What Is a Good Soil Health Number In Ohio?

Soil from corn field

As our understanding of soil health advances, farmers are increasingly interested in assessing and improving soils on their farms. Several commercial labs now offer soil health analyses but generating values in a lab is only the first step. A frame of reference for what constitutes a typical, low, or high soil health value is essential for understanding these tests and inferring soil function. A common question farmers ask is, “What’s a good soil health number?”

A recent report helps answer this question, by providing a state-wide baseline of soil health values from Ohio. This report can now help farmers and landowners assess soil health in their fields. The full report can be found here: go.osu.edu/SH-baseline with a summary provided below.

The assessment was compiled from 10 distinct projects conducted by Ohio State University from 2015 – 2021. These projects involved mostly on-farm research that either included a simple agronomic manipulation or sampled soil in a survey approach. Nearly all soils were from production agricultural fields. Projects were diverse and included field crop fertilizer recommendation trials, certified organic corn fields, soybean fields, hopyards, and tomato fields. A total of 2,454 soil samples came from 75 counties across Ohio (Figure 1). Soils were most commonly a single soil sample per field, but no more than 10 soil samples per field.

A picture containing text, vector graphics

Description automatically generated

Figure 1. The Ohio counties (red shaded) where soil samples were collected from for this baseline soil health assessment.  

Soils were sampled typically in the fall or spring and mailed or transported to Ohio State where they were dried and ground to <2 mm. Soil health analyses (POXC or active carbon, Respiration,  and Soil Protein) were run in the Soil Fertility Lab (soilfertility.osu.edu/protocols), and routine nutrient analysis (pH, Mehlich-3 nutrients, organic matter via loss-on-ignition) was run by Spectrum Analytic with recommended procedures (NCERA-13, 2015).

As expected, soil properties varied greatly across all 2,442 soil samples (Table 1). Fifty percent of the soils had optimal pH values 6.0 – 6.8 and most had sufficient Mehilch-3 P and K values. In general, soil test levels were in optimal ranges for grain crops in Ohio (Culman et al., 2020). Soil organic matter ranged from 0.1 to 9.8% for these soils, with 50% of the values falling below and 50% of the values falling above 2.2% (median value). Soil health measures that reflect biologically active organic matter values varied greatly, with median values of 496 mg/kg for POXC, 46.5 mg/kg for respiration and 4.4 g/kg for soil protein (Table 1).

Table 1. Summary of soil data based on percentiles (n=2442).

Variable

Minimum

25th

50th

75th

Maximum

pH

4.2

6.0

6.4

6.8

8.0

Mehlich-3 Phosphorus (mg/kg)

2

27

44

70

969

Mehlich-3 Potassium (mg/kg)

28

105

140

179

633

Cation Exchange Capacity (meq/100g)

1.9

9.1

12.0

15.3

27.5

Organic Matter (%)

0.1

1.7

2.2

2.7

9.8

Soil Organic Carbon (g/kg)

0.6

1.4

1.7

2.1

7.1

Permanganate Oxidizable Carbon (mg/kg)

55

401

496

617

1433

Respiration (mg/kg)

4.4

32.0

46.5

65.3

458.5

Soil Protein (g/kg)

1.5

3.9

4.4

5.3

25.6

The Importance of Soil Type

Soil type often needs to be considered when assessing soil fertility test values. For example, sandy soils cannot hold as much Mehlich-3 K as a clay soil. Similarly, there is widespread agreement that soil type needs to be considered when evaluating soil health organic matter values. Soils with more clay are inherently capable of holding more organic matter relative to sandier soils. Because of this, we grouped soils by soil type and by CEC (cation exchange capacity).

The tables in the report are intended to provide some reference for typical soil health values based on a given soil type. When a grower gets soil health test results, they can use these tables to see where their soils fall relative to other fields in Ohio. This is an important first step in establishing baseline values. The next step is using this information to understand how management impacts soil health, and ultimately how these values can inform future management and actionable decisions.

More information is provided in the full report: go.osu.edu/SH-baseline

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.