R.J. Godwin

Soil failure with narrow tines

Abstract A force prediction model has been developed for tines of a wide range of working depth/width ratios. The soil worked by the tines is assumed to obey the Mohr-Coulomb failure criterion. The predictions show useful agreement with experimental data for the horizontal force components in two soil conditions with high angles of shearing resistance. A method is proposed for estimating the critical depth of a tine, the depth below which the soil failure mechanism changes.

A Review of the Technologies for Mapping Within-field Variability

Abstract Techniques for mapping soil physical and chemical condition, topography and the weed status of fields, are reviewed from a practical and economic perspective. The conclusions are that it is possible to target sample the soil physical and chemical status of fields and locate areas of high weed density following the use of inexpensive, non-invasive techniques electromagnetic induction (EMI) aerial digital photography (ADP) and radiometry. Semi-automated field reconnaissance systems on all terrain vehicles and combines also assist in locating the position of weed patches. P and K fertiliser can be replenished by using the ‘off-take’ values determined from yield maps, whilst crop density in the spring period shows potential for the management of nitrogen fertiliser in cereal crops using ADP and could also be a benefit in the application of agrochemicals. Currently, the most economically viable method to determine field topography is to use very simple surveying techniques, and there is potential to automate this.

The Analysis of Spatial and Temporal Trends in Yield Map Data over Six Years

Abstract A quantitative analysis of yield data from four fields over 6 years was carried out to identify the spatial and temporal trends. The methodology was modified from previous work to separate the temporal effects into two parts; the inter-year offset and the temporal variance. The inter-year offset quantifies the overall differences in yield between 1 year and the next, whereas the temporal variance indicates the amount of change at a particular point over time. Results from these fields show that the significant spatial variability found within each individual yield map cancelled out over time, leaving a relatively homogenous spatial trend map. The implications of these findings are that each field should be managed according to the current years’ conditions.

An extended octagonal ring transducer for use in tillage studies

Abstract The design and the related development problems of an extended octagonal ring transducer are discussed. The transducer was primarily designed to monitor the two force components and the moment in the plane of the two forces of the soil reaction to simple times. The performance figures of the transducer are given, the sensitivities of the strain gauge outputs are significantly higher than those expected from the prediction equations used to design the transducer.

Water flow to mole drains

Abstract A study has been made of the mechanism by which water flows to a mole drain. Drain discharge hydrographs and fast response tensiometers have been used to compare the differences in performance between mole drains having large implement induced soil fissures above the drain, with drains having no fissures. The results show that in a well structured clay soil, mole drains with large fissures have a significantly faster drainage response to rainfall than drains without them. Mechanically induced fissures become increasingly important for rapid water flow to mole drains as the soil structural conditions deteriorate.

An experimental investigation into the force mechanics and resulting soil disturbance of mole ploughs

Abstract The magnitude of the forces on the foot and leg of a mole plough are presented for a wide range of soils together with the effects of the expander, sliding beam, forward speed and leg rake angle. The use of a shallower preliminary treatment prior to moling at the normal depth to minimize traction requirement is considered and a method of optimizing the working depth for the shallow treatment given. The use of wings to increase soil cracking is investigated. The nature of the soil disturbance is explained by reference to the type of soil failure which is controlled by implement geometry, depth of operation and soil condition.

Calibration Methodology for Mapping Within-field Crop Variability using Remote Sensing

A successful method of mapping within-field crop variability of shoot populations in wheat (Triticum aestivum) and barley (Hordeum vulgare L.) is demonstrated. The approach is extended to include a measure of green area index (GAI). These crop parameters and airborne remote sensing measures of the normalised difference vegetation index (NDVI) are shown to be linearly correlated. Measurements were made at key agronomic growth stages up to the period of anthesis and correlated using statistical linear regression based on a series of field calibration sites. Spatial averaging improves the estimation of the regression parameters and is best achieved by sub-sampling at each calibration site using three 0·25 m2 quadrats. Using the NDVI image to target the location of calibration sites, eight sites are shown to be sufficient, but they must be representative of the range in NDVI present in the field, and have a representative spatial distribution. Sampling the NDVI range is achieved by stratifying the NDVI image and then randomly selecting within each of the strata; ensuring a good spatial distribution is determined by visual interpretation of the image. Similarly, a block of adjacent fields can be successfully calibrated to provide multiple maps of within-field variability in each field using only eight points per block representative of the NDVI range and constraining the sampling to one calibration site per field. Compared to using 30 or more calibration sites, restricting samples to eight does not affect the estimation of the regression parameters as long as the criteria for selection outlined in this paper is adhered to. In repeated tests, the technique provided regression results with a value for the coefficient of determination of 0·7 in over 85% of cases. At farm scale, the results indicate an 80–90% probability of producing a map of within crop field variability with an accuracy of 75–99%. This approach provides a rapid tool for providing accurate and valuable management information in near real-time to the grower for better management and for immediate adoption in precision farming practices, and for determining variable rates of nitrogen, fungicide or plant growth regulators.

The development of a dynamic drop-cone device for the assessment of soil strength and the effects of machinery traffic

A drop-cone penetrometer has been developed as a rapid soil strength assessment device. The technique consists of releasing a 2 kg, 30 ° apex angle cone from a height of 1 m and measuring its penetration. Linear relationships have been established between soil moisture content and cone penetration, and between cone penetration and vane shear strength; the latter being independent of both soil type and crop cover. A linear relationship has also been established between cone penetration and the mean wheelrut depth resulting from machinery operations, thus enabling predictions of potential soil and crop damage to be made before machinery is taken into the field.

Influence of deep loosening techniques and subsequent wheel traffic on soil structure

Abstract This investigation compared the final soil profile conditions, following three deep loosening methods, i.e. deep loosening before (A), after (B) and simultaneous with (C) surface cultivation followed by a subsequent wheeling with either high or low pressure tyres. Only method C combined with low pressure tyres produced a satisfactory final loose subsoil condition, emphasising the need for care in the subsequent management of deep loosened profiles. To retain the deep loosening effect to benefit the next crop, one pass or bed management systems are recommended.

An experimental investigation into factors influencing the soil injection of sewage sludge

Abstract Injection techniques for applying sewage sludge to grassland were investigated. The results have shown injection to be a viable technique for the application of sewage sludge under UK conditions. The technique is also suitable for the application of agricultural slurry, since the physical characteristics of both sewage sludge and slurry are similar. Research has shown an acceptably uniform grass response can be obtained from 280 mm wide winged times operating at a depth of 150 mm and spacing of 650 mm, when the soil is in the moist friable to plastic consistency state. Immediate rolling of the injected zone improved the crop response in the vicinity of the injector path, provided surface contamination was avoided. Injection on sloping land should be conducted downslope, rather than across, to ensure adequate machine stability, providing that maximum application rates are not exceeded. Sludges with dry solids contents in excess of 6% can be injected at application rates of 140 m 3 /ha into slopes of 12°, without down-slope seepage occurring. Rates should, however, be reduced for sludges with lower dry solids content, depending upon field slope. Increasing the injector leg rake angle reduced surface disturbance, with little effect on the resulting draught and vertical forces, until rake angles in excess of 100° were reached. Vibration of the injector tine using a rotating eccentric mass reduced the draught force under dry, brittle soil conditions, but not under more plastic field conditions.