Iowa and Landsat: watching the corn belt from space

Iowa grows more corn than any other state, raises more hogs, and makes more ethanol — nearly 4.5 billion gallons in 2020. All of it rests on fertile soil under growing pressure from land-use change, odd rainfall, heat and extreme storms. For fifty years the Landsat satellites have been watching that soil from space, and Iowa has been one of the main testing grounds for what they can do for farming.

Seeing crops from orbit

Landsat's sensors read the infrared and near-infrared light that plants reflect, which shows how healthy vegetation is. At 30 metres per pixel, the resolution is fine enough to see individual fields, and the archive goes back half a century.

• Mapping what is planted. The U.S. Department of Agriculture's Cropland Data Layer uses Landsat to map crops field by field across the country. In Iowa it shows the two giants: corn, where Iowa is first in the nation, and soybeans, where it is second.
• Crop health and drought stress (Xu and others, 2020).
• How yields vary across fields (Gao and others, 2018).
• Water use, through estimates of evapotranspiration — the water lost from soil and from plant leaves together (Anderson and others, 2012).

The Cropland Data Layer: corn (gold) and soybeans (dark green) dominate Iowa. Image: U.S. Department of Agriculture

The derecho of 2020

Iowa is safe from rising seas and hurricane surge, but it gets violent weather of its own. On August 10–11, 2020, a derecho — a wide, long-lived windstorm, often with hurricane-force gusts — crossed the middle of the state with gusts up to 140 miles per hour. It flattened fields, left tens of thousands without power and seriously damaged nearly a third of the state.

Landsat images taken before and after showed the damage plainly, as they can for floods and tornadoes. They fed a NASA Harvest assessment that put the damaged area at about 1.99 million acres of corn and 0.6 million acres of soybeans (Hosseini and others, 2020).

Before and after: wind-damaged crops show as lighter green.

Tracking how the land changes

Iowa's rivers, lakes and grasslands draw visitors and support prairie wildlife, and turning land over to crops — or changing how it is farmed — affects wetlands and water quality. With a fresh look at every spot every 8 to 16 days, Landsat is the backbone of tracking those changes. Studies built on it have measured:

• the environmental return on federal programmes such as the Conservation Reserve Program (Gallant and others, 2011);
• how high crop prices changed planted acreage and soil carbon (Stern and others, 2012);
• the water-quality effects of fertiliser (Taylor and Heal, 2021).

That kind of evidence feeds directly into decisions Iowans live with.

The program behind it

The USGS National Land Imaging Program supplies satellite imagery and other geospatial data to government, business, universities and the public, and funds the USGS Earth Resources Observation and Science (EROS) Center, which gives worldwide access to the Landsat archive. Landsat is the most widely used land-imaging source among federal civilian agencies, and local, state and Tribal governments use it to monitor and forecast what happens on the ground.

Sources

Written from Iowa and Landsat, a U.S. Geological Survey fact sheet in its state-by-state Landsat series; a work of the United States government in the public domain. Ethanol figure from the USDA Economic Research Service (2022), as cited there.