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Previous work showed that crop yields are higher in the diverse rotations, but when it comes to increasing soil organic matter and carbon storage, this study showed no consistent crop rotation effect. Functionally important mineral-associated (MAOM) and particulate organic (POM) matter pools were not affected by long-term continuous monocropping vs. diverse crop rotations in the wheat and canola systems studied.
Project Summary
Overview
This project focused on assessing the impact of long-term continuous monoculture of cereals (wheat, corn) and canola on the quantity of functionally important soil carbon pools.
The objective of this project is to obtain new knowledge of the impact of crop rotation diversity on soil organic matter stability and functional pools, how long-term crop rotation diversity affects microbial abundance and activity, and the relationships between microbial community dynamics and functionally important pools of soil organic matter.
The study will quantify carbon storage in different soil functional pools.
Methods
Using long-term field experiments for wheat (Swift Current, SK) and canola (Swift Current and Scott, SK and Lacombe, AB), Helgason’s research team measured functionally important mineral-associated organic matter (MAOM) and particulate organic matter (POM) pools in monocropped and diverse crop rotations, along with microbial abundance and community structure and extracellular enzyme activities.
Results and conclusions
As expected, carbon stored in the POM and MAOM fractions differed among sites in the replicated canola systems and the both the mass fraction and amount of carbon stored as MAOM was greater than POM. The mass fraction of POM and MAOM only differed due to rotation in the canola system at Swift Current; where there were differences in the carbon stored as POM and MAOM it resulted from a change in carbon concentration within the fraction.
Microbial abundance in the canola systems was highest at Lacombe where no treatment differences were apparent, followed by Scott and Swift Current. The research team collected samples at peak canola flowering which likely subdued the long-term differences in crop rotation on the microbial community due to the presence of an actively growing common host in all treatments as differences in community structure were only apparent at Scott. Similarly, differences in microbial abundance in the wheat system at Swift Current were only detected at the post-harvest sampling time demonstrating the strong short-term influence of the wheat crop on the microbial community.
Since all soils were fertilized according to soil testing recommendations, some of the long-term effects of the differences in crop residue inputs may be mediated by balanced fertility.
Future research
Future studies focusing on sampling outside the growing season (pre-seeding or post-harvest) are recommended to better capture the long-term differences in crop rotations on soil organic matter quantity and quality, and accompanying responses of the microbial community.
