Soil erosion

Shawn Nield, NRCS Idaho state soil scientist, demonstrates erosion compared to covered soil’s improved aggregation and water infiltration.

Recent heavy rains have provided a mix of benefits and challenges for farmers.

“With the wet spring we are having, our soil profiles are entering the growing season fully water-satisfied,” said Shawn Nield, USDA Natural Resources Conservation Service state soil scientist and snow survey manager. “That’s good if you are a plant that already has roots in the ground, but can make for trying conditions if you are a farmer dealing with fully saturated soils.”

High soil moisture means farmers, once they plant their crops, may save water early in irrigation season. But there are other impacts as well.

“The overabundance of water has been a mixed blessing for some areas,” Nield said. “Late winter-early spring rain and rain-on-snow events have generated a lot of runoff in farm country.”

Farmers in some areas dealt with a soil profile that was beyond saturated. “...Some of these spring events have exceeded the soil’s (water) infiltration capacity,” he said. “That generated runoff and severe erosion.”

Plowed, barren fields with no cover experienced significant erosion, Nield said.

“And it doesn’t take much to make a big difference,” he said, adding that eroding soil the thickness of a dime from an acre represents a loss of 8 tons of topsoil.

“Ground that was covered with residue, had good aggregation or went into fall with a live root in the ground fared much better,” Nield said.

Aggregation refers to organic substances binding sand, silt and clay particles together. Good soil aggregation leaves large and small pores that improve water infiltration, in contrast to soil that is compacted and overworked.

Water availability is crucial in enabling plants to proceed with photosynthesis, “and that’s where a lot of the benefits of soil health start,” Nield said. “Carbon dioxide, sunlight and water combine to produce photosynthate required for building plant parts.”

The plant thus “spends a little to crank up that microbial engine it depends on for turning organic matter back into plant-available nutrients.”

Below ground, plants leak about 10 to 30% of their photosynthates into the soil. “This fuels the microbial community responsible for nutrient cycling and builds organic matter,” he said.

A shovel’s worth of soil may contain “a whole host of critters,” Nield said, from earthworms and fungi to microscopic bacteria. “A strong soil food web improves soil aggregation, infiltration, water availability and discourages waterlogging and pathogens.”

Under heavy rain, soils with good aggregation generate less runoff, infiltrate more and can contribute to aquifer recharge, he said.

Boosted by strong mountain snowpack, irrigation water for farms should be ample this year, he said.

“For irrigation, I don’t think we could ask for a better year,” Nield said. “We should be in fantastic shape.”

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