Controlled drainage systems to reduce contaminant losses and optimize productivity from New Zealand pastoral systems

Abstract

Drainage systems are essential for managing soil water levels, thereby ensuring optimal plant productivity while protecting soil quality. Although beneficial, drainage systems are also known to be a significant loss route for dissolved nutrients. A potential way of reducing nutrient loss through drainage systems is to use weirs to strategically control drainage of excess water from the soil profile. This review evaluates the scientific literature to ascertain whether controlled drainage could be a useful crop productivity and nutrient loss mitigation tool for New Zealand pastoral farming systems. While a range of risks and potential disadvantages have been identified, evidence from studies of cropped systems with controlled drainage in Europe, Canada and the US suggests that suitably managed controlled drainage offers significant benefits for water quality, agricultural productivity and nutrient- and water-use efficiency. The practical efficacy of controlled drainage requires field evaluation under New Zealand farming conditions.