Variability Of Soil Bulk Density Research Articles

Precompression stress and compression index depend on the property used to represent the soil deformation in the compression curve

ABSTRACT: During linear deformation (h) in a soil sample, the variation of the void ratio with respect to deformation (dε/dh) and the respective variation of soil bulk density (dρ/dh) are identical only for a specific value of h. Consequently, if two compression curves are drawn for the same soil sample, one using ρ and the other using ε, there are differences in both the calculated precompression stress (σp) and compression index (Ic). In this study, we highlight the causes by a mathematical analysis and an experimental investigation, quantifying the differences in σp and Ic when using ε and ρ. σp and Ic were calculated for 103 compression curves of an ultisol and 193 of an oxisol. The σp (kPa) using ρ (σpρ) was greater than when using ε (σpε), and differences were rather independent of the soil type. The relations found by linear regression relating σpρ to σpε were σpρ=0.8186σpε+34.202 for the ultisol and σpρ=0.8878σpε+34.875 for the oxisol. In contrast, the used soil property (ρ or ε) as well as soil type affected Ic. Ic calculated using ρ was greater than when using ε in almost all (96%) of the cases for the ultisol, and in only 12% of the cases for the oxisol. For a wide range of ρ, evidence from this study indicated that the use of ρ overestimates σp when compared to the use of ε.

Long-term monitoring of soil management effects on runoff and soil erosion in sloping vineyards in Alto Monferrato (North–West Italy)

Long-term runoff and soil erosion data have been collected from differently managed field-scale vineyard plots within the “Tenuta Cannona Experimental Vine and Wine Center of Regione Piemonte”, located in the Alto Monferrato vine production area (NW Italy). The primary intent of the program was to evaluate the effects of agricultural management practices on the hydrologic, soil erosion, nutrient transport and soil compaction processes in vineyards. Field runoff data have been collected for every event since the year 2000 until now. Sediment and nutrient concentrations in water have been also monitored. Regarding soil properties and initial conditions, surveys have been carried out to investigate spatial and temporal variability of soil bulk density, soil saturated conductivity, soil water content, and penetration resistance. The Cannona Data Base (CDB) includes data for more than 300 runoff events and over 90 soil loss events; moreover, periodic measurements for soil physical characteristics are included for the three plots.Runoff and sediment yield showed high annual and seasonal variability and were strongly affected by the adoption of different soil management in the vineyard inter-rows, especially after some years of observation. Grass cover reduced runoff by at least 37%, in comparison with management by tillage, and average annual sediment yield ranged from 1.8Mgha−1year−1 to 20.7Mgha−1year−1, respectively for the “grass covered” and the “reduced tillage” vineyards. Furthermore, results showed the effect of the adopted soil management on soil properties. The Cannona Data base (CDB) can be accessed via a website (http://sustag.to.cnr.it/index.php/cannona-db) supported by the IMAMOTER-CNR.

Vegetation succession and soil infiltration characteristics under different aged refuse dumps at the Heidaigou opencast coal mine

Vegetation succession and soil infiltration characteristics under five different restoration models of refuse dumps including different-aged revegetated sites (1995, 1998, 2003 and 2005) in the northern, eastern and western open-pit coal mine dump and a reference site with native vegetation, which had never been damaged by coal mining activities on the Heidaigou Open Cut Coal Mine were studied. Changes in the plant species, soil properties and infiltration rates were evaluated at the different refuse dumps. The results indicated that the number of herbaceous species, plant cover, biomass, fine particles, and total N, P and SOM increased significantly with increasing site age. However, the number of shrub species decreased since revegetation, its cover increased from 17% to 41% initially and subsequently decreased to the present level of 4%. The natural vegetation community and the northern refuse dump had the highest cumulative infiltration rates of 3.96 and 2.89 cm s−1 in contrast to the eastern and western refuse dumps and the abandoned land, where the highest cumulative infiltration rates were 1.26, 1.04 and 0.88 cm s−1, respectively. A multiple linear regression analysis indicated that the infiltration rate was primarily determined by the silt percentage, SOM, plant coverage and the variation in soil bulk density. Our results provide new ideas regarding future soil erosion controls and sustainable development at open-pit coal mine refuse dumps.

Seasonal Variation in Soil Bulk Density, Organic Nitrogen, Available Phosphorus, and pH

Scientists are being called on to measure and predict the effects of soil management and climate change on organic matter and other soil properties. The estimates and predictions generated from current conditions and short-term experiments will only be accurate if our measurement techniques produce data that represent actual soil properties during the period of prediction. Perhaps the least studied aspect of soil sampling is the possibility that the timing of samples might introduce large non-random errors. This study sampled replicated plots every month for 39 mo. Even after removing the measurement variation caused by surface soil bulk density fluctuations, variations in organic N, available P, and pH were always >10% of the mean. Much of the variation appeared to be temporally correlated in a seasonal cycle. In this experiment, with a 1-yr crop rotation, averaging 12 monthly samples allowed differences among soil treatments to be detected that were within 2 to 4% of the mean. When highly accurate estimates are desired, researchers need to consider combining multiple sample timings to overcome temporal variability.

Implications of short‐range spatial variation of soil bulk density for adequate field‐sampling protocols: methodology and results from two contrasting soils

SummarySoil bulk density (BD) is measured during soil monitoring. Because it is spatially variable, an appropriate sampling protocol is required. This paper shows how information on short‐range variability can be used to quantify uncertainty of estimates of mean BD and soil organic carbon on a volumetric basis (SOCv) at a sampling site with different sampling intensities. We report results from two contrasting study areas, with mineral soil and with peat. More sites should be investigated to develop robust protocols for national‐scale monitoring, but these results illustrate the methodology. A 20 × 20‐m2 monitoring site was considered and sampling protocols were evaluated under geostatistical models of our two study areas. At sites with local soil variability comparable to our mineral soil, sampling at 16 points (4 × 4 square grid of interval 5 m) would achieve a root mean square error (RMSE) of the sample mean value of both BD and SOCv of less than 5% of the mean (topsoil and subsoil). Pedotransfer functions (PTFs) gave predictions of mean soil BD at a sample site, comparable to our study area on mineral soil, with similar precision to a single direct measurement of BD. On peat soils comparable to our second study area, the mean BD for the monitoring site at depth 0–50 cm would be estimated with RMSE to be less than 5% of the mean with a sample of 16 cores, but at greater depths this criterion cannot be achieved with 25 cores or fewer.

The influence of Caragana korshinskii shrub on soil and hydrological properties in a revegetation-stabilized desert ecosystem

Shrub-induced spatial heterogeneity of soil and hydrological properties are common in arid and semi-arid ecosystems. To examine the influence of shrubs on spatial patterns of soil physical, chemical and hydrological properties, the typical sand-fixation species, Caragana korshinskii, was studied in the Shapotou area of the Tengger Desert, China. Miniature cylinder infiltrometers were used to quantify the spatial variations of infiltration rate in the soils, and were installed at 20-cm intervals around the shrubs. Meanwhile, soil samples were collected at 0–5 cm depth every 10 cm to analyse their physical and chemical properties and soil moisture content. The results indicate that the various measured parameters showed a gradational change from sub-canopy to open space. The establishment of shrubs formed obvious “fertile islands” where more soil nutrients collected. The total nitrogen (TN), soil organic matter (SOM), electrical conductivity (EC) and surface soil moisture content decreased gradually from around shrub stems to the interspace. The sand content around shrub stems was significantly higher (p < 0.05), and decreased gradually from the centre towards the outside microsites. The silt and clay contents showed opposite variability characteristics. The variation of soil bulk density was less within 140 cm distance from the stem, and no abrupt change was found at the shrub’s drip line. No significant tendency was found for the soil pH values. The steady infiltration rates declined with increasing stem distance and then tended to be stable, and no abrupt change occurred at the position of the overhead canopy margin. The increase of infiltration rate was rapid nearer to the stem; the variability trend can be fitted by a log-log (power function) model. This study indicated the gradational change in soil and hydrological properties, which was not consistent with the binary division of shrubs into “canopy” and “interspace” zones.Editor Z.W. Kundzewicz

Seasonal changes in bulk density under semiarid patchy vegetation: the soil beats

ObjectiveWe investigated the temporal variation of soil bulk density (BD) in a semiarid Macrochloa tenacissima grassland where BD plays a key role in the soil–plant feedback mechanisms that are responsible for the patchy distribution of vegetation. MethodsWe used the core method to analyse the soil BD in two experimental sites in microsites that were representative of the spatial heterogeneity of soils and vegetation. The study was performed over two years, in winter (three times) and summer (twice). We studied the changes in BD in relation to the rainfall and to the soil properties that describe or affect the soil structural conditions, such as soil moisture, particle-size, clay mineralogy, the contents of various organic carbon fractions and certain microaggregation indices. ResultsWe found a consistent temporal variation in BD, which was lower in winter (1.22±0.02g/cm3, average±SEM) than in summer (1.33±0.02g/cm3) and depended on the rainfall in the weeks before sampling. The greatest change was observed during the first year of study, when the wettest winter and the driest summer occurred. The variation of BD was most pronounced in the mounds developed under senescent plants (+16.7% average increase from winter to summer), intermediate under adult plants and in the residual mounds (+8.9%) and was weak in the soils of the bare areas or under young plants (+5.1%). This implies that the microtopography should get steeper in winter and flatter in summer. The largest changes in BD were correlated with variables representing organic matter and its action in adhering soil particles. ConclusionWe observed consistent temporal variations in BD that were spatially heterogeneous and related to wet conditions in the soils studied. Research is needed to establish the mechanisms responsible for the changes in BD, which may include greater activity of roots and fauna during the wet season and the enrichment in labile organic fractions that are hygroscopic and can bind soil particles into temporary aggregates. Practice implicationsSpatially heterogeneous temporal variation in BD must be taken into account in inventories of soil nutrients, water or carbon. Moreover, it implies an increased porosity under vegetated patches just when the soil receives the most rainfall, resulting in a positive feedback of plant growth and mound formation. This mechanism might be added to those already described for plant–soil feedbacks in dry lands.

Intervalo hídrico ótimo em um Latossolo vermelho cultivado em sistema semeadura direta por 25 anos

O Intervalo Hídrico Ótimo (IHO) integra atributos físicos do solo relacionados ao crescimento das culturas e corresponde ao intervalo entre os limites superior e inferior do conteúdo de água no solo, no qual são mínimas as limitações para o crescimento radicular. Em áreas agrícolas, o manejo do solo pode alterar sua estrutura, de forma que, principalmente em razão da compactação, a densidade do solo (Ds) poderá ficar fora desses limites em que as condições são ideais para o crescimento das plantas. O objetivo deste trabalho foi utilizar o IHO para avaliação da qualidade física do solo e identificação de áreas com restrição para crescimento de plantas, visando ao manejo localizado. O estudo foi realizado em um Latossolo Vermelho argiloso sob sistema semeadura direta (SSD) com cultivos sucessivos de grãos por 25 anos em Campinas, SP. Foram coletadas amostras volumétricas de solo, nas camadas de 0,00-0,10, 0,10-0,20 e 0,20-0,30 m, destinadas à obtenção dos seguintes atributos: Ds, curva de resistência à penetração, curva de retenção de água e porosidade do solo para determinação do IHO e da densidade crítica do solo (Dsc). Dados de variabilidade e dependência espacial da Ds foram analisados por semivariogramas para elaboração de mapas desse atributo. O IHO diminuiu em profundidade e foi limitado na parte superior pela umidade na capacidade de campo e na parte inferior pela resistência à penetração, nas três profundidades avaliadas. A Dsc foi de 1,42 Mg m-3 para a camada de 0,00-0,10 m e de 1,39 e 1,41 Mg m-3, respectivamente, para as camadas de 0,10-0,20 e 0,20-0,30 m. Verificou-se que a Ds foi maior que a Dsc nas camadas de 0,00-0,10 e 0,10-0,20 m, em porções localizadas no terço inferior do terreno, indicando condição crítica para o crescimento das plantas. A utilização do IHO, associado a mapas de variabilidade espacial da Ds, para determinação de pontos em que ela é maior que a Dsc, auxilia a tomada de decisão para intervenção ou modificação do manejo do solo, enquanto que o critério de escolha do valor crítico da resistência à penetração pode contribuir para a interpretação dos resultados de campo.

Temperature Sensitivity and Basal Rate of Soil Respiration and Their Determinants in Temperate Forests of North China

The basal respiration rate at 10°C (R10) and the temperature sensitivity of soil respiration (Q10) are two premier parameters in predicting the instantaneous rate of soil respiration at a given temperature. However, the mechanisms underlying the spatial variations in R10 and Q10 are not quite clear. R10 and Q10 were calculated using an exponential function with measured soil respiration and soil temperature for 11 mixed conifer-broadleaved forest stands and nine broadleaved forest stands at a catchment scale. The mean values of R10 were 1.83 µmol CO2 m−2 s−1 and 2.01 µmol CO2 m−2 s−1, the mean values of Q10 were 3.40 and 3.79, respectively, for mixed and broadleaved forest types. Forest type did not influence the two model parameters, but determinants of R10 and Q10 varied between the two forest types. In mixed forest stands, R10 decreased greatly with the ratio of coniferous to broadleaved tree species; whereas it sharply increased with the soil temperature range and the variations in soil organic carbon (SOC), and soil total nitrogen (TN). Q10 was positively correlated with the spatial variances of herb-layer carbon stock and soil bulk density, and negatively with soil C/N ratio. In broadleaved forest stands, R10 was markedly affected by basal area and the variations in shrub carbon stock and soil phosphorus (P) content; the value of Q10 largely depended on soil pH and the variations of SOC and TN. 51% of variations in both R10 and Q10 can be accounted for jointly by five biophysical variables, of which the variation in soil bulk density played an overwhelming role in determining the amplitude of variations in soil basal respiration rates in temperate forests. Overall, it was concluded that soil respiration of temperate forests was largely dependent on soil physical properties when temperature kept quite low.

Spatial variability of soil physical properties in two management systems in sugarcane crop

The aim of this study was to characterize the spatial variability of soil bulk density (Bd), soil moisture content (θ) and total porosity (Tp) in two management systems of sugarcane harvesting, with or without burning, in a Haplustox soil, in the 0-0.20 m layer. The study area is located in Rio Brilhante, state of Mato Grosso do Sul, Brazil, in Eldorado Sugar Mill. The plots have presented 180 m length, and 145.6 m width, totaling 90 points distributed in the form of a grid of nine rows by ten columns, with points spaced 20 m from its neighbor. Soil samples were collected at 0-0.20 m layer in 2007/2008 and 2008/2009 crops. The harvest with burning system had a higher density compared to mechanized harvest, in the two study periods. The moisture content as well as the porosity increased proportionally with the decrease of the density of the harvest burning system compared to the mechanized.

Organic C distribution and N mineralization in soil of oak woodlands with improved pastures

Cork oak woodlands in Portugal are a multipurpose agroforestry system occurring in areas mostly degraded by former cereal crops and overgrazing. The objective of this study was to evaluate the effect of scattered cork oak trees (Quercus suber L.) on soil quality, considering two land use systems: unmanaged pastures and improved pastures. Soil samples were collected in a square grid around scattered cork oak trees to evaluate the spatial variability of soil bulk density and chemical properties. In soil samples taken beneath tree canopy and in the open, net N mineralization was evaluated by aerobic incubations. Also, laboratory incubations were carried out to evaluate the effect of roots (tree or/and herbaceous) and water solutions (bulk precipitation, throughfall or stemflow) on net N mineralization.Contents of organic C, total N and extractable P were increased beneath the tree canopy, and gradually decreased with the increase of distance to the tree trunk. Improved pastures established 26 years ago increased organic C (0.76 kg m-2), total N (0.06 kg m-2) and extractable P (2.70 g m-2) amounts in the 0-10 cm soil layer beneath the tree canopy relatively to those of unmanaged pastures. Net N mineralization was significantly greater (about 2 times) in soils beneath the tree canopy than in those of open areas. N mineralization was unaffected by addition of throughfall or stemflow, while a significant reduction resulted from tree roots addition, this effect being stronger for herbaceous plant roots than for tree roots. Maintenance of tree cover combined with permanent improved pastures should be considered to improve soil quality in oak woodlands of Southern Portugal.

Gamma-ray attenuation method as an efficient tool to investigate soil bulk density spatial variability

Abstract The spatial variability of soil bulk density ( ρ b ) was measured by using the volumetric ring method (VRM) and the gamma-ray attenuation method (GAM). Collimated radiation from 3.7 GBq of 241 Am was used to evaluate the soil mass attenuation coefficient and its bulk density. Circular lead collimators were adjusted and aligned between source ( D = 1, 2 and 3 mm) and detector ( D = 4.5 mm). Results of GAM for average ρ b provided good agreement with the corresponding values obtained gravimetrically. Variations in bulk density for different collimator dimensions can be attributed to multiple scattering after photons interaction with soil, mainly for 3 mm collimator size. The best result of ρ b by the nuclear technique was obtained when ρ b represents an average of the measurements for collimators of 1 and 2 mm. Another cause for the differences in ρ b by GAM and VRM is the heterogeneity of soil when the collimated beam can interact with stones or large air-filled holes or channels present in the sample. Therefore, the pattern of spatial variability obtained by VRM was confirmed by GAM for all collimator sizes. This result is a good indication that GAM can be used with success to analyze soil spatial variability.

Variabilidade espacial da densidade e da porosidade de um Latossolo Vermelho Eutroférrico sob semeadura direta por vinte anos

Todas as práticas de manejo causam impacto sobre os atributos do solo que se traduzem em influência sobre o desenvolvimento das culturas. Sabe-se que no sistema de semeadura direta ocorre compactação do solo na camada superficial, com tendência a progredir com o tempo de cultivo. Este trabalho teve como objetivo avaliar a variabilidade espacial da densidade e da porosidade de um Latossolo Vermelho eutroférrico sob semeadura direta por vinte anos. O trabalho foi desenvolvido em Campinas (SP) considerando o período entre 1985 e 2005. Os atributos analisados neste estudo foram: argila (g kg-1), silte (g kg-1), areia (g kg-1), densidade (kg dm-3), porosidade total (%), macroporosidade (%) e microporosidade (%). Ferramentas de geoestatística foram utilizadas para análise dos dados e construção de mapas de variabilidade espacial da densidade e da porosidade do solo. A amostragem realizada em 1985 não foi capaz de detectar a variabilidade espacial da densidade e porosidade do solo. Nos atributos físicos amostrados em 2005, observou-se alta razão de dependência espacial. Nos mapas de variabilidade espacial não se constatou relação clara entre a textura, a densidade e a porosidade do solo. Na área após vinte anos de manejo com semeadura direta não havia problemas com compactação. O manejo do solo com semeadura direta influenciou favoravelmente a variabilidade espacial dos atributos amostrados em 2005.

Temporal and spatial variability of soil bulk density and near-saturated hydraulic conductivity under two contrasted tillage management systems

Physical properties of cultivated soils vary in space and time and according to tillage practices. To characterize this variability, we measured surface and subsurface (15 cm-depth) bulk density and near-saturated hydraulic conductivity of a loamy soil cultivated under conventional and conservation tillage. For each tillage system, hydraulic conductivity measurements were done at different matric potentials, different dates during the maize growing season, and at different sites within the agricultural field according to soil texture and row/inter-row position. Time was the most important source of bulk density variability for surface and subsurface. Whatever the tillage system, we observed an increase in bulk density during the growing season. For subsurface soil, the interaction between time and tillage system was also an important source of bulk density variability with a higher increase with time of bulk density values under conventional than under conservation tillage. Under both tillage systems, for matric potentials ≥ − 0.6 kPa, the position relative to crop rows was the main source of surface hydraulic conductivity variation with the lowest values measured in row positions. For subsurface soil, time and its interaction with tillage were the main sources of hydraulic conductivity variability for matric potentials ≥ − 0.3 kPa. Our results highlight that the effect of time on soil physical properties should be accounted for in transport models through soils, especially when contrasted tillage systems are compared.

Grazing-induced spatial variability of soil bulk density and content of moisture, organic carbon and calcium carbonate in a semi-arid rangeland

Abstract The landscape of many semiarid rangelands is characterized by a two-phase, shrub–intershrub vegetation mosaic, each phase having different soil properties. However, this broad subdivision groups together types of intershrub surface cover that may also differ in their soil properties and play important roles in ecosystem functioning. In the northern Negev region of Israel, we examined the soil properties associated with flock trampling routes and rock fragment clusters, as well as those associated with the remainder of the intershrub area and shrub patches. Moisture content, organic carbon content, bulk density and calcium carbonate content of the soil were determined for the above four types of cover, inside and outside long-term grazing exclosures. Soil was sampled in the peak of the growing season and in the end of the dry season, on a north- and a south-facing hillside, and from two depths. The shrub patches exhibited the highest soil moisture and organic carbon contents, and the lowest bulk density and calcium carbonate contents. The trampling routes showed opposite trends. The rock fragment clusters and the remainder of the intershrub area did not generally differ and had intermediate values of these properties. Grazing did not have a significant effect on soil properties at the whole-plot scale, but there were highly significant interactions between grazing and type of cover. Compared with the former trampling routes in the exclosures, the active trampling routes outside them had higher bulk density and lower moisture and organic carbon contents. The intershrub area had higher moisture and organic carbon contents under grazing than in the exclosures. Grazing increased the spatial heterogeneity of the soil properties examined via the creation of a network of trampling routes on the hillsides. The routes themselves, which constituted over 20% of the landscape cover, had degraded soil properties but they led to the improvement of the properties of the remainder of the intershrub area via functionally important source–sink relationships. The study of the soil of regions in which such networks are apparent should be duly cognizant of this intershrub subdivision in addition to the widely recognized shrub–intershrub dichotomy.

Variabilidade espacial de atributos físicos do solo associados ao uso e ocupação da paisagem

O presente trabalho teve-se como objetivo diagnosticar o uso atual das terras e suas implicações na variabilidade espacial dos atributos físicos densidade do solo (Ds), matéria orgânica (MO), frações texturais (areia, silte e argila) e argila dispersa em água (ADA), na bacia hidrográfica do Ribeirão Marcela, Região Alto Rio Grande, MG, através de técnicas de geoestatística, com a finalidade de observar padrões de ocorrência desses atributos na paisagem. Coletaram-se amostras de solo na camada de 0 a 0,15 m em malha, com intervalos regulares de 240 x 240 m (macroescala) e de 60 x 60 m (microescala), totalizando 165 pontos. A Ds apresentou-se com valores na faixa de 1,05 a 1,15 g cm-3 acima, portando, do valor característico para Latossolos (0,95 g cm-3), enquanto os maiores valores foram obtidos nas glebas sob pastejo. Os valores de MO variaram de 1,5 a 4,5 dag kg-1, detectando-se maiores concentrações nas glebas sob eucalipto, cerrado mais denso e várzeas. As frações texturais variaram seguindo a rede de drenagem e a ADA indicou valores baixos ao longo de toda a bacia. Os mapas de krigagem mostraram-se importante no estudo e compreensão da variabilidade espacial de atributos físicos do solo na bacia hidrográfica, indicando áreas críticas de manejo.

Variation in soil phosphorus, sulfur, and iron pools among south Florida wetlands

To determine relationships between soil nutrient status and known gradients in primary production, we collected and analyzed soils from 17 LTER sampling sites along two transects through south Florida wetland ecosystems. Through upstream freshwater marsh, a middle reach including the oligohaline marsh/mangrove ecotone, and downstream estuarine habitats, we observed systematic variation in soil bulk density, organic content, and pools of phosphorus (P), inorganic sulfur, and extractable iron. Consistent with observed differences in wetland productivity known to be limited by P availability, total P averaged ~200 μg g dw−1 in soils from the eastern Taylor Slough/Panhandle and was on average three times higher in soils from the western Shark River Slough. Along both transects, the largest pool of phosphorus was the inorganic, carbonate-bound fraction, comprising 35–44% of total P. Greater than 90% of the total inorganic sulfur pool in these south Florida wetland soils was extracted as pyrite. Freshwater marsh sites typically were lower in pyrite sulfur (0.2–0.8 mg g dw−1) relative to marsh/mangrove ecotone and downstream estuary sites (0.5–2.9 mg g dw−1). Extractable iron in freshwater marsh soils was significantly higher from the Taylor Slough/Panhandle transect (3.2 mg g dw−1) relative to the western Shark River Slough transect (1.1 mg g dw−1), suggesting spatial variation in sources and/or depositional environments for iron. Further, these soil characteristics represent the collective, integrated signal of ecosystem structure, so any long-term changes in factors like water flow or water quality may be reflected in changes in bulk soil properties. Since the objective of current Everglades restoration initiatives is the enhancement and re-distribution of freshwater flows through the south Florida landscape, the antecedent soil conditions reported here provide a baseline against which future, post-restoration measurements can be compared.

Evaluation of the use of pre- and post-harvest bulk density measurements in wet Eucalyptus obliqua forest in Southern Tasmania

Abstract Criteria and indicators under the Montreal process are intended to provide a common framework for describing and evaluating progress towards sustainable forest management. In 1998 a nationally coordinated project was initiated to evaluate proposed Montreal indicators 4.1.d and 4.1.e and to provide advice to state agencies on how these indicators could be applied. Interim indicator 4.1.e quantifies ‘ Proportion of harvested forest area with significant change in bulk density of any horizon of the surface (0–30 cm) soil ’. Application and evaluation of this interim indicator was conducted as part of the Warra Silvicultural Systems Trial, in Tasmania, Australia. This forest was composed of wet mixed regrowth/mature Eucalyptus obliqua forest with a dense rainforest understorey. Pre-harvest soil sampling was conducted in four stands followed by post-harvest sampling at two of the sites. Pre-harvest sampling according to soil drainage class, showed that there was a high natural variation in bulk density within individual stands and between neighbouring stands. Post-harvest sampling was stratified according to major operational areas and disturbance classes, including snig tracks (major and minor), firebreaks, harvested and unharvested areas, landings and access roads. Forest harvesting substantially increased the variability of soil bulk density. Though moderate and severe disturbance of the snig tracks and firebreaks increased average soil bulk density, changes in soil bulk density were not uni-directional. Many of the post-harvest samples showed a marked decline in soil bulk density due to the incorporation of litter and slash in the upper soil layer. Bulk density changed most in the upper 0–100 mm layer of soil. Hence there is reasonable argument that monitoring changes in bulk density should be limited to this depth. This would substantially reduce the cost of replicate sampling to the 300 mm depth. The high natural variation found for soil bulk density and the fact that changes are not uni-directional means that it is unlikely that the interim indicator proposed can be implemented in a practical, sensitive and cost-effective manner in the forest type examined in this study.

Reducing sampler error in soil research

Most soil sampling techniques are calibrated with standards and against each other, but the error introduced by the individuals performing each technique (sampler error) is often not addressed. We determined that sampler error explains a minimum of 5.5% of the variation in soil bulk density when using a composite coring technique. This source of error is of concern because it could easily obscure the small, but significant differences anticipated with long-term (decadal) research. We suggest three methods for increasing sampling accuracy across spatial and temporal treatments: (1) use > 5 individuals to sample each treatment; (2) consider both the concentration and pool size of soil properties (e.g. nitrate, root mass, etc.); and (3) include measurements of sampler error.

Influence of a compacted loam subsoil layer on growth and yield of irrigated cotton in Southern Spain

Subsoil compaction, which may occur naturally or be a consequence of machinery traffic, causes reductions in crop yields. The aim of this work was to characterize the effects of subsoil compaction on growth and yield of cotton ( Gossypium hirsutum L.) under field conditions. Two field experiments were carried out in Córdoba, Spain, on an Eutric Fluvisol with loam texture. A treatment with a compacted layer (bulk density of 1.6–1.7 Mg m −3) at 0.2–0.4 m depth was compared with a control treatment with maximum bulk density of about 1.4 Mg m −3. Soil resistance to penetration was related to soil bulk density and water content. The compaction provoked reductions in root length (40% in 1996 and 33% in 1997), leaf area index (26% in 1996 and 12% in 1997), evapotranspiration (12% in 1996 and 7% in 1997) and seed cotton yield (28% in 1996 and 10% in 1997). Average resistance to penetration in the compacted layer was above 3 MPa (a threshold for cotton root growth according to the literature) but root growth was observed below this layer. It was speculated that spatial variation of soil bulk density and resistance and temporal variation of soil water content allowed the roots to find weaker path-ways to cross the compacted layer. The effect of the subsoil compaction on the soil characteristics and the root growth remained during the second experimental year but it was less pronounced on the above ground plant growth, development and yield. It was concluded that subsoil compaction influences significantly growth and yield of cotton, but successive cropping may alleviate the effects of the compaction.