Assessing environmental impacts of individual crops in diverse organic vegetable rotations

Summary

Crop rotations are beneficial for agricultural production, especially in organic vegetable production where successful production is dependent on a well-managed crop rotation. Hence, when determining product-level impacts of organic vegetable crops grown in rotations, the interactions with the other crops in the rotation should be accounted for. Here we explore how the choice of a method for handling multi-functionality in organic vegetable crop rotations affects product-level impacts. The 7-year crop rotation included pointed cabbage, cos lettuce, yellow onion, grass-clover and spring barley. Three methods for handling multi-functionality of crop rotations were applied. The crop-by-crop approach assessed single crops, disregarding the crop rotation. A modified crop-by-crop approach considering the crop’s N fertilization service to the following crop was investigated to reflect soil fertility interactions. Thirdly, a black-box approach was applied, where the entire rotation was considered the smallest meaningful unit of investigation. Hence, allocation was needed to determine product-level impacts. Allocation was based on cultivation area, fresh-matter yield, dry-matter yield, economic value and energy yield.
Compared to the crop-by-crop approach, the consideration of the crop’s N fertilization service did not affect environmental impacts of vegetable crops, apart from a 2% increase for pointed cabbage, which followed grass-clover. Depending on choice of allocation key for the black-box approach, the impact of vegetables varied between 42-149% of the impact calculated through the crop-by-crop method. Onion impacts increased with all allocation keys. The forage and cereal crop impacts varied greatly (21-532% relative to crop-by-crop impact), impacts was generally increased, but decreased with the economic value allocation key. We recommend to use the N-flow modified crop-by-crop approach, as this approach reflect management related to crop rotations, while still ascribing activities to the directly affected crops, and can be further expanded with other nutrient flows or crop interactions.