The Soil Health Conservation Field Trial and Case Study was completed in 2002. A copy of the final report can be obtained by selecting this link: Soil Health Case Study 2002.
The Nez Perce Soil and Water Conservation District (District) obtained funds from United States Department of Agriculture Natural Resources Conservation Service (NRCS) through the education component of the Environmental Quality Incentives Program (EQIP).
Six soil quality parameters were evaluated on 20 different sites in Latah, Nez Perce and Clearwater Counties, Idaho. Parameters evaluated included infiltration, bulk density, pH, electrical conductivity, slake, soil respiration, and physical patterns.
The case study’s objectives were to compare and contrast soil health on four different management systems within five soil types.
The management practices evaluated are shown in the table below:
| Direct Seeding (DS)||Soil is left undisturbed from harvest through planting except for strips up to 1/3 of the row width for seed bed preparation|
| Permanent Vegetation (PV)||No disturbance (grazing, tillage etc..) in minimum of 5 years|
| Grass Seed Production (GS)||In production of grass seed a minimum of 5 years.|
| Conventional Tillage (CT)||Any system that does not meet the parameter of the DS definition. Usually included inversion tillage (such as plowing or cultivation)|
The four management systems were evaluated on five soil series. Soil information is shown in the following table:
| Palouse||Genesee Area, Rim of Lewiston Hill||19“||2-8%||SW||Silt loam||grass|
| Broadax||Near Lewiston, by Tammany creek||17”||2-8%||SW||Silt loam||Shrubs and grasses|
| Thatuna||Near Genesee area||20”||5%||SW||Silt loam||Palouse prairie|
| Taney||Near Potlatch Idaho||25”||3-10%||S||Silt loam||forest|
| Southwick||Near Craigmont, on Camas Prairie||24”||3-10%||SE||Silty clay loam||Prairie grass|
The results of the case study are discussed by parameter.
Infiltration is the rate in which water enters the soil. Many factors influence the soil’s infiltration rate. Tillage affects infiltration by immediately increasing the infiltration rate because the soil surface is loosened. Long term tillage decreases infiltration because it disrupts soil aggregates and pores. In addition earthworm burrows, plant roots, organic matter and soil texture (the % of sand, silt and clay particles) influence infiltration rates of soils. Table 1. Illustrates the average data collected at each site.
Table 1. Infiltration in/hr recorded at 2” of water
| Direct Seed||5.2||13.25||1.1||56||.8|
| Permanent Vegetation||56.6||36.08||136||199.5||2.2|
| Conventional Tillage||2.8||2.5||1.9||2.6||4.7|
Overall the PV sites have the highest infiltration rates, especially in the Taney and Southwick Soil Series; this could be because of the high vegetation cover in these forested sites. Southwick DS could have a higher infiltration rate because it has been under the management of DS for over 10 years. The remaining DS sites are newer to the management system.
2. Bulk Density
Bulk Density is defined as the ration of oven dried soil (mass to its bulk volume), which includes the volume of particles and the pore space between the particles. Bulk density varies with the structure and texture of a soil. Compacted soil layers have higher bulk densities, restricting root growth and inhibiting root growth and air and water movement through the soil. These Bulk Density samples were collected from 0 to 3 inches below the surface.
Table 2. Bulk Density g/cm3
| Direct Seed||1.14||1.18||1.23||1.09||1.05|
| Permanent Vegetation||1.19||1.06||.68||.92||1.01|
| Conventional Tillage||1.38||.93||1.39||1.53||1.31|
On the Southwick soil series the site differences could be due to the organic matter differences. The Taney and Southwick soils were forest vegetation. The conventional tillage site on the Southwick soil had very little soil organic matter and tilth.
3. Soil pH
Soil pH is a measure of the acidity or alkalinity of a soil. This is measured by measuring the hydrogen in the soil solution. This affects the availability of plant nutrients, activity of microorganisms, and the solubility of soil minerals. A pH level of 5.5 to 7.5 is optimal for most crops.
Table 3. pH (H+) activity in the soil
| Direct Seed||5.9||5.8||4.8||5.2||4.9|
| Permanent Vegetation||7.1||6.7||6.1||4.9||6.7|
| Conventional Tillage ||5.2||6||4.7||56||5.5|
4. Electrical Conductivity (EC)
EC indicates the amount of salts present in a soil water mixture. Salts are required for plant growth and are found in all soils. At a EC of 7 you get a 10% yield decrease in winter wheat production.
Table 4. Electrical Conductivity (EC) dS/m
| Direct Seed||.08||.11||.21||.13||.11|
| Permanent Vegetation ||.08||.06||.08||.07||.09|
| Conventional Tillage ||.05||.08||.23||.09||.1|
Soil slake occurs when a ped or clod of soil is immersed in water. Slaking refers to the breakdown of the soil particles when the aggregates are saturated with water. This occurs because the aggregates are not strong enough.
Slake is measured on a scale of 0-6. Soil fragments or aggregates which fall into classes 0 to 3 are relatively unstable. Class 4 indicates some stability, but very little strength. Classes 5 and 6 represent relatively stable soil fragments or aggregates. Soil strength relates to the ability of the soil to resist loss of its structure.
Table 5. Slake
| Permanent Vegetation ||5.25||6||6||5.7||6|
| Conventional Tillage ||3||3.5||3.5||3||2.6|
6. Soil Respiration
Soil Respiration is the production of CO2 as a result of biological activity in the soil by microorganisms, live roots, and macro organisms such as earthworms, nematodes, and insects. Carbon Dioxide emitted from the soil is odorless gas that enter the atmosphere and annually exceeds the amount emitted by all human activities. The activity of organisms in the soil is an indicator of good soil quality.
This indicator is measured in (CO2 – C/a/d) a range from 32-64 lbs C02 – C/a/d is a ideal soil activity.
Table 6. Respiration (CO2 – C/a/d)
| Direct Seed||41.4||47.6||19.2||80.7||44.3|
| Permanent Vegetation ||25.1||33.9||127||134.9||48.7|
| Conventional Tillage ||18.5||10.8||26||10.8||9.4|
Respiration rates were highest on sites with high amounts of residue and organic matter.
Figure 1. Broadax Conventional Tillage Site
Figure 2. Broadax Direct Seed Site pit.
Figure 3. Broadax Grass Site
Figure 4. Broadax Permanent Vegetation Site
Figure 5. Palouse Conventional Tillage site
Figure 6. Thatuna Direct Seeding site
Figure 7. Taney Minimum Tillage Site