Brief Overview of Similkameen Valley Soil Health Assessment

By Julia Wagner

Click here to see the Detailed Report

The results summarized here are the product of trials of a proposed soil health assessment conducted in the Similkameen Valley, in the Interior Plateau in south central British Columbia, Canada. The majority of farms in this semi-arid valley are tree fruit orchards, but there are also vineyards and ground crops, and a small number of other types of farms. According to Edwards (2002), almost half of all tree fruit production acreage in the Valley (ca.2000 acres), is certified organic ("Orcharding in an arid climate"; EcoFarm&Garden 5(4):28-30, p28).

The soil health assessment included on-farm assessments of some physical indicators of soil health and an earthworm count (as a biological indicator of soil health), as well as a standard laboratory analysis of soil chemical properties.

As much as possible, the producers themselves were actively involved in the assessment process.

Summary of Results

In total, Soil Health Assessments were conducted on 24 plots on 15 farms, plus one farm with a soil test only. The complete assessment for each plot included a laboratory soil analysis and a series of on-farm observations and measurements.

Summary of Laboratory Soil Test Results

• Organic Matter
  Given the semi-arid climate, the organic matter levels were in the range expected. Monitoring organic matter levels over time is recommended to ensure levels are staying stable or increasing. Further investigation is proposed to investigate how organic matter management can be optimized to maximize internal nutrient cycling and reduce the need for external inputs, as well as to provide important benefits to soil physical properties and water management.
  
  
• pH
  With very few exceptions, soil pH was between 7 and 8: alkaline as expected for the Similkameen Valley. One notable exception: a plot with pH 6.5. Was this the result of the elemental sulfur (S) application made 8 years ago? Is pH increasing or decreasing over time on this farm? Can growers who have made applications of elemental sulfur (S) tell us about their experience with the value of this practice to nutrient management?
  
  
• Salinity
  Fortunately soil test results did not indicate any concerns with elevated sodium levels which can be detrimental to soil physical properties and crop health. However, E.C. values high enough to classify soils as saline (E.C. >4 dS/m) were found on two plots. Eleven others plots had E.C. values between 2 to 4 dS/m that should be monitored for further increases. To what extent are various management practices contributing to elevated salt levels in soils: irrigation? compost? sulfur applications? Are any crop health effects being observed? Continued systematic monitoring of E.C. could help identify any threats of developing salinity problems and determine if preventative management practices need to be considered.
  
  
• Nutrient Management
  Overall, the soil test results generally indicated high to very high values for all nutrients, often exceeding the optimum range. There were only a few individual plot results indicating possible nutrient deficiency (below the optimum level), and these should be further evaluated for need for nutrient additions.

The high values indicate that there is little need for soil application of nutrients. However, high levels also suggest the need for improved nutrient balance. High levels of one nutrient tend to be associated with negative interactions in plant uptake of other nutrients, creating a complex situation for management. This exacerbates the difficulty of nutrient management already created by the high pH conditions of Similkameen Valley soils. Leaf analysis and visual observations of crop health are recommended to further evaluate how soil test results are manifesting themselves in the crop.

Summary of On-Farm Assessments

• Baseline Assessments (one-time only, not expected to change significantly over time):
  • Rooting Medium Depth
    No true restricting layers were found. Gravelly layers were the main type of 'restricting' layer, which made digging difficult but these do not necessarily restrict root growth. However, such gravelly layers may be important in terms of nutrient availability (less soil in the rooting zone) and water movement in the soil. Some layers of higher clay content were also observed: again these will affect water movement in the soil.
  • Depth to Free Lime
    Free lime was identified in all but 5 plots, indicating the high-buffering capacity (resistance to pH change) of the soils in the region and the large amounts of acidifying materials that would likely be necessary to reduce pH.
  • Coarse Fragment Content (c.f.%)
    Coarse fragment content - the gravel and small rocks in your soil - influences the water- and nutrient- holding capacity of soil. The higher the coarse fragment content, the less volume of soil your crop roots have to obtain nutrients and water. Coarse fragment content of the plots assessed varied from none to up to 75% of soil volume.
  • Soil Texture
    The hand-texturing estimation of soil texture indicated higher levels of clay than expected based on soil survey reports. Our assessments identified textures ranging from coarse-texture to fine-textured: loamy sand, sandy loam, loam, silt loam, sandy clay loam, clay loam, silty clay loam, clay and silty clay.
  • Subsurface Soil Test (15-30cm)
    Sampling from as much of the crop rooting zone as possible is important for a more complete understanding of the nutrient supplying capacity of the soil. The soil test results indicate that soil management activities (e.g. cultivation, soil amendment applications) concentrated in the surface 0-15cm zone have changed the soil chemical properties relative to the less intensively managed 15-30cm zone. However, for management purposes, soil properties are fairly uniform throughout the rooting zone.
    
    
• On-Farm Assessments for on-going monitoring (expected to change over time)
  • Structure
    Structure is related to the degree of "clumping together" of soil particles which influences soil aeration and water supply. Almost all soils were identified as being somewhere along the continuum from granular to blocky. This is a good sign, generally indicating 1) good physical soil condition with no extreme compaction that has compressed soil particles and pore space and 2) adequate organic matter to create structure in coarse-textured (sandy) soils.
  • Compaction
    The compaction tester measures "penetration resistance" in pounds per square inch (psi): a general guideline is that roots cannot grow in soils with penetration resistance >300 psi. A common trend among all tree fruit plots was a compacted layer (>300 psi or relative evaluation of increased resistance) between 15 to 30cm (6 to 12 inches) in the tree row. The compaction assessments also indicated a highly compacted surface layer (0-3cm) in the wheel track, that often could not even be penetrated by the compaction tester. This is not a concern for crop health for most high-density tree fruit plantings since the roots are not expected to be found in this area, however it should be considered when replanting the orchard.
  • Water Infiltration
    Few problems have been observed with water infiltration: water tends to enter the soil without any ponding. Again, this is a good sign meaning minimal problems with surface compaction and soil structure. Water infiltration is best observed after a heavy rainstorm: keep your eye out after the next one for further observations!
  • Earthworm Count
    Generally speaking, the presence of earthworms is a positive sign for soil health, as they increase soil microbial activity, improve soil chemical fertility and enhance soil physical properties. The number of earthworms counted in the 15cm x 15cm hole to a depth of 30cm ranged from 0 to an astounding 47 earthworms. In many cases there was a considerable range in the number of earthworms between the three assessment holes within each plot. This reflects the patchy distribution characteristic of earthworm populations, which can make them difficult to use as an indicator of soil health.
    
    
• Crop Health and Other Vegetation Observations
  • Weeds
    A diversity of weeds was observed on all farms. Many of the weeds are recognized as indicators of fertile soil and many are also commonly related to cultivation. Observing changes in the populations over time may indicate changes in soil properties.
  • Cover Crop/Orchard Floor
    Lush orchard floor vegetation was observed in the majority of plots, except those drip irrigated or where irrigation problems were noted. Ground cover was also patchy in some wheel tracks, an indication of the effect of compaction on plant growth.

Combining the Laboratory Soil Test and the On-Farm Assessments
There are many interactions between the soil's chemical, physical and biological characteristics and processes. For example earthworms (our biological indicator) can improve soil chemical and physical properties, and at the same time soil physical and chemical properties such as compaction and organic matter (as a food source) can influence the presence or absence of these creatures.

Click here to see the Detailed Report

Contacts:
For further information E-mail Julia Wagner or
E-mail Dr. Art Bromke, co-supervisor of the project