Plow layer depth

Two-Dimensional Numerical Model, Application of DBCP by shank injection in a pineapple bed (Maui fields) provides a line source of pesticide at a depth of about 30 cm which cannot be modeled in a one-dimensional mode without first evaluating the impact of initial concentration distribution. The geometry of the system is indicated by the cross-sectional diagram of two pineapple beds in Figure 1, The section of Figure 1 delineated by AA-BB represents a typical section. The objective was to model the movement of DBCP from an assumed source zone (8 cm wide x 10 cm deep section centered at 30 cm depth) to determine the approximate time required to justify the assumption of a uniform lateral distribution of DBCP in the plow layer for subsequent one-dimensional modeling. An appropriate model and numerical solution for this case was given by Hemwell (15) and the details of the present application are presented elsewhere C3 ). In brief, the two-dimensional equation solved is... 

Much emphasis has been placed on the plowed layer and its contribution to crop production, and comparatively little research has been done on the subsoil. In fact, in general discussions of the depletion of soil fertility the subsoil is often ignored, even though we know that it is often higher in essential nutrients, other than nitrogen, than is the A-horizon. These mineral nutrients may be less available to plants than those in the surface layer that is constantly subject to weathering and oxidation, but nevertheless subsoils do contribute in a major way to plant feeding. The plowed layer is only 6—12 inches deep whereas the subsoil tapped by the root system may have a depth of several feet. 

The Rooting-Zone Soil Root-zone soil includes the A horizon below the surface layer. The roots of most plants are confined within the first meter of soil depth. In agricultural lands, the depth of plowing is 15-25 cm. In addition, the diffusion depth, which is the depth below which a contaminant is unlikely to escape by diffusion, is on the order of a meter or less for all but the most volatile contaminants. Soil-water content in the root zone is somewhat higher than that in surface soils. The presence of clay in this layer serves to retain water. Contaminants in root-zone soil are transported upward by diffusion, volatilization, root uptake, and capillary motion of water transported downward by diffusion and leaching and transformed chemically primarily by biodegradation or hydrolysis. 

The experimental results show that deep plowing of most reasonably normal soils does not have much effect on the depth to which roots penetrate. The depth of penetration does vary markedly with both soils and crops, but depth of plowing has a minor effect except where there is a very impervious layer. This fact is one of the main ones advanced by the advocates of no plowing or minimum tillage. 

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