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.
Rintaro Kinoshita, Lindsay Fennell, Michael Davis, Aaron Ristow, Bob Schindelbeck, and Harold van Es
Soil and Crop Sciences Section, School of Integrative Plant Science, Cornell University
Background Deep soil layers can be a significant sink of soil organic carbon and an important source of soil moisture and nutrients for crop growth. Distinct soil microbial communities may also be present in subsoil layers compared to topsoil due to nutrient dynamics, soil physical properties and drainage. In addition, the ‘transition layer’ between topsoil and subsoil layers may form a plow pan, resulting in compaction, and restricted root growth. With concerns about crop production under changing climate and weather patterns, we need to better understand how soil management practices impact these deeper soil layers.
Traditional soil testing on grower fields has been limited to topsoil nutrients (typically 0-6 inches in depth). Shallow soil sampling has been justified due to the challenges of sampling to deeper depths and also the relative importance of topsoil when adequate growing conditions are met. More recently, the Comprehensive Assessment of Soil Health approach, which includes analysis of soil physical, biological and chemical properties, has gained acceptance in providing information on crop growth constraints, but these assessments have also only been applied to surface soil layers. The objective of this study was to investigate the impacts of crop and soil management on soil health conditions throughout the entire soil profile.
Procedures The soil health impacts of 40-year long continuous corn cropping under two tillage systems (plow-till vs. no-till) crossed with two residue management practices (removed vs. returned) were assessed at different soil depths. (0-to-24 inches; Fig. 1). The unique history of this experiment – conducted at the Miner Institute near Chazy, NY with four replications for each treatment — allowed us to look at the long term effects from reduced tillage, which generally improves soil aggregation, enhances soil biota, and changes rooting patterns. It also allowed us to evaluate whether reduced tillage has more or less benefits than returning corn stover as residue, which feeds the soil microbiota and provides macro-nutrients like potassium.
Using the Cornell Comprehensive Assessment of Soil Health (http://soilhealth.cals.cornell.edu/) approach, we analyzed aggregate stability in addition to the soil biological indicators of soil organic matter, active carbon, soil respiration and protein. The chemical indicators phosphorus (P) and potassium (K) were also analyzed.
Results and Discussion Table 1 shows mean values measured for each treatment in various soil layers. We used a color scheme to help interpret the numbers from best to worst (blue-green-orange-red). For biological and physical indicators the order of the measured indicators was generally: No-till-Residue Returned > No-till-Residue Removed > Plow-till-Residue Returned > Plow-till-Residue Removed. The pattern was consistent, although the effects were statistically significant only in the topsoil layer. This shows that eliminating tillage had greater benefits for soil health throughout the soil profile than returning residue, though stover return was shown to be important in avoiding the depletion of macro- and micro- nutrients, especially potassium, under No-till below the surface layer.
Interestingly, the continuous No-till-Residue Returned maintained soil conditions closest to a benchmark comparison sample from continuous mixed sod, compared to Plow-till or Residue Removed treatments. It is noteworthy that, under No-till-Residue Removed, subsoil nutrient values were the lowest. This demonstrates possible nutrient mining when crop residue is removed for other uses and emphasizes the importance of full soil profile nutrient budgeting for long-term management decisions (Note: fertilizer applications were uniform across treatments)
Finally, we found unique soil conditions in the transition layer (7-to-12 inch depth, Table 1) where the relative benefits from the treatments were different from the other layers, because the surface residue is placed at this depth under Plow-till. This seems to benefit the transition layer only and not the layers above or below. In deeper soil layers, Plow-till had lower soil organic matter content and related soil physical, biological and chemical properties due to a lack of transfer from the topsoil to subsoil layers.
These are interesting results as they show that No-till benefits soil health not only in the surface layer but also deeper into the soil, especially when corn stover is left in the field. Conversely, Plow-till places organic residues at the bottom of the plow layer (transition layer), but does not show benefits in other layers. Why is this the case? We hypothesize that the main benefits come from greater and deeper biological activity under No-till, especially when residue is left in the field (Fig. 1). We now have a better understanding of how critical decreasing soil disturbance through reduced tillage enhances biological activity, which may extend deep into the soil with worm species like night crawlers. They transport organic material from the surface deep down into the profile. The continuous deep soil pores may also transport dissolved organic carbon deeper into the soil with percolating water. We also generally see more vertical and deeper roots with No-till, which additionally helps transfer organic material down to deeper layers.
Figure 1. Experimental design. A transition layer between the topsoil and subsoil can potentially form a plow pan and lead to compaction resulting in restricted root growth. In contrast, the absence of the plow pan may facilitate the transport of organic material from the surface deeper into the profile.
Conclusions This study found that combinations of tillage and residue management affect soil health at different depths, which can in turn affect the overall availability and accessibility of soil moisture and nutrients from the soil system. The direct impacts of tillage and residue management occur mostly near the soil surface, but also have effects on soil properties deep in the profile, where no-tillage and residue return positively influence subsoil conditions. The long term yields from these plots have followed the same pattern as the soil health measurements, where plots with no-tillage and residue return out yield those with plowing and residue removal.
Acknowledgements
This article is based on a paper titled “Quantitative soil profile-scale assessment of the sustainability of long-term maize residue and tillage management” (Kinoshita et al., 2017; accepted in Soil and Tillage Research).
This work was supported by grants from the Northern New York Agricultural Development Program.
Lindsay Fennell, Aaron Ristow, Robert Schindelbeck, Kirsten Kurtz and Harold van Es Soil and Crop Sciences Section, Cornell University
The Comprehensive Assessment of Soil Health (CASH) provides a framework for measuring the physical, biological and chemical aspects of soil functioning. The assessment includes specific measurements, selected from an original list of 42 potential soil health indicators, evaluated for their relevance to key soil processes (Table 1), sensitivities to changes in management, and cost of analysis.
As a framework, CASH encompasses not only soil health testing, but also outlines field-specific planning strategies and management approaches. In 2016, the Cornell Soil Health Laboratory released the third edition of the Comprehensive Assessment of Soil Health Training Manual (bit.ly/SoilHealthTrainingManual) (Fig. 1). The manual contains information on introductory soil health concepts, a detailed discussion of individual soil health indicators, laboratory procedures, a step-by-step guide to our soil health management framework, and an extensive list of additional resources.
Figure 1. The third edition of the Comprehensive Assessment of Soil Health Cornell Framework Manual is now available. Printed copies can be purchased or it can be downloaded for free from the CASH website.
Out of this training manual, we have developed the Soil Health Manual Series of Fact Sheets (bit.ly/SoilHealthFactSheets) to further facilitate the guide’s utility as an educational tool for growers, extension agents, and Ag Service Providers. The fact sheets are one page, two-sided handouts, designed to explain different soil health concepts and show how we measure soil health. Purveyors of soil health can easily download and print the sheets to be handed out at field days and other outreach events (Figure 2). They are available on the CASH website (http://soilhealth.cals.cornell.edu/).The entire collection is also available as a booklet or “mini-manual”.
Figure 2. The Soil Health Manual Series fact sheets are designed to explain different soil health concepts and show how we measure soil health in downloadable, one page, two sided, easy to read handouts.
Below are links to the fact sheets that are currently available online. New handouts will be posted as they are added to the series.
