Biodiversity Effects on Soil carbon Gain in Annual and Perennial Cropping Systems

View the project final report

Commodities

• Agronomic: corn, rye, soybeans, wheat, grass (misc. perennial), hay
• Fruits: apples, berries (strawberries)

Practices

• Animal Production: feed/forage
• Crop Production: application rate management, catch crops, conservation tillage, continuous cropping, cover crops, crop rotation, no-till, nutrient cycling
• Education and Training: extension, on-farm/ranch research, participatory research, study circle, workshop
• Energy: bioenergy and biofuels
• Natural Resources/Environment: biodiversity, carbon sequestration, indicators
• Production Systems: agroecosystems, holistic management
• Soil Management: nutrient mineralization, organic matter, soil analysis, soil chemistry, soil microbiology, soil physics, soil quality/health

Soil carbon (C) is the most important variable in sustaining annual and perennial cropping systems both in terms of increasing crop productivity and enhancing soil health. Recent research shows that crop biodiversity could play an instrumental role in increasing soil C in both annual and perennial based cropping systems due in large part to increased root production. As soil C levels decline in the Mid West due to intensive management practices, utilizing crop diversity as a tool to increase soil C could become a necessity. Furthermore, managing for soil C on-farm can be challenging because it can take years for total C to respond to changes in management. However, the total C pool consists of several different pools that have different turnover times. One pool is the labile C pool or active C that has a short turnover time and changes with crop growth and responds to different management practices. Currently, soil tests available to farmers only represent the total C pool, which may not fully reflect soil health.

Here, we examined the role that plant diversity has on root production and soil carbon dynamics in annual and perennial crops in a controlled cropping systems experiment. We also wanted to address soil biodiversity and managing for soil C on-farm. To do this we sampled 52 farm fields in Michigan and compared the total soil organic matter test to the active C test and determined which test better reflected farmer perceptions of soil organic matter.

Overall, we found that diverse perennial systems produce more fine roots and accumulate more C in the active pool, while annual crops and monoculture perennials produce less roots and accumulate less soil C. This suggests that crop diversity in perennial-based cropping systems should be promoted to replenish soil C for increased soil health and climate change mitigation.

Our on-farm work demonstrates that the total soil organic matter test is insufficient at determining differences in soil C between farmer-described Best vs. Worst fields. In contrast, we found that the active C test revealed significant differences between the Best vs. Worst fields and strongly supported farmer descriptions that we gained through farmer interviews and investigator observations of fields. In the future, commercial and university labs should offer the active C test to better guide farmer management decisions.

Introduction:

Soil fertility management and reductions in crop productivity often stem from inadequate soil organic matter levels on-farm. Midwestern soils have lost between 30 and 50% of historic carbon (C) levels, negatively impacting soil health within agroecosystems (Lal, 2004). Such reductions in soil organic matter have also contributed to enhanced CO₂ emissions from agriculture. Thus, restoring soil C levels on farm would improve soil health and crop production as well as increase soil C accumulation, which is important for climate mitigation.

An approach that could be adopted by farmers to significantly build soil C is increasing crop diversity through planting cover crops, incorporating crop rotations, and by planting perennial mixed grass systems in place of fallow land. Plant biodiversity is key to maintaining ecosystem stability and ecosystem function, in large part due to its role in increasing productivity and retaining nutrients (Tilman, 1996). Increasing biodiversity in annual and perennial based systems can lead to increased root production and thus increases in soil organic matter (SOM), which improves soil health and increases cropping productivity.

One problem that farmers often face when testing soil organic matter is that soil C is insensitive to changes in management because it is large (in comparison to annual inputs) and consists of C that has persisted in the soil for periods ranging from days to millennia (Wander, 2004). This means that even after a farmer adopts a more sustainable practice, improvements in soil C could take years to detect. However, researchers have developed tests that can identify changes in the labile portion of soil C, which consists of recently deposited material that typically decomposes within a year and is sensitive to changes in management.

Our goal was to measure soil C on farmer fields in Michigan and communicate with farmers how management practices, including increasing biodiversity in both annual and perennial cropping systems, can affect soil C accrual. We met with farmers individually and in groups to discuss soil testing and certain management practices that could be used to increase soil organic matter and improve overall soil health. Ultimately, we wanted to introduce soil health tests that could be used to inform better management decisions in terms of soil organic matter management.

The objectives for this study were two-fold. First, to determine the extent that biodiversity accelerates SOM accrual in both annual and perennial cropping systems. Second, to provide farmers with practical information (soil carbon test results) that will lead to opportunities for better management of soil carbon and potentially lead to more management practices that incorporate increases in crop diversity. 

More specifically:

1A. Determine the effect of biodiversity on fine root production and biomass allocation.

1B. Document the effect of biodiversity on soil carbon quantity and quality.

2. Measuring the labile soil carbon pool on Michigan farms and discussing results with farmers individually.