Building Resilient Soils

For many Ontario farmers, the 2021 season has been a weather roller coaster. Throughout much of the province, the season started out extremely dry, with some regions receiving less than 20% of normal precipitation for the month of May. Late June brought relief for many parts of Southern Ontario, with regular rainfall that continued throughout July. Some areas, however, in particular parts of Kent and Essex counties, received excessive rainfall and quickly went from too dry to far too wet. Other parts of the province continued to experience serious water deficits.

We have experienced other challenging seasons recently in southern Ontario, including extremely dry weather in 2016 and very wet springs in 2017 and 2019. Each of them, like 2021, have provided lessons in the importance of resilient soils. Resilient soils result in resilient cropping systems, which produce higher, more consistent yields and are better able to bend without breaking under stress.

Not all soils are alike

A soil’s resiliency is in part determined by its texture and natural drainage. Fine-textured soils, such as clays, contain many very small pores which contribute to high water storage, but hold some water too tightly to be accessed by roots. They also tend to drain very slowly. Loams and silt loams have a variety of pore sizes including many medium-sized pores, which drain moderately and store lots of plant available water. These soil types tend to be inherently more resilient than clays or sands. It’s important to recognize these natural limitations.

Managing for resilience

While the specific set of practices that work best vary by climate, soil type and farm operation, there are a common set of practices that will serve any farm well in building more resilient soils. Adequate drainage and soil fertility are prerequisites. That means subsurface drainage for soils with poor natural drainage, lime application to address soil acidity and sufficient nutrients provided for crop growth. Assuming drainage and fertility have been addressed, the following best management practices (BMPs) are at the top of the list to improving cropping system resilience

Diverse crop rotations and reduced tillage

A recent North America-wide study compared simple crop rotations to complex crop rotations from a group of 11 long-term trials (including two in Ontario). They found that corn yields were, on average, 28% higher in the most diverse rotations compared to the simple (1-2 crop) rotations. In drought years, corn yield losses were reduced by 14-90% in more diverse rotations; there was also a much lower risk in crop failure at 8/11 trial sites.

Closer to home, analysis of yield and weather data from 31 years at the University of Guelph’s long-term tillage and rotation trial at Elora found greater yield stability for corn and soybeans when small grains were added to the rotation. The effect was especially dramatic in hot and dry seasons, where the addition of a small grain, combined with reduced tillage, increased corn and soybean yields by 7 and 22%, respectively. The addition of wheat and red clover dramatically increased the stability of soybean yields in droughty years.

Maintenance of carbon inputs

Retaining crop residues also plays a critical role in building resilient soils. They help to maintain soil organic matter, which provides both water storage and improved drainage. When left on the soil surface, residue further enhances water infiltration and reduces evaporation during hot, dry weather.

A recent study in Nebraska found that 50% corn stover removal in a continuous corn system reduced plant available water by 32% and significantly reduced water infiltration after 5-6 years. The practice also lowered soil organic matter. Although an extreme example, it highlights the impact that residue removal can have on soil resilience – that soil now takes in water more slowly and provides less to growing crops. The inclusion of a cereal rye cover crop in the study was helpful but did not fully offset the negative effects.

While crop residues may sometimes be taken for granted, they play a critical role in helping to maintain resilient soils.