Drainage Water Management Online Advisory

The successful management of controlled drainage systems focuses on two important objectives. The first is achieving optimum production efficiency and maximum nutrient utilization by the crop; the second is attaining maximum water quality benefits. Controlled drainage structures require that the topography be relatively flat. The costs to production and water quality will usually exceed benefits when the land slope exceeds 0.5%. As a consequence, controlled drainage is most practical in the Lower Coastal Plain and Tidewater regions of North Carolina. The predominant cropping sequence in these areas is a two-year rotation of corn, wheat, and soybean. General guidelines for management of controlled drainage under this cropping sequence are given in Table 1. The general guidelines present an attempt to achieve a balance between production and water quality goals. Many of the management indicators are hidden from view, and the response to adjustments is not immediate. Intensive management with long- term monitoring is necessary to develop a site-specific understanding of the system. Productivity and water goals are compatible during some years, or at least seasonally during most the year. Under some conditions, however, productivity, water quality, or both goals may need to be mutually compromised for the benefit of the other. For example, management throughout the year is necessary to achieve maximum water quality benefit and drainage control to reduce nitrogen transport is most effective during winter and early spring periods. When fields are fallow, there is no significant production cost associated with holding water levels high to achieve the maximum water quality benefit. But productivity of some crops such as winter wheat may be reduced by high winter water table levels.