Actual versus environmentally recommended fertilizer application rates: Implications for water quality and policy

Abstract

Excessive application of crop nutrients has been identified as a threat to surface water quality in many jurisdictions. The Western Basin of Lake Erie Collaborative Agreement commits the governments of Michigan, Ohio and Ontario to reduce phosphorus entering the Lake Erie’s western basin by 40% by 2025/2026 from 2008 levels by, among other things, reducing fertilizer use in agriculture. The International Joint Commission (2014) estimates that agriculture accounts for 44% of total phosphorus loadings to Lake Erie. Our study uses a unique micro level data set of 16 farms over 6 years that allows us to examine 397 individual nutrient application choices at the field and farm level. If efforts to reduce excessive application of nutrients are to be successful at aggregate level, they need to be informed by an understanding of how farmers make nutrient application decisions within existing production systems. The study aims to enhance our understanding by determining whether farmers applying nutrients to maximize yields, to maximize net returns or to meet environmental targets, and whether over-application depends on factors such as farm size, crop type, manure use, and type of nutrient. We compare actual nutrient application rates with site specific rates intended to minimize excess nutrient application and we regress nutrient application levels against potential explanatory variables including farm size, crop rotation practices, and application of livestock. The data were collected from farmers in the Gully Creek watershed in Ontario. We found that excess nutrient applications, as a percentage of the total nutrient applications, are much higher for phosphorus than for nitrogen and higher for wheat than for corn. While most of the farmers in the study are not required to comply with provincial nutrient management regulations, many of them apply fertilizer at rates close to that recommended by those regulations and some at rates significantly less. While most farms are applying fertilizer, particularly nitrogen, at rates close to the minimum crop requirements, nevertheless, a few farms apply much more phosphorous than recommended. Policy and research efforts should be directed toward targeting these individuals that appear to be the primary contributor to the nutrient loading issue.