Non-compacted Soil Research Articles

Uncovering root compaction response mechanisms: new insights and opportunities.

Compaction disrupts soil structure, reducing root growth, nutrient and water uptake, gas exchange, and microbial growth. Root growth inhibition by soil compaction was originally thought to reflect the impact of mechanical impedance and reduced water availability. However, using a novel gas diffusion-based mechanism employing the hormone ethylene, recent research has revealed that plant roots sense soil compaction. Non-compacted soil features highly interconnected pore spaces that facilitate diffusion of gases such as ethylene which are released by root tips. In contrast, soil compaction stress disrupts the pore network, causing ethylene to accumulate around root tips and trigger growth arrest. Genetically disrupting ethylene signalling causes roots to become much less sensitive to compaction stress. Such new understanding about the molecular sensing mechanism and emerging root anatomical traits provides novel opportunities to develop crops resistant to soil compaction by targeting key genes and their signalling pathways. This expert view discusses these recent advances and the molecular mechanisms associated with root-soil compaction responses.

Soil compaction effects on arbuscular mycorrhizal symbiosis in wheat depend on host plant variety

Background and aimsSupporting arbuscular mycorrhizal (AM) nutrient acquisition in crops may reduce the need for fertilizer inputs, leading to more cost effective and sustainable crop production. In wheat, AM fungal responsiveness and benefits of symbiosis vary among varieties. This study explored the role of soil compaction in this variation.MethodsWe examined in a field experiment how soil compaction affects AM fungal colonization and biomass in five spring wheat varieties, and how these varieties differ in their AM-mediated phosphorus (P) uptake. We also studied soil properties, and AM fungal community composition in roots and soil.ResultsSoil compaction increased AM fungal colonization in the variety Alderon, characterized by root traits that indicate inefficient P uptake. Wheat P concentration and P:N ratio in Alderon and Diskett increased with increased root AM fungal colonization and biomass. In Diskett, which is the most cultivated spring wheat variety in Sweden and has intermediate root traits, total P content per m2 also increased with root AM fungal colonization and biomass.ConclusionsSome wheat varieties, potentially those characterized by P inefficient root traits, such as Alderon, may depend more on AM-mediated P uptake in compacted than in non-compacted soil. Increased P uptake with increased AM fungal colonization in Diskett suggests that efficient root and AM-mediated nutrient uptake can occur simultaneously in a modern variety. Breeding varieties that use roots and AM symbiosis as complementary strategies for nutrient uptake could improve nutrient uptake efficiency and help farmers achieve stable yields in varying conditions.

Effect of Plant Metabolism and Fertilizer Type in the Production of Root Exudates Under the Influence of Root Mechanical Stress

The current study was carried out in order to know the effect of plant metabolism, fertilizer type and michanical stress (soil compaction) factors on the content of root exudates of mungbean plant Vigna radiate L. and maize plant Zea mays L. from primary and secondary metabolites. Root exudates were collected and their contents of metabolites such as total sugars, total proteins, total phenols, total flavonoids total terpenoids, Hormons (gibberellic, abscisic and jasmonic acid), and enzymes (ATPase, catalase and DNase) were estimated using spectrophotometric and HPLC technology, and the results showed the following: (1) Significant superiority in the content of root exudates of maize plants (C4) from all metabolites except for total sugars and gibberellin hormone where their concentration decreased significantly Compared to the root exudates of mungbean plants (C3). (2) Significant superiority in the content of root exudates of plants grown in compacted soils from all metabolites except for gibberellin hormone and DNase, where theirconcentration decreased significantly compared to noncompacted soils. (3) Significant decrease in the concentration of most of the Components of the root exudates of mungbean and maize plants affected by different types of studid fertilizers from metabolites compared to the root exudates of plants not affected by those fertilizers. The complete randomized block design (RCBD) was adopted with a factorial experiment with three factors, namely metabolism (C), fertilizer (F) and mechanical stress (S), and with three replications, and averages of the trasactions were compared using the least significant difference (RLSD) test at the probability level 0.05.

Mechanization Assessment of Soil Compaction Induced by Traffic of Farm Machinery

This study was conducted to investigate the impacts of compacted and non-compacted soils induced by traffic of farm machines and equipment during the agricultural operations on some mechanization properties (e.g. Draught Force, Specific Resistance, Energy Use Efficiency and Soil resistance to cutting and shaping). The experiment was conducted during the spring agricultural season of 2022 in one of the farms that located about 30 km Northwest Mosul city - Nineveh Governorate - Iraq. Randomized Complete Block Design (RCBD) was used for data analyses with four replications (n=4). The experimental site was divided into two main blocks based on the investigated factors (1) two levels of rear tire pressure were tested (8 psi and 15 psi), (2) number of traffic (no traffic, one traffic, two traffics and three traffics). These variables were investigated under two different soil textures (clay soil, silty loam soil). Duncan’s multiple range test was utilized to compare between the means at a 5% probability level. The results showed that CTF system represented by non-trafficked soil has achieved the best values (P< 0.05) for all studied indicators, particularly when practiced under clay soil. Draught force was significantly better with non-trafficked soil compared to the one-traffic, two-traffics and three-traffics by approximately 30%, 33% and 40%, respectively. Energy Use Efficiency was also increased under non-trafficked soil (no-traffic) by approximately 30%, 45%, 48% compared to the one-traffic, two-traffics and three-traffics of farm machinery, respectively. The best values of the investigated indicators were reported when CTF has practiced (no-traffic) in the clay soil using 15 psi tire pressure.

Linking wheat nitrogen use to root traits: Shallow and thin embryonic roots enhance uptake but reduce conversion efficiency of nitrogen

Nitrogen (N) is considered quantitatively most important for crop growth and productivity. The improvement of crop N use efficiency is economically beneficial to farmers and reduces the negative environmental impact of agriculture. Root traits are promising, yet underexploited breeding targets to improve N use efficiency. We aimed to evaluate (1) the effects of genotype and environment on N use efficiency and various root architectural and anatomical traits; and (2) the relationships between root traits, N uptake and conversion efficiency. Nine spring wheat genotypes were grown on compacted and non-compacted soil during two years with contrasting weather conditions in Central Sweden. Wheat genotype and year caused considerable variation in several root and N use efficiency traits. Negative correlations were found between N uptake efficiency and N conversion efficiency; root number and diameter; root number and angle; and metaxylem number and diameter. The N uptake efficiency increased with shallower root angle, higher root number, smaller root diameter, higher metaxylem number and smaller metaxylem diameter; whilst N conversion efficiency showed the opposite pattern. We conclude that a negative relationship observed between N uptake efficiency and N conversion efficiency can be linked to trade-offs between embryonic root traits. • Root and nitrogen (N) use efficiency traits varied greatly between wheat genotypes. • Thinner roots and shallower root angle increased N uptake efficiency. • Trade-offs between root traits are linked to trade-offs between N use traits. • Root traits can be used in the breeding towards improved N use efficiency traits.

3D-printed biological habitats for the protection and persistence of &lt;em&gt;Rhizobia&lt;/em&gt; species in compacted soils

Microorganisms in soils are responsible for many ecosystem services. However, in degraded soils microbial abundance and function are limited which compromises several biologically facilitated processes. Inoculating soils with desirable microbes can help to re-instate or initiate a viable functioning microbial community. However, establishment success is reliant on the survival of the microorganism in an adverse environment. In this proof-of-concept study, artificial microbial refugia have been developed using resin and light-emitting diode array (LED) 3D printing technology. We assessed whether the artificial refugia, termed a Rhiome, would support better microbial growth in degraded soils. Soil compaction, a form of soil degradation, and Rhizobium, an important microorganism for global agriculture, were both selected as the use case application for this assessment. Different materials together with resin were assessed for their suitability as a 3D printing material and for supporting rhizobial growth. The best result was found in materials constructed with a combination of polylactic acid (PLA) resin, yeast extract and mannitol. In a soil compaction experiment with inoculation of rhizobia, the addition of Rhiome significantly increased bacterium survival in the compacted soil to a level similar to, or higher than, the rhizobial loading in non-compacted soils. Augmentation of the resin with yeast extract and mannitol increased Rhizobium growth significantly compared with the Rhiome constructed only with resin. These results indicate that the Rhiome was highly beneficial for instigating and maintaining significant rhizobia survival and growth in compacted soils. Further work, including near-to-field assessments, are required to assess Rhiome performance in a range of applications and to refine material properties relative to important context-specific performance metrics such as degradation rate. We propose the Rhiome concept as a promising asset in the toolbox for soil ecological restoration as a means of improving soil resiliency.

Bio‐tillage improves soil physical properties and maize growth in a compacted Vertisol by cover crops

AbstractBio‐tillage has recently been proposed as a measure to alleviate soil compaction through biopores created by cover crop roots. The objective of this study was to determine the effect of different cover crops on soil physical properties and the succeeding maize (Zea mays L.) growth in compacted soil. Four treatments, including no cover crop as a control (Con), alfalfa (Medicago sativa L.), oilseed rape (Brassica napus L.), and radish and hairy vetch mixture (Raphanus sativus L. and Vicia villosa Roth), were carried out under both compacted and noncompacted soil conditions. Soil physical properties, such as the volumetric soil water content (SWC), bulk density, saturated hydraulic conductivity (Ks) and air permeability at water potential of −60 hPa (Ka60), and maize root characteristics and yield were measured. The cover crops did not affect the soil bulk density but significantly decreased the SWC in both the compacted and noncompacted soils relative to the Con treatment. The alfalfa treatment presented significantly higher Ks in the noncompacted soil and Ka60 in both the compacted and noncompacted soils than the Con treatment in the soil layer depth of 20–50 cm. The three cover crop treatments improved the maize root biomass density (173.2% for 2018 and 35.6% for 2019) and root length density (50.9% for 2018 and 51.8% for 2019) relative to the Con treatment in the soil layer depth of 10–70 cm in 2018 and soil layer depth of 10–50 cm in 2019 in the compacted soil rather than in the noncompacted soil. Compared with the Con treatment, the radish mixed with hairy vetch treatment in 2018 and the oilseed rape treatment in 2019 significantly enhanced the maize yield in the compacted soil. Our results suggest that alfalfa is the best crop for improving air permeability; however, the oilseed rape and mixture of radish and hairy vetch lead to better maize growth in the compacted soil. Bio‐tillage using cover crops is effective in alleviating soil compaction.

A modeling framework to quantify the effects of compaction on soil water retention and infiltration

AbstractThe water retention curve (WRC) of arable soils from the southeastern United States at different levels of compaction (no compaction, and 10 and 20% increases in soil bulk density) was estimated using the van Genuchten–Mualem (VG) model. The VG water retention parameters of the noncompacted soils were obtained first by fitting measured soil hydraulic data. To construct the WRC of the compacted soils, gravimetric values of the permanent wilting point (θgw, 1,500 kPa) and the residual (θgr) water content were assumed to remain unchanged with compaction. The VG parameter α and exponent η after compaction were estimated using two approaches. In Approach 1, α and η were estimated from saturation, the permanent wilting point, and the residual water content. In Approach 2, the value of η was assumed to remain unchanged with compaction, which allowed α to be estimated immediately from the VG equation. Approach 2 was found to give slightly better agreement with measured data than Approach 1. The effect of compaction on the saturated hydraulic conductivity (Ks) was predicted using semitheoretical approaches and the VG‐WRC function. HYDRUS‐1D was further used to simulate vertical infiltration into a single‐layered soil profile to determine the impact of compaction on the infiltration characteristics of the soils used in our analyses. Results showed that a 10–20% increase in soil bulk density, due to compaction, reduced cumulative infiltration (Ic) at time T = Tfinal (steady‐state) by 55–82%, and the available water storage capacity by 3–49%, depending upon soil type.

Effects of soil compaction on grain yield of wheat depend on weather conditions

The use of heavy farm machinery has resulted in widespread soil compaction in many regions of the world. Compacted soil limits the access of crops to soil water and nutrients and is expected to reduce crop productivity, but the influence of weather conditions on the interactions between compacted soil and crop productivity is unclear. Furthermore, early vigor has been regarded as a promising trait for improving the yield of crops grown under edaphic stress such as soil compaction. We aimed to assess the combined effects of soil compaction and contrasting weather conditions on growth and grain yield of spring wheat, and to evaluate the association between early vigor and grain yield under temporal variations of the soil physical conditions. Nine spring wheat genotypes were grown on compacted and non-compacted soils during two cropping seasons with contrasting weather conditions in Central Sweden. Compared to the non-compacted treatment, soil compaction increased the relative growth rate of shoot biomass from sowing to stem elongation, and from stem elongation to flowering in the drier year (2018), but decreased the same traits in the wetter year (2019). The contrasting effects of soil compaction on shoot growth in the two years could be explained by soil moisture and penetration resistance associated with the interactive effects of soil compaction and weather condition. Higher early vigor, here indicated by higher relative growth rate from sowing to stem elongation, was associated with reduced grain yield under the progressively drying and hardening soil conditions during the entire cropping season of both years. We conclude that the interactive effects of soil physical and weather conditions need to be considered when evaluating the impact of soil compaction on crop growth and productivity. The potential of early vigor to increase grain yield is strongly influenced by the temporal dynamics of soil physical conditions.

A meta-analysis of the impact of traffic-induced compaction on soil physical properties and grain yield

Soil compaction caused by wheel traffic is a major driver of soil degradation in modern agriculture and thus, a threat to agricultural sustainability. To improve the predictive capacity of compaction models and to support decision-making that implements site-specific practices for ameliorating soil compaction effects in modern agriculture, we need quantitative syntheses of the effect of soil compaction on soil physical properties and crop types. In this work, we used a meta-analytical approach to summarize results from 51 published articles on the impacts of soil compaction attributed to machinery axle load, wheel passes, compaction events and tire inflation pressure on soil bulk density (ρb), degree of compactness (DC), penetration resistance (PR), volume of water filled pores at field capacity (θFc), air permeability (ka) at field capacity, saturated hydraulic conductivity (ksat), and grain yield of corn (Zea mays L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and soybean (Glycine max L.). Results from this meta-analysis (MA) showed that compaction increased soil mechanical strength shown by increased soil ρb, DC and PR. However, an increase in soil strength was more pronounced in the medium- and coarse-textured soils, and mainly in the topsoil (0–30 cm depth). Penetration resistance for the non-compacted soil (control) treatment was 1.21 MPa for the coarse-textured, 1.11 MPa for the medium-textured and 0.93 MPa for the fine-textured soils. Soil compaction on average, increased PR by 99, 94 and by 41 percent in the medium-, coarse- and fine-textured soils. Compaction decreased hydraulic conductivity characterized by ka and ksat from the topsoil down to the subsoil (>40 cm depth), and grain yield of corn, wheat, barley, and soybean. Overall, compaction decreased grain yield on average by 6–34 percent. Findings of the MA suggest that soil hydraulic properties may be more sensitive indicators to reflect the impact of soil compaction on soil structure and pore system functions in the soil profile. Future efforts should place a greater emphasis on the publication of complete metadata that allows replication and accurate comparison of results across studies and on providing open access to original datasets that can be used to improve our understanding of the effect of traffic-induced compaction on soil functioning, including crop production.

Controlled traffic farming delivers improved agronomic performance of wheat as a result of enhanced rainfall and fertiliser nitrogen use efficiency

ABSTRACT This study investigated the agronomic response and economic return of wheat grown in compacted and non-compacted soils to represent the conditions of non-controlled (non-CTF) and controlled traffic (CTF) systems, respectively. Yield-to-nitrogen responses were derived after application of urea, DMPP-treated urea, and UAN at rates between 0 and 300 kg ha−1 N. Soil properties were measured to guide parametrisation of APSIM, which was used to assess long-term (50 years) effects of CTF and non-CTF soil conditions on crop productivity, rainfall-use efficiency (RUE) and surface runoff. Grain yield and yield components were significantly higher in CTF compared with non-CTF. When N inputs were optimised, N use efficiency (NUE) was more than double in CTF (≈23%) compared with non-CTF (≈9%). RUE was about 15% higher in CTF, which concurrently reduced the amount of surface runoff compared with non-CTF. For years with average rainfall (240-mm in-crop), yield penalties of up 12% may be expected in non-CTF. APSIM simulations showed that increased productivity, and inter-annual yield stability, can increase gross margin of wheat by AUD30-50 ha−1 depending on in-crop rainfall and the tillage method used. In non-CTF systems, improvements in NUE and RUE are constrained by soil compaction. Enhanced efficiency fertilizers cannot compensate for other stresses caused by compaction and therefore cannot achieve the same NUE and RUE as the CTF system. Adoption of CTF in water-constrained environments improves profitability and resource-use efficiency.

Controlled traffic farming effects on productivity of grain sorghum, rainfall and fertiliser nitrogen use efficiency

Controlled traffic farming (CTF) is a mechanisation system in which all machinery has the same (or modular) working and track width so that field traffic can be confined to the least possible area of permanent traffic lanes. CTF enables productivity of non-compacted crop beds to be optimised for given energy, fertiliser and water (rainfall) inputs. This study investigated the agronomic response and economic return of grain sorghum grown in compacted and non-compacted soils to represent the conditions of non-CTF and CTF systems, respectively. Yield-to-nitrogen (N) responses were derived following application of urea, 3,4-dimethyl pyrazole phosphate-treated urea (DMPP), and urea ammonium nitrate (UAN, 32% N) at rates between 0 and 300 kg ha −1 N. Selected soil properties were measured to guide parametrisation of the Agricultural Production Systems Simulator (APSIM), which was used to assess long-term (55 years) effects of CTF and non-CTF soil conditions on crop productivity, rainfall use efficiency (RUE) and develop rainfall-runoff relationships. Grain yield and yield components (harvest Index, grain thousand-grain weight, number of grains) were significantly higher in CTF compared with non-CTF. On average, the most economic N rates, and corresponding grain yields, were 144 and 3428 kg ha −1 , and 100 and 1796 kg ha −1 for CTF and non-CTF, respectively. When N inputs were optimised, agronomic efficiency calculations showed 18% increase in CTF compared with non-CTF. Nitrogen use efficiency (NUE) was 1.75 times higher in CTF than in non-CTF. Rainfall-use efficiency was about 65% higher in CTF, which concurrently reduced the amount of runoff compared with non-CTF. Average rainfall season (330–450 mm in-crop) grain yield was 30% lower in non-CTF compared with CTF. For subtropical conditions of Australia, long-term APSIM simulations showed that increased productivity and inter-season yield stability can increase gross margin of grain sorghum by AUD74 ha −1 or greater depending on the adopted tillage system and in-crop rainfall. In non-CTF systems, improvements in NUE and RUE are constrained by soil compaction. Enhanced efficiency fertilisers, such as DMPP-treated urea, cannot compensate for other stresses caused by soil compaction and therefore cannot achieve the same NUE and RUE as the CTF system. Adoption of CTF delivers improved resource-use efficiency and profitability in rainfall-limited environments. Long-term (1960–2015) simulation of grain yield (A) and runoff (D) as a function of in-crop rainfall. Modelled data for grain sorghum-fallow cropping on a Red Ferrosol in Toowoomba (Queensland, Australia) in controlled (CTF) and non-controlled traffic farming (non-CTF) systems, respectively. Continuous lines show the best fit to predicted data. Dotted vertical lines show the 30th (left) and 70th (right) percentiles rainfall, respectively. • Controlled traffic farming (CTF) increased long-term grain yields by 30% in average-rainfall seasons. • Fertiliser nitrogen use efficiency (NUE) was 1.75 times higher in CTF compared with non-CTF. • Rainfall use efficiency (RUE) was 65% higher in CTF compared with non-CTF, which significantly reduced runoff. • Avoidance of (random) field traffic is a pre-requisite for jointly improving fertiliser NUE and RUE. • In non-CTF, improvements in NUE and RUE are constrained by compaction. • Enhanced efficiency fertilisers cannot compensate for other stresses caused by compaction.

Soil compaction and cover with black oat on soybean grain yield in lowland under no-tillage system

ABSTRACT: Brazil is the largest exporter and second largest producer of soybean grains. Most of this production is from plants grown under no-tillage system (NT). This research evaluated the effect of soil compaction, and different amounts of black oat residues on the soil surface on soybean growth and grain yield in lowland under NT. The experiment was conducted in a completely randomized design with seven treatments and four replications, in the 2016/2017 and 2017/2018 crop seasons. The treatments consisted of: 1) winter fallow without soil compaction (WF); 2) winter fallow with soil compaction (WF-C); 3) black oats and complete removal of surface residues, with soil compaction (0R-C); 4) black oats and removal half of surface residues, with soil compaction (0.5R-C); 5) black oats without surface residue removal, with soil compaction (1R-C); 6) black oats without surface residue removal, plus the residues from treatment 3, with soil compaction (2R-C); 7) black oats without surface residue removal, without soil compaction (1R). When the soybean plants were at the phenological stage R2, they were evaluated nodule, root and shoot dry matter, nitrogen contents, plant height, and grain yield. The soil physical properties were evaluated in the 0.0-0.05, 0.10-0.15 and 0.20-0.25 m layers. The soybean aerial dry matter is &gt; 38% in non-compacted soil in year with soil water excess, regardless of the amount of surface oat straw. In year with small water deficit, soil with more surface oat straw produced &gt; 5% shoot dry matter and &gt; 4% of soybean grain, regardless of compaction. The plant growth and grain yield soybean in lowland varied according to the water conditions, and were affected by soil compaction and amounts of black oats residues on soil surface.

Stability analysis of vegetated residual soil slope in Thailand under rainfall conditions

The effects of climate change including intense rainfalls have resulted in many slope failures. The bioengineering method using vegetation is an environmentally friendly alternative for slope stabilisation. This paper presents the effect of root reinforcement on the stability of vegetated slope under rainfall condition. A transient seepage and slope stability analysis was conducted based on the finite-element and limit equilibrium methods. Field monitoring on a residual soil slope in Thailand was numerically modelled. In transient seepage analysis, the soil-water characteristic curve and the saturated permeability measured from laboratory and in situ tests were used, and the results were comparable with the monitored values from the site. For slope stability analysis, the effective shear strength parameters from direct shear tests were used to model the well-compacted and non-compacted soil slopes. The additional shear strength of soil from the root cohesion was modelled for vegetated soil slope. The results show that the contribution of root cohesion to slope stability was more significant for the non-compacted soil condition than for the well-compacted one. Both modelled and monitored pore-water pressure reached the highest values about 1 d after the daily rainfall had reached its peak. This finding has a significant implication for landslide warning based on rainfall.

Study on Compaction of Reclaimed Soil of Nonmetallic Mining Area in Northern Foothills of Tianshan Mountains in Xinjiang, China

This study focused on the changes of the compaction of the reclaimed soil after the reclamation process and the one-year maintenance period of the nonmetallic mines in north foothills of Tianshan Mountains in Xinjiang. The plate load experiment method was employed to simulate the compaction effect of various times of compaction from the reclamation machine on a different thickness of the reclaimed soil. The experimental data were analyzed by multivariate statistical analysis. The experimental results showed both compaction frequency and thickness of the reclaimed soil were key factors affecting the compaction of the reclaimed soil, and the interaction between them had a dramatic impact on the soil compaction. The difference of the porosity between the three-time compacted soil by the compaction machine and the noncompacted soil was significant. The effect of a single compaction dampened with the increasing times of compaction. The porosity of the 50 cm and 70 cm thick topsoil continuously decreases with the increasing times of compaction at the depth of 10 cm from the surface soil. The porosity at the 30 cm depth of the 50 cm and 70 cm thick topsoil decreased first and then increased with the increasing times of compaction. At the end of the one-year maintenance period, samples from different depths of the reclaimed soil of various thicknesses were collected to investigate the changes of porosity. The results showed the porosity of the reclaimed soil at different depths was changed due to irrigation. The porosity of the uncompacted soil decreased progressively from the surface to the deep region. The porosity of the compacted soil at the 10 cm depth was lower than that at the 30 cm depth due to soil sealing, whereas the porosity decreased with the increasing depth in the deeper region. The results from this study could provide a fundamental reference for the reclamation of nonmetallic mines in northern foothills of Tianshan Mountains in Xinjiang, China.

Natural regeneration of Pinus brutia Ten. in a recreational public forest in Zawita-Kurdistan region, Iraq

Zawita natural forest has recently has been subject to mass recreational activities during spring that have denuded large areas of the forest. It was thus essential to assess regeneration before designing optimizing strategies. To this end, we studied the overstory canopy and microhabitat conditions for recruitment of Pinus brutia Ten in 10 plots (20 × 25 m) on the southern aspects where the Zawita natural forest is still present. In total, 1540 regenerating P. brutia were recorded, 854 seedlings, 597 saplings, and 89 trees. Seedlings and saplings were more frequent beyond the canopy than under the canopy of the parent trees. Regeneration requirements differed between seedlings and saplings. The probability of the occurrence of seedlings was negatively correlated with increasing litter depth and increasing soil compaction. The density of saplings only showed a positive significant correlation with increasing slope. The nearest neighbor index showed a trend toward a positive spatial association between understory shrubs with their neighboring seedlings at a mean distance of 1.6 m. Overall, the study highlighted the requirements for seedling regeneration as a relatively open canopy cover, a light understory litter layer, and non-compacted soils. These results are a step towards designing effective management and restoration programs.

Nitrous oxide emissions from cattle urine deposited onto soil supporting a winter forage kale crop

ABSTRACTWintering cows on forage crops leads to urine being excreted onto wet, compacted soils, which can result in significant emissions of nitrous oxide (N2O). A field trial was conducted to determine the N2O emission factor (EF3; proportion of urine-N lost as N2O-N) for dairy cows wintered on a kale forage crop on a poorly drained soil. Urine was collected from non-lactating dairy cows on a forage kale diet and applied at 550 kg N ha−1 to artificially compacted soil to simulate trampling and non-compacted soil in a kale field. Cumulative N2O losses over four months were 7.38 and 2.64 kg N2O-N ha−1 from urine applied to, respectively, compacted and non-compacted soil. The corresponding EF3 values 0.75% and 0.30%, respectively, differed (P = .003) due to compaction. Combining our results with previous studies, where brassica-fed livestock urine was applied to soils supporting a forage brassica crop, suggested a significant relationship between soil water-filled pore space (WFPS) and brassica-derived urine EF3 (P = .005).

Can biochar alleviate soil compaction stress on wheat growth and mitigate soil N2O emissions?

Soil compaction occurs widely in modern agriculture, leading to reduced crop yields and enhanced soil N2O emissions. Biochar, an emerging biomass-pyrolysis product with porous structure, is hypothesized to alleviate soil compaction problems. A field mesocosm experiment involving biochar addition and soil compaction in a factorial design was conducted on a land cultivated with wheat. The results showed that biochar had little effect on wheat grain yield, but it increased wheat vegetative growth and reduced seasonal cumulative soil N2O emissions from both compacted and non-compacted soils. Across all treatments, biochar-induced changes in individual soil N2O fluxes mainly occurred within a couple of days after nitrogen fertilization, and were sensitive to soil moisture, with an average increase of 13% under low soil moisture conditions (<70% water holding capacity (WHC)) that was likely driven by increased abundance of ammonia-oxidizing archaea and bacteria, and an average decrease of 36% under high soil moisture conditions (>70% WHC) that was likely induced by raised abundance of N2O-reducing bacteria. The stimulated population sizes of nitrifiers and denitrifiers in biochar-amended soils were more dependent on biochar's chemical mediation (a shift of soil pH from moderate acidity towards neutrality) than physical mediation. This study indicated that biochar could alleviate soil compaction stress on wheat growth and mitigate soil N2O emissions, and to promote biochar's role in reducing soil N2O emissions, the best practice for nitrogen fertilization is before precipitation or followed by irrigation.

Soil precompression stress, penetration resistance and crop yields in relation to differently-trafficked, temperate-region sandy loam soils

Compaction of the subsoil due to heavy traffic in moist and wet soil is widespread in modern agriculture. The objective of this study was to quantify the effects from realistic field traffic on soil penetration resistance and barley crop yield for three Luvisols developed from glacial till. Undisturbed soil cores were used for quantifying the precompression stress (Ͽpc) of non-compacted soil. Tractor-trailer combinations for slurry application with wheel loads of ⿼3, ⿼6 and ⿼8Mg (treatments M3, M6, M8) were used for the experimental traffic in the spring at field-capacity. For one additional treatment (labelled M8-1), the soil was loaded only in the first year. A tricycle-like machine with a single pass of wide tyres each carrying ⿼12Mg (treatment S12) was included at one site. Traffic treatments were applied in a randomized block design with four replicates and with treatments repeated in four consecutive years (2010⿿2013). After two years of repeated experimental traffic, penetration resistance (PR) was measured to a depth of 1m. The yield of a spring barley crop (Hordeum vulgare L.) was recorded in all four years of the experiment. The results did not support our hypothesis of Ͽpc as a soil strength measure predicting resistance to subsoil compaction. The tyre inflation pressure and/or the mean ground pressure were the main predictors of PR in the upper soil layers. For deeper soil layers, PR correlated better to the wheel load. The number of wheel passes (M-treatments vs the S12 treatment) modified this general pattern, indicating a very strong impact of repeated wheel passes. Our data indicate that a single traffic event may mechanically weaken the soil without inducing major compaction but with influence on the effect of subsequent traffic even after as long an interval as a year (treatments M8 vs M8-1). Crop yields were much influenced by compaction of the plough layer. Due to the repeated wheel passes for the M-treatments, significant yield penalties were observed, while the single-pass treatment with 12 Mg wheel load in S12 did not have significant effects on crop yield. Our hypothesis of 3 Mg wheel load as an upper threshold for not inducing subsoil compaction was confirmed for the tractor-trailer treatments with repeated wheel passes but not supported for the single-pass machinery. The results call for further studies of the potential for carrying high loads using wide, low-pressure tyres by crab steering/dog-walk machinery.

Occurrence and dynamics of Impatiens parviflora depending on various environmental conditions in the protected areas in Slovakia

Abstract Biological invasion as one of the main threats to natural ecosystems has big economic impact on conservation of nature. Studies of the population biology of invasive species may allow more precise focus on specific plant and soil characteristics involved in invasiveness. The aim of the study was to investigate the relationship between selected biological population characteristics of Impatiens parviflora and a few chosen chemical and physical soil features. Sites were selected because of the poor mapping of invasive plants in the protected natural areas and their interactions with specific soil characteristics. Research on I. parviflora was realised during a vegetation season in three forest nature reserves in Prešov district, Slovakia. Some population biological characteristics of I. parviflora as one of the most invasive plant species in Slovakia and Central Europe were surveyed. The correlation between the numbers of plants was analysed, as well as select population biological characteristics of I. parviflora (plant height, width of the largest leaf and the number of flowers/fruits) on some select chemical and physical soil attributes (soil pH, bulk density, porosity and soil moisture) were analysed. The results suggest that biological characteristics of I. parviflora in three different microhabitats – a meadow (a habitat without tree vegetation), a habitat close to the stumps and a habitat under dense tree vegetation seemed to influence the selected soil parameters. Our results showed that I. parviflora prefers acidic and non-compacted soil conditions. Sunlight and soil moisture do not show statistically significant differences on any biological characteristic of the population. The results also suggest that the autecology of I. parviflora in Western and Central Europe is not very well known and deserves further study.