Joseph Amsili, Harold van Es, and Bob Schindelbeck Soil and Crop Section, School of Integrative Plant Science, Cornell University
Soil health metrics were sensitive to long-term tillage practices.
Biological indicators related to labile carbon and nitrogen were best correlated with crop yields.
Soil health has been defined as the “the capacity of the soil to function as a vital living ecosystem that sustains plants, animals, and humans” (NRCS). The soil health concept recognizes that biological, physical, and chemical constraints must all be addressed for the soil to reach its full potential. Soil health assessment has become a powerful tool to diagnose biological and physical constraints in addition to the more traditionally measured chemical limitations (nutrients and pH).
In 2017, Roper et al. published an article using Cornell University’s Comprehensive Analysis of Soil Health (CASH) approach to link soil health indicators to different agronomic management systems in North Carolina. The results from this experiment allowed us to explore the linkages between soil health and yield, which has remained an important gap in the soil health literature.
Soil samples were collected from three long-term experiments (20+ years) in the coastal plain, piedmont, and mountain physiographic regions of North Carolina. Samples were sent to Cornell University to be analyzed for the standard CASH package, which includes two physical indicators – wet aggregate stability (AgStab), and available water capacity (AWC); four biological indicators – organic matter (OM), active carbon (ActC), autoclavable citrate extractable protein (Protein), and respiration (Resp); and seven chemical measurements (pH, and extractable P, K, Mg, Fe, Mn, and Zn). The results were made available in a supplemental table in the Roper et al. paper and re-analyzed by us.
Results and Discussion
Sensitivity of Soil Health Measurements
The coastal plain and mountain region experiments involved different tillage practices combined with organic vs. conventional management. When the CASH values were analyzed, we found significant differences in AgStab, ActC, P, and Zn at each site (Table 1), while the mountain site also showed differences in Protein and several other chemical indicators. The effects on chemical indicators were primarily related to the organic vs. conventional treatments as compost applications tended to increase nutrient levels. But the physical (AgStab) and biological indicators (ActC and Protein) were mostly influenced by tillage practices.
The piedmont experiment involved different levels of tillage intensity including moldboard plowing, chisel-till and no-till, and almost all CASH indicators were affected by the treatments (Table 1). Over all three sites, no-till treatments had higher soil physical and biological indicators than conventional tillage (data not shown). These findings are in agreement with many other studies that have demonstrated that CASH indicators are sensitive to management.
Soil Health and Yield
Establishing positive relationships between soil health and crop yield is a difficult task because soil health effects are often masked by non-soil factors such as pest and weed pressures, erratic weather, and management effects. However, in the piedmont study, several individual CASH indicator values were positively correlated with mean corn and soybean yield (annual yield variability was not considered here). Specifically, eight CASH indicators (in order of correlation strength: Protein, ActC, Mn, Resp, AgStab, P, Mg, and OM) displayed significant linear relationships to mean corn yields (Figure 1). Each indicator tended to be highest under minimum-till, intermediate under chisel-till, and lowest under moldboard plow.
This implies that reducing tillage positively impacted these SH indicators, which in turn benefitted crop yield. Most notable is the fact that the indicators related to labile carbon and nitrogen (Protein, ActC, Resp, and AgStab) showed the strongest correlations with mean corn yield, while total organic matter content showed weaker relations (Figure 1). This suggests that organic matter quality may be more important for improving corn yield than total organic matter quantity. When we analyzed the relationship between soil health indicators and mean soybean yield at this site, we found that Protein was a much weaker predictor of soybean yield than it was for corn yield (not shown). This makes sense because a legume crop would be less influenced by nitrogen supply from soil organic nitrogen sources (Protein reflects the largest such pool) than a non-legume crop. Additionally, we found that Mn showed a strong positive relationship to both corn and soybean yield, which is explained by Mn’s important role in organic matter decomposition.
Soil health data from three long-term field experiments in North Carolina showed that the CASH indicators were sensitive to agricultural management at each location, which is in line with previous results from our work in New York. Furthermore, soil health indicators were positively correlated with long-term average cash crop yield at the piedmont site, which illustrates the benefit of labile organic matter for crop growth. These results help to demonstrate the linkage between tillage, organic additions, soil health, and crop yield, which had remained an elusive goal.
We acknowledge the work and funding of the original paper by Roper et al., 2017 (Soil Science Society of America Journal 81: 828-843).
This article was based on Harold van Es and Douglas Karlen’s article titled, “Reanalysis validates soil health indicator sensitivity and correlation with long-term crop yields” (van Es and Karlen, 2019; accepted in Soil Science Society of America Journal).
The condition of a farm’s soil has an important impact on crop production and the environment. Healthy agricultural soil holds adequate nutrients, absorbs heavy rainfall, and stores water. But in many annual production systems these functions are compromised by tillage that diminishes soil organic matter and creates compaction, ultimately restricting crop growth while increasing susceptibility to drought, erosion, and nutrient losses. Healthy soil, containing substantial levels of organic matter and beneficial pore space, can be developed over time by reducing tillage and using cover crops. But both strategies require significant investments of time and resources, while the benefits may require some years to take effect and are difficult to quantify.
To help clarify exactly what costs and benefits farmers in New York experience when using these soil health-enhancing practices, we conducted a state-wide survey during the winter of 2017-18. Over 180 farmers from 46 NY counties provided information about the crops they grow, and how using reduced tillage and cover crops have impacted their farm business. From the survey results, we identified the most frequent expenses and benefits (Table 1).
Note that costs and benefits reported in Table 1 go beyond revenue associated with yield, to include increases or decreases in annual input costs, as well as avoided investment costs (e.g., drainage systems). The most common benefit of both reduced tillage and cover crops was less erosion or sedimentation repair. Greater yield was reported by 52% of farmers using reduced tillage, and by 50% of those using cover crops. Lower yield was reported by 10% and 3% of farmers using reduced tillage and cover crops respectively (Table 1). When asked about profitability, less than 5% reported that either practice had a negative net impact (data not shown).
Our survey also found distinctions in the costs and benefits depending on the type of cash crop being produced, for example greater yield of cash crops attributed to the use of cover crops was more frequently reported for vegetable systems than for corn and soybean, while corn and soybean systems in particular were more likely to benefit from forage uses of cover crops (data not shown). These results emphasize the differences that exist between cropping systems, and show that any decision to implement a specific soil health practice should be made on a case-by-case basis, carefully evaluating both the positive and the negative impacts that could occur following a shift in management practice.
Some benefits that result from these practices are realized over many years as the productivity and function of the soil is gradually improved. We asked farmers how long they had been using reduced tillage and cover crops, and found that there was an association between the length of time a farmer had been using those practices and what benefits they saw. Farmers that had been using reduced tillage and cover crops the longest saw greater benefits. One such benefit is less erosion or sedimentation repair. While about 66% of farmers who had used reduced tillage for less than 5 years reported this benefit, after 10 years that number approached 100% (Fig 1). Similarly, among farmers who used cover crops, greater yield of cash crops was associated with long-term cover crop use (Fig 2).
We also wanted to know if farmers in New York state are improving their resilience to severe weather events by using soil health practices. Rainfall patterns in the region could change in the future, and we hypothesized that enhanced soil health provides protection against flooding and erosion from especially heavy downpours due to the presence of stable aggregates and the soil’s increased capacity to absorb water. That same healthy soil may also help a farmer during times of drought by storing water in the soil profile and making it available for crop growth. Both reduced tillage and cover crops were found to help farmers cope with extreme weather events, with over 60% reporting resilience benefits (Fig. 3).
This study was conducted by New York Soil Health, and funded by NYS Dept. of Ag & Markets and Cornell University College of Agriculture and Life Sciences (CALS). To learn more about soil health in New York, visit newyorksoilhealth.org.
Bob Schindelbeck, Aaron Ristow, Matthew Ryan and Harold van Es Soil and Crop Sciences Section, School of Integrative Plant Science, Cornell University, Ithaca, NY
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.
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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