Robert L. Schafer

Future Research Needs in Soil Compaction

Knowledge of soil compaction and the relation of soil compaction to the cropping system are important inputs for effective management of soil physical condition to improve crop production. The desired degree of compaction depends on the intended purpose; for example, the requirements for traction and mobility are quite different from those for infiltration and root propagation. Much information has been learned in the last two decades with regard to soil compaction behavior and its implications for crop production. However, significant knowledge gaps exist in the description and modeling of soil compaction behavior, in relating soil compaction behavior to agronomic responses (biological and physical) and to conservation of soil and water resources, and in describing and modeling other aspects of soil compaction so that management decisions can be made in production agriculture and conservation of natural resources. A description of the necessary coupling of the engineering mechanics aspects of soil compaction to the agronomic aspects of crop production is emphasized. Research challenges are described which must be pursued in order to provide the knowledge and models that are needed as tools in the management of compaction in soil-machine-plant systems.

Hydrostatic Compaction of Agricultural Soils

ABSTRACT A three-parameter multiplicative model for soil compaction was developed and evaluated using triaxial tests on two agricultural soils. The model satisfied the boundary conditions at low and high stress levels. The effects of moisture content on the three coefficients were investigated.

An Automatic Guidance System for Tractors

ABSTRACT A digital controller is described which is used in a guidance system for automatic steering of an agri-cultural tractor. This controller is constructed from digital logic elements. Field performance experience with the controller is also described.

A rationale for modeling soil compaction behavior: an engineering mechanics approach

ABSTRACT Modeling agricultural soil compaction is important as one input to a system of effective management of soil physical condition to improve crop production. The desired degree of compaction depends on the intended purpose; for example, the requirements for traction and mobility are quite different from those for infiltration and root propagation. Our goal is to develop a compaction model and related soil and soil-machine behavior models which can be used to design systems for effective management of soil physical condition. In this article we discuss our rationale in modeling soil compaction and related soil-machine systems. The status of the various modeling efforts is discussed, as are plans and needs for the future.

Some soil-tool analogs.

ABSTRACT THE feasibility of using analog tool data with scale model data to predict draft forces on a prototype tillage tool was investigated using three analog-prototype systems. The three analog-prototype systems were a cone penetrometer-chisel, a cone penetrometer-disk, and a chisel-disk. These systems were operated at low speed in six soil conditions, and data were analyzed for three scaled-depth levels. The cone penetrometer-disk system proved to be the best analog-prototype system.

Computer automation of soil dynamics research

Abstract The rapid development of computer technology in the past few years, combined with the accompanying reduction of costs, has resulted in the availability of a very powerful tool to researchers. A real-time multiprogramming digital computer system has been in use at the National Tillage Machinery Laboratory for 8 years. This system supports about 90% of the Laboratorys data acquisition, analysis, storage, and display requirements. The computer has had considerable impact on the productivity of the research program at the National Tillage Machinery Laboratory.

DISK SPACING MODEL FOR OPTIMIZING GANG PERFORMANCE

ABSTRACT The effect of disk spacing and gang angle on gang forces was investigated. Two conventional disk shapes were used at two gang angles. One angle provided soil clearance on the back side of the disk; the other was a commonly used angle which resulted in soil pressure on the back side of the disk. All tests were mn at a speed of 1.3 m/s and a depth of 150 mm. The forces on a disk gang were found to vary linearly with the spacing as disk spacing was varied from 100 to 500 mm. A model was developed which described the soil forces as a function of the number of disks and the spacing of the disks in a gang. Results showed that changing disk spacing significantly changed disk gang forces. The disk gang force model was used to explore possibilities for design of disk harrows for maximum or minimum forces. The model was also used to determine the disk spacing at which no ballast was needed to force the harrow to operating depth.

Verification of Tractor Guidance Algorithms

ABSTRACT ALGORITHMS, developed through the use of simulation techniques, for guiding agricultural machines were verified and tested by implementing them on scale model machines. The models were unpowered and maneuvered laterally across a moving belt which simulated forward motion. Machine configurations tested were front-steered tractors with towed implements and rear-steered machines with front-mounted headers. The guidance algorithms were developed to maintain an implement control point on a predefined path. They were programmed on a microcomputer, which controlled the steering of a scale model tractor and also collected performance data from the instrumented models.

Vehicle Guidance Simulator for Digital Automatic Control

ABSTRACT A mechanical vehicle guidance simulator has been con-structed for laboratory research of direct digital automatic control systems to guide agricultural vehicles. It facilitates ground speed simulations in the range of 1.4 to 13.7 km/h and steered wheel lateral displace-ments of ± 0.7 m. A new 8-bit digital electrohydraulic servovalve is currently being tested on the simulator as a final control element.

Front Matter (Preface, Dedication, etc.)

Front Matter: Title page, copyright page, Editorial Board, Preface, Acknowledgements. Dedication, List of Authors, Table of Contents