.e. maize leaves) based on the natural abundance of δ13C. In all cases, there was a positive priming effect on native SOM decomposition when fresh organic matter (maize leaves) was added. The temperature sensitivity of priming effect (calculated as the difference in SOM decomposition due to the addition of maize leaves) in the bare fallow soil and the old field soil was quite different: increasing temperature significantly enhanced the magnitude of priming effect in the bare fallow soil, whereas had no effect on the magnitude of priming effect in the old field soil. The increase of the amount of microbial biomass C by maize leaves application was higher in the bare fallow soil than in the old field soil. Furthermore, for maize leaves-treated soil, temperature increase significantly increased the rate of microbial N mining throughout the incubation in the bare fallow soil, but had minor effect on microbial N mining in the old field soil at the end of incubation. We conclude that the priming effect of the relatively stabilized SOM was sensitive to temperature increase, which may be mainly driven by greater microbial growth and microbial demand for N. This work highlights the vulnerability of stabilized SOM to priming effect under global warming and reveals the potential role of microbes in regulating soil C dynamics under future climate change.

Metagenomic approaches reveal differences in genetic diversity and relative abundance of nitrifying bacteria and archaea in contrasting soils

The abundance and phylogenetic diversity of functional genes involved in nitrification were assessed in Rothamsted field plots under contrasting management regimes—permanent bare fallow, grassland, and arable (wheat) cultivation maintained for more than 50 years. Metagenome and metatranscriptome analysis indicated nitrite oxidizing bacteria (NOB) were more abundant than ammonia oxidizing archaea (AOA) and bacteria (AOB) in all soils. The most abundant AOA and AOB in the metagenomes were, respectively, Nitrososphaera and Ca. Nitrososcosmicus (family Nitrososphaeraceae) and Nitrosospira and Nitrosomonas (family Nitrosomonadaceae). The most abundant NOB were Nitrospira including the comammox species Nitrospira inopinata, Ca. N. nitrificans and Ca. N. nitrosa. Anammox bacteria were also detected. Nitrospira and the AOA Nitrososphaeraceae showed most transcriptional activity in arable soil. Similar numbers of sequences were assigned to the amoA genes of AOA and AOB, highest in the arable soil metagenome and metatranscriptome; AOB amoA reads included those from comammox Nitrospira clades A and B, in addition to Nitrosomonadaceae. Nitrification potential assessed in soil from the experimental sites (microcosms amended or not with DCD at concentrations inhibitory to AOB but not AOA), was highest in arable samples and lower in all assays containing DCD, indicating AOB were responsible for oxidizing ammonium fertilizer added to these soils.

Agrophysical and agrochemical properties of dark grey forest soils under different systems of basic tillage

The effect of long-term use of different systems of basic tillage of dark grey forest soils on the agrophysical properties, nutrient regime and yield of grain crops in grain-fallow crop rotations was determined. The study was carried out in the conditions of the Northern Trans-Urals in a stationary experiment in 1996-2018. The traditional moldboard and resource-saving systems of basic tillage were studied. The experiment took place during the third-sixth rotations of two grain-fallow crop rotations spread in time and space: bare fallow - winter rye - spring wheat - spring vetch - spring barley; bare fallow - winter rye - spring wheat - spring wheat - spring barley. When cultivating a grain crop that completes a grain-fallow crop rotation, in the fourth field after the fallow with a legume forecrop (spring vetch), it is advisable to use systems of basic tillage with elements of minimization. These include non-moldboard and combined tillage with subsurface loosening by a plow with SibIME tines to a depth of 20-22 cm differentiated with stubble-mulch at 12-14 cm and disk harrowing at 10-12 cm. The studied tillage systems ensured the conditions of the water regime, soil composition and nutritional regime close to the moldboard tillage system. The yield of barley almost equal to the moldboard system was formed: against the background of natural land fertility - 2.97-3.03 t/ha, with the use of N40P40P40 - 3.47-3.65 t/ha. Application of tillage systems with minimization elements in a grain-fallow crop rotation without planting a leguminous crop with a given crop for a repeated grain crop (wheat) led to the following results. Productive moisture availability in the soil layer 0-1.0 m decreased by 8.6-28.0%, the nutrient regime worsened significantly, especially nitrogen (by 15.5-43.8%) and phosphorus (by 39.1-51.1%), with the negative differentiation of soil fertility, and reduction of grain yield by 0.09-0.40 t/ha.

Optimizing Carbon Sequestration in Croplands: A Synthesis

Climate change and ensuring food security for an exponentially growing global human population are the greatest challenges for future agriculture. Improved soil management practices are crucial to tackle these problems by enhancing agro-ecosystem productivity, soil fertility, and carbon sequestration. To meet Paris climate treaty pledges, soil management must address validated approaches for carbon sequestration and stabilization. The present synthesis assesses a range of current and potential future agricultural management practices (AMP) that have an effect on soil organic carbon (SOC) storage and sequestration. Through two strategies—increasing carbon inputs (e.g., enhanced primary production, organic fertilizers) and reducing SOC losses (e.g., reducing soil erosion, managing soil respiration)—AMP can either sequester, up to 714 ± 404 (compost) kg C ha−1 y−1, having no distinct impact (mineral fertilization, no-tillage), or even reduce SOC stocks in the topsoil (bare fallow, business-as-usual). AMP can sequester between −20 ± 210 (mineral fertilization) and 714 ± 404 (compost) kg C ha−1 y−1 in the topsoil. No-tillage practices have no distinct impact, and bare fallow or “business-as-usual” scenarios even reduce SOC stocks in the topsoil. Overall, the carbon sequestration potential of the subsoil (>40 cm) requires further investigation. Moreover, climate change, permanent soil sealing, consumer behavior in dietary habits and waste production, as well as the socio-economic constraints of farmers (e.g., information exchange, long-term economic profitability) are important factors for implementing new AMPs. This calls for life-cycle assessments of those practices.

Changes in the hydrophobic-hydrophilic properties of the organic matter of the chernozems of the Kamennaya Steppe

Soil samples and physical size-density fractions isolated from them (silt particle size less than 1 µm, light fraction (LF) with a density of less than 2 g/cm3 and a fraction of the residue) of ordinary chernozem were studied in three contrasting variants of the experimental fields of the Kamennaya Steppe agrolandscape of the Voronezh region: mowed steppe, long-term permanent bare fallow and permanent corn – the main differences of which are in tillage (cultivated and not cultivated lands) and in the supply/absence of plant residues and root secretions. The LF content changes in the series: “mowed steppe” > “permanent corn” > “permanent bare fallow”, which corresponds to the direction of changes in the total carbon content of the soil and a decrease in the value of the contact angle of wetting (CA) of the surface of the solid phase of the studied chernozems. The determination of the total C and N content revealed the change in the qualitative and quantitative composition of the size-density fractions for different land use cases. Chromatographic fractionation of alkaline extractions of humus substances (HS) of chernozem samples and size-density fractions revealed an increase in the degree of hydrophilicity of HS while simultaneously increasing the hydrophobicity of the solid phase surface and the carbon content in the soil. HS of LF of the “mowed steppe” turned out to be by 63% more hydrophilic than HS of LF of “permanent bare fallow” and by 47% more hydrophilic than HS of LF of “permanent corn”. While the hydrophilicity of the HS silt differed by 16 and 27%, respectively. The hydrophilicity of the HS of the original soil in the plot of the “mowed steppe” was by 41% higher than the hydrophilicity of the HS in the soil in the plot of “permanent bare fallow” and by 24% higher than in the soil of the plot of “permanent corn”. In addition, changes in the hydrophilicity of HS of size-density fractions are more intense than the HS of the soil, so the change in the degree of hydrophilicity of HS of size-density fractions is an indicator of soil degradation under different agrogenic pressue.