Zum Vergleich von Penetrometermessungen,durchgeführt bei unterschiedlichem Wassergehalt

Penetrometer measurements at different soil water contents With use of a large number of field measurements an empirical relation between soil water content and penetrometer resistance was derived. For this purpose the soils were subdivided with respect to their texture and bulk density. The derived relations enable a comparison of penetrometer values derived at different soil water content.     

Soil strength and crop emergence in direct drilled and ploughed cereal seedbeds in seven field experiments

Cone resistance and vane shear strength were measured in the top 50–100 mm of seven soils. Bulk density and water content were also measured in the same layer by coring. At each site cone resistance and vane shear strength tended to decrease with increasing water content and decreasing bulk density down to 1300 kg m-3, but at lower densities they were not related to bulk density. Cone resistance and vane shear strength tended to decrease with increasing coarseness of texture but also depended on soil structure and organic matter content. Plant populations, mainly spring barley, were reduced in soils with cone resistances and vane shear strengths greater than 2500 kPa and 65 kPa respectively. Such high strengths in undisturbed soils were associated with wheeling during harvesting, were apparently independent of soil type and, at the only site of measurement, apparently decreased during weathering in the subsequent season. In contrast to the cone penetrometer, the vane shear tester has minimal shaft friction in undisturbed soils and is more sensitive to soil differences and less sensitive to water content differences than the penetrometer. It is apparently more suitable for indexing the suitability of undisturbed soils for the penetration of direct drill coulters and for subsequent plant establishment.     

Multivariate approach to evaluate the penetrometer resistance in different tillage systems

At present, the penetrometer is the most widely used instrument for assessing in situ soil strength, one of the extrinsic factors affecting plant growth and crop productivity. In this paper we propose a method that discriminates penetrometer resistance due to different soil treatments, by means of Principal Component (PC) analysis. We hypothesized and demonstrated that penetrometer resistance values measured at different soil depths are correlated among themselves (multicollinearity). Considering measurements at each depth as different variables, PC analysis restructured data sets containing these correlated variables into a smaller number of components, whose scores were utilized in univariate analysis of variance (ANOVA) to test differences among imposed soil treatments. We applied the procedure to penetrometer resistance values measured by means of a hand-held cone penetrometer in two long-term experiments conducted in southern Italy, on durum wheat (Triticum durum Desf.) under continuous cropping. In the first trial, four different soil tillage treatments were compared; in the second, two different tillages and two residue management systems were examined. In both trials, PC analysis reduced the original 14 depths of measurements into only 4 PC's, based on correlations of their resistance values, explaining more than 80% of the total variation. Furthermore, ANOVA applied to the scores of each PC, clearly indicated treatment effects on soil strength.

The proposed method has thus allowed assemblage a posteriori of penetration resistance data into only a few significative intervals, using correlations among the measurements made at the different depths. This way, the possible resistance differences due to tillage and/or management treatments have been more easily and more unambiguously showed.     

Simultaneous measurement of soil water and soil hardness using a modified time domain reflectometry probe and a conventional cone penetrometer

Soil strength and water content are important indices for assessing soil resistance to root growth and soil compaction both of which affect other soil properties. Therefore, simultaneous measurement of soil penetration resistance (PR) and soil water content can aid agricultural land management. We measured PR with a conventional cone penetrometer, followed immediately by determining water content using a modified TDR probe inserted into the penetrometer hole. From the results of a field feasibility test, soil water content was measured satisfactorily and correlated well with data obtained by the gravimetric method, except for those data from near the surface owing to soil disturbance when the cone penetrometer was extracted after the PR measurements. Field results demonstrate that PR and soil water content have three‐dimensional variability, with a markedly different distribution pattern between cultivated and subsoil layers at the field scale. Overall, the variability in the PR and soil water data is similar to that reported in previous studies. We conclude that our method produces results helpful to field management of soil and water because it is based on a simple and easy technique for the simultaneous measurement of soil water content and PR.     

The analysis of ranked observations of soil structure using indicator geostatistics

Structure is an important physical feature of the soil that is associated with water movement, the soil atmosphere, microorganism activity and nutrient uptake. A soil without any obvious organisation of its components is known as apedal and this state can have marked effects on several soil processes. Accurate maps of topsoil and subsoil structure are desirable for a wide range of models that aim to predict erosion, solute transport, or flow of water through the soil. Also such maps would be useful to precision farmers when deciding how to apply nutrients and pesticides in a site-specific way, and to target subsoiling and soil structure stabilization procedures.

Typically, soil structure is inferred from bulk density or penetrometer resistance measurements and more recently from soil resistivity and conductivity surveys. To measure the former is both time-consuming and costly, whereas observations made by the latter methods can be made automatically and swiftly using a vehicle-mounted penetrometer or resistivity and conductivity sensors. The results of each of these methods, however, are affected by other soil properties, in particular moisture content at the time of sampling, texture, and the presence of stones. Traditional methods of observing soil structure identify the type of ped and its degree of development. Methods of ranking such observations from good to poor for different soil textures have been developed. Indicator variograms can be computed for each category or rank of structure and these can be summed to give the sum of indicator variograms (SIV).

Observations of the topsoil and subsoil structure were made at four field sites where the soil had developed on different parent materials. The observations were ranked by four methods and indicator and the sum of indicator variograms were computed and modelled for each method of ranking. The individual indicators were then kriged with the parameters of the appropriate indicator variogram model to map the probability of encountering soil with the structure represented by that indicator. The model parameters of the SIVs for each ranking system were used with the data to krige the soil structure classes, and the results are compared with those for the individual indicators. The relations between maps of soil structure and selected wavebands from aerial photographs are examined as basis for planning surveys of soil structure.     

Soybean seedling root growth as influenced by soil texture,matric suction and bulk density

Abstract

Laboratory experiments were conducted under controlled conditions to determine the effect of five matric suctions (0.05, 0.10, 0.30, 1.00 and 3.00 bars) and three bulk densities (1.10, 1.30 and 1.50 g.cm^?3) on the moisture content, penetrometer resistance and soybean (Glycine max L.) root growth in six different soil textural groups (sand, silt, clay and their combinations).

The different textural groups were compacted in PVC pipes 4.4 cm ID and 10 cm long and placed in pressure cells to obtain the desired matric suction. After equilibrium five pregerminated soybean seedlings were fixed on the soil surface. At the end of 48 hours root elongation was measured.

There was an increase in root growth in all the textural groups at all the bulk densities when the matric suction was increased from 0.05 to 0.30 bar. There was however a gradual decrease in root growth as the matric suction increased from 0.30 to 3.0 bars. The reduction in root growth at low and high matric suctions was related to moisture content, change in soil resistance and redox status of the soil system.

The measured penetrometer resistance values were directly related to the level of compaction, soil matric suction and also were dependent upon the texture. Close relationships were recorded between redox potentials and soil matric suction.     

Penetration resistance of gypsiferous horizons

To assess the importance and the possible causes of penetration resistance of horizons with gypsum, 20 horizons in seven irrigated profiles were studied. Gypsum contents ranged from 0 to 900 g kg^?1. Penetrometer tests were performed on undisturbed soil cores by means of a needle penetrometer at different matric potentials. The increase of penetration resistance on drying was caused by changes in the effective stress of the soils, calculated from their soil water characteristic curves. Multiple regression tests showed that besides water content and bulk density, gypsum content was positively correlated with penetration resistance. It seems that in the soils studied the increase of penetration resistance caused by gypsum is due to the growth of gypsum crystals in pre-existing pores, which reduces the volume of regular and continuous voids necessary for root growth.     

Calculating the density of loamy sandy soddy-podzolic soils from penetration resistance diagrams

The possibility for the calculation of the soil bulk density from two-dimensional penetration resistance diagrams drawn using a penetrometer during the vertical sounding of the soil has been discussed. A method has been proposed for calculating the bulk density of loamy sandy soddy-podzolic soils from the soil penetration test diagrams. The model for the calculation of the soil bulk density is based on the general physical concepts with the involvement of similarity theory methods. The adequacy and quality of the model have been studied statistically. The model has been found to be suitable for calculating the bulk density of loamy sandy and sandy podzolic soils.     

An index for soil pore size distribution

An index for classifying soil pore size distribution is proposed. The arithmetic mean change in percent soil water content by weight as the tension changes from zero to 1.5 bars is used as the index. This number characterizes the size distribution of pores with a radius of one micron or greater. A simple equation is presented to calculate the index from soil water contents at pressure plate settings of zero, 0.2, and 1.5 bars. Moisture release curves from 3 different soils show that the index does tend to characterize the shape of the release curve and that it is sensitive to past management which affects the distribution of large soil pores. When all other conditions are optimum, it appears that there exists a specific value of the index which indicates when the soil pore size distribution may be expected to limit plant growth. It is further suggested that the index, together with penetrometer measurements made at the 1.5-bar water content, may be used as “soil test values” for making practical management decisions and for predicting the stability of soils under varying field conditions.     

Effects of 'Agri-SC' soil conditioner on the erodibility of loamy sand soils in East Shropshire, UK: preliminary results

Abstract. The effect of Agri-SC' soil conditioner on the erodibility of loamy sand soils has been investigated at the Hilton experimental site, Shropshire, since March 1988. Factors measured have included runoff and erosion, soil structure, crust strength, splash susceptibility, aggregate stability, soil micromorphological properties, response to compaction and penetrometer resistance.
Treatment decreased runoff and erosion rates, bulk density, splash erosion, crust strength and penetrometer resistance, and increased pore space and aggregate stability. The effects on crust strength, aggregate stability and bulk density were statistically significant. The results suggest that applications of 'Agri-SC' could have beneficial effects for soil conservation.