ABSTRACT.

One of the most significant soil parameters affecting root growth is soil compaction. It is therefore important to be able to determine the presence of compacted layers, their depth, thickness and spatial location without the necessity of digging a large number of holes in the field with either a spade or backhoe. Previous investigations have identified soil compaction by different methods such as: using ground penetrating radar, acoustic systems, vertical and horizontal penetrometers and instrumented wings mounted on the faces of tines. Linking the output from these sensors to global positioning systems would give an indication of the spatial patent variation. The aim of this study was to evaluate the performance of a soil compaction profile sensor in both controlled laboratory and field conditions. The sensor consisted of a series of instrumented flaps; a flap is defined as the sensing element which comprises one half of a pointed leading edge to the leg of a tine to which strain gauges are placed on the rear face of the flap. Studies measured the effect of compaction on the changes in the soil resistance acting upon a flap face in a soil bin laboratory and under field conditions. The results indicated that the sensor was sensitive to differences in soil strength at different depths in soils. A technique was developed to identify the soil compaction resulting from different tyre inflation pressures and loads. The soil compaction profile sensor was tested on a number of fields in south‐eastern England to determine the changes in soil strength below the wheelings of a pea harvester operating at different tyre inflation pressures.

Tension infiltrometry is a useful in situ technique that is commonly used to determine hydraulic conductivity of the soil near saturation; however, the measurements are time consuming and costly. The aim of this study was to develop a fully automated tension infiltrometer for field use based on already existing designs. Differential pressure transducers were used to automate water level measurements, and the tension settings were automated by a set of solenoid valves. The effects of different design parameters on water level measurement fluctuations created by bubble disturbances (noise) were studied in the laboratory. The differential transducer provided less noisy measurements than the single transducer. The measurement noise was significantly smaller when a large‐diameter reservoir was used. The measurement noise was further reduced by using a reservoir system made of two tubes of different diameters slotted into each other. The effect of an increasing flow rate on the water level fluctuations was also investigated. Based on the design parameters tested, three identical tension infiltrometers connected to a single Mariotte bottle were built and tested under laboratory and field conditions. The pressure‐dependent hydraulic conductivity, K(h), values for all three replicates applied in the laboratory did not significantly differ from each other. In the field, the infiltration experiments were performed on a sandy loam soil on sites with and without wheel tracks. A significant reduction of K(h) values for most of the applied pressure heads was observed in the wheel track. The improved automated tension infiltrometer requires only a little operator intervention.

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