Abstract
The application of tractors and equipment may produce compaction and parti-cle size of soil of such values that may greatly affect the emergence pressure and growth of seedlings. This study was accordingly undertaken to investigate the effects of such parameters under varying conditions of soil moisture. On the basis of rele-vant investigations, it was recommended that the use of heavy tractors and equip-ment be avoided so as to achieve a happy balance between the air, water and solid components of soil.
INTRODUCTION
The importance of design, construction and operation of tillage and traction equip-ment in creating soil conditions conducive to plant growth, has long been recognised by agricultural engineers. The application of such an equipment may produce the particle size of soil and compaction pressure of such values which are likely to upset the balance between air, soil and water components. The coarseness or fineness of the soil in the vicinity of seeds, and the level of its com-paction alongwith moisture will affect the emergence pressure of seedlings and the fi-nal yield of crops. This study was accordingly undertaken to investigate the effect of size of soil particle, compaction pressure and moisture on the emergence pressure and growth of seedlings with a view to select a suitable size of tractor and allied equipment.
MATERIALS AND METHODS
An instrument was developed for mea-suring the force or pressure exerted by a mechanical seedling having a diame-
ter equal to the diameter of alfalfa seedling (0.12 cm) and was forced to move through the soil in a. manner similar to that of an emerging seedling. A cantilever beam attached to a rect-angular plate was constrained to move up and down on the two guide rods of the instrument at the rate of 20 cm per minute. An SR-4 strain gauge bridge, fixed at the end of cantilever beam, was employed for sensing the force exerted by the mechanical seedling. ii. An Offner Dynograph was used to am-plify and record the force of pressure, on a two channel oscillograph. Hi. A hydraulic press fitted with a pressure gauge was employed for packing the soil to a desired compaction pressure. iv, An electric sprayer 'was used for spraying water on the soil to increase the moisture content of the soil. v. A rotary sieve was used for separating various grain sizes of soil.
