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Streamlines for Diffusive Flow in Vertical and Surface Tillage: A Model Study

Evapotranspiration Lab., Dep. of Agronomy, Kansas State Univ., Manhattan, KS 66506

*Corresponding author.

ABSTRACT

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 chisel holes oriented vertically and horizontally (surface tillage) in the soil to plant roots. Streamlines are perpendicular to equipotential lines. They also have the property that the difference in value between two streamlines gives the quantity of fluid (in this case, O₂) flowing between them. Therefore, streamlines are often more important than equipotentials. Streamlines for flow of O₂ from the chisel holes in the 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 (1.27 cm on a side) were used. Transit times were calculated from the flownet resulting from the streamlines and equipotential lines. Calculations 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 fine grid, the values are 63 and 37% for the two sides of the chisel hole, respectively. For both the vertically and horizontally tilled cases, stagnant areas were identified in the soil. Transit times were short for both tillage cases (on the order of minutes), confirming the general assumption that diffusion is the major mechanism of gas transport in soil.

Contribution 93-333-J from the Kansas Agric. Exp. Stn., Manhattan.

Received for publication February 24, 1993.

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