A model for predicting the effect of drainage on soil moisture, soil temperature and crop yield

The primary objective of this study was to develop a methodology that combines climatological data, soil properties, crop drainage requirements and drainage theory into a design method called water management model. The aim of this type of approach is to characterize the effect of drainage on soil moisture, soil temperature and crop yield. The final result of the application of the methods presented in this study is a decision on optimum drainage parameters, i.e. drain spacing and depth, and drainage coefficient.

Determination of the soil water retention curve, the unsaturated hydraulic conductivity function and soil thermal conductivity is discussed. Methods for describing the movement of water and heat in a seasonally frozen soil are presented. A model for estimating the effect of soil moisture on crop yield is described. When tested by comparisons with analytical solutions, laboratory data and field experiments, the results were favourable.

It was shown that the methods presented in this study can be used in estimating the proper drainage coefficient, i. e. the design flow that the pipe system must be capable of conveying. Accordind to the results obtained, it seems realistic to decrease the design flow; this would reduce the total costs of drainage system by 1 – 5 %. Another pratical result was obtained, indicating that the optimum drain spacing is not only dependent on the soil type and crop grown; the choice is also affected by the time period used in the economic analysis and by overall maximum yield level, which is an indication of the efficiency of the cultivation techniques used on the farm.