STREAMLINES FOR DIFFUSIVE FLOW IN VERTICAL AND SURFACE TILLAGE - A MODEL STUDY

Methods of tillage must permit adequate flow of O2 to plant roots. The objective of this work is to calculate streamlines of O2 flow from ch isel holes oriented vertically and horizontally (surface tillage) in t he soil to plant roots. Streamlines are perpendicular to equipotential lines. They also have the property that the difference in value betwe en two streamlines gives the quantity of fluid (in this case, O2) flow ing between them. Therefore, streamlines are often more important than equipotentials. Streamlines for flow of O2 from the chisel holes in t he soil to plant roots were calculated by use of the relaxation method , in which both a coarse grid (2.54 cm on a side) and a fine grid (1.2 7 cm on a side) were used. Transit times were calculated from the flow net resulting from the streamlines and equipotential lines. Calculatio ns with the coarse grid showed that, for the vertical chisel case, 75% of the flow goes out of the side of the chisel opening closest to the sheet of plant roots and 25% of the flow goes out of the side of the chisel opening farthest away from the sheet of plant roots; for the fi ne grid, the values are 63 and 37% for the two sides of the chisel hol e, respectively. For both the vertically and horizontally filled cases , stagnant areas were identified in the soil. Transit times were short for both tillage cases (on the order of minutes), confirming the gene ral assumption that diffusion is the major mechanism of gas transport in soil.