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Soil fertility testing
 

Soil fertility testing

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  • Not all soil organisms are beneficial. Some are pathogens , which cause diseases such as root rot of raspberries and scab on potatoes. Moles can damage crops and lawns, and slugs are a serious pest in many Northwest gardens.

Soil fertility testing Soil fertility testing Presentation Transcript

  • Vineyard Soil Testing
    • Soil sampling and testing in viticulture is most important prior to vine establishment.
    • However, soil evaluation in mature vineyards is conducted when nutritional disorders are observed in vines or fruit yield or quality changes significantly.
    • The most common type of soil testing is related to soil chemistry (e.g. pH or boron).
    • Soil can also be evaluated for physical properties (e.g. water retention and release) and biological properties (e.g. nematodes, microbial populations).
  • EXAMPLE: Lab Tests for Root Munchers
    • Not all soil organisms are beneficial and not all are visible. There are times when a nematode or fungal pathogen test may reveal a hidden source of productivity decline.
  • Many of the soils in Western Oregon share some common ‘nutritional concerns’ based on either low content or availability, natural imbalances or other problems related to prior uses, crops, or management history. Cations (+) Anions (-) Potassium, Manganese, Zinc Sulfate-S, Phosphorus, Boron Other Issues Soil acidity (< 5.5), high magnesium Vine Nutrients – The Typical Soil Test
  • Soil pH and Nutrient Availability Soil pH is an important chemical property influencing vine nutrient bioavailability Grapes are generally adaptable to soil pH ranges of 6 to 7.5 where most nutrients are most soluble. Toxicity problems can occur at low pH where Al, Mn, and Fe have increased solubility in soil solution
  • Factors Affecting Soil Availability
    • Nitrogen (N) – Organic, ammonium (NH 4 + ), nitrate (NO 3 - )
      • Low vine N is more common than excessive vine N
      • Soil Organic Matter
      • Organic N may be up to 99 percent of total soil N
      • Microbial activity (soil temperature, moisture , oxygen)
      • Soil pH
      • Clay content (protein adsorption, humus stabilization)
      • Fertilizers – (differences between organic and inorganic)
      • Volatilization, Denitrification, Leaching
      • Tillage, cover crop practices, mowing
  • Factors Affecting Soil Availability
    • Phosphorus (P) – soluble (as H 2 PO 4 - , etc.) organic forms,
    • bound with Al, Fe, and Ca compounds
      • Soil pH – effect on free (reactive) Al 3+ , Fe 3+ , and Ca 2+
      • Low pH increases free Al and Ca, decreases P
      • High pH increases free Ca, decreases P
      • Clay content and type (adsorption potential)
      • P binds to Exch. Al or Fe, greatest in acid clay soil
      • Active (microbial) and Passive (humus) SOM
      • Microbial activity (soil temperature, moisture , oxygen)
      • Fertilization and N availability
      • Growth rate and size of root system
    - - - + + - - - - - - - - - - - + + - - - - - - - - - - - + - - - + + - - - - - - - - + + + + + + + + + + + + + + + + + - - + + + + + + + + + + + + Clay H 2 PO 4 -
  • Factors Affecting Soil Availability
    • Potassium (K) - soluble, exchangeable, fixed, insoluble
    • CEC, clay type (illite, vermiculite clay minerals)
    • Diffusion
    • Affected by moisture , soil structure, clay, temperature
    • Form of N in soil
    • High soil nitrate increase K absorption, high ammonium decreases K
    • Solution and exchangeable Mg and Ca
  • Factors Affecting Soil Availability
      • Sulfur (S) - soluble (as SO 4 2- ), organic, adsorbed to Al and
      • Fe compounds, inorganic compounds
      • SOM (all forms)
      • Organic S may be up to 90 percent of total soil S
      • Soil pH – acidic lower, alkaline higher
      • Amount of free Fe and Al (acidity)
      • Competition at root surface with soluble soil P
      • Soil texture
      • Soil moisture and leaching
    • Zinc (Zn) - soluble, exchangeable, adsorbed to Fe and Al
    • compounds, low solubility SOM complexes and
    • mobile chelates , insoluble Zn-minerals
      • Total soil Zn from parent material
      • Soil pH
      • SOM
      • Weather
      • Cloudy (low light) and cool conditions decreases uptake and transport
      • Soil solution P
      • High P reduces Zn uptake (competition), binding with P possible
      • High P-induced reduction of mychorrizal infection reduce Zn absorption
    Factors Affecting Soil Availability
      • Boron (B) - soluble (neutral and anion), OM complexes,
      • adsorption by Fe and Al compounds
      • B tends not to be in insoluble inorganic compounds
      • Total amount of B from parent material
      • Soil texture and moisture
      • Soil pH
      • Leaching
    Factors Affecting Soil Availability
  • What Type of Soil Test? Few commercial laboratories offer every type of soil test Engineering properties, hazardous chemicals, nutrient analysis, diseases, nematodes, microbial diversity Become informed about various agricultural ‘package’ options and costs before you submit your soil Soil testing encompasses a bewildering number of methods and costs from kits to laboratories Why use a lab when you can buy and use a kit? Higher ‘resolution’ and certified objective results
  • Soil Sampling and Testing The simple and critical key to getting any value from soil testing is collecting a representative sample What is your question? How large is your block? How many sub-samples? How deep is your soil? How uniform is your soil?
  • Soil Sampling and Testing The simple and critical key to getting any value from soil testing is collecting a representative sample Sample the entire effective root zone depth based on soil and vine age/size
  • Soil Sampling and Testing The simple and critical key to getting any value from soil testing is collecting a representative sample Sample the entire effective root zone based on soil profile depth
  • Soil Sampling Approaches Random or ‘Zig Zag’ For uniform sample areas Targeted or Sub-Sampled When properties are known or suspected of having significant variation Fixed Grid Applied in planted blocks/fields. Establish fixed locations for long-term monitoring of changes The first step is to assess the area of interest How uniform is the topography? Does the current vegetation show uniform growth? Topsoil color or texture changes Take some pre-samples to your depth of interest
  • Row Direction Soil Sampling Approaches Fixed Grid Random Zig Zag Eroded upper slope Darker color down slope Targeted
  • The ‘Typical’ Soil Test – What happens in there?
    • Generally lab procedures for handling (extraction) and quantitative analysis are similar for labs within a region
    • There may be important differences between regions that will make lab more appropriate than another.
    • Sample preparation
    • Drying, sieving, and grinding
    • pH and ECe methods
    • Chemical extractants and sample digestion methods
  • The ‘Typical’ Soil Test – What happens in there?
    • METHODS
    • Soil samples are first dried, ground and sieved for different analyses.
    • Extraction and Digestion
    • For availability analyses, samples are treated with different chemical solutions (water, salt, dilute acid or alkaline solutions) that displace the target nutrient [s] from soil.
    • For total nutrients (e.g. SOM, organic N) a finely ground sample may be decomposed in hot acid (wet combustion) or high temperature oven (dry combustion)
    • Sample Analysis
    • Drying, sieving, and grinding
  • Testing for Available Soil N
    • The dynamic nature of inorganic N in soil is difficult to ‘chase’ and most often the results from a conventional lab test are not very useful. The exception may be for deep profile sampling for specific residual N tests for crops other than grapes.
    • Typical lab reporting of nitrate and ammonium-N on dried and sieved samples have little value
    • If necessary, soil nitrate and ammonium tests are best performed on fresh moist soil, not dried or overly sieved
  • The Soil Report – Concepts and Units There are no standard formats for soil test reports. While generally lab procedures for handling (extraction) and quantitative analysis are similar for labs in regions, there may be differences between regions. The biggest challenge is in deciphering the interpretation. Labs provide results in many different formats, and may (or not) include diagnostic interpretations like low, medium, or high. Soil test reports will, at a minimum, report nutrient levels on a concentration basis.
  • The Soil Report – Concepts and Units Total vs. Available As example, a test for organic N says very little about the bioavailability of soil N. In the early portions of the 20 th century, soil tests estimated the total nutrient. However, these results did not correlate well to crop productivity. Therefore, modern soil testing attempts to determine the availability of a given nutrient by extracting more easily soluble forms. Many field experiments have been conducted to evaluate how different crops respond and accumulate nutrients in different soils and after fertilization. By correlating extraction methods and results to crop responses, the indicies of available nutrients have been developed
  • The Soil Report – Concepts and Units Exchangeable versus water soluble While most labs will report the major exchangeble cations (e.g. Ca, K), few conduct either water- or dilute acid soluble extractions that better mimic the soil solution. Units ppm = mg/kg and mg/L % = 10,000 ppm Meq = milliequivalents (exchangeable cations Other units ECe = Electrical Conductivity or salinity = mmhos/cm (mmhos x 640) = Soluble salts in ppm
  • The Soil Report – Concepts and Units Conversion of concentration (ppm) to lbs per acre requires an ‘average’ assumption about bulk density and depth of soil. e.g. 30 ppm P (12 inch sample) x ~4 = 120 lbs/acre 30 ppm P (6 inch sample) x ~2 = 60 lbs/acre Conversion of nutrient concentrations in soil samples to estimates of the quantity present in a field, orchard, or vineyard, is typically done to provide available nutrients on a per acre (or hectare) basis. Recall the concept of an acre furrow slice (one acre, 6 inches deep). While labs do not measure (or know) the actual bulk density of a soil, they use a standard conversion:
  • The Soil Report – Interpretation Questions to ask yourself Did the lab estimate lbs per acre based on your actual soil sample depth? Have you sampled the potential or existing root zone? Are the roots in your vineyard horizontally distributed throughout the entire soil? In drip-irrigated vineyards… are there differences between the drip zone volume and remaining soil?
  • The Soil Report – Interpretation ___________________________________________________ Exchangeable Cations Ratios ------------- percent of total ---------------- Ca Mg K Na Ca:Mg K:Mg ___________________________________________________ 60-80 15-30 5-10 < 6 2-10 0.1-0.4 ___________________________________________________ Criteria for Sustainable Vine Health CISRO, Australia 2004 As grapevines are tolerant and reasonably adaptable to differing soil environments there is a broad acceptable range for typical soil nutrient properties. The below ranges for exchangeable cations (as a percentage of CEC) have been published in Australia. (Note these numbers are not actual quantities, but reflect the distribution as a percentage of total soil CEC)
  • The Soil Report – Interpretation ___________________________________________________ Nutrient Deficient Marginal Adequate High Toxic ---------------------- mg/kg ----------------------- ___________________________________________________ Nitrate < 1 1-2 2-10 > 10 -- P < 25 25 -35 35-70 > 70 -- K < 50 50-100 100-250 > 250 S < 10 -- -- -- Zn < 0.5 0.5-1 1-2 2-20 > 20 B < 0.1 0.1-0.5 0.5-1 1-3 > 3 Al > 100 ___________________________________________________ CISRO 2004
  • Soil pH and Nutrient Availability Lime is used to effectively increase soil pH Sulfur or ammonium sulfate is used to decrease soil pH pH Buffering Capacity Clay and organic soils resist changes in pH Sandy soil pH is more easily changed
  • Soil pH and Nutrient Availability Determining Lime Requirement pH Buffering Capacity is determined by measuring soil pH in distilled water and after ‘equilibration’ with a salt solution that is strongly ‘buffered’ at pH 7.5 (SMP buffer) SMP Tons lime needed to pH pH 5.3 5.6 6.0 6.4 6.6 - - - 1.1 6.4 - - 1.1 2.2 6.2 - 1.0 2.0 3.2 6.0 1.0 1.7 2.9 4.2 5.5 2.6 3.6 5.1 6.8 5.0 4.2 5.4 7.3 9.4
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