Issues in using Land Use Capability class to set nitrogen leaching limits in moisture-deficient areas—a South Island case study

Abstract

ABSTRACTIn setting catchment nutrient limits aimed at meeting water quality objectives, some regional councils have adopted or are considering a natural capital approach to set farm-scale nutrient discharge allowances, whereby soils with a higher natural capital are given a higher discharge allowance. Land Use Capability (LUC) classes have been adopted as a proxy for natural capital. We examine the suitability of LUC for this purpose and identify issues that should be considered when using LUC in the context of a natural-capital-based approach to set nutrient limits, particularly in moisture-deficient areas where irrigation is becoming a major management tool, such as in Canterbury. The main issues are that LUC classes 1–4 are assessed on arable suitability not pastoral suitability, the high variability of pastoral productivity within an LUC class, and the limited correlation of LUC class with nitrogen losses. We propose some modifications to the LUC-based approach to address these issues.