Soil Physical Conditions Research Articles

English

Characterization of soils is helpful in the appraisal of soil productivity. The study investigated detailed physico-chemical characterize of the soils developed on basaltic parent materials on the Jos plateau, Nigeria. The aim was to assess appropriate management practice for their sustainability in agricultural production. Four profiles pits were dug and studied, soil samples collected from pedogenetic horizons were analysed for particle size distribution, pH, fertility related properties. Results indicated that the soils were deep, clayey and reddish in colour (2.5YR 3/3-5YR 3/4). In terms of chemical characteristic, the soils are acidic (pH ranged between 4.6 and 5.6) with low to high CEC values (between 4.3 and 14.8 cmol (+) kg-1) and generally low in organic matter on the average (<1.5%) and exchangeable bases. The four profiles developed on basaltic parent materials on the Jos Plateau of Nigeria were characterized and classified as Typic Haplustusts and Andic Haplustepts. All the soils were well drained in spite of high percent clay above 40% and silt fraction of 20 to 30%, which is apparently kaolinitic, with moderate to high aluminium saturation. Higher agricultural productivity of these soils is constraint by low nutrient-holding capacities and strong acidity. Ways to ameliorate these problems include; to raise the exchangeable Al3+ above toxicity and to supply Ca and Mg contents besides improving soil physical conditions.      Key words: Basaltic, typic haplustusts, andic haplustepts, kaolinitic, aluminium toxicity. &nbsp

Development of Tuberous Cassava Roots under Different Tillage Systems: Descriptive Anatomy

The interaction between the roots of cassava (Manihot esculenta Crantz) and soil physical properties has previously been analyzed. This interaction results in differences in production of plant material and in the physicochemical features of the roots, suggesting that changes in soil physical conditions may be related to changes in root anatomy. This work described the anatomical development of the tuberous cassava roots (cv. IAC 576-70) under different tillage systems. Roots grown under three different tillage systems (minimum, conventional and no tillage) were examined at 15, 30, 60, 90, 120, 150 and 180 days after planting (DAP). The tillage systems did not appear to influence root anatomy during root development; at 15 and 30 DAP roots had early secondary growth; at 60 DAP the process of tuber formation had started; at 90 DAP the secondary xylem had completely differentiated to allow storage of starch; at 120, 150 and 180 DAP roots exhibited a similar anatomical structure to that observed at 90 DAP. From these results we conclude that the anatomical structure of cassava tuberous roots is established by 90 DAP and the sequence of establishment and development of tissues that make up the tuberous roots is not influenced by tillage systems during the first 180 DAP.

Actual soil conditions of tsunami-hit farmland : 1. Influence of soil physical conditions on eluviation of salt in terms of soil EC in non-cropped paddy fields in Iwate Prefecture(Progress Review: Tsunami affected farmland)

Actual soil conditions of tsunami-hit farmland : 1. Influence of soil physical conditions on eluviation of salt in terms of soil EC in non-cropped paddy fields in Iwate Prefecture(Progress Review: Tsunami affected farmland)

Determination of wear pattern of cutting elements of tillage machines

The problems of theoretical researches of wear surface of the working tools’ cutting elements of tilling machines are shown in the article. The main aim of the research is to develop a process of hardening, providing increase their longevity and quality of soil treatment. The interaction process of working tools of tilling machines with soil abrasive environment during their movement is characterized by the interaction of abrasive soil on wedge with a flat working surface. This article describes how to influence the impact of soil on a wedge from material deformation nature, the wedge parameters, physical and mechanical properties and soil conditions. The theoretical dependence of these parameters allows to provide the wear of the cutting elements of tilling machines, which will contribute to reduction of the dynamics of their wear. To ensure the longevity of cultivator tooth is necessary reducing the size of their wear is necessary to reduce the ability of abrasive wear out and will provide options of cultivator tooth, which will reduce the dynamics of wear. The research results will select and apply an effective technology of hardening of cutting elements of tilling machines during wear and recovery.

Effect of tillage, lime sludge and cover crop on soil physical state and growth of spring oilseed rape

Research was carried out during 2008–2010 at the Joniskėlis Experimental Station of the Lithuanian Research Centre for Agriculture and Forestry on a clay loam Endocalcary-Endohypogleyic Cambisol (CMg-n-w-can). The aim of the present study was to determine effects of deep (20–23 cm) and shallow (15–17 cm) ploughing, ploughless tillage (10–12 cm), combinations of ploughless tillage (10–12 cm) with incorporation of lime sludge and cover crop (mixture of field pea, common vetch and blue lupine) for green manure and application of the same cover crop for mulch without autumn tillage on soil physical properties and growth of spring oilseed rape (Brasica napus L.) crop. After shallow ploughing the soil water content in seedbed (0–5 cm) for spring oilseed rape right after its sowing was significantly lower in droughty years (with duration of post-sowing period without rainfall for 18 and 20 days in 2008 and 2009, respectively) and crop emergence was worse compared to deep ploughing. Due to ploughless tillage, the soil water content in seedbed was significantly lower in droughty years and seedbed structure was worse in sufficiently wet year compared to deep ploughing. Incorporation of lime sludge by ploughless tillage resulted in significantly higher soil water content at 5–15 cm depth, better seedbed structure and greater crop germination rate compared to ploughless tillage alone. Incorporation of lime sludge also increased oilseed rape yield by 11.1% in droughty year. Having incorporated the cover crop for green manure late in autumn by ploughless tillage the oilseed rape in droughty years germinated significantly worse, the soil water content remaining in the seedbed after emergence was lower and the yield decreased by 19.8% compared to ploughless tillage. Having left the cover crop mulch over winter without autumn tillage demonstrated significantly higher soil water content at 5–15 cm depth after oilseed rape sowing; however, in droughty years the seedbed became drier, its structure deteriorated, the crop germinated worse and yield decreased by 12.1–17.3% compared to ploughless tillage. Spring oilseed rape germination rate in droughty years was influenced by the soil water content in the seedbed after sowing (r = 0.56, P < 0.01), content of 2–5 mm soil aggregate fraction in seedbed (r = 0.50, P < 0.05) and by the seedbed structure, expressed as an index (r = 0.50, P < 0.05), while crop yield – by the seedbed structure (r = 0.67, P < 0.01) and by the germination rate (r = 0.74, P < 0.01).

Soil Fertility under Improved and Conventional Management Practices in Sanga, Kavrepalanchowk District, Nepal

A study was carried out to compare the fertility of soils under improved soil management practice with that of prevailing conventional practice and to assess the farmers’ perception on the improved practice in the upland farming system. The study was carried out in Nasikasthan Sanga of Kavrepalanchok district of Nepal. Soil samples were collected from fields under improved conventional practice. Samples were taken at 0-15 and 15-30 cm depths and were analyzed for various physico-chemical properties to compare the fertility status of the soils under both the practices. Altogether 68 farmers were interviewed to have information on farming practices and information pertinent to improved soil management practice being adopted by them. Results from soil physico-chemical analysis showed higher fertility of soils under improved practice in terms of more favorable pH level, contents of exchangeable bases, available phosphorus and soil organic matter compared to prevailing conventional soil management practice. Moreover, majority of the farmers believed that soil fertility and physical condition of their upland soils had improved and that the productivity of major upland crops had also increased after the adoption of improved soil management practice. Improved practice could play an important role in the sustainable management of upland soils in the mid hills of Nepal. It is however, desirable to conduct long-term research to further ascertain the effect of the practice on soil fertility of different soil types and land uses.Nepal Agric. Res. J. Vol. 9, 2009, pp. 27-39DOI: http://dx.doi.org/10.3126/narj.v9i0.11639

Effects of saturated hydraulic conductivity on volunteer potato (Solanum tuberosum L.) tuber survival

In situ observations were conducted at eight fields in the Tokachi region of the northernmost island of Japan to assess the effects of soil physical conditions on the survival of volunteer potato (Solanum tuberosum L.) tubers. Statistical analyses revealed a positive correlation between the survival rate and the lowest value of saturated hydraulic conductivity to a depth of 0.5 m, except for data from one field where potato tubers were killed by low temperatures below –3°C during winter and from another field with poor drainage despite high soil permeability to 0.5 m in depth. Incubation experiments indicated that potato tubers survived in saturated soil at 0 and 6°C, which respectively matched soil temperatures during the snowmelt period and 1 week thereafter. This result suggests that potato tubers can survive prolonged exposure to moist surface soil caused by large amounts of snowmelt water during the spring snowmelt period. The incubation experiment results also indicated that potato tubers were killed in saturated soil at 15°C. This temperature was almost equal to the average air temperature during the period when volunteer potato tubers were sprouting in the field. Therefore, this result implies that the potato tubers will be killed after a substantial amount of rainfall during the subsequent warm period at poorly drained fields.

Soil Bulk Density and Moisture Content Influence Relative Gas Diffusivity and the Reduction of Nitrogen‐15 Nitrous Oxide

Nitrous oxide is a greenhouse gas and contributes to stratospheric ozone depletion. Soil physical conditions may influence N2O reduction and subsequent N2O emissions. We studied how soil water‐filled pore space (WFPS) and soil bulk density (ρb) affect N2O reduction and surface fluxes. Columns were repacked with soil and arranged in a factorial design at three levels of WFPS (60, 75, and 90%) and three levels of soil ρb (0.94, 1.00, 1.07 Mg m−3). Over 19 d, 15N‐enriched N2O was introduced at the base of the soil columns and N2O fluxes were measured. Relative gas diffusivities (Dp/Do) were also calculated. Soil ρb and WFPS interacted to affect the recovery of N2O‐15N and the antecedent inorganic‐N contribution to surface fluxes. Reduction rates of N2O‐15N ranged from 0.15 to 0.47 mg N2O‐N g−1 soil d−1. Calculated Dp/Do values correlated (P &lt; 0.01) with soil NH4+–N (r = −0.73), NO3−–N (r = 0.93), cumulative N2O‐N flux (r = 0.76), and N2O‐N 15N enrichment (r = 0.80) and were affected by a soil WFPS × soil ρb interaction. Soil N transformations and the net surface N2O flux is dependent on the soil's Dp/Do, and WFPS alone does not suffice to discriminate between N2O emission sources. Consequently, the soil surface N2O flux may be comprised of N2O originating from deeper soil layers transported upward and/or from production in the topsoil.

Quantifying soil physical condition based on soil solid, liquid and gaseous phases

Soil is a three-component system comprised of solid, liquid, and gas phases distributed in a complex geometry that creates large solid–liquid, liquid–gas, and gas–solid interfacial areas. Three soil phase index (TSPI) was developed to characterize the physical condition of a medium-textured soil based on solid, liquid, and gaseous phases by utilizing the concept of diminishing marginal productivity expressed in the Cobb–Douglas (C–D) production function. The index was defined as TSPI=[(Xs−C) XlXg]N. Where C and N are the constants for a given soil, X is volumetric proportion of the soil phases, the subscripts S, L, and G denote solid, liquid and gaseous phases, respectively. The use of TSPI is exemplified with soils under a series of tillage and traffic practices. To evaluate this new concept, the effects of machinery compaction on TSPI values were compared to selected credible methods for characterizing compaction effects on soil structure. A strong positive relationship was observed. TSPI had a significant relationship with selected soil properties, such as bulk density, oxygen diffusion rate, redox potential, and grain yield which were measured in a field experiment reported in the literature. Furthermore, the correlation of TSPI and the soil physical parameter S which is defined as the slope of the soil water retention curve at its inflection point was investigated and a significant linear relationship was also found for soil with given water contents. Overall, the primary advantage of TSPI is that it allows characterizing and evaluating the effects of management practices (e.g., tillage and/or traffic) on the three soil phase condition. Additional testing is needed to evaluate the utility of the index for predicting soil productivity under a wide range of conditions.

Comparison of ecosystem characteristics between degraded and intact alpine meadow in the Qinghai-Tibetan Plateau, China

Climate warming and overgrazing are inducing degradation of the alpine meadow ecosystem on the Qinghai-Tibetan Plateau. The Plateau is an important pastoral region in China and controversy surrounds the estimated carbon release occurring in this region of the world. Nevertheless, little comprehensive research analyzing land degradation has been conducted involving multiple factors in this region. Using two years of observational data, we compared differences in air temperature and relative humidity, soil temperature and moisture, soil texture, soil bulk density, soil organic carbon, soil respiration, vegetation height, coverage and biodiversity, above- and below ground biomass between moderately degraded and intact alpine meadow, and analyzed their relationships. The results show that the main process occurring during degradation was that Spenceria species and weeds with deep roots and a relatively high ability to resist drought replaced Kobresia species that previously exhibited high vegetation coverage and low vegetation height in alpine meadows of the Qinghai-Tibetan Plateau; these changes fundamentally affected corresponding changes in soil physical, chemical and thermal characteristics of the meadows. The change of vegetation species is believed to be the result of drought in the shallow soil of this habitat and is controlled by temperature and precipitation. The results suggest that a good collocation between temperature and precipitation is beneficial to the development of the alpine meadows; conversely, a poor pairing of temperature and precipitation not only causes the degradation of alpine meadows, it can even continually intensify the process by creating a vicious circle involving changes in soil physical, chemical, thermal and hydraulic conditions.

Alkalinity and structure of soils determine the truffle production in the Pyrenean Regions

Aim of study: The program "Typology of truffle stations in the Pyrenean Regions" aimed to define the ecological conditions and culture practices that favor Tuber melanosporum growth and fruiting in this area.Area of study: Navarra, Catalonia, Midi-Pyrénées and Languedoc-Roussillon.Material and methods: The program was based on the survey of 212 wild and cultivated truffle beds of evergreen oaks (Quercus ilex). The data collected in the field consisted of photographs, samples of soil, roots and mycorrhizae, and information on cultural practices followed by truffle growers.Main results: (i) truffle soils are alkaline, from neutral, dolomitic, to moderately or very calcareous soils; (ii) truffle soils are light, well-structured and stable to water immersion; (iii) mycelium that colonizes roots survives in suboptimal conditions, but it does not necessarily bear ascocarps. Finally our results suggest that T. melanosporum is a relatively ubiquitous fungus able to grow, or at least to persist, in a wide range of physical and chemical soil conditions. We propose a probabilistic model of the environment favorable for fruiting, built around a two-dimensional graph with an axis for the chemical conditions, like soil alkalinity, and another axis for the physical conditions, like soil structure. Research highlights: Soil alkalinity and structure allow to built a convenient representation of the ecological capacity of a place to be good T. melanosporum habitat, and thus of the probability for truffle growers to harvest truffles according to the environmental properties of their truffle orchards.Keywords: dolomite; limestone; mycorrhizae; Quercus ilex; field survey; Tuber melanosporum.

Is truffle brûlé a case of perturbational niche construction?

Aim of study: in the context of niche construction theory, the investigation was aimed at assessing if truffle brûlé is a case of niche construction by testing if the disappearance of grasses in the brûlé induces a non-arbitrary perturbation in the soil physical environment and, in that case, which are the physical processes involved.Area of study: a natural truffle bed located in the Italian Apennines inside an experimental truffle-producing area of the University of Perugia.Material and methods: Three aggregate size classes in the soil of a brûlé and of the neighbouring grass-covered area were determined with the wet-sieving technique in accordance with international standards. In the first part of the investigation, the area was sampled according to a systematic sampling design and the spatial patterns of aggregate size classes in the brûlé and in the neighbouring grass-covered area were compared by means of geostatistics. In the second part, the suppression of grasses in the brûlé was mimicked in the laboratory by removing roots from a sample collected in the grass-covered area and the effect of freeze-thaw cycles was tested by comparing a control treatment to other four treatments consisting in sub-samples equilibrated at a water tension of -2.5, -5, -10 and -20 kPa. Samples were submitted to a number of freeze-thaw cycles equal to those recorded in the area, analysed for aggregate size distribution and compared with univariate ANOVA.Main results: The aggregate size classes larger than 0.25mm displayed a spatial pattern comparable to that of the brûlé, with sharp changes along the boundaries of the brûlé itself. The laboratory experiment showed that such changes are attributable to freeze-thaw cycles that in one winter season may produce a significant decrease in aggregate size compared to the grass-covered area. Both results indicate that the disappearance of grasses in the brûlé fulfils the requirement of perturbational niche construction.Research highlights: the observed change of soil aggregation in the brûlé can be useful in delineating soils suitable for truffle farming and in creating suitable soil physical conditions for truffle production by exploiting freeze-thaw cycles after irrigation in winter.Keywords: aggregates; brûlé; niche construction; Tuber, soil structure.

Irrigation of deciduous orchards and vineyards influenced by plant-soil-water relationships in individual situations

Irrigation of deciduous orchards and vineyards influenced by plant-soil-water relationships in individual situations

Triaxial Testing to Determine the Effect of Soil Type and Organic Carbon Content on Soil Consolidation and Shear Deformation Characteristics

The purpose of this paper is to determine the effect of soil type and organic matter on the deformation characteristics of soil. We used triaxial testing to measure both the consolidation and shear deformation of soil. The novel application of this method was applied to soils from two experiments: on a clay loam and a sandy loam. The clay loam soil was from the long-term Broadbalk Experiment at Rothamsted Research, UK, where contrasting treatments had been applied since 1843. The sandy loam soil was from a straw incorporation experiment started in 1986. The clay loam soil from selected treatments from the Broadbalk Experiment had large difference in soil organic C (SOC) content due to additions of farmyard manure (FYM) or inorganic fertilizers for over 170 yr. There were no detectable differences in SOC or microbial biomass C in the sandy loam soil where straw had been incorporated. In addition to triaxial testing, we assessed soil physical condition with measurements of aggregate stability and aggregate tensile strength. From triaxial tests of the repacked soil, we found that soil type and SOC affected the compression characteristics. We also observed that deformation characteristics are more sensitive to small changes in soil management practices designed to increase the SOC content, than measurements of aggregate tensile strength, friability, or stability. We suggest that measurement of deformation characteristics is a potentially powerful approach for detecting or predicting changes in soil physical conditions as impacted by small changes in SOC content resulting from management practices.

Nitrogen mineralization and gaseous nitrogen losses from waterlogged and drained organic soils in a black alder (&amp;lt;i&amp;gt;Alnus glutinosa&amp;lt;/i&amp;gt; (L.) Gaertn.) forest

Abstract. Black alder (Alnus glutinosa (L.) Gaertn.) forests on peat soils have been reported to be hotspots for high nitrous oxide (N2O) losses. High emissions may be attributed to alternating water tables of peatlands and to the incorporation of high amounts of easily decomposable nitrogen (N) into the ecosystem by symbiotic dinitrogen (N2)-fixation of alder trees. Our study addressed the question to what extent drainage enhances the emissions of N2O from black alder forests and how N turnover processes and physical factors influence the production of N2O and total denitrification. The study was conducted in a drained black alder forest with variable groundwater tables at a southern German fen peatland. Fluxes of N2O were measured using the closed chamber method at two drained sites (D-1 and D-2) and one undrained site (U). Inorganic N contents and net N mineralization rates (NNM) were determined. Additionally a laboratory incubation experiment was carried out to investigate greenhouse gas and N2 fluxes at different temperature and soil moisture conditions. Significantly different inorganic N contents and NNM rates were observed, which however did not result in significantly different N2O fluxes in the field but did in the laboratory experiment. N2O fluxes measured were low for all sites, with total annual emissions of 0.51 ± 0.07 (U), 0.97 ± 0.13 (D-1) and 0.93 ± 0.08 kg N2O–N ha−1 yr−1 (D-2). Only 37% of the spatiotemporal variation in field N2O fluxes could be explained by peat temperature and groundwater level, demonstrating the complex interlinking of the controlling factors for N2O emissions. However, temperature was one of the key variables of N2O fluxes in the incubation experiment conducted. Increasing soil moisture content was found to enhance total denitrification losses during the incubation experiment, whereas N2O fluxes remained constant. At the undrained site, permanently high groundwater level was found to prevent net nitrification, resulting in a limitation of available nitrate (NO3−) and negligible gaseous N losses. N2O flux rates that were up to four times higher were measured in the incubation experiment. They reveal the potential of high N2O losses under changing soil physical conditions at the drained alder sites. The high net nitrification rates observed and high NO3− contents bear the risk of considerable NO3− leaching at the drained sites.

Weekly gridded Aquarius L-band radiometer/scatterometer observations and salinity retrievals over the polar regions – Part 2: Initial product analysis

Abstract. Following the development and availability of Aquarius weekly polar-gridded products, this study presents the spatial and temporal radiometer and scatterometer observations at L band (frequency ~1.4 GHz) over the cryosphere including the Greenland and Antarctic ice sheets, sea ice in both hemispheres, and over sub-Arctic land for monitoring the soil freeze/thaw state. We provide multiple examples of scientific applications for the L-band data over the cryosphere. For example, we show that over the Greenland Ice Sheet, the unusual 2012 melt event lead to an L-band brightness temperature (TB) sustained decrease of ~5 K at horizontal polarization. Over the Antarctic ice sheet, normalized radar cross section (NRCS) observations recorded during ascending and descending orbits are significantly different, highlighting the anisotropy of the ice cover. Over sub-Arctic land, both passive and active observations show distinct values depending on the soil physical state (freeze/thaw). Aquarius sea surface salinity (SSS) retrievals in the polar waters are also presented. SSS variations could serve as an indicator of fresh water input to the ocean from the cryosphere, however the presence of sea ice often contaminates the SSS retrievals, hindering the analysis. The weekly grided Aquarius L-band products used are distributed by the US Snow and Ice Data Center at http://nsidc.org/data/aquarius/index.html , and show potential for cryospheric studies.

The role of humic substances in mitigating the harmful effects of soil salinity and improve plant productivity

The environmental, social and economical reasons indicate that the conventional agriculture constitute a continuous pressure contributing to the progressive worsening of environmental conditions, especially by an increasing apply high level of inputs. In this matter, the increasing use of saline irrigation water is one of the main factors resulting in salt accumulation in the plant rhizosphere influencing both physical, chemical and biological soil properties and agroecosystem productivity. In this situation, soil degradation emphasized the need to develop strategies of salt effected soil reclamation. One of the possible solutions is to use humic substances (HS), since there is an increasing need to their utilization in agriculture. They are the major components of soil organic matter, have multiple roles in plant growth and are the subject of study in various areas of agriculture, such as soil chemistry, soil fertility and plant physiology. Thus, our hypothesis account for a beneficial effect of HS in salt affected rhizosphere likely due to a 'direct' action on the plant together with an 'indirect action' on the metabolism of soil microorganisms, the dynamics of uptake of soil nutrients and soil physical conditions. In this paper we review the HS formation and components and their influences on improving saline soil properties as both direct and indirect effects. Keywords: Humic substance; Salt accumulation; Soil degradation; Plant productivity; Hormone-like activity.

3D finite element simulation of a single-tip horizontal penetrometer–soil interaction. Part II: Soil bin verification of the model in a clay-loam soil

Horizontal penetrometers have been recently examined as instruments for on-the-go mapping of soil strength/compaction. Since the horizontal penetrometer resistance (PR) provides a composite soil strength parameter, it needs to be characterized with respect to variations in soil physical properties as well as standardized with respect to the operational parameters of the device. In a recent study, a 3D finite element (FE) model was developed for a single-tip horizontal penetrometer–soil interaction (cf. Part I of this study; Naderi-Boldaji et al., 2013b) and the effect of some soil/operational parameters (mechanical properties of soil, model boundary effects, penetrometer tip extension, working depth and soil failure mode ahead of the tine) on PR was investigated. In the second part of this study, two soil bin tests were conducted to evaluate the PR predictability of the FE model. This is a crucial step for finite element modelling of soil compaction reflected by PR as affected by soil water content, bulk density and texture. The soil bin tests were carried out in a clay loam soil at two different water contents of 0.171 and 0.183gg−1 and dry bulk densities of 1.64 and 1.59Mgm−3, respectively, to evaluate the model at two different levels of PR. The soil elastic parameters (i.e. Young's modulus of elasticity and Poisson's ratio) were estimated from oedometer (uniaxial compression) tests on confined and unconfined undisturbed samples taken within the working depth of the penetrometer whilst the plastic parameters (the parameters of the Drucker–Prager constitutive model) were determined by triaxial tests at three levels of confining stress. The results indicated the practical and efficient use of oedometer tests for estimating soil elastic parameters for numerical simulations. The FE model predicted the measured PR with a small error (<12%) when modelling the soil as elastic-perfectly plastic material, whilst the prediction error was found to be significantly higher when soil hardening was included. This may suggest that the confinement of soil around the moving cone is different than in a confined compression test. It is concluded that the FE model presented here and the procedures used for estimation of the model input parameters reflected well the change in soil physical conditions of the two tests. Further evaluations are needed to generalize the model predictions across soil types and characterize PR with respect to soil physical properties.

Changes in organic carbon in topsoil and subsoil and microbial community composition caused by repeated additions of organic amendments and N fertilisation in a long-term field experiment in Sweden

The effects of 13 years of biennial application of four organic amendments (compost, green manure, farmyard manure and sewage sludge) on soil organic carbon (SOC) stocks, microbial biomass and community structure were compared with those of bare fallow, an unfertilised control and N-fertilised treatments. The experiment was conducted on a clay soil in western Sweden, in a randomised block design with four replicates. The crops grown were spring barley and oats. Changes in SOC mass were estimated by the ‘equivalent soil mass’ concept. Carbon inputs from crops were calculated from grain yields using linear allometric functions. The decomposition rate of soil organic matter was derived from a bare fallow treatment. Humification coefficients, defined here as the fraction of C input entering the SOC pool, for the organic amendments and crop residues were estimated by fitting a single-pool first order model to the final SOC stocks. The humification coefficient was highest for domestic waste compost (0.9) and lowest for above-ground crop residues (0.19). Crop yields were highest in sewage sludge-amended soil, probably due to favourable physical soil conditions, as indicated by lower bulk density (1.27–1.30gcm−3) than in the other treatments (1.32–1.38gcm−3). Despite addition of relatively high amounts of organic N, yields in other treatments receiving organic amendments were significantly lower than in those receiving mineral N fertiliser. In particular, the compost material was found to be highly recalcitrant, as indicated by its low C/N ratio (10) and low crop yield. Comparison of the correlation between phospholipid fatty acid (PLFA) concentration and SOC showed that compost supported relatively less microbial biomass than the other substrates tested. An important finding was that differences in SOC between treatments were significant to 40cm depth and that up to 27% of the SOC changes observed to 40cm depth occurred in the upper subsoil (25–40cm). Thus, SOC changes below ploughing depth should be considered in SOC balance studies.

Soil structure and greenhouse gas production differences between row and interrow positions under no-tillage

No-tillage in Brazil is an efficient agricultural system that improves crop productivity whilst controlling erosion caused to the soil by degradation. However, there is some concern regarding soil compaction. Our objective was to determine whether the function of soil structure in sustaining crop growth was dependent on row and interrow positions in long-term no-tillage. We took soil samples from a field in a commercial farm under long-term no-tillage since 1979 on a clayey Oxisol in Southern Brazil. We assessed soil physical quality using the revised Peerlkamp technique and measured bulk density, air-filled porosity and air permeability of intact soil cores. Samples were incubated to assess in vitro N2O and CO2 production. The soil physical and structural properties showed consistent differences between interrow and row positions, where the properties measured were more favorable. The revised Peerlkamp technique proved as efficient as quantitative parameters in discriminating treatment differences. Overall, soil physical conditions in the interrow were less favourable than in the row. Pore continuity did not vary as regards position. This may explain why row position did not influence in vitro N2O and CO2 production. Soil physical quality under no-tillage system is enhanced, at least in the short term, by superficial disturbances in the row as a result of the action of the coulters of the no-tillage seeder.