Could your soil hold more water?

Wednesday, January 29, 2025

‘Increasing soil water-holding capacity is really a long-term game.’

By Emily Mckinlay

Drought is not uncommon in the Prairies, and precipitation and soil moisture can often be the determining factor in crop success.

Ashley Ammeter, whole farm specialist at Manitoba Crop Alliance, says that management of soil water-holding capacity can be critical for grain and oilseed farmers.

“Water is critically important to our ability to grow crops, particularly in Western Canada where often water is a limiting factor,” says Ammeter.

“The ability to manage soil water-holding capacity, to the extent that we can, could be the difference between having a crop and not having a crop.”

Managing land to improve soil water-holding capacity is a long-term process. While producers may have goals to improve, they must also understand their soil’s current capacity and how to work with it.

What is soil water-holding capacity?

Soil water-holding capacity is a measurement that can help farmers understand how their soil handles moisture.

“It’s quite simple,” explains Ammeter. It is “the amount of moisture soil can hold, in this case, for plant uptake. When we think about the soil-water relationship, we can think about soil as a sponge.”

Texture and organic matter are the two soil characteristics influencing its ability to hold moisture. Soil texture would be determined by the makeup of the soil, related to the proportions of clay, sand, and silt. Organic matter refers to the decomposing matter, from plants or animals, in the soil.

Jeff Schoenau, a professor of soil fertility at the University of Saskatchewan’s College of Agriculture and Bioresources, says that he looks at clay content and organic matter when considering the soil water-holding capacity.

“The clay content is governed by the parent material upon which the soil formed, so there’s not a lot you can do for management,” says Schoenau.

“But soil organic matter, sometimes referred to as humus, is something that can be altered by management.”

He also notes that these two soil colloids, in the form of clay minerals and humus, play a significant role in soil structure.

“Pore size distribution in the soil – which refers to the relative amount of small versus large pores or holes in soil – affects the ability of soil to hold water against gravity,” says Schoenau.

“This is affected by the minerals and organic matter and how they are stuck together. When we think about soil with good soil structure, it has mineral particles cemented together by organic matter to form larger aggregates. This creates a distribution of pores ranging from small micropores, which are effective at retaining water against gravity, to larger macropores that are necessary for drainage to occur and allow the exchange of gases between the soil and external atmosphere.”

Ammeter adds, “Soil has the ability to hold water on soil particles and organic matter, but also in pores spaces. The soil texture will also determine the size of pore spaces. Clay has many small holes that hold lots of water, whereas sandy soils have fewer large holes which hold less water.”

Producers looking to improve capacity can manage their soils to increase organic matter. They can also pay more attention to improving water infiltration and reducing evaporation.

Improving it

The clay, silt, and sand content of a soil, termed soil texture, cannot be significantly influenced by management. Instead, farmers can best manage their soil to increase organic matter, which has many benefits in addition to improving water holding capacity. Soil organic matter can also support soil fertility, biology, and structure, improve infiltration of water, and reduce erosion.

“Organic matter is critically important. Any practice that will negatively impact soil organic matter will also negatively impact soil water-holding capacity,” says Ammeter.

“To improve water-holding capacity, do the opposite. Use practices which will increase organic matter, including reduced tillage, maintaining crop residue on fields, and avoiding baling or burning crop residue.”

She notes that soil erosion can be particularly damaging to soil water-holding capacity, as the topsoil is typically highest in organic matter.

Schoenau, whose research focuses largely on soil fertility and chemistry, says that his lab has also found that some crops will utilize water from different depths depending on their rooting habit. He recommends rotating these crops to use available soil water in the soil profile more efficiently.

“The kind of crops you grow, particularly in a rotation, can affect soil water use efficiency,” says Schoenau.

“In recent research, we looked at cereals in rotation with pulses, specifically wheat and peas. We noticed that wheat tends to take water from a deeper depth, and peas tend to use water from shallower depths. Over the course of a rotation, we saw improvement in water use efficiency and reduced water footprint with those deeper and shallower rooted crops together in rotation.”

Avoiding moisture loss to evaporation can also help farmers who are concerned about their soil moisture retention in the soil profile.

“We want the water that comes down as rainfall or from snowmelt to enter the soil rather than run off the surface into depressions,” explains Schoenau.

“That can cause erosion, nutrient transport off-site, and flooding. Infiltration is important to get water into the soil and keep it in the field.”

He recommends using crops that add residue coverage to the soil surface and create root channels to aid in water filtration. Leaving standing stubble in the field also helps capture snow, reduce evaporation, and conserve that moisture.

Ammeter reminds producers that improving water-holding capacity is a long process.

“There are practices that can increase the amount of water available in the soil in the short term, like maintaining crop residue to catch snowfall and decrease evaporation, but increasing soil wataer-holding capacity is really a long-term game.”

Working with current conditions

Since increasing capacity is a slow process, producers strive to do their best with the water they already have stored in the soil and will receive precipitation during the growing season. It is good to have an idea of what their soil’s capacity is and know how to manage it accordingly.

“Look at your soil profile,” says Schoenau.

Take a core and look at what it’s made of for organic matter and clay content and how that composition changes with depth. It will give you an idea of what you have for available water for your crop. A foot of moist soil that is high in clay and organic matter will contain more available water for the crop than a foot of moist sandy, low organic matter soil. Determine how many feet of moist soil you have to help tell you how much stored soil moisture you have.”

He notes that while investigating their soils, producers may find other conditions that could limit water infiltration, water-holding capacity, and usage in their crops.

“Gravel lens, saline and hardpan layers can restrict root growth, as shown in our recent research work. This reduces water utilization from the soil,” says Schoenau.

His soil fertility research has also suggested that it is valuable for producers to have an idea of their expected growing season precipitation along with stored soil moisture and soil water-holding capacity to create an appropriate fertility plan.

“For the most accurate fertilizer recommendations, knowing the available moisture you have stored in your soil profile at the start of the season is important,” says Schoenau.

“The amount of water you can have stored in your soil profile, along with growing-season precipitation, drives crop yield and nutrient demand. It gives you a better idea of your yield potential and how much fertilizer you need to apply to meet that crop’s nutrient demand.

“Fertilization with nutrients like phosphorus can also promote early root growth and efficient soil water use early in the season.”

Producers who know their soil and its capacity for holding water and soil water status will have more information to determine relationships between moisture and their crop’s yield potential, and the need for added fertilizer to optimize the yield and water use efficiency.

Moisture is an annual concern for many producers, and while long-term efforts can continue to improve soil water-holding capacity and potentially ease those concerns, collecting data on current soil moisture can help producers manage their land in its current state. BF