America's Salad Bowl

Salad
Source: Image by Michael Moriarty from Pixabay

Christmas comes in the summer in New Zealand where I grew up.  For me, the season connotes 9pm sunsets, trips to the beach, and summer foods like meat on the grill, a cold beer, and a fresh salad.

The COVID pandemic means I won't experience a summer Christmas this year, but I'm imagining summer today by writing about salad. Specifically, the Salinas Valley, where the ingredients of your summer salad are likely grown. 

Salinas Valley grows almost half of the nation's lettuce (including head, leaf and romaine) and a third of its spinach, thus its moniker as America's Salad Bowl. It also produces half the nation's broccoli and cauliflower and over 80% of its artichokes. 

Lettuce Production
Sources: California Crop Reports for Monterey County production, NASS quickstats for US production

 

Salinas Valley does not jump out of the California map the like its bigger and more famous cousin, the Central Valley.  Salinas Valley is 90 miles long and less than 10 miles wide. It follows the Salinas River from San Ardo north west to Monterey Bay and sits entirely within Monterey County. In contrast, the Central Valley is 450 miles long, up to 60 miles wide, and touches 19 counties.

California
Source: Google Maps​​​​

 

This gif shows the location of crops in California as estimated from satellite imagery. I made it using our Cropland Data Layer data app, following the instructions in this Ag Data News article, Note the dominance of rice in the north (light blue), grapes in the Napa Valley (purple), alfalfa throughout the Central Valley (pink), and the expansion of almonds (teal) and pistachios (lime green). Salinas Valley appears as a small mostly purple sliver south east of Monterey Bay.

California Crops
Source: Our Cropland Data Layer data app

 

The map below zooms in on Salinas Valley. Farmers grow grapes on the edges of the valley and fruit and vegetables in the interior. 

Salina Valley Agriculture
Source: Our Cropland Data Layer data app

 

The precise location of each fruit and vegetable crop is unclear in currently available satellite data, as revealed in the image below.  Each point on the map corresponds to a 30m x 30m pixel and is colored according to a satellite-based estimate of which crop is grown on that pixel. These estimates come from the USDA's Cropland data Layer product. Note the contrast between the rectangular purple shapes, which represent fields planted with grapes, and the apparently random assortment of colors representing other crops. 

Salinas zoomed
Source: Our Cropland Data Layer data app

 

Farmers make planting decisions at the field level, and fields are much bigger than pixels. It is clear that the satellite identifies grapes well, but finds it difficult to tell the various vegetables apart. In their 2019 accuracy report, USDA estimates that it correctly identified 92% of grape pixels, but only 72% of lettuce pixels and 48% of broccoli pixels. As outlined in this Ag Data News article, improving satellite estimates of field-level planted crops is a topic of my ongoing research.

The maps in this article come from our Cropland Data Layer data app. I made the pie chart in this Excel file — no R code today!