Border towns like Nogales, Arizona are fascinating places full of people and goods passing from one side to the other, usually funneled through ports-of-entry (POE) where their flow is regulated by various government agencies. With inputs, outputs and regulation of flow, POEs offer a large-scale, physical example for describing Systems Thinking. Sankey Diagrams depict energy flows and work especially well within the context of POEs and Systems Thinking (see Figure 1).
Figure 1. Fresh Produce imports through the Nogales, AZ port-of-entry, 2017, organized by item type (i.e. grape tomatoes), general term (i.e. tomatoes), plant family (i.e. Solanaceae) and general terms used to describe rotational crops (i.e. fruits, roots, beans, leafy).
A watershed includes the tributaries that contribute to a river and in a similar way a foodshed includes the tributaries of a food system. The Sankey diagram above depicts fresh produce imports through Nogales, Arizona, one of the largest inland POEs for food in the world, in truckload equivalents of 40,000 lbs. The commodity types are organized by their plant families as well as more general terms used in describing rotational crops, before feeding into all fresh produce imports through the Nogales, AZ POE from 2017.
The practice of continuous cropping, planting the same crop from year after year, leads to a host of problematic issues including depletion of soil nutrients, declining yields over time, soil compaction, etc. Farmers that have made infrastructure investments such as drip irrigation or protected structure (greenhouse, shade house, etc.) or investments into their operation’s capabilities, for example, Food Safety or Organic certifications to enable market access, are incentivized to use their improved land or operations each year. Markets develop around their product but at the same time the practice of continuous cropping becomes reinforced from one season to the next.
Rotational crops are one effective way to address the practice of continuous cropping and may be described in general terms of “fruits,” “roots,” “beans” and “leafy.” In more technical terms, different plant families (i.e. Solanaceae, Apiaceae, Fabaceae, Brasicaceae) are generally suitable as rotational crops, though, resource availability, soil type, climate, pathogen pressure, markets, post-harvest requirements, etc. also need to be carefully considered.
While also enhancing biodiversity, planting different plant families from one season to the next helps to break the cycle of pathogen build-up and other problems related to continuous cropping. The annual rotation of crops also helps reduce costly external inputs such as fertilizers, herbicides, fungicides, pesticides, etc., all of which contribute to greenhouse gases including nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2).
Rotational crops can be non-commercial, such as Sunn Hemp, a legume that works well for building organic Nitrogen in the soil and Soil Organic Matter (SOM) to support microbial activity. Certain rotational crops can also be harvested for commercial use while achieving similar benefits for the soil as the non-commercial rotational crop options. Farms with limited land or improved infrastructure may be more interested commercial rotational crops as they may not be able to afford to leave fallow their improved infrastructure.
Farmers and their marketer counter-parts in a globalized world can use Sankey Diagrams of their international foodsheds to better understand their food systems and to make informed decisions for potential commercial rotational crop options that ultimately benefit the farmer, the environment and the bottom-line.