Ploughed Soil Research Articles

Measurements of Mouldboard Plow Draft: II. Draft-Soil-Crop and Yield-Draft Associations

The primary objective of this investigation was to evaluate some potential causal associations between draft derived from a 3-bottom mouldboard plow during normal fall field operations and soil-crop properties at a field site near Winchester, Ontario, Canada. A secondary objective was to investigate, in a preliminary manner, associations between draft and crop yield (corn, soybean, and wheat). Regression tree analysis indicated that draft variability was best explained by field location, crop type, soil cone penetration resistance in the plow layer, and soil texture in the plow layer. Draft was found to generally increase with cone penetration resistance in the plow layer and soil clay content. Corn yields were negatively associated with draft. The reverse was true for the soybean yields, and a combination of negative and positive draft vs. yield relationships existed for the wheat plots. The overall results indicated that draft data collected during normal field operations can be useful for producers interested in identifying areas in the field where soil strength/compaction might be problematic with regard to crop yields.

Agri-Engineering and Irrigation Technology for Hill Agriculture in Germany

Agricultural use in Germany ends at a slope angle of about 25%. For slope gradients >25% the exclusive use as grassland; first of all predominantly as meadow, then as pasture begins. At a slope angle of more than 45% the possibility of mechanized processing ends. On suitable locations crop growth up to a slope gradient of 60% is possible. Wine is an example; but here the slopes are more or less terraced. The agricultural use of slopeland increases the appearance of water erosion. In Germany altogether 28% of the arable land are endangered through water erosions. To decrease the erosion danger in maize, sugar beets, and occasionally also at cereals direct seed in dead plant residues (mulch), combined with non plough soil tillage is used more and more. Especially in low range mountains the drizzling-irrigation of spring water on grassland was wide spread in former times. Irrigation is an important instrument for stabilization and increasing yields. However, irrigation water is only in limited quantities available. Because of these limited water quantities, water saving irrigation systems are needed. One method is the transition of basin irrigation to sprinkler systems. Sprinkler irrigation requires no levelling of the irrigation farmlands. The employment of these machines has at least three disadvantages: 1. The machines demand relatively large farmlands; there the productivity can be raised noticeably. On the other hand small farm-structures are little suitable. 2. Usually high investments are necessary, combined with imports from industrialized countries. 3. On unfit locations the employment of modern sprinkler machines causes irrigation erosion. Irrigation erosion can appear, when the intensity of the artificial rain exceeds the infiltration intensity of the soil at the location. For the most of the sprinkler machines this fact applies.

Modificações na população de plantas espontâneas na presença de adubos verdes

A adubação verde pode provocar modificações na população de plantas espontâneas devido aos efeitos alelopáticos e à competição por luz, água, oxigênio e nutrientes, acarretando supressão de algumas delas. Por outro lado, as leguminosas, pelas melhorias que promovem nas condições do solo, favorecem espécies com maior capacidade de ciclagem de nutrientes e produção de biomassa. O objetivo deste trabalho foi avaliar as modificações na população de plantas espontâneas por leguminosas usadas como adubo verde. O experimento foi realizado em Sete Lagoas, MG, na Embrapa-Centro Nacional de Pesquisa de Milho e Sorgo. O solo local é um Latossolo Vermelho distrófico típico, e o clima, do tipo Aw (tropical estacional de savana). O experimento consistiu de seis tratamentos, sendo cinco espécies de leguminosas (feijão-de-porco, feijão-bravo-do-ceará, mucuna-preta, lab-lab e guandu), cultivadas na presença de plantas espontâneas, e a testemunha (solo preparado e deixado em pousio com as plantas espontâneas), e as leguminosas, cultivadas em dois anos agrícolas. O feijão-bravo-do-ceará, seguido da mucuna-preta e do feijão-de-porco, foram as leguminosas com maiores produtividades de biomassa. A mucuna-preta demonstrou maior potencial para cobertura do solo e supressão de plantas espontâneas. O uso de leguminosas para adubação verde promove modificações na dinâmica de sucessão das espécies espontâneas.

Carbon dioxide fluxes following tillage from a mollisol in the Argentine Rolling Pampa

Carbon dioxide emission from soil plays an important role in the global carbon cycle. Short term losses of soil carbon due to tillage are of a variable magnitude. Our objective was to evaluate the effect of plowing the soil on CO 2-C emissions during summer in a coarse-loamy mixed thermic Typic Hapludoll from the Argentine Rolling Pampa. Temperature after tillage was higher in the plowed soil than under no-tillage, being higher the soil water content in the later treatment. Plowing the soil did not produce an immediately impact on soil surface CO 2-C emission, but induced an important CO 2-C flush few days later. A difference of 16 up to 25 kg C ha –1 d –1 in the CO 2-C emissions was observed from the second up to the fourth sampling dates after tillage. Difference in total CO 2-C emissions between the plowed soil and the no-tillage treatment was 580 kg C ha –1, during the 40 days measurement period. This difference in CO 2-C emission was partitioned between residue decomposition and humus mineralization. Carbon mineralized from humus was 270 kg C ha –1 higher under plow tillage than under no tillage. This figure represented an important extra loss of 0.48% of the soil organic carbon content from the 0–30 cm depth, as consequence of plowing in the warmest season of the year.

Effect of tillage and farming system upon VAM fungus populations and mycorrhizas and nutrient uptake of maize

Low-input agricultural systems that do not rely on fertilizers may be more dependent on vesicular-arbuscular mycorrhizal [VAM] fungi than conventionally managed systems. We studied populations of spores of VAM fungi, mycorrhiza formation and nutrient utilization of maize (Zea mays L.) grown in moldboard plowed, chisel-disked or no-tilled soil under conventional and low-input agricultural systems. Maize shoots and roots were collected at four growth stages. Soils under low-input management had higher VAM fungus spore populations than soils under conventional management. Spore populations and colonization of maize roots by VAM fungi were higher in no-tilled than in moldboard plowed or chisel-disked soil. The inoculum potential of soil collected in the autumn was greater for no-till and chisel-disked soils than for moldboard plowed soils and greater for low-input than conventionally farmed soil. The effects of tillage and farming system on N uptake and utilization varied with growth stage of the maize plants. The effect of farming system on P use efficiency was significant at the vegetative stages only, with higher efficiencies in plants under low-input management. The effect of tillage was consistent through all growth stages, with higher P use efficiencies in plants under moldboard plow and chisel-disk than under no-till. Plants grown in no-tilled soils had the highest shoot P concentrations throughout the experiment. This benefit of enhanced VAM fungus colonization, particularly in the low-input system in the absence of effective weed control and with likely lower soil temperatures, did not translate into enhanced growth and yield.

Subcritical Water Repellency of Aggregates from a Range of Soil Management Practices

Subcritical water repellency is a poorly acknowledged physical property of soil. It refers to soil where water uptake appears to occur readily, get is impeded to some extent by the presence of hydrophobic surface films. It was only after the recent development of a sensitive testing technique that subcritical water repellency was shown to be a common feature of many soils. It is a fundamental physical property of soil and has implications for the resistance of soil structure against disruption by wetting, bypass now, and surface runoff Using a technique adapted by Hallett and Young (1999), we assessed a water repellency index, R, of individual soil aggregates from a range of cultivation practices with different fertilizer inputs and depths. The parameter R is extremely powerful since it is directly proportional to the decrease in water sorptivity caused by repellency. The hypotheses tested are (i) that soil disturbance reduces R and (ii) that high levels of plant nutrients (fertilizer) will enhance R, Cultivation was found to cause a twofold decrease in R for all soils tested except one pasture treatment. Pasture soil from another site had an R value that was three times higher to a depth of 60 cm than an adjacent plowed soil. Soil aggregates were more repellent from no-till than plowed treatments. Higher levels of N added to field soil did not affect R.

A simple parameterization of the L-band microwave emission from rough agricultural soils

A simple model for simulating the L-band microwave emission from bare soils is developed. The model is calibrated on a large set of measurements obtained during a three-month period over seven plots covering a wide range of surface roughness (representing the total range which can be expected on agricultural fields), soil moisture, and temperature conditions. The approach is based on the parameterization of an effective roughness parameter as a function of surface characteristics: surface roughness (standard deviation of height and correlation length) and the surface soil moisture. The parameterizations that are developed are independent of incidence angle and polarization and are valid over a large range in surface roughness conditions, representative of most of typical agricultural bare fields, from very smooth (rolled field after sowing) to very rough surfaces (deeply plowed soil). This approach will enable the use of microwave radiometric observations for soil moisture retrieval over agricultural areas.

Effects of soil type upon metolachlor losses in subsurface drainage

A field experiment at La Bouzule (Lorraine, France) investigated metolachlor movement to subsurface drains in two soil types, a silt loam and a heavy clay soil, under identical agricultural management practices and climatic conditions. Drainage volumes and concentrations of metolachlor in the soil plough layer and drainwater were monitored after herbicide application from May 1996 to February 1997, and from May to August 1998. Total losses in drainwater were 0.08% and 0.18% of the amount applied to the silt loam compared with 0.59% and 0.41% for the clay soil, in 1996/97 and 1998, respectively. In 1996/97, 32% of total metolachlor loss from the silt loam and 91% from the clay soil occurred during the spring/summer period following treatment. Peak concentrations were 18.5 and 171.6 μg l −1 for the silt loam and 130.6 and 395.3 μg l −1 for the clay soil during the spring/summer periods of 1996/97 and 1998, respectively. During the autumn/winter period, concentrations did not exceed 2.2 μg l −1 for the silt loam and 2.6 μg l −1 for the clay soil. The experimental results indicate that metolachlor losses in drainwater were primarily caused by preferential flow (macropore flow) which was greater in the clay soil than in the silt loam, and occurring mainly during the spring/summer periods.

Effects of N-fertilization on shoots and roots of rape (Brassica napus L.) and consequences for the soil matric potential

The underlying question of these investigations asked, how and to which extent rape plants react with transpiration and soil water uptake to different degrees of nitrogen fertilization. Therefore repeated campaigns with concurrent measurements of plant surfaces (leaves, stems, pods), diurnal courses of leaf transpiration and root length density of rape plants growing on heavily (240 kg ha -1 ), moderately, (120 kg ha -1 ), and nil N-fertilized plots of an experimental field in northern Germany were performed during two growing seasons. Additionally, matric potentials at different soil depths were measured. In the first year (1994) investigations were concentrated primarily on shoot area development and transpiration, whereas in the subsequent year (1995) root measurements were mainly undertaken. Also, the influence of soil management (ploughing, conservation tillage) was taken into consideration. The plots where the shoot measurements were carried out were ploughed in 1994 and rotovated in 1995. Matric potentials were measured in both years in ploughed soil and, for comparison, also in soils with conservation tillage. Shoot area index, as measure of the transpiratory capacity of the canopy, increased on ploughed soil and reached a maximum before flowering. Thereafter it decreased until harvest when the relative amount of green stems and pods was increasing. Then, the measured transpiration rate per pod surface area was equal to, or higher than, the transpiration rate per leaf surface area. Plant surface area was smaller in plots with conservation tillage and decreased generally with decreasing N-fertilization. Increasing plant surface area was joined by an increasing density of plant canopy. Light interception was thus highest in the plots receiving 240 kg N ha -1 . Although the shading effect may cause a reduction of transpiration per plant, the total plant mass per area generally resulted in a greater water loss from these plots. Roots reached at least 110 cm depth. Root length density was significantly higher in the upper 10-30 cm of soil than at greater depths. Root mass was smaller in soil with conservation tillage than in ploughed soil. Oscillations of soil matric potentials in the diurnal and long-term periods were highest in the upper 10 cm of soil. Here, they corresponded well with the cumulative diurnal transpiratory water loss. It is concluded that the soil water dynamics depends largely on the distribution of plant roots. As a result, rape plants did not change their specific transpiration capacity as a response to increased nitrogen fertilization. However, the transpiring plant surface and root length density increased the turnover rate of water by a higher plant density per plot. This effect was more pronounced in ploughed than in rotovated plots.

Soil strength and soil pore characteristics for direct drilled and ploughed soils

Direct drilling has often been reported to increase density and strength and to affect pore continuity and tortuosity of the upper soil layers. In this study these aspects were studied for three texturally differing soils 4–6 years after initiation of continuous trials with direct drilling and mouldboard ploughing. The soils studied were a coarse sandy soil (Korntved, 5% clay), a sandy loam (Ballum, 8% clay) and a silty loam (Højer, 19% clay). The crop rotation at Korntved was spring barley and winter rye while at Ballum and Højer it was spring barley and winter wheat. Both crops were grown every year. All fields had been mouldboard ploughed for decades prior to the trial period. The ploughed treatment (PL) was imposed in the autumn and the seedbed preparation and drilling were performed with an S-tined seedbed harrow and a traditional drill. The direct drilled (DD) treatment received no tillage other than the drilling which was performed by a triple-disc drill. Straw and stubble were burned. In the 4th, 5th and 6th years of the trial period, minimally disturbed soil cores were taken from the 4 to 8, 14 to 18 and 24 to 28 cm depths, i.e. two horizons above the ploughing depth of 20 cm, and one horizon below this depth. Longer cores were sampled in the 18–27 cm depth in order to include this transition layer. Furthermore, in the 4th year of the trial period shear strength was measured in the field at 2-week intervals in the spring with a vane shear tester in the two upper layers mentioned. All samplings and measurements took place in the field grown with spring barley. In the laboratory air diffusivity and air permeability were measured at field-sampled water content and again when the soil cores were drained to a matric potential of −100 hPa. Cone penetration resistance was measured with a 2 mm diameter penetrometer. Separate core samples from the 14 to 18 cm depth of the Korntved and Højer soils were used for estimating soil cohesion and soil internal friction by a shear annulus method at field-sampled water content. For all soils, DD increased soil bulk density in the two upper soil layers. The shear vane tester also generally estimated higher shear strength for the DD compared to the PL treatment. The shear annulus measurements in the laboratory revealed no differences between tillage treatments for the Korntved soil, while a tendency of higher cohesion and internal soil friction was found for the DD treatment on the Højer soil. The cone penetration measurements indicated a stronger top-soil and fewer high-strength soil elements in the 24–28 cm horizon for the DD than for the PL treatment. Generally the DD treatment had lower volume of macropores (i.e. pores>30 μm ) in the 4–8 and 14–18 cm depths than the PL treatment. This was reflected in reduced air diffusivities and air permeabilities for these horizons. An exception was the 14–18 cm depth of the Ballum soil, where increased air diffusivity and air permeability was measured at field-sampled water content. Continuity indices calculated from air diffusivity and air permeability measurements showed that the DD soil from the 4 to 8 and 14 to 18 cm depths had less continuous and more tortuous macropores than the ploughed soil.

Ecological correlates of weed seed size and persistence in the soil under different tilling systems: implications for weed management

In the pursuit of more sustainable approaches to agricultural management, there is an obvious need to integrate knowledge of the agricultural sciences and ecology. We used recent findings on ecological correlates of seed characteristics as a framework to discuss the impact of shifting from soil ploughing to farming with reduced or zero tillage on weed communities. In the future, knowledge about seed bank ecology may become increasingly applicable towards improving the way we manage weeds. It is also possible that the effects of cultural activities on moulding weed characteristics will become more apparent.

Influence of a grass layer on vineyard soil temperature

Vineyard grass cover can modify soil variables such as temperature and water content, which in turn influence berry quality at harvest. Such effects require further documentation and this study was conducted to determine how a grass layer could change soil thermal behaviour compared to bare soil. Soil temperature, soil water content and net radiation were measured in a Médoc vineyard, Château Talbot (France). The field used for the experiment was divided into two parts, one with a bare ploughed soil and the other with a partial grass cover. The same measurements were taken on both parts. Bare soil temperatures were generally higher, and the difference between the two treatments was greater in the middle of the inter-row, just under the grass layer. Nevertheless, net radiation above the vegetation, which represents the radiative available energy, was the same for the two plots. Soil conduction heat flux (G) was calculated from temperature measurements. Under the grass layer, the horizontal component of G was barely detectable, whereas under bare soil, G was essentially vertical. The grass layer was therefore acting as an insulating layer, preventing exchanges between soil and atmosphere. Soil temperature and thermal behaviour are heavily influenced by soil surface management practices. The field experiment provided a large data set of measurements which will be used to calibrate a heat and mass transfer model.

Plough effect in Eucalyptus globulus biomass growing in southwest Spain

The aim of the study was to asses the plough effects in the above and below ground biomass Eucalyptus globulus plantations. At the same time the root damage was evaluated. The project was carried out in two experimental stands, three trees were chosen by stand and plought treatment. The above ground biomass was determining harvesting the tree. The coarse and fine root were evaluated in 3.6 and 0.688 m3 of soil volume, respectively. Furthermore the root damage were analized in 50 trees. Afterward the predawn leaf water potential were determining in plough and unplough trees. The total above ground biomass have not statistical differences between treatments. The coarse roots represent a high percentage of the below ground biomass and the fine root biomass is higher near the stump. The plough effect was concentrated within the 0-20 cm soil profile. In the plough assay the amount of fine root was higher in the undisturbed than in ploughed soil. Greater part of more superficial fine roots were cuted and linearly decrease the predawn leaf water potential when increase the root damage.

Ploughing effects on soil organic matter after twenty years of conservation tillage in Lower Saxony, Germany

Conservation tillage may concentrate organic matter and carbon in the soil, thus improving soil quality and counteracting CO 2-increase in the atmosphere. In parts of Germany however, continuous conservation tillage can cause problems in soil and crop management, resulting in a need to shift to short-term conventional tillage, such as mouldboard ploughing. The objective of the present research was to follow the fate of soil organic matter, when soil is ploughed after long-term minimum tillage in the temperate climate of Lower Saxony. In minimum tillage, shallow cultivation was restricted to stubble cleaning and seedbed preparation, using a rotary harrow or rototiller. After 20 years of shallow cultivation, soil organic carbon, soil nitrogen and microbial biomass carbon were concentrated in the top 5 cm of a loess-derived silt loam (Orthic Luvisol). In the 50 cm soil profile, mass of soil organic carbon tended to be higher by about 5 Mg ha −1 as compared to conventionally ploughed soil, which contained roughly 65 Mg ha −1. In the ploughed soil, soil nitrogen amounted to about 6.8 Mg ha −1, whereas in the minimum tilled soil it was roughly 1.0 Mg ha −1 higher. Total microbial biomass carbon fluctuated between 800 and 1300 kg ha −1, the differences between tillage systems being less distinct. Ploughing the old minimum tilled land destroyed the stratification of soil organic matter. Moreover, during the winter months (November–March) the surplus of soil organic carbon and nitrogen masses, enriched by conservation tillage, was completely decomposed, presumably a consequence of its labile quality. Inverting the minimum tilled soil did not increase concentrations of organic carbon and nitrogen in the lower part of the A p-horizon, but it did increase concentration of microbial biomass carbon. We conclude that organic matter stratification and accumulation as a result of long-term minimum tillage were completely lost by a single application of inversion tillage in the course of a relatively mild winter.

Fine-earth translocation by tillage in stony soils in the Guadalentin, south-east Spain: an investigation using caesium-134

Tillage erosion is increasingly recognised as an important soil erosion process on agricultural land. In view of its potential significance, there is a clear need to broaden the experimental database for the magnitude of tillage erosion to include a range of tillage implements and agricultural environments. The study discussed in this paper sought to address the need for such data by examining tillage erosion by a duckfoot chisel plough in stony soils on steep slopes in a semi-arid environment. Results of the investigation of coarse fraction (rock fragment) translocation by tillage in this environment have been presented elsewhere and the paper focuses on tillage translocation and erosion of the fine earth. Tillage translocation was measured at 10 sites, representing both upslope and downslope tillage by a duckfoot chisel plough on five different slopes, with tangents ranging from 0.02 to 0.41. A fine-earth tracer, comprising fine earth labelled with 134Cs, was introduced into the plough layer before tillage. After a single pass of the plough, incremental samples of plough soil were excavated and sieved to separate the fine earth from the rock fragments. Translocation of the fine-earth tracer was established by analysing the 134Cs content of the samples of fine earth. These data were used to establish translocation distances for each combination of slope and tillage direction. Translocation distances of the fine earth were not significantly different from translocation distances of the coarse fraction. For all sites, except uphill on the 0.41 slope, translocation distances were found to be linearly related to slope tangent. The soil flux due to tillage for each site was calculated using the translocation distance and the mass per unit area of the plough layer. For slopes with tangents <0.25, the relationship between soil flux and tangent was linear and the soil flux coefficient derived was 520–660 kg m −1 per pass. This is much larger than the coefficients found in other studies and this high magnitude is attributed to the non-cohesive nature and high rock fragment content of the soil in this investigation. A second contrast with previous studies was found in non-linearity in the relationship between soil flux and tangent when steeper slopes were included. This was a product of variation in plough depth between the steepest slopes and the remainder of the study area. On the basis of the study it is suggested that an improved understanding of tillage erosion may be obtained by considering the dual processes of tillage detachment (mass per unit area of soil subject to tillage) and tillage displacement (equivalent to translocation distance per pass) in assessing, comparing and modelling tillage translocation. An improved model is proposed that recognises the complexity of soil redistribution by tillage, provides a framework for process-based investigation of the controls on tillage fluxes, and allows identification of potential self-limiting conditions for tillage erosion.

Soil mineral nitrogen and nitrate leaching losses in soil tillage systems combined with a catch crop

Annual nitrogen leaching losses from arable land in south Sweden usually amount to 15–45 kg ha −1. The objective of this three-year study was to investigate the timing effect of mouldboard ploughing (early autumn, late autumn or spring) on soil mineral nitrogen content and nitrate leaching in a cropping system with spring-sown small grain crops (barley, oats and wheat). Late autumn ploughing was studied with and without perennial ryegrass ( Lolium perenne L.) as a catch crop, and with and without preceding stubble cultivation. The effects of removal compared to incorporation of straw were also studied. Soil mineral nitrogen in the 0–90 cm layer was determined on 4–5 occasions each year. Nitrate was determined in soil water sampled with ceramic suction cups at 60 and 90 cm. Total nitrogen in above-ground catch crops, weeds and volunteer plants was determined at ripeness of the main crop and before tillage operations. Time of tillage, as opposed to catch crop or crop residue management, influenced nitrogen leaching. After early tillage, soil mineral nitrogen increased during autumn. In November, the nitrogen content was on an average 68 kg N ha −1 in 0–90 cm in early ploughed soil and 39 kg N ha −1 when ploughing was delayed to spring. Also nitrate leaching was greater in treatments with early than with late tillage. This was probably because of increased nitrogen mineralization. However, when tillage was delayed there was also a substantial growth of weeds and volunteer plants during autumn, particularly couch-grass ( Elymus repens L.). This caused grain yield to decrease by up to 40% when tillage operations were delayed until late autumn or spring. Delaying tillage operations to late autumn or spring seems to be necessary to reduce the risk of nitrogen leaching. Swedish regulations for farmers to control nitrogen losses have been changed as a consequence of these results.

Shear effects on gas transport in soil

The impacts of soil deformation on crop production and the environment depend on the structure of the deformed soil. In this investigation, we aimed to develop techniques for measuring the effects of compressive and shear deformation on the capacity of soil to transmit gases. We built an apparatus that deforms a specimen at constant normal stress in `simple shear', such that a cross section parallel to the direction of deformation is a parallelogram. This type of deformation closely simulates that under a wheel. We designed the shear box to allow us to measure properties that vary with the structure of the soil after deformation. The box consisted of nine, 5 mm thick brass plates, bored out to 110 mm diameter and stacked vertically to accommodate intact test specimens. The required type of deformation was achieved by constraining adjacent plates to move the same distance relative to each other. After deformation, we took core sub-samples for measurement of gas permeability and diffusivity. We tested both intact specimens of ploughed soil and specimens prepared in the laboratory from aggregates, all from the same sandy silt loam (eutric cambisol, FAO). Deformations within the specimens were fairly uniform. Shear stress measurements were satisfactory up to shear strains of about 0.25 but were somewhat variable at greater strains up to a maximum of about 0.35. Gas diffusivity and air permeability of both aggregate and intact samples increased exponentially with air-filled porosity and were typical of soil with no preferred macropore orientation. The intact samples, which were at the plastic limit when tested, compressed on shearing at normal stresses of 100 kPa or less. Shearing caused no additional compression in samples subjected to a normal stress of 200 kPa. This simple shear box allows us to investigate the effects of changes in soil structure caused by deformations that closely imitate those under a slipping wheel. The compaction caused by a shear strain of 0.35 on this soil was roughly equivalent to the result of doubling the normal stress in the range of 30 to 100 kPa.

Soil erosion under different harvesting managements in steep forestlands from northern Spain

In spite of the high risk of erosion, highly mechanized operations, in which humus layer removal and down-slope ploughing are practised, are often employed to prepare steep forestlands for planting. The purpose of this study was to evaluate the effect on soil loss of three post-harvesting management systems usually used in a mountainous region of northern Spain. The techniques evaluated were (a) conventional stem-only harvesting, (b) whole-tree harvesting and humus layer removal and (c) whole-tree harvesting and humus layer removal followed by down-slope deep ploughing. Soil erosion was measured in a total of 39 recently clear-felled Pinus radiata plantations over the period between the stand harvesting and establishment of understorey vegetation. They were located on slopes with gradients of between 40 and 50 per cent. For all treatments the associated runoff–rainfall ratios were high, indicating inherent low permeability of the soil. Intense site preparation resulted in considerable decreases in soil organic matter and increases in bulk density, which decreased the hydraulic conductivity and subsequently produced higher runoff. These deteriorations of soil properties delayed the establishment of pioneer vegetation thus extending the period of high erosion. In the ploughed soils, the higher soil erodibility and the removal of slash and vegetation cover resulted in a four-fold increase of soil losses when compared with no mechanical site preparation. The results indicate that, in order to maintain the soil productivity, and for conservation purposes, harvesting management should minimize the soil disturbances and maintain the slash and vegetation cover. Copyright © 1999 John Wiley & Sons, Ltd.

Soil erosion under different harvesting managements in steep forestlands from northern Spain

In spite of the high risk of erosion, highly mechanized operations, in which humus layer removal and down-slope ploughing are practised, are often employed to prepare steep forestlands for planting. The purpose of this study was to evaluate the effect on soil loss of three post-harvesting management systems usually used in a mountainous region of northern Spain. The techniques evaluated were (a) conventional stem-only harvesting, (b) whole-tree harvesting and humus layer removal and (c) whole-tree harvesting and humus layer removal followed by down-slope deep ploughing. Soil erosion was measured in a total of 39 recently clear-felled Pinus radiata plantations over the period between the stand harvesting and establishment of understorey vegetation. They were located on slopes with gradients of between 40 and 50 per cent. For all treatments the associated runoff–rainfall ratios were high, indicating inherent low permeability of the soil. Intense site preparation resulted in considerable decreases in soil organic matter and increases in bulk density, which decreased the hydraulic conductivity and subsequently produced higher runoff. These deteriorations of soil properties delayed the establishment of pioneer vegetation thus extending the period of high erosion. In the ploughed soils, the higher soil erodibility and the removal of slash and vegetation cover resulted in a four-fold increase of soil losses when compared with no mechanical site preparation. The results indicate that, in order to maintain the soil productivity, and for conservation purposes, harvesting management should minimize the soil disturbances and maintain the slash and vegetation cover. Copyright © 1999 John Wiley & Sons, Ltd.

Ancient Fields Excavated

In this paper, I discuss the importance of fossil fields and traces of ancient agriculture as archaeological source material. Examples from excavations in the Väderstad area in Östergötland, Sweden are given. In the article, I describe and contrast two different methods of excavation: (A) The digging of long trenches through visible features, a method here used as a means of trial excavation but previously often the only method used in the excavation of ancient fields. This method gives at the best a framework for interpretation. Though it does enable dating, the intensity, extent and content of different phases cannot be established with any degree of certainty. (B) The removal of the ancient plough soil over the full extent of the ancient field, a method here used for final excavations. With this method, enough information was acquired for the derivation of a detailed interpretation. The results will be detailed enough to allow comparison of the excavated fields with other categories of excavated monuments and thus give a new perspective on general archaeological problems. The RAÄ 166 site at Hogstads socken is given as an example of this approach.