Nematode Pests of Horticultural Crops and their Management (1+1)

Practical 2

Exercise - 2

Exercise: Collection of Soil and Root Samples

Objective: To be aware of the procedure of collecting samples from soil and plant parts for qualitative and quantitative analysis of suspected nematode populations in soil and plant roots with minimum possible error.

What is a sample?

Sample is a representative of the particular area (which may be a field, district, state or country) for which information is required.

When to Sample?

The most appropriate time to sample depends on the crop and the purpose of the sampling.

Predictive essays: In general, nematode populations are highest at the end of growing season and drop as the soil temperature declines.

For annual crops, sample at or immediately after harvest.

For orchards and nurseries, collect samples during early and mid season.

For turf and ornamental plants, sample before planting.

Diagnostic assays: Sample the soil of living plants showing symptoms at the onset of symptoms during growing season. Separate samplings from healthy and diseased plants, help to compare the population densities. Also include roots, if possible, because some nematodes spend part of their life cycle inside the roots and more accurate diagnosis of nematode damage can be made from samples including roots.

Materials required: Sampling tools like soil auger/ hand hoe/ cheese sampler (Figure 1), polythene bags, aluminum foil labels, rubber bands.

How to Sample?

Always collect sample from within the feeder-root zone that varies from crop to crop. Avoid collecting samples when the soil is extremely dry or extremely wet. DO NOT add water to the soil after sampling. Collect samples from areas of common crop history. For example, if one half of the field is planted to corn and the other half to soybean, sample each area separately.

1. Collect vertical core sub samples of soil with a soil sampler or shovel within the feeder-root zone. The depth of the feeder-root zone varies depending on the crop. For most annual crops and turf a 6" depth should be adequate. Nematodes do not occur uniformly throughout a field; thus, more than one sub sample must be taken from the same field. The number of sub samples needed depends on the size of the field:

o For small fields (less than four acres), collect at least 20 sub samples.

o For large fields (more than four acres), divide the field into four-acre sections and collect at least 20 sub samples from each section. If the field consists of several soil types, divide the field into as many sections as there are soil types. Collect at least 20 sub samples from each section.

2. Mix the sub samples in a clean bucket.

3. Place at least 500 cc of the soil mixture into a nematode soil sample bag or plastic bag.

4. LABEL COMPLETELY with the grower's name, address, crop information, previous crop, date of collection and field or sample number. Optionally soil status at the time of sampling can be noted.

Where to sample?

• The sampling pattern for soil and root samples depends upon the type of crop and pattern of planting. Use the following guidelines to determine the sampling pattern.

Samlog S

Sampling Methodology:

Plant parasitic root nematodes are present either in or around the roots of their host plants and some genera prevail the above ground parts like stem, leaves, spike or buds.

Samples are procured differently from annuals and perennials.

Fig. 2.1.Sampling Tools

• Sampling from vegetable field (Figure 2)

• Select six rows of a field (two from the beginning, two from the middle and two from the far end of the field).
• Collect 8-10 sub samples up to a depth of 20-30 cm (active feeder root zone) from each pair of rows in a criss-cross (zigzag) manner (Fig.2).
• Place all the sub samples in the same polythene bag and label it for the crop, locality, crop status, visible symptoms if any, crop history (if known as previous crop), Date of collection and farmers name .
• Label information should be written separately in a note book also.

Fig. 2.2 Row wise sampling pattern in vegetable crops

• Sampling from field crops (Figure 3)
• Leave about one meter periphery of the field.
• Remove two-three cm upper layer of the soil with the help of an auger/ hand hoe.
• Collect 50-100 cc soil along with feeder roots up to depth of 15-20 cm. this will make one sub sample.
• Draw 10-20 such subsamples from an area of one hectare area in a zig-zag manner (fig. 3)
• Place all the subsamples in one polythene bag so as to make one composite sample.
• Put an aluminium foil label bearing the sample number in the polythene bag and tie it with a rubber band.
• Write the details of labeling in a separate note-book also.

Fig. 2.3 Sampling pattern in field crops

• Sampling from an orchard (Figure 4)
• Take two subsamples from one tree up to a depth of 30 to 60 cm (feeder root zone) depending upon the type and age of the tree.
• Atleast ten trees should be sampled at random to cover an area of one hectare (Fig.4).
• Pool all the subsamples in polythene bag and label it properly for the fruit, orchard site, orchard age, symptomatic information, orchardist name, date of collection etc

 

Fig. 2.4 Sampling pattern inorchards

Sampling from a single plant e.g. Tree/shrub

• Collect 10 sub samples, five near the trunk and five from drip line (Fig. 5) i.e. from inner and outer rhizosphere of the tree by the method described above.
• The depth of the sampling will vary with the kind and age of the tree and depth of its feeder root system. Spatial distribution; horizontal as well as vertical should be standardized.
• Put all the subsamples in the same polythene bag and label it.

Fig. 2.5 Sampling pattern for a tree

Sampling from a fallow area

• This type of sampling is done in the areas showing a poor crop yield history.Sampling should be carried out at the depth between 8-12 inches below the soil surface.

Storage of the samples:

• Samples should be stored in a refrigerator (about 100C) for a few days only if immediate processing is not possible.

Precautions:

• Samples should always be collected from diseased and apparently healthy plants separately. Dead plants should be avoided.
• Sampling should always be done from optimum depth where maximum nematode fauna is expected.
• Extremely dry and wet soils should be avoided for sampling.Soil collected for sampling should have optimum moisture and sample should be sealed properly to maintain moisture.
• Sample should be washed as early as possible. Refrigeration is a must if samples are to be stored for some period

Questions:

1) With what objective will you collect soil and plant samples?
2) Write down the steps to be followed while collecting samples from vegetable field.
3) Discuss the steps to be followed while collecting samples from field crops.
4) Discuss the method of sampling for suspected nematode population in a tree.
5) How will you do samping for nematode population in an orchard?
6) What are the precautions that should be taken while sampling?