No description available.

No description available.

No description available.

No description available.

This research was conducted to 1) evaluate the use of drain tile (subsurface drainage) in an irrigated and dryland management system in both a cotton and soybean production system and 2) determine an herbicide program to control Palmer amaranth (Amaranthus palmeri S. Wats.) in the absence of dicamba. Neither drainage or drainage spacing had any effect pre-plant soil conditions, plant growth parameters, or yield in either production system. Stand counts were reduced in narrow tiled spacings (4.5 m) in the dryland cotton study. However, there was no reduction in lint yield due to the reduction in plant stand. Moreover, residual control was maximized with the use of fluridone and fomesafen as PRE emergence treatments. Glufosinate provided the greatest control of Palmer amaranth in the absence of dicamba. Lint yield was maximized with the application of glufosinate in the absence of dicamba. These data indicate that subsurface drainage had no effect on cotton or soybean performance in Mississippi. Moreover, in the absence of dicamba Palmer amaranth control options can be optimized by using fluridone or fomesafen as PRE emergence applications and glufosinate as POST emergence application to minimize yield reductions due to Palmer amaranth.

No description available.

Thesis (M. Sc.)--University of Hong Kong, 1998. / Includes bibliographical references.

Thesis (M.P.A.)--University of Hong Kong, 1999. / Includes bibliographical references.

Thesis (M.P.A.)--University of Hong Kong, 1999. / Includes bibliographical references. Also available in print.

Literature on subsurface drainage theories, determination of drainage parameters, and analysis approaches of uncertainty was reviewed. Sensitivity analysis was carried out on drain spacing equations for steady state and nonsteady state, in homogeneous soils and in layered soils. It was found that drain spacing is very sensitive to the hydraulic conductivity, the drainage coefficient, and the design midspan water table height. Spacing is not sensitive to the depth of the impermeable layer and the drain radius. In transient state, spacing is extremely sensitive to the midspan water table heights if the water table fall is relatively small. In that case steady state theory will yield more reliable results and its use is recommended. Drain spacing is usually more sensitive to the hydraulic conductivity of the soil below the drains than to that of the soil above the drains. Therefore, it is desirable to take samples from deeper soil when measuring hydraulic conductivity. A new spacing formula was developed for two-layered soils and a special case of three-layered soils with drains at the interface of the top two layers. This equation was compared with the Kirkham equation. The new formula yields spacings close to the Kirkham equation if the hydraulic conductivity of the soil above the drains is relatively small; otherwise, it tends to give more accurate results. First and second order analysis methods were employed to analyze parameter uncertainty in subsurface drainage design. It was found that conventional design methods based on a deterministic framework may result in inadequate spacing due to the uncertainty involved. Uncertainty may be incorporated into practical design by using the simple equations and graphs presented in this research; the procedure was illustrated through an example. Conclusions were drawn from the present study and recommendations were made for future research. / Applied Science, Faculty of / Graduate