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.
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.
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.
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”.
Below are links to the fact sheets that are currently available online. New handouts will be posted as they are added to the series.
Aubrey K. Fine, Aaron Ristow, Robert Schindelbeck and Harold van Es
Soil and Crop Sciences Section, School of Integrative Plant Science, Cornell University
Comprehensive Assessment of Soil Health Soil health refers to the ability of a soil to function and provide valuable ecosystem services. The Comprehensive Assessment of Soil Health (CASH) is a testing approach developed at Cornell University that measures multiple physical, biological, and chemical soil properties linked to key soil processes (Table 1). It remains largely unclear how soil health varies in different agro-ecological regions, and whether interpretation schemes should therefore be adjusted. As a preliminary investigation into these questions, we used the CASH sample database to compare the soil health status of 5,767 samples collected from the Mid-Atlantic, Midwest, and Northeast regions of the United States.
Database Analysis CASH uses scoring functions that are developed using the cumulative normal distribution (CND) of measured values in our database for each indicator. Scoring functions for physical and biological CASH indicators are calculated using the CND, whereas chemical indicators are scored based on experimentally-established thresholds. Some, but not all, indicators showed texture-dependence; in these cases, separate scoring functions for coarse, medium, and fine textures were developed. The scoring function allows for the interpretation of the measured value for each indicator on a scale ranging from 0 to 100. This approach lets us assess how a particular soil sample scores relative to other similarly-textured soil samples in our records, and thereby make some judgment on the relative health of that soil to identify possible problems.
Since it began offering soil health testing services in 2006, the Cornell Soil Health Lab (CSHL) sample database has grown considerably in size and geographic scope. After evaluating the number of samples analyzed from each of the 48 continental United States, we identified three regions having sufficient sample size (n=5,676 total) including the Mid-Atlantic, Midwest, and Northeast. These regions align with the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Major Land Resource Areas (MLRA) (Fig. 1). Descriptive statistics and ANOVAs of sub-datasets by region and soil textural class for all CASH indicators were performed, allowing comparisons among these three regions in measured values of soil health indicators. The medium textural group made up the largest proportion of our database, and for brevity we only report this textural group results here (Table 2). A manuscript that also includes results of fine and coarse textural groups is in preparation for publication by Fine et al. (2017).
Results With this investigation, we observed significant regional differences in mean measured values for most physical, biological and chemical indicators (Table 2).
For medium-textured soils, significant differences between regions were observed for most indicators except subsurface compaction (PR45) and extractable potassium. In general, soil health values for the Midwest region were less favorable compared to the Mid-Atlantic and Northeast, notably for Wet Aggregate Stability, Organic Matter, Active Carbon, Protein, Respiration, and Root Health. Extractable phosphorus levels were notably higher in the Mid-Atlantic region. Although sample sizes between regions were unequal, Midwestern soils generally showed lower variability (standard deviations) in measured values.
These results offer insights into regional soil health differences that can be attributed to genetic and management factors. The lower mean values observed for biological indicators and Wet Aggregate Stability in Midwest soils counter the common notion that Midwestern soils are of superior quality than those in other regions. How can this be explained? First, there are likely differences in cropping systems. Northeast and Mid-Atlantic soils generally receive more organic inputs (especially manure) and are often managed to include diverse rotations with perennial crops, as opposed to typical corn-soybean rotations in the Midwest. Second, the standard CASH is limited to the 0-to-6 inch depth interval, and, therefore, the deeper soils and organic matter accumulation in many fertile Midwestern prairie soils is not captured by the test. Finally, these findings could suggest an inherent bias in our data set, so conclusions should be interpreted with some caution.
Conclusion What have we learned? An investigation into regional soil health status (Mid-Atlantic, Midwest, and Northeast) showed significant differences in mean measured values for most physical, biological, and chemical indicators. Evidence suggests that the development of region-specific scoring functions may be appropriate, but would require more complete regional soil health data collection and analysis. In all, this project provided valuable insights into the soil health status of three different agro-ecological environments. We conclude that the CASH approach can be successfully applied to evaluate the health status of soils of differing agro-ecological environments, but that interpretations likely need to be regionally adapted to be most meaningful.
Reference Fine, A.K., van Es, H.M., and R. R. Schindelbeck. 2017. Statistics, Scoring Functions and Regional Analysis of a Comprehensive Soil Health Database. Soil Science Soc. Am. J. (in preparation).
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