January 31, 2023

Adding organic matter to soil improves water holding capacity

CHICAGO — Soil is the living skin of the earth.

“We want to treat soil for it to be as healthy as possible because when it is healthy it provides ecosystem services that allow many things to thrive,” said Janel Louise Ohletz, principle agronomist and regenerative agriculture advocate.

Soil and organic matter differ from place to place.

“You can have the same soil type in two different places, but because of many other factors those soils are going to act completely different,” said Ohletz during a webinar hosted by Food Animal Concerns Trust. “So, it is really important to understand what type of soil you have.”

Soil is dynamic and always changing.

“If I took a soil test today and went out again tomorrow and took a soil test in the same location, they would likely be different,” Ohletz said. “The moisture will change the amount of nutrients available and chemistry in the soil.”

A healthy soil will have about half air space and water, the agronomist said.

“The other half will consist of about 45% minerals and 5% organic matter,” Ohletz said.

“We aim for 5% organic matter, but in the south where it is warm much of the year it’s really hard to build 5% organic matter,” she said. “In New Hampshire, the soil has 10% organic matter.”

Three main mineral particles in soil are sand, silt and clay.

“How much sand, silt or clay there is really changes the properties of how the soil is going to act,” the agronomist said. “The type of soil you have will effect how you manage water and plants.”

Ohletz talked about a study that looked at the diversity of plant life and how it affected the porosity of soil.

“This area had 60 species of plants, and because of the different types of roots, the bulk density was reduced,” Ohletz said.

“You can’t do much to change sand, silt and clay. However, you can influence it greatly by what you plant and how you treat the soil to help change the properties in a favorable way,” she said.

Organisms in the soil require other organisms to help them have life.

“Without things breaking down, the organisms don’t have anything to eat,” Ohletz said.

Living plants on the landscape and how the soil system is managed are important for how much water will leave when there is a rainstorm or will be held and stored within the soil.

“Regardless of the type of soil we have, even if you have sand, if you add organic matter you will increase the amount of water that can he held,” Ohletz said.

Soil contains both mobile and immobile nutrients.

“Mobile nutrients can move through the soil pretty quickly and to the roots,” Ohletz said. “But they can also be leaked easily, as well.”

Immobile nutrients move slower in the soil.

“A root has to intercept phosphorus in order to take it up,” Ohletz said.

“All nutrients are made available because of the organisms living in the soil, so if you don’t have microbial activity within your soil, your soil is dead,” she said. “If you don’t have nutrients available easily for the plants to take up, you have to supply everything.”

There are a variety of practices farmers can do to improve the health of soil such as integrated pest management for insects or weeds.

“Try to reduce what allows that thing you don’t want to survive,” the agronomist said. “Get rid of the pest or reduce the thing that makes it grow best.”

Proper rotation of grazing animals by moving them will be really important for improving the health of the soil, Ohletz said.

Managing water is not just about how water drains.

“It is also about where you put water for the animals to drink,” Ohletz said. “The best place to put that water will effect how healthy the soil will be around the area.”

Ohletz recommends reducing soil disturbance as much as possible.

“Sometimes you need to rejuvenate a field, but maybe you can do that with a no-till drill instead of tilling the whole field,” Ohletz said.

“Keeping living roots on the land as much as you can is really important for keeping the soil alive,” she said.

“You are not a grass farmer — you’re a microbe farmer,” the agronomist said. “If you keep the microbes happy, the soil will be happy and your plants will grow much better.”

For more information about the Food Animal Concerns Trust, go to www.foodanimalconcernstrust.org.

Martha Blum

Martha Blum

Field Editor