Sampling

Plants

General Instructions
A general rule of thumb is to collect the most recently matured or fully expanded leaves.

Sampling the proper part of the plant at the right growth stage allows comparison of the data to a known standard. The crop nutrient status of the field can then be evaluated. The greater the number of plants sampled, the better the data will represent the area.

Nutrient Analysis

For most plant analysis, the leaf is analyzed for all macro and micro nutrients (N, P, Ca, Mg, Na, K, Fe, Mn, Zn, Cu, B, S). The levels of these elements indicate the nutrient status of the current crop.

The petiole or midrib is tested for nitrate nitrogen (NO3-N). Additionally, phosphate phosphorus (PO4-P), potassium (K), sulfate sulfur (SO4-S) and chloride (Cl) levels can be determined from the petiole analysis. Testing the petiole provides an early warning. If nutrient levels are low, the leaf will soon become deficient.

Nitrate levels of the soil can also be useful in making nitrogen recommendations during the growing season.

When a nutrient deficiency is suspected, samples should be taken from the affected area as well as from normal plants in the same or adjacent field. Plants sampled should be at the same growth stage. A soil sample should be taken from the affected area at the same time.

Plant Sampling Guide:

  • Walk the field in a V or X or diagonal-line pattern collecting samples from various rows in the field.
    • Don’t take samples from border rows or within 50 feet of the end of the row.
    • Sample the proper plant part.
    • Collect 20 -30 leaves and/or petioles.
    • Separate the leaf from the petiole or midrib immediately.
    • Select plants that represent the average condition of the entire field.
      • Don’t sample insect damaged or diseased plants.
      • Don’t collect leaves that are dusty or dirty.
      • Collect the sample during daylight hours.
      • Use a porous holding container for the sample like a paper bag.
        • Don’t store the sample in plastic.
        • Record the growth stage of the plant.
        • Record water stress if present.
        • Note any recent fertilizer application.
        • Deliver samples to a laboratory within 24 hours of sampling.

Soil

General Instructions
Successfully using soil test results for crop management depends upon obtaining a reliable sample. Collecting a representative soil sample is difficult due to the variability within a given area.

The sampling area should be grouped or divided into areas that are managed or fertilized separately or by the homogeneity of the soil. Subsamples are taken from the plow layer, ( 0-8 inches or 0-12 inches), the top inch of each core discarded, and the remaining soil thoroughly mixed and combined into one composite sample. Submit about one to two pounds of soil to the laboratory for testing. (~ one quart of soil).

Depth samples can be taken once every five years, or when new ground is being planted. Depth samples are collected from one location in the field below the surface soil at one foot intervals down to three or four foot in depth @ 1-2 feet, 2-3 feet, 3-4 feet.

This soil profile analysis can aid the grower and consultant in understanding the soil chemistry below the plow layer. Plant growth of deep rooted crops or orchards can be influenced greatly by subsurface soil conditions. Changes in texture and hardpans should be noted when taking the sample.

Nutrient Analysis

A surface sample is analyzed for all major and minor soil nutrients (NO3-N, PO4-P, Ca, Mg, Na, K, Fe, Mn, Zn, Cu, B, S, EC, pH). A texture analysis may also be performed. Depth samples are tested for major soil nutrients (NO3-N, PO4-P, Ca, Mg, Na, K, pH, EC) and texture analysis.

When a nutrient deficiency or toxicity is suspected, a sample should be taken from the affected area as well as from an adjacent area where healthy plant growth is occurring. Comparing good and bad areas can provide quick answers when problem solving.

Simultaneous collection of a plant sample taken from both areas for nutrient analysis or visual inspection can help clarify the situation.

Soil Sampling Guide

  • Prepare a sampling plan, simple random sampling or a grid layout, prior to entering the field.
  • Walk into the field at least 300 feet when taking a depth sample.
  • Take samples prior to planting.
  • Take samples from the side of the planting bed.
    • Don’t take samples from the strip of soil where banded fertilizer has been applied.
  • Collect 25-30 subsamples for a surface sample.
    • Don’t sample small sections of different soil texture within the field.
  • Take all surface subsamples from the same depth.
  • Use a soil probe or auger and a clean bucket.
    • Don’t contaminate samples with sampling tools, for example, a rusted shovel.
  • Transport the sample in a container that will not break or leak if soil is moist, such as a plastic bag.
  • Record the previous crop of the field.
  • Record the crop to be grown.
  • Record the type of irrigation being used.
  • Record any recent fertilizer application.
  • Keep soils cool when temperatures are high, refrigerate if possible.
  • Deliver samples to a laboratory within 24 hours of sampling.

Water

General Instructions
A water sample is collected at the site or origin of the irrigation system. This is typically a well on the site. The water source should be turned on for a minimum of fifteen minutes. Allow the lines to clear to obtain a proper water sample. Rinse a clean container and the lid three times with the water to be tested. Fill the collection bottle to the top and seal tightly. Refrigerate the sample when transporting.

Nutrient Analysis

Test the water for complete irrigation suitability and evaluation. Nutrients typically included are Ca, Mg, Na, K, B, S, Cl, NO3-N, PO4-P, HCO3, CO3, pH and EC.

Routine Sampling verses Problem Solving

When water or an injection system is suspected to be a problem, samples should be taken before and after the addition of fertilizer.

Water Sampling

  • Use a plastic container.

Don’t use glass or soda pop bottles.

  • Use a one quart sized container.
  • Allow the water lines to be flushed out before taking the sample.
  • Label the sample.
  • Note any fertilizer being injected into the system.
  • Keep water cool when temperatures are high, refrigerate if possible.
  • Deliver samples to a laboratory within 24 hours of sampling.
  • Record the crop to be grown.