Inderjot Chahal, David Hooker, Bill Deen, Ken Janovicek, and Laura Van Eerd. 2021. Long-term effects of crop rotation, tillage, and fertilizer nitrogen on soil health indicators and crop productivity in a temperate climate. Soil and Tillage Research. doi: 10.1016/j.still.2021.105121
Study Summary by Inderjot Chahal and Cameron Ogilvie
key messages
- Diversifying crop rotations with perennials, small grain cereals, and cover crops improved crop yields and soil health indicators
- Higher soil carbon levels were related to better crop yields and higher Solvita® soil health test scores
The corn-soybean rotation is the dominant cropping system on farmland throughout central Canada and the midwestern United States. However, long-term research shows that this rotation has lower crop yields, soil quality, resilience to climate change, and profitability. These pitfalls can be avoided by diversifying corn-soybean rotations with small grain cereals, perennial forages, and cover crops. But the final impact of better crop rotations will depend on many other factors: growing regions, soil types, tillage, and nitrogen fertilizer use. To better understand how crop rotations interact with these factors, University of Guelph researchers used two long-term experiments at Ridgetown and Elora and measured impacts on crop yield and a range of soil health indicators. Soil health was measured using the Solvita® CO2-Burst and SLAN tests, along with soil organic carbon and total nitrogen.
WHAT THEY FOUND
Diversifying crop rotations with small grain cereals, perennials, and cover crops improved crop yields and soil health indicators at both Elora and Ridgetown. But, as expected, the size of treatment differences and the level of improvements depended on the location. For instance, corn yield was 16% greater at Ridgetown and 10% greater at Elora with winter wheat and a red clover cover crop added to a corn-soybean rotation. And at Elora, corn yield was 25% greater with alfalfa in rotation with corn compared to continuous corn. Adding winter wheat and red clover to the corn-soybean rotation increased Solvita® CO2-Burst by 12%, SLAN by 16%, and soil organic carbon by 6% at Ridgetown. Likewise at Elora, rotations with alfalfa or small grain cereals underseeded with red clover increased Solvita® CO2-Burst by 37%, SLAN by 13%, and soil organic carbon by 9% compared to continuous corn or the corn-soybean rotation. For all of these indicators greater values indicates better soil health.
As soil organic carbon levels increased, winter wheat yields at Ridgetown; and corn, soybean, and oat yields at Elora increased as well. This study also found a similar relationship between crop yields and the Solvita® CO2-Burst and SLAN test results. And again, soil organic carbon and total nitrogen were positively related to Solvita® CO2-Burst and SLAN test results. Together, these results suggest that these commercial soil health tests may be useful indicators of soil productivity and can detect long-term differences in soil health caused by management.
WHY IT MATTERS
Many other studies have shown that soil organic carbon is an important indicator of productive and resilient soils. This study additionally shows that the Solvita® soil health tests can be useful as well. But while this study demonstrated that diversifying crop rotations improved soil health indicators and crop yields, it’s not as simple as adding more crops to the rotation. Yield and soil health improvements depend on the type of crop grown, as well as regional and soil limitations and other management practices. Keeping living roots in the ground is key to improving crop yields, soil health, and farm resilience.
HOW THEY DID IT
To evaluate study objectives, surface (0-15 cm) soil samples were collected from each crop phase (corn, soybean, winter wheat, and oat) in June 2016 from the long-term experiments at Ridgetown (21 yr) and Elora (36 yr). Soil organic carbon, total nitrogen, Solvita® CO2-Burst , and SLAN were measured. Solvita® CO2-Burst and SLAN are commercially available soil health tests which measure the amount of CO2 and NH3 gases produced by soil microorganisms. Likewise, crop yield was measured in 2016 from each crop phase at both sites. The relationship between soil health indicators and crop yield was assessed; the association of soil organic carbon and total nitrogen with Solvita® CO2-Burst and SLAN was also evaluated. At each site, soil health and crop yield from crop rotations with small grain cereals, alfalfa, and red clover were compared with the continuous corn, soybean, and corn-soybean rotations.
