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Reduced Tillage and Cover Crops Have Additive Effect for Improving Soil Health

Bob Schindelbeck, Aaron Ristow, Matthew Ryan and Harold van Es
Soil and Crop Sciences Section, School of Integrative Plant Science, Cornell University, Ithaca, NY

Background
Soil health constraints may significantly limit crop productivity and sustainability in New York.  Typically, soils with poor soil health are less resilient to drought and flooding impacts, and are more prone to soil erosion and chemical runoff during heavy rainfall events.  Moreover, building and maintaining healthy soils is essential to supporting a robust population of beneficial soil organisms crucial to the cycling of carbon, nitrogen and other plant nutrients, as well as additional biological processes like disease suppression, and root proliferation.

Cornell University led the development of a suite of soil health measurements that focus on optimization of physical, chemical and biological soil properties for sustained productivity and minimal negative impacts on the environment (soilhealth.cals.cornell.edu). Our Comprehensive Assessment of Soil Health (CASH) approach includes a scoring function framework for interpreting soil health laboratory test results and identifying remediation options.   Increasingly many farmers, government and non-government organizations, and researchers are interested in understanding how cover crops, reduced tillage, crop rotation, intercropping, and organic amendments help to improve soil health.  We are using a long-term tillage study, with recently incorporated cover crops, to quantify the soil health and yield benefits of these practices.

Procedures

Figure 1. Growth of the cover crop cocktail
shown about 6 weeks after interseeding.

Beginning in 1994, continuous corn grain management was implemented on replicated (6) plots on a Lima Silt Loam under strip-till (ST) vs. plow-till (PT) treatments.  In 2013, we added cover cropped (CC) vs. no cover crop (NC) management in subplots, for a total of 4 individual treatments (PT-NC, PT-CC, ST-NC, ST-CC). The cover crops were established as a “cocktail” of grasses and legumes (Figure 1) using a drill interseeder in late spring (just after sidedressing nitrogen to the corn).  The mix included annual ryegrass (10 lb/a), Red Clover (5 lb/a), Crimson Clover (10 lb/a) and Hairy Vetch (7.5 lb/a). Corn yields were assessed by representative sampling (four twenty-foot long row sections per plot).

In the early spring of the 2016 season we collected a composited CASH soil sample from each of the four tillage x cover crop treatments to get a summary report of the soil health status.

Results
Soil Health Indicators
Table 1 shows the 2016 measured values of the physical and biological soil health parameters for each treatment. We included the continuous sod (sample from adjacent field border) as a benchmark of the soil health potential of these soils.  The table uses the same color scheme as in the CASH report to interpret the laboratory values from very low (red) to very high (dark green).  These results demonstrate that a change from plow to strip-till resulted in clear benefits for soil health and that combining strip-till with cover cropping had an additive benefit vs. just reducing tillage alone. We observed this pattern for the indicators of Aggregate Stability, Organic Matter, Soil Protein, and Active Carbon, with approximately equal and additive benefits from reduced tillage and cover cropping.  For Available Water Capacity and Soil Respiration, however, we observe primary benefits from transition from plow to strip-till, and less benefits from cover cropping.  Surface and subsurface hardness (penetrometer measurements) were not affected by these management changes. Overall, it appears that soil health differences between plow-till and no-till are expressed through the physical indicators (Available Water Capacity and Aggregate Stability), while the benefits of the cover crop cocktail are additionally apparent in the biological indicators.   Notably, Aggregate Stability, a critical soil physical property, showed substantial additive benefits of tillage and cover cropping changes with a total increase from 17.0 to 57.6% from the conventional (continuous plow-till, no cover crop) treatment to the strip-tilled, cover cropped treatment.  The biological indicators of Soil Protein and Active Carbon also demonstrated substantial improvement in measured values (increases of 40% and 24% in measured values, respectively).

As a result, the overall soil health score (Table 1) increased 7 points for strip-till over plow-till (41 to 48 and 49 to 56), and increased 8 points when adding the cover crop cocktail (41 to 49 and 48 to 56), which are remarkably consistent results. It is noteworthy that the cover crop treatment had only been in place for 3 years, while the tillage treatments had been in place for 22 years, suggesting that cover cropping results in faster soil health benefits, especially for biological processes.     The sod benchmark comparison shows that none of the corn-based treatments were able to reach soil health values that are similar to an undisturbed and continuously covered reference site, although the strip-tilled, cover cropped treatment was closest.

Yields
Improved soil health does not always translate into higher crop yields due to annual variations in weather and management.  However, for the recent 5 years, we observed an increase of 12 bu/a on average from the strip-till treatments compared to plow till. It is important to note that these results are based on just 3 seasons, and that it is still too early to determine the full extent of yield improvement from the recent addition of cover crops into the rotation.

Conclusions
The results of this study are interesting in that they show measurable soil health increases from reducing tillage over the long term. Adding cover crops resulted in benefits after only a few seasons, and these were observed in addition to the benefits from reducing tillage. This study involved a continuous corn experiment, and showed that the sustainability of such an intensive row crop system can be considerably improved with reduced tillage and the use of cover crops.

Acknowledgements
We are grateful for the funding support from the New York Farm Viability Institute, the Northeast Sustainable Agriculture Research and Education program, the New York State Department of Agriculture and Markets, USDA-NRCS, and the USDA-AFRI Water Quality Grant.

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