Soil compaction is one of the major problems facing modern agriculture. Overuse of machinery, intensive cropping, short crop rotations, intensive grazing and inappropriate soil management leads to compaction. Soil compaction occurs in a wide range of soils and climates. It is exacerbated by low soil organic matter content and use of tillage or grazing at high soil moisture content. Soil compaction increases soil strength and decreases soil physical fertility through decreasing storage and supply of water and nutrients, which leads to additional fertiliser requirement and increasing production cost. A detrimental sequence then occurs of reduced plant growth leading to lower inputs of fresh organic matter to the soil, reduced nutrient recycling and mineralisation, reduced activities of micro-organisms, and increased wear and tear on cultivation machinery. This paper reviews the work related to soil compaction, concentrating on research that has been published in the last 15 years. We discuss the nature and causes of soil compaction and the possible solutions suggested in the literature. Several approaches have been suggested to address the soil compaction problem, which should be applied according to the soil, environment and farming system. The following practical techniques have emerged on how to avoid, delay or prevent soil compaction: (a) reducing pressure on soil either by decreasing axle load and/or increasing the contact area of wheels with the soil; (b) working soil and allowing grazing at optimal soil moisture; (c) reducing the number of passes by farm machinery and the intensity and frequency of grazing; (d) confining traffic to certain areas of the field (controlled traffic); (e) increasing soil organic matter through retention of crop and pasture residues; (f) removing soil compaction by deep ripping in the presence of an aggregating agent; (g) crop rotations that include plants with deep, strong taproots; (h) maintenance of an appropriate base saturation ratio and complete nutrition to meet crop requirements to help the soil/crop system to resist harmful external stresses.

Soil compaction in cropping systems: A review of the nature, causes and possible solutions

https://pubag.nal.usda.gov/download/26859/pdf

Pedotransfer functions: bridging the gap between available basic soil data and missing soil hydraulic characteristics

This paper reviews research performed at the Justus-Liebig-University of Giessen, Germany into the impact of different tillage systems on soil properties and quality. The impact of intensive soil tillage treatments on several soil properties was described by means of selected data obtained through long-term interdisciplinary research. The experiments were based on comparative application (long-term, up to 18 years investigations) of the respective tillage options on different soils (e.g. Eutric Cambisol, Eutric Fluvisol) ranging in texture from sand to a silt loam. These soils are located at five field sites with different crop rotations in the central German state of Hesse. Tillage intensity of the systems was considered to decrease in the following sequence: Conventional plough tillage (CT), reduced tillage (RT), and no-tillage (NT). For elucidating the impact of tillage intensity, the tillage extremes CT and NT were compared. Physical conditions of soil as influenced by the application of RT were considered to be intermediate between CT and NT. In general, bulk density in the upper layer of NT soils was increased, resulting in a decrease in the amount of coarse pores, and a lower saturated hydraulic conductivity when compared with the CT and RT soils. Surface cover by crop residues and higher aggregate stability under NT protected soil fertility by avoiding surface sealing and erosion. Lateral losses of herbicides were also reduced under NT conditions, whereas the susceptibility for preferential vertical transport of herbicides needs further evaluation. Accumulation of organic matter and nutrients near the soil surface under NT and RT were favorable consequences of not inverting the soil and by maintaining a mulch layer on the surface. Those improvements were associated with enhanced biological activities in NT and RT topsoils. Increased earthworm activity in NT treatments was associated with a system of continuous macropores which improved water infiltration rates. Earthworms support decomposition and incorporation of straw. Soils which have not been tilled for many years were more resistant to vehicle passage; consequently, the compaction by traffic was lower. Penetration resistance curves indicate that a uniformly stable structure had developed over the years in NT soils. Overall, the results show that RT and NT were beneficial to the investigated soil properties. If crop rotation, machinery, and plant protection are well adapted for the introduction of conservation tillage, these systems may replace conventional ploughing systems in many cases in German agriculture.

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Reducing tillage intensity : a review of results from a long-term study in Germany

Grazing effects on soil chemical and physical properties in a semiarid steppe of Inner Mongolia (P.R. China)

We reviewed the use of the van Genuchten–Mualem (VGM) model to parameterize soil hydraulic properties and for developing pedotransfer functions (PTFs). Analysis of literature data showed that the moisture retention characteristic (MRC) parameterization by setting shape parameters m = 1 − 1/ n produced the largest deviations between fitted and measured water contents for pressure head values between 330 (log10 pressure head [pF] 2.5) and 2500 cm (pF 3.4). The Schaap–van Genuchten model performed best in describing the unsaturated hydraulic conductivity, K . The classical VGM model using fixed parameters produced increasingly higher root mean squared residual, RMSR, values when the soil became drier. The most accurate PTFs for estimating the MRC were obtained when using textural properties, bulk density, soil organic matter, and soil moisture content. The RMSR values for these PTFs approached those of the direct fit, thus suggesting a need to improve both PTFs and the MRC parameterization. Inclusion of the soil water content in the PTFs for K only marginally improved their prediction compared with the PTFs that used only textural properties and bulk density. Including soil organic matter to predict K had more effect on the prediction than including soil moisture. To advance the development of PTFs, we advocate the establishment of databases of soil hydraulic properties that (i) are derived from standardized and harmonized measurement procedures, (ii) contain new predictors such as soil structural properties, and (iii) allow the development of time-dependent PTFs. Successful use of structural properties in PTFs will require parameterizations that account for the effect of structural properties on the soil hydraulic functions.

Using pedotransfer functions to estimate the van Genuchten-Mualem Soil Hydraulic Properties: a review.

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Die physikalische Untersuchung von Böden

/pdf/einfuhrung-in-die-bodenphysik-2nkbesynk7.pdf

Einführung in die Bodenphysik

Die Bedeutung der Herabsetzung der Benetzbarkeit von Bodenaggregaten durch eine organische Umhullung fur die Aggregatstabilitat wurde mit einem Zerfallstest an kunstlichen Aggregaten einer Parabraunerde (Bt) aus Los und eines Pseudogley-Pelosols (P) aus Tonstein untersucht Die Ergebnisse zeigen, das sowohl die Wasserinfiltration ins Aggregat als auch der Aggregatzerfall durch die Anwesenheit der organischen Umhullung deutlich verlangsamt werden Diese Wirkung der organischen Substanz nimmt mit zunehmendem Humifizierungsgrad zu Die abgelosten Bruchstucke von den Aggregaten mit organischer Umhullung sind deutlich grober als die von den Aggregaten ohne organische Umhullung Der Grund ist eine durch die organische Umhullung eingeschrankte Wasserinfiltrationsrate ins Aggregat, so das der Aggregatzerfall langsam vor sich geht und explosionsartiger Zerfall vermindert wird Es spielt dabei eine wichtige Rolle, das wegen der Benetzungshemmungen am Anfang die Fliesstrecke und/oder der Flieswiderstand fur die weitere Infiltration in die Aggregate mit organischer Umhullung langer und groser sind als die in die Aggregate ohne organische Umhullung Teile der organischen Substanz konnten auch mit dem infiltrierenden Wasser ins Aggregatinnere transportiert werden



Effect of differently humified organic matter on aggregate stability by reducing aggregate wettability



The subject of this study was to examine the significance of the contribution of organic matter to the aggregate stability against slaking by reducing aggregate wettability Artificial spherical aggregates were formed from about 50 g paste each of a loessial (Bt-horizon) and of a clayey soil (P-horizon), which were then coated with ground peat moss (strongly and slightly humified) The slaking behavior of the air-dry aggregates was determined by measuring the water infiltration rate and the aggregate breakdown as a function of time



The results show, not only the water infiltration rate but also the aggregate breakdown were slowed down in presence of the organic coating This effect of organic matter increased with increasing huminification The fragments derived from aggregates with organic coating were significantly larger than those from aggregates without organic coating The main reason for this difference is the reduced water infiltration rate into aggregates, so that the aggregates break down rather slowly and progressively than explosively It plays an important role, that because of the wetting inhibition at the beginning the distance is longer and/or the resistance is greater for the further water infiltration into the aggregates with organic coating than those into the aggregates without organic coating The organic matter would possibly also be transported into the inside of the aggregates by water flux

Zur Auswirkung organischer Substanz verschiedener Humifizierungsgrade auf die Aggregatstabilität durch Reduzierung der Benetzbarkeit

Measurement of soil strength with sophisticated parameters is tedious and expensive. Therefore, we developed two straightforward methods to determine this parameter down to about 80 cm, based on the classical measurements of bulk density and penetration resistance as a function of depth. They were applied to three profiles of arable Luvisols, all developed from glacial till. For each method, a procedure was worked out that allows expression of the results in terms of a normal (NC) or precompacted (PC) state. We defined the NC state as that observed in packing characteristics of virgin soils like forests and meadows, and the PC state as the packing characteristics that exist in the topsoil of agricultural soils and intensely grazed areas. Bulk density data were used to examine the packing characteristics and overburden pressures with the assumption that the horizon was in a NC state below 80 cm. For penetration resistance, we assumed a linear increase in penetration resistance with depth to represent the hydrostatic stress distribution in the NC state and deviations of measured values from this line as the PC state. The upper approximately 60 cm of all three soils were compacted, which is proofed both for the penetration resistance and for the bulk density data. For both approaches, the dimensionless coefficient of "stresses at rest," K 0 , was calculated following the line of thought used in engineering soil mechanics (K 0 = σ x /σ z , where σ x and σ are the horizontal and vertical stresses, respectively). The K 0 values are highest in the precompacted soil horizons and decrease with depth.

Karl Heinrich Hartge

Papers

Die physikalische Untersuchung von Böden

Einführung in die Bodenphysik

Zur Auswirkung organischer Substanz verschiedener Humifizierungsgrade auf die Aggregatstabilität durch Reduzierung der Benetzbarkeit

Mechanical Stresses in Soils Assessed from Bulk‐Density and Penetration‐Resistance Data Sets

Essential Soil Physics