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Irrigation test site in Kansas
September 10, 2019

Climate change: a dirt-y business

Increased rainfall may threaten food security

Author: Jules Bernstein
September 10, 2019

Groundwater is essential for growing crops, but new research shows climate change is making it harder for soil to absorb rainfall. 

While the idea that soil particles rearrange themselves in response to environmental conditions is not new, scientists once thought these shifts in the ground happened slowly. Not anymore. 

Experimental soil sample
Scientists preparing a soil sample from the Kansas site for transport to a laboratory. (Daniel Hirmas / UCR)

A study published today in Science Advances shows increased rainfall reduces the rate at which water can move into the soil, and that this change happens fast — it only takes a few years or decades, not centuries as scientists previously assumed. 

UC Riverside soil scientist Daniel Hirmas, who participated in the study, said the repercussions of rainfall-induced changes to soil’s ability to absorb water extend beyond agriculture. 

“These findings mean that more water heads into streams or lakes instead of into the ground, potentially increasing susceptibility to flash floods,” he said. 

“The ability for soil to store carbon is also dependent on groundwater,” he said. “Thus, carbon stores may be impacted via this change in soil properties. There is the potential for carbon to move into other places either in the environment or atmosphere if it isn’t being retained in the ground as much.”

Hirmas and a team of scientists examined the dirt from different plots of prairie land in Kansas, some subjected to 25 years of simulated extra rainfall from sprinklers, and some that were not. 

The team, including scientists from Rutgers, Temple, University of Kansas, Kansas State and Colorado State universities, then examined samples of soil from both the sprinkler irrigated and nonirrigated sites. 

They found that the architecture of the soils, meaning the organization of particles and large pores in the samples, were different. 

In the irrigated soil, plant roots clogged the open pores more often, causing samples to retain slightly more water than the soil not affected by simulated rainfall. The roots respond to extra water either from rain or atmospheric humidity, taking up residence in and reducing the space available in soil pores.

The team also found irrigated soils were less able to expand or contract because of more constant soil moisture conditions. Soil expands when it gets wet and shrinks when it dries. If conditions are more consistently wet, the expansion and contraction isn’t happening as much. 

Given that rainfall and other environmental conditions are likely to continue shifting rapidly across the globe, it follows that soil conditions worldwide could also shift fairly rapidly. 

The next step is to expand these investigations to a wider array of soil types and environmental conditions, so scientists can eventually apply what they’ve learned to other regions of the world. 

In addition, these findings are likely to have implications for climate modeling work. 

“Future climate models need to account for these dynamic soil changes to more accurately predict effects of climate change on groundwater, carbon storage, and food security.”

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