2.5 Soil Health

Soil health is the capacity of the soil to function productively and sustainably without jeopardizing the environment. From its definition, soil health focuses on maintaining the soil in an optimally productive state while at the same time balancing the need for resource sustainability and environmental conservation.

Functions of a good soil in relation to crop production and environmental conservation include:

·         good physical medium that can support healthy crop growth on sustained basis

·         good nutrient retention and release for crops

·         adequate moisture storage and release for crops

·         good partitioning of surface water preventing erosion and runoff

·         support of a healthy population of beneficial soil organisms to suppress harmful organisms and

·         buffer against toxic substances and environmental pollutants

 

Soil health emphasizes the integration of the different aspects of the soil which is broadly classified into the physical, biological and chemical categories (Figure 2.5.1). However, these different aspects of the soil are interrelated and each aspect cannot be seen independent from the other.

Figure 2.5.1. Processes affected by the physical, biological and chemical aspects of the soil.

 

Figure 2.5.1 shows the interdependence between the different soil aspects along with different soil processes belonging to each aspect. Understanding these inter-relationships and managing them for optimal soil performance are important to maintaining healthy soils. For example, aggregation in the surface soil is favored by organic matter, surface residue, and an absence of erosion and forces that cause compaction. A continuous supply of organic matter provides food for a variety of soil organisms. Large pieces of fresh organic material are used by macro-organisms such as spiders and ants that will pulverize the substrate and make it available for use by microorganisms. In the breakdown of the organic materials, substances are derived that can glue soil particles into aggregates. These organic compounds, mostly polysaccharides, are then used by other organisms and will decompose over time. Therefore, a continuous supply of fresh organic materials and roots of living plants as well as healthy and diverse soil organisms are needed to maintain good soil aggregation. Figure 2.5.2 shows the relationship between the aggregate stability and the total organic matter in some NY soils. The higher the soil organic matter in mineral soils, the higher the soil aggregate stability.

 

Figure 2.5.2. Relationship between aggregate stability and soil organic matter in some selected soils from the Cornell University research sites in NY.

 

For good soil health to be maintained, all the different aspects of the soil, physical, biological and chemical, must be well balanced and in good condition. Functionally, good soil health connotes that the soil can supply adequate amounts of nutrients but does not contain excessive levels, has appropriate pH levels, has high moisture availability, is well aerated, is penetrable to roots, has low erosion andrunoff potential, and is biologically balanced. A soil’s health is affected by inherent soil factors, such as texture, and management-related factors, such as fertility levels, compaction, and past erosion.

 

Soil health assessment relies on the measurement of carefully chosen soil indicators. From these, we can infer the health or the quality of the soil. The validity and the usefulness of any soil health assessment is as good as the set of indicators chosen. The criteria for choosing soil health indicators are often based on:

 

i.      sensitivity to management (does the soil measurement show distinct changes under contrasting management practices)

ii.     how variable are the measured values of the indicator (is the measurement so variable that it becomes difficult to show distinct differences between management practices)

iii.    how relevant is the measurement to soil processes (does the measurement integrate functional soil processes such as infiltration, aeration, nutrient cycling etc.)

iv.    the cost and ease of sampling

v.     the cost of soil analysis

 

A comprehensive soil health assessment combines indicators that cut across the physical, biological and chemical attributes of the soil.

 

2.5.1 The Cornell Soil Health Test

The Cornell Soil Health Test (CSHT) was developed in response to this need and to provide a holistic soil test that can be applied at the field level. It comprises of 15 field and laboratory soil measurements as shown in Table 2.5.1. Each measurement is related to fundamental processes occurring in the soil.

 

Samples for the CSHT can be taken from the field in the early spring between April 15 and June 1 at a depth of 0-6”. The area to be sampled should be carefully studied so as to separate the field into relatively homogenous sections. Sections with different soil types or management history or differing slopes should be sampled separately. For

 

 

penetrometer measurements, the maximum resistances are recorded for the 0-6 inches and 6-18 inches depth. As with the standard soil test, additional information should be provided on the intake form to allow for the interpretation of the test results. Samples should be kept cool and out of the sun until they are sent to the laboratory. Detailed sampling instructions are provided at http://soilhealth.cals.cornell.edu.

 

A typical Cornell Soil Health Test report (Figure 2.5.3) consists of:

 

i.      Measured values of soil health measurements

ii.     Ratings of each measurement on a scale of 1 to 10, scores less than 3 are color coded red, scores greater than or equals 3 but less than 7 are colored yellow and scores greater than or equals 7 are colored green.

 

 

 

Table 2.5.1. Indicators of physical, biological and Chemical health of soil and their associated soil processes.
Soil Health Assessment Indicator	Soil Function Process
Physical Indicators
Aggregate Stability	aeration, infiltration, shallow rooting, crusting
Available Water Capacity	water retention
Surface Hardness	rooting, water transmission
Subsurface Hardness	rooting at depth
Biological Indicators
Organic Matter Content	energy/C storage, water and nutrient retention
Active Carbon Content	organic material to support biological functions
Potentially Mineralizable Nitrogen (PMN)	N supply capacity, N leaching potential
Root Health Rating	soil-borne pest pressure
Chemical Indicators
pH	toxicity, nutrient availability
Extractable Phosphorus	P availability, environmental loss potential
Extractable Potassium	K availability
Minor Element Contents (4)	micronutrient availability, element imbalances

 

 

iii.    Lists of constraints when an indicator rating is in the red (low), highlighting the soil processes affected by the low score of the indicator.

iv.    Percentile rating of the indicator value in the database of soil health measurements in New York State.

v.     Composite soil health score (out of 100)

vi.    Measured soil textural information

 

The coded ratings of the measurements are based on the scoring curves developed for the different soil health indicators. The generalized patterns for these scoring curves are the “more is better” (e.g. aggregate stability and organic matter); “the less is better” (e.g. surface and subsurface hardness) and an optimum curve (e.g. pH and phosphorus; Figure 2.5.4).

 

The Cornell Soil Health Test can assist growers to make informed soil management decisions by identify soil indicators below optimum levels. Based on the list of constrains highlighted on the Cornell Health Test report, the grower can target management efforts to address specific constraints.

 

Figure 2.5.3. A specimen copy of a Cornell Soil health Test Report.

 

The Cornell Soil Health Report also provides suggestions on addressing constraints in the short- and the long-term (Table 2.5.2).

 

The management methods that are implemented to address soil health constraints often depend on soil type, and specific farm and grower situation. The general principles guiding the interpretation of the Cornell Soil Health Test report are given below:

 

1. The report is a management guide:
The report basically shows the aspects of the soil needing attention in order to enhance productivity and sustainability. Growers should see this report as a tool in planning the best soil management strategies for their fields.

 

2. Different management approaches can be used to mitigate the same problem:

The choice and details of management efforts to be used in overcoming soil health constrains are dependent on resources available to the farmer. For example, growers seeking to increase the soil organic matter of their fields might approach this either by using reduced tillage practices or by adding organic manure or by combining both methods, the latter generally yielding the best results.

 

3. In addressing some soil constraints, management practices can affect multiple indicators:
Many of the soil health indicator measurements can benefit from a single management practice. For example, adding manure to the soil improves soil aggregation; increases organic matter and active carbon content; and improves soil nutrient status.

 

4. Soil health changes slowly over time:

Soil health is a long term commitment that generally requires a long time for the desired effects to manifest. This is unlike the chemical amendments such as fertilizers which affect the soil and crop almost immediately.

 

 

Figure 2.5.4. General patterns of this scoring curves for soil health indicators.

 

To learn more about the Cornell Soil Health Test, visit the soil health website at http://soilhealth.cals.cornell.edu

 

 

Table 2.5.2. Short- and long-term management strategies to address soil health constraints.
Constraint	Recommended Management Practices
	Short term or intermittent	Long term
Physical
Low aggregate stability	Fresh organic materials (shallow-rooted cover/rotation crops, manure, green clippings)	Reduced tillage, surface mulch, rotation with sod crops
Low available water capacity	Stable organic materials (compost, lignaceous/cellulosic crop residues, biochar)	Reduced tillage, rotation with sod crops
High surface density	Limited mechanical soil loosening (e.g. strip tillage, aerators); shallow-rooted cover crops, biodrilling, fresh organic matter	shallow-rooted cover/rotation crops; avoid traffic on wet soils; controlled traffic
High subsurface density	Targeted deep tillage (zone building, etc.); deep rooted cover crops	Avoid plows/disks that create pans; reduced equipment loads and traffic on wet soils
Biological
Low organic management content	Stable organic matter (compost, lignaceous/cellulosic crop residues, biochar); cover and rotation crops	Reduced tillage, rotation with sod crops
Low active carbon	Fresh organic matter (shallow-rooted cover/rotation crops, manure, green clippings)	Reduced tillage, rotation
Low mineralizable N	N-rich organic matter (leguminous cover crops, manure, green clippings)	Cover crops; manure; reduced tillage
High root rot rating	Disease-suppressive cover crops, disease breaking rotations	Disease-suppressive cover crops, disease breaking rotations; IPM practices
Low bacterial counts	Fresh organic matter (shallow-rooted cover/rotation crops, manure, green clippings)
Low fungal counts	Stable organic matter (compost, lignaceous/cellulosic crop residues, biochar); cover and rotation crops	Reduced tillage, organic nutrients
Chemical
Low CEC	Stable organic matter (compost, lignaceous/cellulosic crop residues, biochar); cover and rotation crops	Reduced tillage, rotation
Unbalanced pH	Liming materials or acidifier (sulfur, alum, ferrous sulfate)	Repeated applications based on soil tests
Low P, K	Fertilizer, manure, P-mining cover crops, arbuscular mycorrhizae promotion	Repeated application of P/K materials based on soil tests; reduced tillage
High salinity	Subsurface drainage and leaching	reduced irrigation rates, low-salinity water source, water table management
High sodicity	Gypsum, subsurface drainage, and leaching	reduced irrigation rates, water table management